#5 not firing right
 

I have a 2.8 LS race motor with twin plug and Electromotive TEC3 fuel injection and ignition actuation. Clewett offset crank toothed wheel pickup and his pulley and wheel. I bought the motor running, replaced the 40mm throttle bodies with 46s and appropriate manifolds, and with help from a guy who knows this stuff worked out some irritating bugs and got it running great. After I built a replacement SS 2.8, I pulled the LS down to refresh what needed refreshing. Turns out many valves were seating sort of off center, so other than replacing bearings which really didn't need replacing despite 125 hours of racing, most of them shifting at 8,200 rpm, valves were about the only change.

The SS had the intake stuff bolted on with no changes. Seemed to run OK until it pulled a piston apart on the chassis dyno. So back to the rebuilt LS. To make the swap easier, I undid the 12 TB to manifold bolts, and left all the intake stuff hanging. Shorter profile motor for R&R, no spilled fuel, much easier deal. And put the LS in and bolted everything back up.

I now know I should, when doing something like this, go through the usual checking and adjusting - do the throttles on each side open at the same time. Check and rebalance the idle air flow as needed. Check and redo the programming for sensor values. After working my way through issues related to those and other not surprising things, I am down to just one mystery.

The #5 cylinder isn't firing as well as the others. The exhausts are much cooler for #5 than its neighbors. #5 and #2 have EGT probes, and #2 rises appropriately but #5 does not, though once or twice it did rise as it should compared with the other, but then got tired and dropped back down. The plugs are a bit wet when pulled, and it seems to be gasoline, though I'm not getting black smoke.

I have pulled both plugs, reconnected to the plug wires, and both spark. They sparked the same when I swapped in a different plug wire (Magnecores). The plugs are the fancy Bosch with the small pin electrode and a tapered side pin rather than the more common overlapping ground lug. I bent the center pin in a bit to close the gap on these very well used plugs (as are all the others on this motor), but no change in behavior.

I swapped the #4 and #5 injectors. Same issue, so it oughtn't to be a bad injector. On dry running (cranking with no fuel pump) both #4 and #5 injectors click the same, so I don't think I have bad wiring for the #5.

The problem is clear at idle-2,000 rpm. It seems to clear up when I take the motor up higher.

A quick CR check indicated 130 psi at about 6,000' altitude, which should be good enough for consistent firing. Haven't gotten around to leakdowns or CR checking of everything, but not sure that's going to tell me much. I can measure plug wire resistances with neighbors, to see if enough for a spark out in the open isn't enough for idling. I should have swapped plugs between cylinders. I haven't done the spray a combustible gas around the intake tracts exterior to see if I've got an air leak somewhere (I didn't leave out a whole gasket), but don't such leaks usually lead to faster idling and a leaner burn? Beyond these seemingly unlikely possible causes, I'm out of ideas.

TEC3 allows individual cylinder trims, but without fire I don't see how I could use that to help. The TEC3 gives more fuel for the 1st second (start enrichment), and also for the first 20 seconds (startup enrichment). But if every other hole is getting enough fuel and spark for idling beyond 20 seconds, why wouldn't this one fire also?

Suggestions or speculations about possible causes and cures gratefully accepted.

Ignition wire?

Air leak?
It might upset the fuel/air ratio.
I would look for a gasket leak...or worst case...a crack in the runner?
Next up...perhaps a bad dist cap if there is one...or is it direct separate coil to plug?
Thats about all I can think of at this time.
Bob

Depends on the installer. Tec is normally wasted spark with three re-stickered GM two post coils. I would pick up quantity 6 of 12v LEDs to test all injector outputs first. You'll need a helper to crank while you observe the LED fires in place of the injector. If still misfire and injector channels test out then I would check the matched cylinder on the wasted spark coil to ensure it is firing. If it is, swap the plug wire with #5 and try again.

If spark and fuel check out then I suspect a valve may not be behaving as intended.

I need to check resistance on the wires just to be sure. And for the lower plug, I pulled the wire from the coil, attached another one, and tested the plug. It sparked, just as it did with its regular wire and the plug out.

This is twin plug run from two banks of coilpacks. It is waste spark, with three coils, each with two plug wire terminals, on each bank. One bank serves the uppers, and one the lowers. So if a coil is bad, it should be bad on both sides of the motor. And for both plugs in one hole to look about the same, you'd pretty much have to have the same problem on the hole on the other side which fires 360 degrees out.

Could an air leak so upset the A/F ratio that the gasoline injected into the TB just above the port wouldn't even ignite? I need to do the standard tests, though cracked manifolds (stout PMOs) or TBs (TWMs, or is it TMW?, now Borla) are unlikely candidates.

How might one check a spark to see if it was powerful enough, assuming that one could have a spark with the plug out in the air, but under idle compression pressures it wouldn't spark? I can see some new plugs in my future to see if maybe these gaps (not easily adjustable) have grown so wide that with higher compression, those extra air molecules might be just enough extra insulation so the spark might not jump? But do cylinder pressures rise as RPMs go up, at least until the torque peak?

Keep those thoughts coming.

Also double check your firing order, possible a couple are crossed. I've seen that before... normally spark error but could be injector too if you're set for sequential injector control.

When racing my VW beetle convertible in the Carrera Panamericana in 1991, I passed a for real 4 cam 550 Spyder on one leg. Made me feel like a really hot shoe. Two days later the German co-piloto/mechanic of that car asked me what his firing order was. When I explained I had zero experience on any twin plug car (at that time), much less an exotic one like his, he said it was the same as my VWs. Oh, I knew that by heart. And yes, they had two leads going to the wrong plugs. Walked right by me next time we met on the road.

But my wires are of lengths and loomed so attaching to the wrong plugs isn't really possible, and they never come off the coil. And no other cylinder exhibits any signs of distress.

The word on the race motor street is that sequential firing isn't useful, because the injector can't get enough in during its one carefully timed squirt. It seems that batch firing, sort of like waste spark I suppose, is simpler. And it doesn't require a cam sensor. Might well be different for street motors. The TEC won't sequential fire without a cam signal anyway, so it can't be that.

A friend who is using Megasquirt wondered if I was having a minimum on time issue at idle, but that seems improbable for just one injector.

I've been wondering about a valve issue. So I'll do a leakdown in addition to the compression test I did. Valves all checked out good after I reground them and seats, but maybe something is going on, and somehow affects things more at idle speeds than higher RPMs.

I've seen injectors jam shut (killed a piston like that myself last year-Siemens Deka 60lbs) and it was only noticeable at idle. The engine would fool me with acoustics above 2500rpm. I went through the exercise of replacing the piston and test driving before I found it by reading the plugs compared to neighbor plugs. I think this may be quite likely here.

Well, I swapped the injector on the bad hole for its neighbor on #4. 4 still good, 5 still bad. Acoustics may have fooled me into thinking my issue clears up with RPM, because the EGT doesn't really support that. Test conditions weren't conducive to much higher RPM running, though.

No fuel killed the piston? Wonder how it did that, though obviously it did. There is lean burn, but no fuel ought to be no burn?

Walt, I would move forward with the LED test at the injector harness. Might be wiring between the connector and ecu for that one cyl. Not sure if you've done this test before but be sure not to use a conventional bulb as it may overload the ecu injector driver and burn it out. LED only, RadioShack will have them in 12v.

The failure happened at a really bad time; ~25lbs of manifold boost and high rpm. I felt it break up and lifted the throttle immediately and went to the clutch.

First found the spark plug broken, oil soaked and quite lucky it did not come apart and drop the bits into the cylinder to be pounded into the head. Only piston in the engine to have any damage...

http://i458.photobucket.com/albums/q...-36-26_572.jpg

http://i458.photobucket.com/albums/q...-29-47_785.jpg

Well, I can try the LED bit. I can make them up with a resistor (forget just what value, but can find it) and LED from my stashes. Or just purchase. Since it clicked, same as its neighbor, I'm not holding out much hope for something as simple as wiring. My TPS issues were a crimp connector which had somehow pulled apart - bad crimp and I guess tension while the assembly was hanging from some bungees as car sat in trailer as it moved, etc. Calls for opening up the carefully zip tied loom, but what the heck.

Is the damage to rings and lands on that cylinder due to detonation? Looks like the kind of thing which led my wife to veto my 2.16L turbo motor project - didn't want to learn by breaking. But that can follow you anywhere.

Walt...before you go for resistor/LED combos...be advised there are such things as 14V LEDs.
There are also bi-directional LEDs....meaning they light up one color when (+) is applied to a lead...and a different color when reversed.
It might make things quicker and easier for you to have some of these around.
As long as you rely on the LED just lighting up (dont care about color) they work great.
Bob

Sunday I got in the trailer to check things out a bit more.

Leakdown on #5 (problem hole) ~3.75%, #4 4%. All leakage was through rings, which is normal. At 100 psi, valves should not leak at all. Combined with compression check of 130 psi, I don't think I have a low speed valve sealing issue.

Intake valve had proper lash. Didn't remove exhaust covers, but next time in there will see if I can get a brass drift down to edge of exhaust rocker. It should wiggle, though obviously it isn't being held open or it would leak and I'd have heard it in exhaust, because I was listening with my stethoscope's rubber tube. I'll have to take the car out of the trailer to jack it up enough to get at exhaust valve covers.

Upper plug coil wires for #4 and #5 had about same resistance - ~7.5Kohms. Coil packs really can't be at fault, because if #5 has a weak or no spark, #2 should also as it runs off the same coil. Next I'll check the #5 exhaust plug wire after bringing a longer test lead, as the lowers are sort of built-in where they pass under the frame rail.

Plugs look OK, and at least center electrodes are patent, and no VOM level leakage between center and shell. To address possible spark problems, I found I could purchase the Bosch plugs which have a pointy side electrode which is no higher than the tip of the ground electrode. This is what is in there now. Expensive plugs, but needed for clearance per the previous owner, who built the motor, so I'll replace those in this cylinder just in case.

Used borescope. Nothing remarkable down the throttle bodies to the valve stems. I felt around the exhausts to see if perchance I'd let a gasket get crosswise and block things, but all seemed OK. But the intake pocket of the #5

http://forums.pelicanparts.com/uploa...1369092052.jpg

looked cleaner, less carboned, maybe more fuel washed? than the #4

http://forums.pelicanparts.com/uploa...1369092117.jpg

Both pistons had dark crowns, as compared to the valve pockets. Not sure what this means, other than possibly a spark problem.

Someone suggested I check valve springs. While my experience is that these motors will run up to 7,600 rpm happily with broken inners (I ran most of an hour endure that way), and they all seemed their normal hard to compress selves when I reassembled the heads after doing the valves and seats, I can't afford to overlook anything at this point of bafflement. Maybe something broke during its very short running time post rebuild, while I was trying to sort it out.

I might be tempted to swap the entire coil with the coil for another pair and see if the problem follows to the new pair. Could be weak enough that it won't fire both and #2 is getting just enough... I had this experience on a gm style two pin coil from Jegs out of the box. They replaced free of charge.

Inline tester takes guess work out:

http://www.jegs.com/i/MSD+Ignition/121/3503K/10002/-1

Walt,
Is it possible 5A and 5B leads are reversed going to the wrong DFU, respectively?

Edit: The more I think about it, the idea doesn't seem to hold water, but I would go over the DFU to plug wiring just confirm everything is right. Sure sounds like an ignition issue.

Here's an illustration for a Porsche twin-plug, wasted spark, Electromotive TEC-3.

http://forums.pelicanparts.com/uploa...1369166837.jpg

It does sound like an ignition issue. Maybe if a coil is on the ragged edge, small differences in impedance or resistance on one plug run of a pair might lead to one getting just enough, and one not?

I've got a new coil. Carried it for years as a spare just in case. I can swap it for the 2/5 uppers, and see what's what. And if no change, for the 2/5 lowers. Since by chance 2/5 have the EGTs, any change will jump right out.

I can also find and reinstall the ground wires I used to have attached to one of the mounting screws for each coil pack. Since the packs are bolted to brackets I fabricated and welded to part of the roll cage, I've never thought these were all that useful, and when I switched from HPV1 ignition only to the TEC3, I didn't reinstall - with no apparent bad effects.

For a while, my friend and I wondered if we might be getting a minimum on time complication, but I've kind of discounted that.

Still no joy
 

I'm getting pretty stumped.

#5 compression good, leakdown good, intake valve spring (levered against it and #4 for comparison, wasn't budging with pushing with fingers)and lash good, exhaust lash good, and spring seems OK (checked indirectly).

Sprayed brake cleaner around outside of #5 TB. No change in engine. Sprayed some down throat of #5 TB - engine picked up for a while.

Swapped spare ignition module into upper, then lower 2/5 slots. No change. Swapped right and left side wires at module. No change. Put in new wires for #5 upper and lower. No change. Measured resistance on old wires and new ones - same at about 7.5K ohms. New plugs right side upper and lower, no change. Plugs out, no fuel pressure, connected the upper #5 and grounded it, watched the upper #5 plug spark away.

All injectors clicking away with engine running. 12V LED attached to #5 injector plug, blinked away. Plugs out, throttles open, crank engine with one injector attached. #5 sprayed just like the three or four others I checked. Checked continuity of injector wiring to the positive wiring point - just fine. And pulled the white plug and checked from ECU to #2 and 5 injectors. About 0.3 ohms resistance, same with one or two others.

But the brand new plugs in #5 show no signs of ignition. EGT for #5 doesn't rise. IR gun heat readings show header for #5 significantly cooler (more like base engine temp) than the five cylinders which are firing.

Only oddity I noted was that #5 on the Unisyn was pretty close to all the rest (adjusted mid-range with idle air screws on TBs). But the idle air screw made no difference at all. Though without fire, perhaps that is what one would expect?

About all I can think to do is reduce the ignition advance at idle. Starting (600) is 14 degrees, 1000 is 16, 1500 is 18, and 2000 is 26. I made a map with starting the same (it starts right up, and I'm now using a remote starter so I can start and futz from behind), 1000 at 12, 1500 at 14, 2000 at 20. This on the off chance that for some reason #5 (which has the best VE because it is shortest) is having trouble dealing with the big cam (even though #2 isn't).

I'm open to suggestions. Next beyond futzing with the programming is to check cam timing. If it is a bit off on the right side, maybe somehow that affects #5 more than #s 4 and 6? 4 does some backfiring, and the plug is blacker than #6, which has the best looking plug, considering all my starting and testing has put almost an hour on the engine meter.

Open to more suggestions.

Walt,

I had an engine brought to us to dyno. I go through the normal hookup, of which one thing we do is crank the engine over without spark plugs until the oil pressure comes up. It didn't dawn on me at the time, but I remember thinking .....gee, this engine seems like it cranks slower than what I am used to hearing. So everything is hooked up and it starts up fairly normal, but sounds off key, like maybe down one cylinder, and a little weird popping now and then. So I am leaning into the engine and the left side of the muffler was cool, like I could put my hand on it. This engine had stock heat exchangers and stock early dual in single out muffler, so I could not isolate the cold cylinder easily. All of the spark plugs looked weird, with only one wet one and the others on that bank were black but not wet. My gut instinct said the cam was out 180 degrees, and after a quick check, sure enough it was. The engine builder had done these engines before, but somehow it got put together 180 out. The cam was reset and everything was good..... and the engine cranked faster with plugs in, now with good cam timing , than it did before with the plugs out.

After reading through your posts on this, I would have to think this is the only thing left. You have done the proper diagnosing, but the cam being out 180 is something you don't commonly see...first time for me in many years. So this one really throws everyone a curve ball.

You will get it sorted..be strong.

This tells me fuel related because brake clean is super combustible. How old is the fuel in the tank?

Scotty - for sure I'll check cam timing. With a big cam I'd not have thought it would turn over without interference, but easy enough to check. The one time I got an SC (964 cam) wrong, we discovered it while installing rockers. Waste spark system might help it run this way?

Fuel is over a year old, but why would one hole not fire when the rest do?

Out with the pair of dial indicators and Z blocks. I'll feel stupid, but relieved if this is what is ailing it.

Pulled a few cars from extended rests with aged gas... even without gumming it burns terribly. Uneven firing, stink, way down on power etc. No off the shelf additives help bring it back. Siphon out and burn off in a lawn mower or wife's Camry. :)

Walt,
You're running batch injector firing, correct? I know you've swapped injectors on #5, but have you tried swapping injector leads on #5? Using the IR gun, you should see the bad cylinder shift from #5 to whichever cylinder injector lead you swapped. There is the possibility that you could have a bad injector driver in the Tec3r. If that is the case, the good news is you have 8 channels for injectors and your using 6 of them.
You will only get black, sooty exhaust if there's a PARTIAL burn. Going beyond that, there is no ignition, just wet plugs.
Can you operate #5 butterfly separately? I suspect if you open #5 butterfly all the way, with the engine idling, #5 will start firing.

Dave - I had been wondering if a driver (or something) was bad inside the TEC3R ECU. Sending the ECU back to Electromotive is part of the plan down the road if I don't turn up something. But here are reasons to think ECU failure is not the case.

1) The #2 and #5 injectors share a common driver. The wire from the ECU splits, so to speak, where the loom splits to serve the two sides. So if the driver is bad for 5, it should be bad for 2. #2 is firing normally.

2) I opened the butterfly with spark disabled and plugs out to make spinning the motor easier, and watched the injector fire, like the other injectors I reconnected for comparison. Unless a load affects something, it is hard to see how injector timing is part of this deal.

3) I inherited the loom, which is from the factory, and I inferred that the connection where the driver (ground) wires split was good. Testing with ohmmeter also said things were good. Alas, as a bad connection to just that injector would have explained all.

Electromotive's manual is pretty good. My engineer friend who installed Megasquirt on his 928 says it is better than the MS information. However, it is not perfect. For instance, you can chose from three different basic setups for a 6 cylinder dual plug engine on a basic setup screen. Unfortunately, the terminology on the screen is not the same as the terminology in the manual. Basic, staged, phased, sequential, TBI, maybe more terms. Grrrrrr.

By checking back on many saved maps, I see I am using the same setup as previously, when all worked just fine. Which is part of the frustration here - worked fine, no wiring changes, put rebuilt engine in, now this. Rebuild included new bearings, rebushed and refurbished rockers, valve job, and aluminum flywheel with Tilton 5.5" clutch. Shouldn't have affected anything other than perhaps fine tuning.

If I have it right, first off, sort of like waste spark, but not wasting anything, as I have it set up, each injector fires twice per 720 degrees of crank rotation - once timed around when intake opens, and once one revolution later (during ignition). And with cylinders firing at 360 degrees from each other, one driver, like one spark coil firing, works fine for both cylinders.

Not having a cam signal, I can't use full sequential, and think I don't want to anyway because I'd need huge injectors to get enough in with one squirt at high RPMs. So I think what I am running is called phased sequential. If it involves a "batch," it is batches of only two injectors times three.

The ECU has 8 injector drivers in two clusters. I am using three (which are siamesed) of four from one cluster, the 4th being for 8 cylinder motors. I confirmed I am using the proper three. Had I found something obviously wrong with injector firing as such, I would have looked into using the appropriate lead from the other cluster. The second cluster is for use with a two injector per cylinder system, which I don't have.

I can't easily switch injector leads around the way they are loomed. I could switch 4 to 5, and 5 to 6, but 6 would need a patch cable to get back to 4. And it would be a stretch to go the other way, omitting 6. I have some spare female connectors from old CIS looms, but nothing to simulate the male connector of an injector, so it would be quite a cobble.

However, the fact that I got fire in that hole when I squirted brake cleaner into the throat suggests there is something about the timing of at least that one injector which is off. Is brake cleaner so volatile that it could fire off from compression like a diesel, so spark being off timing also wouldn't prevent it having some effect?

So I need to stop thinking, and Monaco FI is over, so I need to be getting out to the trailer to check cam timing. If that is off on the right side, it could explain all. In any event, one basic parameter of a motor which needs rechecking.

Because it is in the trailer, which is stored in a rural area, I've been running it there (lots of people, new baby, etc. where I live, and open exhaust). Which means I haven't had an exhaust valve cover off yet, as I can't jack it way way up on one side in the trailer. Jack parallel to car = ripe for disaster. To back car out of trailer I need to start it (or enlist someone to push), and I am using the orange silicone or whatnot valve cover gaskets. These are the bee's knees, but the motor has to be stone cold when you remove the gaskets from the studs or they tear. Always some complication.

Thank you for trying to help me dope this out.

You are a sharp guy Walt. You not only understand what makes your engine & EFI tick, you didn't say who won the F1 race!!! I appreciate that. I'm watching it later.

I'm not feeling all that sharp right now.

The good news is that the cams were not installed with the right side 180 degrees out. That's also the bad news, as I'm not really getting closer to solving this.

Pulled the intake valve covers, watched what was happening. All six intakes started opening in their proper order. Set up the dial indicators (had to get new batteries for both) and took measurements for #1 and #4. Got basically same lift. Cam is GE80, and spec is 6mm.

When I was assembling the engine, I noticed that the Clewett crank pulley and 60 (-2) toothed wheel are pinned together (as I recall), so no manual setting of the wheel. This is the offset type using the distributor hole and stud to hold the sensor holder off to the left side. I wondered if this was an artifact of machining, as the guy who originally built this motor had a machine shop combine two different good halves into one good whole. That might offset things some?

But I also tested to see where true piston TDC was, and found it was not lining up with Z1 on the fan housing marking (or maybe it was with the case centerline). The pulley has three marks around Z1. The middle is marked Z1, and there is a mark at what I guess is 5 degrees off on each side of the marked Z1. I'm regretting not writing this down, but if I use the right side mark, which would be 5 degrees to the right, that is about where TDC is, and the reading is at 6mm more or less.

If I read the dial indicators at the marked Z1, I get about 6.5mm of lift at overlap.

However, the sensor, reading the trailing edge of the 11th tooth, is (if the right side mark is, indeed, TDC) is reading the "true" 12th tooth, which is a 6 degree change.

The TEC3r manual says you can use the software to adjust for mechanical tooth variances, and gives examples. In my case, if I figured this correctly, I'd want to tell it to use the 10th tooth, which would get things only one degree out (one degree "retarded", so to speak). Alas, when I use the software, it won't allow me to enter "10". The software listed range of adjustment is 11 (standard) to 18 (way retarded)!! I'm going to have to contact Electromotive about this.

I can easily enough pull 5 degrees of timing out of the ignition map, and try that. However, the toothed wheel and sensor also control the timing of the injectors. I'm not finding any discussion of how to adjust injector timing. All discussion about injectors is about a percentage change in pulse widths, not pulse initiation. Perhaps Electromotive can enlighten me there as well.

It has been suggested that old fuel may be part of this. About 5 gallons in the tank is year old 110 octane mixed about 75% of that with 25% of pump premium (that for another motor with higher CR). I added 5 gallons of 91 octane pump fuel last month when I first tried running this motor on the track. So it isn't all all that old, and in any event the fuel is good enough for the other 5 cylinders, and because the #5 injector sprays like the others visually, I can't see jellied old bad fuel somehow interfering with the #5 (which used to be the #6 and working, so it seems it can't be internal either). The injectors are on a fuel ring, so a single obstruction somewhere ought not to affect things either.

Here is something to ponder, though. Using the Unisyn I found that the idle air bleed for the misbehaving #5 didn't really have any effect at all on where the little plastic ball was in its tube. Naturally it didn't affect idle, because the cylinder wasn't firing. But the ball was sort of close to where I had adjusted all the others. It was a bit short of the middle mark, which I was using. So air was being sucked in at almost the rate it was on the others.

I would have thought that I'd see some effect - less vacuum with more bleed, and thus a lower ball? (or is it the other way? - in any case, some effect).

So that's where I am. I sure am glad I have those orange silicone gaskets - as long as the engine is cold, I can reuse them forever.

Hey Walt,
This is certainly a challenging bug, wouldn't you say? Could you post a pic of the sensor and Clewett pulley on your engine?
The older saw-toothed pulleys were pinned together, but the newer Clewetts are billet/CNC machined as one piece. I'll check when I get home. Are you using the older saw-toothed pulley or the square-toothed pulley?

The Unisyn on #5 was operating properly. An engine is nothing more than one big pump and since the Unisyn is only monitoring the intake valve opening creating vacuum while the piston is retreating.

Have you retraced all the spark plug leads back to the DFU's?

Dave

This has baffled better minds than mine.

The Clewett pulley has the toothed wheel attached to it with, I think, four screws into the pulley. So the only misalignment there would be at least 90 degrees off. While my other Electromotive setups use the wheel on the back (rear of car) side, with a case centerline sensor location, and thus are easy to check for 11th tooth register, the distributor side Clewett mounting is not so obscured that I can't verify that I'm not 90 degrees off. It is just a bit harder to count teeth despite using magic marker to help.

In addition to the fact that the spark wire (and injector wire) loom/lengths are set up so you can't easily make mistakes, and the fact that none of that has changed since 2010 when first I ran this motor, and the fact that waste spark should mean if one is wrong, so is another, I have, indeed, retraced many times. And found nothing, alas.

I kind of figured the Unisyn is just measuring intake "suction," which ought not to be much, if at all, influenced by whether a cylinder is firing or not. So I thought that the idle air bleed screw ought to have the same effect on the Unisyn whether the hole is firing or not. And it doesn't.

So I need to bring my propane torch with a piece of hose attached to it to use propane, and not sprayed brake cleaner, as a better reverse sniffer tool to check for massive air leaks in the intake tract. Nothing suggests itself, but a better check is a better check.

Now if I can figure out whether I should tell the TEC3r that it should use tooth 10 or tooth 12 in order to retard the timing of all events (spark and injection initiation) by 6 degrees, I can see if that brings #5 to life. I think (from reading the manual, which isn't quite as clear as I would wish on this point, it is 10 I want for retard, but I may have that backward.

And I will reinsert the piston stop in a spark plug hole to recheck where TDC really is on this setup. One theory I have come up with is that the right bank is right on the ragged edge of something, and since #5 has the best flow (straight, not curved, manifold) it is over that edge. And that a small cam setting variation for the left bank has that side on the good side of ragged.

Have you confirmed that plugs 5A and 5B are firing? If you have a clamp style timing light, you can at least narrow the scope of your problem to ignition or fueling. Just don't know if the 6 degree shift in events could make any kind of difference for cylinder #5. That is more in line with improving engine efficiency than whether a cylinder fires or not.

Now if you have an injector firing AFTER an ignition event, that could be a problem. But since the injectors are fired phase sequential. that can't be it. #2 is firing both ignition and fueling in sequence confirm by your IR gun.

Is the trigger pulley a transplant from the 2.8LS engine? I'm trying to figure why the tooth-offset is different than before. Could earlier cranks have a different woodruff key offsets than later cranks?

Those coils do go bad. Id replace the offending one and try it. I had similar symptoms where one cylinder would randomly not fire and then BaNG would fire strangely.

Still no joy
 

I took a spare (unused, been sitting trailer for 10 or more years just in case) coil. Replaced the upper 2/5 coil. No change. Put old 2/5 coil back, put spare in lower 2/5. No change. I can dig out my DFX-1 plug only crank fire, and keep substituting coils off of it, but I don't hold out much hope there.

In addition to just pulling the plug, attaching the coil wire, and turning the motor over watching it spark, I used my clamp timing light. The engine runs a bit uneven at that level, but every one of the 12 wires from the coils appears to light off the timing light the same (as long as I get the arrow on the clamp right). Jumps around a bit when shone on the pulley, and pulley has no marks in the vicinity of 16 degrees advance or so, but all that part looks OK.

I got out my hard piston stop, and redid what I had done on the engine stand to locate "true" TDC. This time I used #4 instead of #1, but surprise - results the same. This time I measured things and wrote them down. However, the 6mm cam timing is set using the "true" tdc, but because the difference between the fan timing groove and the pulley is very close to 5 degrees, and true is about 5 degrees counterclockwise from the groove (to the left), I can use the first or most clockwise pulley mark, and the fan housing groove, and come up with the same overlap readings - at least enough for present purposes.

http://forums.pelicanparts.com/uploa...1369888091.jpg

I was all excited about the TEC's ability to alter, electronically, the mechanical (tooth) advance. The crank wheel sensor is basically set to the pulley, so I'm assuming that timing is off. So I made up a bin (program) using putting in 10 instead of 11 where this is done on the screens. Didn't help. Well, maybe I had that backward - maybe it needs to be 12 instead of 11. Other than idling at around 1,000 RPM instead of the 1,200, nothing was different. #6 exhaust at idle 400 F. #4 same. #5 160F. #5 upper plug inner insulator looks white as new (is new plug), and the steel has zero deposits.

I didn't recheck the left bank, but all my previous readings showed header temps all to be in that vicinity and fairly even. And all I have to do is look at the dual EGT. Left needle is up some, right needle just sits down at the bottom. But it works - I've confirmed that.

Everything seems to point to fuel (because when brake cleaner is squirted into #5, things pick up for a while. So after I do a propane check to see if that finds an air leak the brake cleaner didn't reveal, I think I'll switch all the left bank injectors over to the right bank. No matter that switching #s 4 and 5 didn't do anything, etc. And if the loom will stretch, I'll see if I can have the left loom fire the right bank, and vice versa.

I think I'll pull the Buckley headers off, so I can look up the exhaust port, and confirm there isn't somehow something obstructing the exhaust. Seems implausible, but they are relatively easy to R&R due to careful design.

So what's different about the motor after the rebuild?

Lightweight clutch/flywheel? Wouldn't do this. Maybe cams were originally timed using the normal marks? That would mean a nominal 6mm overlap cam (that's a lot, by the way - almost half total lift!) was actually timed at around 5.5mm? That might explain why the torque curve up high is so healthy - I only dynoed up to 8,200 RPM, but my optimum shift RPM calculator says I should be shifting some unknown number of RPMs higher. Advancing the cam ought to bring that top end down a bit, which wouldn't necessarily be bad. But how could any of that affect only one hole?

My using 10, 11, and 12 tooth parameters means five of six fire reasonably well over a 12 degree range.

I am also running a fuel pressure regulator with a vacuum port. Hard to see how that would do this. Pinching off the hose to the regulator port doesn't change anything.

I had used a slightly altered program when I was dynoing my ill fated 2.8 short stroke, but I've put back in various previous LS programs, and checked all the sensor inputs, modifying the fractious TPS as needed. Don't think that is what's doing this.

Something mechanical with the #5 valves that I can't spot?

Which cylinder quit previously?

Walt,

Did you say you were running sequential injection and now changed to batch? If so the timing of the batch fire on #5 may be wrong. If the injector fires when the intake valve is open the fuel doesn't get a chance to rest on the back side and evaporate. Makes for a poor burn in that cylinder.

Just a thought I had.

Tom Knoblauch

Good thinking Tom. Depends on the injector style. The Siemens Deka are a fine spray rather than a jet spray so injector timing is less important... many injectors are mounted at an angle so they impact the port wall first with the jet spray rather than the valve. Good thinking outside the box. Could contribute if the injector is aimed and timed wrong and is jet spray pattern.

I'm not running sequential (or sometimes "full sequential"). Electromotive is not 100% consistent in their terminology. The option I use has injection pulses coming once per engine revolution, like the waste spark. This is the same setup which worked fine before. Electromotive is also set up to use a secondary or high speed injector, but I'm not doing that.

The confounding factor to normal diagnosis here (other than my hard head) is symmetry. Not only are all five other cylinders firing, but because they are paired, why would one cylinder in a pair work, but the other not? You'd think swapping components around would reveal one as bad, but that's not the case.

At least so far. I keep hoping I'll hit pay dirt.

Walt...the more I read...the closer I come to the idea that you have an air leak.
Cracked head?...or intake runner?
Perhaps a stuck exhaust valve?...letting some of the charge out?
Maybe a piece of crud on the exhaust seat?
Bob

Bob

I am thinking similar black thoughts.

Problem is, some of the possible mechanical causes should also show up as low compression or bad leakdowns, or both. And the PMO manifolds are pretty darn stout, as are the TWM throttle bodies.

Still to come, a more calculated infusion of propane around all parts (except the throats) of the #5 intake tract. Squirting brake cleaner did not show up any leakage.

Walt...we had a problem one time with an engine that ran lean on one cylinder.
After about a week of chasing our tails...we tore it down partially.
We found a piece of gasket hanging in the chamber near the intake valve...it must have upset the flow of the incoming charge just enough to make it run leaner than the other 7.
I know that Porsches don't have head gaskets as such...but the small piece of gasket leads me to believe that any slight difference in configuration in only one cylinder can upset the apple cart.
Any possibility that one piston has some sort of profile difference?
Or..rings...top ring on #5 different?
Reaching for straws here.
Bob

Me too.

Leakdown arguably slightly better than #4 suggests not ring issue. All of intake basically to valve visible down ITB throat with butterfly open. Plus I borescoped it. Nothing in there.

That leaves exhaust, so pulling header is on the list. Because I installed the headers with engine in car, the possibility of a problem with a gasket there exists, though inspection of outside doesn't show anything amiss, and I put a dab of grease on the gaskets to hold them to the port while putting the individual primaries up there and getting nuts on to keep things from falling down. Pretty fail save, but something is wrong.

And it has been suggested that I disconnect the #2 injector, and see if allowing all the current for the injector solenoids for that pair to run through #5 makes it fire (even though this means #2 won't be working. Easy enough to do.

I thought #5's spark plugs were wet when you pulled them out?

Could you check the crank sensor to toothed pulley air gap?

Oh to have an o'scope at this time would be invaluable. The engine is acting like it is in some sort of "limp mode" doesn't it? Are there on-board diagnostics where you can monitor MAP, O2, crank sensor in real-time?