#5 not firing right

[JJ 911SC]

Originally Posted by Walt Fricke

I couldn't figure out how you get a post to appear in italics, so I'll wing it...

You highlight the text you want to italicized and choose the I button which is in between the B and U buttons just below the Fonts pull down menu

[Lapkritis]

Originally Posted by Walt Fricke

--REASONABLE SUSPICIONS, but why would the ECU fire (by grounding) the #2 but not the #5, which uses the same ground - separate supply wires from a panel external to the ECU to each injector, but the ground wires are connected for each pair - come together in the middle - and a single wire goes to the ECU, which dictates when and for how long it is grounded. If one of the two wires from the injector plug were bad, swapping sides should have made a difference. But it doesn't. James Bricken suggested I pull the 2 to see if the 5 would then fire (he'd run across something like that), but that didn't work either. Which is why I am thinking of carbs.

Bad power side or loose/dirty injector connector.

[Walt Fricke]

Well, I don't have a fonts menu. My screen has internet connections on top along with some other stuff, but nothing by way of editing. Then there is the Pelican screen, whose top doesn't have editing stuff on it either. Not like my E-mail or Word or the like.

I tried the 9 volt battery. It clicked the #5 injector just fine. When I powered up the fuel pump (about 44 psi static) and applied 9 volt power via a spare plug with wires exiting it I could clamp onto, I got a nice spray.

Then I used the regular 12V+ power from the regular plug, connected it to one of my spare plug's wires, and grounded via the spare plug. Same spray.

Then I plugged the regular plug back on, pulled the connector at the ECU, attached a wire to that plug's connection to #s 2 and 5, powered the pump, and grounded there. Same spray.

So, per these tests the wires are all fine, the plugs are all fine, and the injectors are all fine.

It was getting late at night, so I didn't try to start the engine after all this, not that any of it was likely to fix what ails it.

I've pretty much run out of things to try short of plopping carbs back on to try to prove that it isn't anything mechanical in the head/cam/valve/piston seal arena.

[Walt Fricke]

Bob

Wondering if there were some obstruction in the fuel delivery, I pulled the rail. It is fed from both ends, and the two injectors which flank the #5 work fine and those cylinders fire.

But the fuel rail was clean as a whistle. No possible obstruction. If there could be some odd resonance which allowed pressure from one end of the rail to cancel that from the other end in the middle, where the #5 is, you'd think that would also happen on the left side, as the rails are identical.

There is still one test. With a running engine, I will use the 9V battery to actuate the #5 injector by tapping one of the wires at the battery while the other is connected. And see if that causes that hole to fire. Kind of like squirting the starting fluid in.

[JJ 911SC]

Originally Posted by Walt Fricke

Well, I don't have a fonts menu. My screen has internet connections on top along with some other stuff, but nothing by way of editing. Then there is the Pelican screen, whose top doesn't have editing stuff on it either...

So I'm guessing your PP screen does not look like this:

[Lapkritis]

Originally Posted by Walt Fricke

.

There is still one test. With a running engine, I will use the 9V battery to actuate the #5 injector by tapping one of the wires at the battery while the other is connected. And see if that causes that hole to fire. Kind of like squirting the starting fluid in.

Be careful with the tests not to back feed the ECU circuit. Sounds like you're fine but just wanted to state to obvious in case. The dead time for this injector may end up being greater than your idle pulse width from the ecu or the volume of spray is lower than the other injectors. Could still be faulty injector even if it sprays with 9v test...

[HawgRyder]

Walt...all things considered in the fuel rail...one of the rules of hydraulics is liquids for the most part do not compress...so pressures at one end of a pipe will be the same at the other end...and hence...pressure should be constant throughout the rail.
What I was suggesting is that the fuel may be entering the intake passage...but because the #5 is the last one to fire on the cycle...the charge might be dissapating before ignition.
The only reason I can come up with is that (for whatever reason)...the charge is being expelled back out the stack of the ITB.
Like a back up of air blowing the charge out...sounds wierd to me even as I type it.
I know you have conducted a compression test that turned out OK.
If I am right...the valve opening of the intake is somehow to blame.
I can't think of any reason really...too tight a setting on intake?
Cam holding intake valve open at wrong time?
Piece of grunge on backside of lobe? (causing second opening).
I know that when you find the answer...we will all sleep better.
Bob

[Eagledriver]

Maybe the ECU itself is the problem. Could the part of the ECU that fires that batch not have enough current capacity to run the two injectors? Can you switch with another batch?

-Andy

[Walt Fricke]

Andy - that was sort of the basis for what James Bricken suggested. It was the best fit suggestion I had heard or come up with, so I was excited. I pulled the #2 injector plug to see what happened. Alas, the #2 stopped firing without the #5 deciding it would. Same result with the plugs for each bank swapped over.

[Walt Fricke]

Bob - these injectors fire twice per cycle of each individual cylinder. The "first" firing is at a suitable interval related to when the intake valve opens. You can set this (though only for all injectors). I don't recall what it is, except that it is a standard setting I didn't fiddle with. The duration of the injection is what varies with RPM, throttle position, and load (MAP). You can fiddle with that, too, but it is the same for all and I haven't fiddled with what worked before.,

The second firing happens at 180 cam degrees (or 360 crank degrees) out from the first. This is the one which "prefills" the intake space between the injector and the backside of the intake valve.

The "twinned" cylinder (#2 paired with #5 in this case) gets the same signal, and thus about the same amount of fuel from the same timing and the same duration. Except that what "prefills" one is the "just in time" squirt for the other.

There are various other ways to set up EFI. Sequential, so you have only one big well timed squirt for each opening of the intake valve. Staged sequential, so you have the main timed squirt, plus a second high rpm injector which kicks in as RPMs and fuel need go up. These require a cam position sensor, which I don't have, so I don't use these. I think there is another (throttle body injection?) which I also don't use.

This "two squirt per cycle" system is a bit like the CIS, which works fairly well for street motors by squirting all the time, though if you use hot cams with these motors, the reverse waves play hob with things.

I am familiar somewhat with fuel blowback (or fuel standoff), typically from intake/exhaust overlap. The bottom side of the air filter shields on some of my carbureted motors used to have spotting on them from fuel being blown upward before it could be sucked back down, even if this did not noticeably affect running. If the motor wouldn't run, I'd be wondering if my cams were way off and something like that were happening. But it is just this one cylinder. so things can't be that far off in this regard. At least not from any mechanism yet identified.

Here is an observation, though. Using the synchronizer (comparing air flow into each throttle body, I can't get the pith ball (it is that older kind, not the dial Unisyn) to rise as high in #5 as in the others of this bank. If I ignore the compression and leakdown tests, I might think this showed the vacuum in #5 wasn't as high as in the others for some reason, and maybe that had something to do with something. However, this is EFI and not a carb which depends on a pressure differential to get the fuel to spray. And spraying starter fluid makes the cylinder fire and thus isn't affected by any such effect. And I think what explains this is the effect of exhaust extraction even at idle increasing the vacuum and thus air flow in a little bit.

I don't have vacuum ports to directly read intake vacuums overall with a gauge. The TEC3r, when hooked up to my computer, will tell me in KPa what manifold pressures overall are, based on taking vacuum from #s 1, 2, 4, and 5. But that's overall, and can only be further refined by blocking off either the 1/2 or the 4/5 line to the central vacuum accumulator which connects to the vacuum regulated fuel pressure regulator, and to the MAP sensor.

So this is another thing to try - hook up computer and block off first one side and then the other and see what the KPa readings are and how they change, if at all.

My continuing thanks for help in head scratching.

[thumbdoctor]

Any chance something dropped into the intake port and is holding the valve open intermittently. I had a brass pipe plug find its way into a VW Type 4 and do the same thing.

[Walt Fricke]

Initially, there certainly was a chance (along with a long list of other possible blunders on my part).

But a) #5 is a straight shot into the port, so I can see most of the valve's backside, and don't see anything, b) I ran a bore scope into the combustion chamber through a plug hole, and didn't see anything, and c) one would think that at least one of the compression and leakdown tests I have done would have let the foreign object intermittently cause suspicious test results. Oh, and d) if it were really intermittent, the cylinder should fire sometimes. Alas, it only does when I spray starter fluid or its like.

But I can see I'm going to get out the borescope anyway, and look down there.

[HawgRyder]

Walt...I use the same type syncro unit...the one with the pith ball.
You say the vacuum reading on #5 is down from the others.
When I do a comp test...I jack open the throttle with a wedge or other suitable instrument so that all throttles are open the same amount.
I also remove all 6 plugs so that the engine will spin at the same RPM during the test.
Assuming you follow the same procedure....#5 being low on vacuum has to be the key here.
How about a cracked intake manifold? ... or a bad gasket between the ITBs and the mainifold?
If the setup is basically the same as with MFI...you have the head...then a gasket...then the manifold...then another gasket...then the ITB.
So...you have at least 3 places for a leak.
You are using the old ITBs and I assume the same manifold...so perhaps the gaskets are the culprit.
Unless...some kindly assistant dropped a manifold and didn't tell you?
Is it possible to swap left to right manifolds (checking the gaskets at the same time)..?
Obviously if the problem moves to #2...you have the baddy.
Bob

[Lapkritis]

^I like that idea. An air leak under the butterfly would cause a lean condition which would mean higher egt though... not much to lose if we're exhausting all options however.

[Walt Fricke]

Well, I've squirted the starter fluid all around each of the two gaskets in question. No response. They were in reasonable shape when installed. I think I dressed the gaskets around the heat insulators (each ITB has three gaskets, two for the engine to insulator to manifold, and one for manifold to actual ITB).

I guess I could put my palm over the top of #5 so the vacuum is max, and squirt again to see if anything coughs.

The syncro testing was with a running engine. I've never tried that with just cranking. Is that worthwhile? I have had the plugs out so many times once more wouldn't matter. If you do that, would you screw even more closed the adjuster? These are good only for relative readings (adjust so the balls rise the same amount on each intake bell), unlike the kind with numbers which I think is set for gauge readings.

Can't switch manifolds, as they are set up to hold the throttle cross bar and throttle bell crank.
Plus they are PMO aluminum, and you can't crack them short of dynamite.

ITBs also can't be reversed - the butterfly levers would be on the wrong end, as would the TPS. And the ITBs simply sat quietly hanging from their hoses and a bungee or two for the better part of a year. Not dropped, and they, too, are sturdy aluminum castings with no signs of cracks and such.

Even CIS and 3.2 Motronic motors with dried out and slightly loose gaskets seem to run on all six, just leaner than desirable, no?

[HawgRyder]

Walt...I have never tried a Comp test with a running engine...new one on me.
I usually jack the throttles open fairly WOT so that it stays as a constant and is not a factor in checking the compression numbers accross the engine.
With 6 plugs out and only one cylinder being tested at a time...you get a more consistant reading of cranking compression numbers.
Running comp numbers can be all over the place because of air induction/turbulance/ring seating/etc.
I have found some engines that build compression with RPM something fierce (Dykes type rings) they need some RPM and back pressure to work properly....so crank comp compared to running comp is way different.
Still can't come up with a solution for you...but brain is working away at it (keeping me young at the same time...ty)...LOL
Ooops...re-read your post...old eyes saw comp test not sync test....silly me.
Yes Sync test is correct...but also...check for consistant throttle openings (plates resting on stops at idle)...and yes...you can try the palm on ITB test...but I suspect the high vacuum caused will mask the results.
Bob

[Lapkritis]

Have you tried increasing the injector pulsewidth at idle with the engine running? I'm thinking injector dead time... ie, the signal to open is too short for a damaged injector. It would still pass the 9v test and the prime pulse is often longer than the idle pulse.

[Walt Fricke]

Bob - I too do compression checking with a compression checker screwed into a spark plug hole. All plugs out, one hole at a time, cranking only. And since I have so much interest here, I remember to block the butterflies wide open (I'm using an SC rear brake pad, as a used one was close at hand).

What I was ruminating on was use of the Uni-Syn or its ilk, which I believe pretty much has to be used with a running engine. I was wondering if differences in its readings, if they can't be adjusted with the air bleed screw, were of some significance. Or whether a running cylinder produces a better air flow than one which is at the same RPM but not firing.

I'll just test that by pulling the injector plug with the device on a running cylinder and see what the difference, if any, is.

[HawgRyder]

Walt...yup uni-syn when idling is the way to go...and yes...you should get the 6 ITBs balanced ...if they are all working properly.
If #5 does not show vacuum at idle...my question would be..how is it supposed to pull in the charge?
Is it possible that the butterfly on #5 is misadjusted?
It might be tightly closed instead of sitting on the stop screw.
Or (happened to me once) the throttle plate shifted because of loose screws on the shaft and that messed up the vacuum.
On an ITB...is it the same basic bypass of air passageway around the throttle plate...controlled by the air bleed screw?
If so...could the passageway be blocked?
Still thinking .
Bob

[Walt Fricke]

Andrew - I'll see if I can do that. The software has startup enrichments, which are for set durations. Otherwise, things at idle get adjusted by the engine temperature sensor (which I don't use - it doesn't work on air cooled motors, which either heat up too fast or not fast enough, depending on what temperature you are measuring), and adjusted by the intake air sensor. Which generally seems to mean that after things heat up for a while, idle speed drops some.

I ran the motor while manually operating the #5 injector using the 9V battery and tapping one wire onto one battery terminal. This did perk up the #5. If anything, it seemed easy to add too much fuel, as the perking up tended to take a bit of time after I stopped spraying from the injector.

Next is finding my notes on injector on times from when I had the computer hooked up to the TEC. That is adjustable, both as to a fixed amount and as a percentage.