3.2: not firing on 3 & 5

[chrisf]

I’ve developed an issue with my car and think I am pretty close to running out of options here. I am running a turbo charged ’86 3.2 with about .5bar boost. The car has been running extremely well for a few years now.

I have been doing a little work fixing a few oil leaks, etc. over the last several months, and had finally gotten to a place where I thought I would be done for a while, right? Hahahaha…..

A little bit of a back story that might be relevant: the last week of February we had a few days of pretty warm weather, and I thought I’d take the opportunity to lean the idle out a little. Since I have turbo’d the car, I find that the mixture changes noticeably winter to summer, so I have been tweaking it a little to compensate. So, the next morning I notice a little bit of a whine sound, and then I notice the car seems to be running a little leaner than what I adjusted for the previous day. The whine sound is a little louder as the day goes on. I check the alternator bearing by removing the belt, and still the sound is there. I start freaking out b/c I am leaving for Colorado the next day, and I will simply not be able to relax with this on my mind. I keep starting/stopping the engine trying to identify the sound. After a 1/2 hour of this I am kneeling behind the car defeated. I don’t want to get up to shut the car off, so push my hand over one of the silicon intake pipes (by now I have the intercooler off b/c I was going to go ahead and turn the 3mm screw back to where it was, richen it up a little) to kill the engine. As I am pulling my hand off the pipe, I quickly realize the engine had stopped turning, but I thought I could still the whine sound. I start the engine again, and this time keep my hand over the pipe. The engine died, but by keeping vacuum on the intake system, the whine sound was indeed there!! For about 10 seconds. Of course, an intake leak!! Which would explain both the sound and the fact that it was running leaner than I expected. I put the car away and left town relieved. When I returned, I found that the intake bolts on the passenger side where a little loose, particular those for cylinder 5. I tightened them up and was good to go.

This past week, I drove the car quite a bit. It has been running great. On Thursday I ran the car until it was almost empty. I normally don’t let it get below 1/8 of a tank. I put gas in the car, with no issues on the way home. However, on Friday I noticed at idle the AFR was at 18 (max on gauge). Not usual, and not what I had adjusted for. I ran a few errands, and noticed that while cruising the car was showing 15-16 AFR. A little to lean. I took a moment to check the AFR with heavy throttle and boost, and noticed the typical drop to 12-13. But regardless of rpm, the AFR was just too high with light throttle. I thought: “I’ll just get back to the house, and richen the mixture on the AFM, and I’ll be alright.” By the time I got back, the idle seemed to be pretty lumpy. But I didn’t noticed any missing when the car was driving. Just at idle. I tried adjusting AFM/idle mixture…and it had no effect! I even fully seated the screw (full clockwise rotation), and there was no effect. I returned to the original position I had. Then I started to investigate the lumpy idle/miss firing. This wasn’t idle surge, but missing. I started pulling plug wires. Pulling 3 & 5 had no effect on idle. I noticed clean/strong arching from the plug wires. I swapped wires up with other cylinders. No effect, still not firing on 3 & 5. I check the plugs. They seem wet, particularly on 5. I could brush the plugs completely clean with a brush!! I checked the firing of plug 5 while out of the cylinder, and from what I could tell, it is firing strong. I swapped 4 & 5 plugs and installed them. Still no effect. I rev’d the engine to about 2K and thought maybe pulling these wires (3&5) had an effect…maybe? But nothing like pulling #4 while rev’d up. I did a quick compression check on 5 & 4 (to compare). The engine was warm, and they both were dead on 140psi. (When reading up on this a little later in the evening, I see that this might be a little low, but then saw a little blurb about the throttle being open, which I stupidly didn’t do…so maybe a little bit higher than 140psi.

I began to think that it must be related to running the tank empty (crud) and/or maybe bad gas. I ordered a new fuel filter. Yesterday, I changed out the filter, and removed all the fuel injectors. I blew air thru the fuel rails, and then cleaned, blew out the fuel injectors. Still……no change. The car still doesn’t seem to be firing cylinder 3 & 5. I had noticed that at idle (as good as the car can idle now), that the vacuum pressure it almost nonexistent. I can rev the engine, chop the throttle and the boost gauge will show full vacuum, but upon returning to idle, the gauge is almost at atmosphere (I also checked the back of both my gauges, and there is no leak there). Soooo…I started in with the spraying of starting fluid. Doesn’t seem to effect the running condition when sprayed around the intake runners/fuel injectors, or any of the boots/hoses ect…I did spritz a little across the AFM/pipe opening and boy, did the engine ever like that! I tried pulling the injector connectors. 5 didn’t seem to have an effect. Pulling 4 & 6 did, but not like pulling the plug wire.

Another test: at idle I started pulling plug wires. I pulled 6, then 1, then 4, then 2. I think I recall the engine dying at this point. I pulled all the wire except for 5. I tried starting the car. It turns over, and I can tell that wants to fire on 5. It’ll sputter and cough. Same thing with 3. When I tried 5 & then 3 with another cylinder, it will fire but won’t run. I am lead to believe at this point that I am getting some type of ignition on 3 & 5 but…..I just don’t know. I drove it to get some more starting fluid yesterday, and while driving/cruising it seems fine, but at this point the AFR gauged is maxed at 18, where normally it was running 13.5-14 or so.

I thought about maybe running/driving it to blow any crud out of the injectors (I put a bottle of tehcron and some fresh gas in it) but I don’t want to drive the car with an AFR of 18 or even greater. I am afraid of burning up the engine! To be honest, I am worried I might have already done some damage. The few times I opened the throttle and put positive pressure in the manifold, the AFRs were low, but I am afraid the lean condition while cruising for an hour or so was too much. If it is a fuel issue on cylinder 3 &5, then I might have been running ok on the other cylinders, but extremely lean on 3 & 5. Scary. I am hopeful I am ok because I am seeing even compression between what I consider a good cylinder and cylinder 5. A leak down test would probably put this issue to rest.

Along the lines of a little summary I have in my mind: A lean condition could exist (regardless of spark) if 3 &5 were not getting any fuel. Those cylinders are still pushing air, mixing with the combusted gasses of the other cylinders, diluting the air by the time it reaches the O2 sensor, leading to a lean reading. If I was getting fuel to these two cylinders, but no ignition, it seems that I would be reading way too rich, unburned fuel mixing with the exhaust.

I tried/reading searching for quite a while last night, and found a few things I might try, but nothing quite like this scenario. I read of a story about a difficult start/bad idle Carrera, that would start right up and idle if the AFM was disconnected. Seems weird, but I might try that. I also have my original AFM unit pulled out and ready to put on. I’ll also try that to see if I can affect the AFRs, achieve some adjustability.

But, the first thing I’ll do is start up the engine and keep my hand on the 3&5 cylinder exhaust header to see if they warm up as fast as the others.

I am also thinking about just pulling the entire intake system off and rebuilding it. That, or maybe just put the big turbo on it, replace the waste gate spring with the 2 bar one, disconnect the AFR gauge, and just drive it!

Thanks for reading (sorry to ramble on for so long), and any insight would be greatly appreciated.

[Trakrat]

Have you thought about replacing your 02 sensor?

[chrisf]

I am not running the factory O2 sensor. For my AFR gauge, I am running a wide band after the turbo, but it is not in anyway connected to the DME or the rest of the system in anyway.

Upon power up, the gauge defaults to 14.4, and then goes thru a little startup routine. If the sensor is cold it slowly goes to 18 as it warms up. Once the engine is started, it would then drop to 13 or 14 or so....whatever I had dialed in using the screw on the AFM.

If it is warm, when powered up it reads 14.4 and then goes to 18 pretty quickly. Again, starting the engine, it would drop to 13 or 14 or so.

Now....once warmed up it reads 18 and stays there during idle, running. If I give it gas.....it will drop the AFR until I let off the gas...then back to 18.

This is why I think the wide band O2 sensors is still good. I think the AFR issue is somewhere else.

And this sensor, i don't think, has anything to do with poor running on 3&5.

[RLJett]

What about a bad injector? You said you cleaned them and checked for seal leakage but what if they are just not squirting fuel like they should? Is it easy for you to swap your 3 and 5 with other cylinders and see if your problem follows where those injectors got moved to?

[chrisf]

forgot to mention, I did swap out 4 & 5 yesterday. no effect.

A buddy suggested checking a screen up by the pump. I'll do that this afternoon.

[chrisf]

update:

I removed the pump, but didn't find a screen anywhere in it or the assembly. I did look into the tank (I have a center fill on my tank) and I did see a big screen down in there around where the feed line for the pump goes, but I couldn't see any debris or crud in there.

I put everything back together, and started the car up. within a minute all the headers except 5 & 2 where hot. I thought it was number 3 that was not firing, but it got pretty darned hot, pretty quickly. I shut it down and decided I would check the fuel injectors on 4-6. I removed them, cleaned them with pressure and a 12v source. They all sprayed as they should. I then swapped injectors 4 & 5, and reassembled everything. Started the car up, and now its seems as if 1-3 heated up at the same rate, as did 4 & 6, but nothing on 5!!

I then cleaned the distributor cap and rotor. I swapped the wires for 4 & 6. still nothing on 5. I pulled the plugs for 4-6. 4 & 5 I had swapped and clean yesterday, they were both still pretty clean. 6 seemed like it was really beginning to foul up. It was black and thick. I swapped the plugs around again, and still nothing on 5.

I did another compression check on 5, and it is showing about 150psi. While maybe a little low, I believe this to be more the adequate for getting everything blowing up in there correctly, right? I also put a bore scope in the spark plug hole, and it looks in order. nothing odd or chunks of whatever. I took off the intake valve cover, and everything was good there. I didn't remove the exhaust valve cover, as I didn't want to get into that this evening. I also swapped out the DME relay, again, and I re-plugged the DME itself. still no change.

I am thinking that I am not getting any fuel in 5. Perhaps the injector is not being cycled. I have swapped plugs, wires, and cleaned and swapped injectors.

The reason I think it is fuel and not spark is that my AFR gauge is reading very lean, yet the other plugs I have checked show signs that I am running very rich. I dialed the idle mixture up to just about fully enrich the system. If I was getting fuel into 5 but no spark, I would think the gauge would show rich....because of the unburned charge. But, if I was exhausting nothing but hot air from 5, would that be enough on a 6 cylinder engine to show the system running lean?

Maybe I should check the fuel pressure at the rails?

[brighton911]

From your description, it seems like a fuel injector is not "firing". My thoughts are you may have a broken wire to the injector(s) of the affected cylinders. Injectors have two leads, one is always 12V+ and the other is a ground pulse from the DME to cause the injector to open. Have you checked to see if the dead cylinders are indeed getting the ground signal for the injectors to open? You can use a "noid light" to detect if they are getting a ground from the DME. Assuming you are running the stock DME, injectors 1-3 are driven from pin 14 of the DME, and 4-6 are on pin 15. Therefore, they trigger in groups of three (on each bank).

[gtc]

Have you inspected your injector harness?
The wires in my original harness wore through where the harness was folded back against itself. I couldn't see it until I had removed the harness from the fuel rail when I tore the engine down for a rebuild. I'm pretty sure that contributed to the knocking i was having on two cylinders.
Edit: Ha, looks like we had the same idea.

[chrisf]

whoa. are you guys saying that the injectors for cylinders 4-6 all fire at the same time?

Is this why the injector wiring harness has only 4 pins: (2) for 12v for each bank, and (2) more for the ground on each bank?

if the lead for the connector on 5 is bad, could I jumper from the connector on 4 and drive both the injectors properly?

[brighton911]

Yes, that is correct. Go with your idea and report back, inquiring minds need to know what the issue is/was!

[chrisf]

Made a light to test the connector on the wiring harness. Light began to glow faintly When connected to the 5 lead. Checked the 4 lead as well and the light behavior was the same. Let the car run,and again the number five header was cold..

I swapped the 4 & 5 lead, and let it run again and like before, the 5 header is still cold.

How can I have fuel, spark, and compression with no Ignition !?

[chrisf]

Tomorrow I am going to pull the rail on Cyl 4-6, put those injectors into containers of some fashion, and crank the engine to see if I’m getting equal flow through all three injectors. If I’m low on fuel pressure then perhaps injector number five just happens to be the one that is most starved

[ischmitz]

There are individual wires to each bank of injectors. But inside the DME there is only one output that drives both wires and thus all injectors fire at the same time. You could have a harness issue (affecting one bank) or a single injector. All injectors are wired in parallel.

As others said the easiest would be a set of NOID lights or an LED test light to confirm all injectors are driven.

Ingo

[Flat6pac]

Possibly your valve lash is too tight.
Bruce

[chrisf]

Originally Posted by ischmitz

There are individual wires to each bank of injectors. But inside the DME there is only one output that drives both wires and thus all injectors fire at the same time. You could have a harness issue (affecting one bank) or a single injector. All injectors are wired in parallel.

As others said the easiest would be a set of NOID lights or an LED test light to confirm all injectors are driven.

Ingo

I put the light on the plug for 4 (which I know should be good) & 5, both were making the light bulb glow a little. I then swapped the connection for 4 & 5, and still, the header for 5 is cold.

[chrisf]

Originally Posted by Flat6pac

Possibly your valve lash is too tight.
Bruce

I don't think it is. I've done/checked all the valve lash twice so far this year (while I was in there type stuff.)

I checked the intake valve yesterday, and it had that typical movement at TDC, and was opening/closing as it should.

However........I started thinking about the exhaust valve this morning. Is it possible that maybe the rocker shaft has backed out just enough to allow the rocker to fall into a pocket not hitting anything? And the rocker shaft is now sitting in just the right position to not allow any oil leak? So now, the exhaust valve is not opening. During the exhaust stoke, the burnt charge is just being re-compressed. During the intake stroke, there is a recycling thing that is going on. A mixture/struggle of combustion product trying to leave while fresh air is trying to make its way into the cylinder. And would the result be a cold exhaust header?

Is this possible?

[Tippy]

So if I read right, you used a noid and determined all the injectors were firing properly along with swapping both injectors, spark plugs, and spark plug wires to no avail along with checking compression?

Only thing that would make sense to me is your cam went flat on those cylinders at this point. Not trying to scare you, just a thought....easy to see lobes through valve cover removal.

[ischmitz]

Have you done a compression test or leak down?

[chrisf]

Yes. Compression check done. Intake valve is functioning. Will check exhaust valve this evening.

[brighton911]

When you say you put "the light" on the injector wires, you are talking about a Noid light, is this correct?