[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.