Yeah, wired up a little dash bulb with pins on the end of the wires. I pushed those into the connector on the harness. Both connectors 4&5 caused the bulb to glow/pulsate.

for today, I first removed the lower valve cover. exhaust valve of cylinder 5 looks good, everything in good condition. It is moving as it should. put the cover back on.

I removed fuel injectors 4-6 from the intake runners, and placed them into little bottles. Turned the engine over. All sprayed correctly with equal volumes of gas delivered. Replaced everything. Still the same.

I did noticed that all headers seemed to heat up quickly except for 5.

Changed all the plugs. Still, no change. #5 is not firing.

So, started talking with my buddy again: I know I have compression (at least enough for combustion, even if I have cylinder/head/valve damage). I know I have intake stroke (fuel & air), & I know I have exhaust stroke. Just no combustion. Now.....I say I have spark. I have swapped plugs, I have swapped wires, and I have checked the distributor cap. NOthing seemed wrong. He is now sure it is my ignition system.

I mention to him that last night I was thinking about over the weekend I was sure that number 5 AND 3 were not firing. 3&5 are next to one another on the distributor. So as the car was trying to idle, I grabbed the cap and started to sort of push it around a little. I could have sworn for a second or two the engine came alive and was starting to idle...and then back again to missing. I also mentioned at this point I was starting to get shocked. I could feel it in my hand, and moving up my arm. He immediately said: "you have a bad distributor cap!"

uh. ok. So I pulled the cap again, and the little graphite post in the center falls out of the cap! It has cracked apart and is laying of the floor. Could this be the problem ?! This whole time !?
I inspected it yesterday and it seemed fine. the cap is not even a year old.

Cap is about the only thing left unique to the cylinder. As a simple test connect the output of the cap to a used spark plug instead of to #5 plug,
ground that plug to the block and have an assistant crank the engine. Watch for spark.

If that makes no spark there you go. But even a weak spark at ambient isn’t sufficient proof there is spark under compression. Case in point I had a nasty misfire on my V8 in the ML430. It’s twin plugged and I did the aforementioned test. It fired the plugs. I was convinced root cause was NOT spark. But here is what I found when I opened the connector:

https://uploads.tapatalk-cdn.com/201...fc8396d611.jpg

This is under a metal cap and only under compression did it short out. I almost wrote the engine off before finding this.

Update:

Nothing!! No change, from what I can tell, in anything.

Yesterday I tried

• (2) different distributor caps
• Changing the rotor
• Changing the coil
• Just to investigate, I unplugged the idle switch. The idle jumped up quite a bit, but it seemed to still be running rough/not firing on 5.
• I also ran a jumper from the grounds on the intake manifold directly to the battery (-) terminal. Didn’t seem to change anything. (In 2014, after I got the car on the road, within a few days, I developed a poor running condition. The car would die, and then would be very hard to start. Eventually just wouldn’t start. I jumped the manifold grounds to the battery, and it fixed it. So now I have an additional ground from the manifold grounds directly a good ground back by the engine. I also removed and cleaned the transmission ground strap)

After changing these components, I again started swapping the wires from the cap to the plugs. No change. With a new distributor cap on it, I let it idle to warm it up a little. I checked the headers again, and #5 is the only one that seems to take a while to warm up. The others are hot to touch within a minute. After it had warmed up a little, I removed the plugs. While they were out, I put the bore scope back into cylinder 5. I took my time checking everything out. The cylinder wall looks good. I could see no scarring or marks/indications. The top of the piston looks good, however, it was a little wet. I could see the exhaust valve opening and closing. I could not see the intake valve with the scope I had. I changed the plugs back to the ones I had originally been running it when all this happened. No change.

My buddy came over with his timing light, a glass spark plug, and fuel pressure gauge. We did the following:

1. Removed the plug from #5. We put the glass plug in there & got everything wired up. We attached the timing light to the #5 plug lead. We started the engine, and could see the timing light pulsing correctly, but could not see any ignition or combustion inside cylinder number 5.
2. We removed the glass plug/timing light, and decide to run the engine briefly to see if we could see any fuel coming out of the cylinder on 5. Engine was started, and no fuel was coming out of the hole. Nothing at all.
3. Removed the intake valve cover for 4-6 to see the cam/rocker/valve movement. Everything is good there. We put the scope as close as we could get it to the valve stem & head, and could see no evidence of leaking on the intake valve stem. Replaced the valve cover.
4. We removed the fuel injectors/rail for 4-6. Removed and tested fuel injectors 4 & 5. They seem to be good. Swapped them.
5. Before reassembling the rail, we put the scope down into the injector holes. We could see the valve moving as it should in cylinder 5. We could see evidence/remnants of fuel having been there when the valve was seating in the head. It was still a little wet. Intake valve for 4 & 6 looked good as well.
6. Put everything back together and ran the engine. Same poor running/idle condition. However, when my buddy grabbed and started moving the injector electrical connection on 5, we seemed to think the idle improved a little. But not really enough, if you know what I am saying. It seemed to sound a little better/smoother and idle up. But there was no increase in vacuum pressure at idle on my boost gauge. We swapped the injectors lead on 4 & 5. I think we were in agreement: no real change. Pulling the plug wire on 5 had no effect.

Things at this point are a little hazy. One of the things we discussed was the fact that there a small little pops or back fires coming back thru the intake. Enough to hit the boost gauge and make the needle bounce. I noticed these occurring the last couple of days. It was not happening during the weekend or on Monday. Just Tuesday and last night. And it seems to be only happening for a short period while the engine is coming up to temperature. I am pretty sure that it subsides as the engine reaches a stable idle temp. My friend is pretty sure it is coming from multiple cylinders. I would agree.

7. We hooked up the fuel pressure gauge to the fuel rail system. I started the car. My friend was back there smoking a cig while very, very closely staring at the connection of the gauge to the fuel rail to ensure we had no high pressure fuel leak. He, of course, had a fire extinguisher handy. Safety first. Hahahhahaha. Fuel pressure is good.
8. I think at this point, we were just messing around with it. I showed my friend how to jump the B & C terminal for idle adjustment on the Carrera. When I did this, the idle dropped noticeably. I could adjust it back up and when I removed the jumper, the normal idle is too high. Even with this high idle, it does not idle smoothly. So I adjusted the idle back down.
9. Moved some plug wires around, still nothing.
10. Put the timing light back on, and it seems to be timed correctly.

At this point, I believe, I pulled some plug wires. While idling:

• Pull 1, idle affected
• Pull 2, no effect
• Pull 3, no effect
• Pull 4, idle affected
• Pull 5, no effect
• Pull 6, idle affected

I also revved the engine steadily a bit while he pulled plug wire 4 (the engine loaded up) and plug wire 5 with no effect. We didn’t continue this test on the rest of the cylinders.

My friend is convinced that there is something aside from the engine itself that is wrong. I think I agree at this point. It seems to be ignition related. And we are both pretty sure that at idle cylinder 2,3, & 5 are not running very well.

I will next check the flywheel sensors. I had an 89 that did seem to run and idle well enough, but didn’t want to rev above 5K. First thing I did was confirm the correct spacing of the sensors to the flywheel. I readjusted them and that fixed the problem.

I am also wondering about the plug wires themselves.

Do you have a spare dme? While the sensor spacing is critical and will cause ignition issues, your issue sounds like a failing dme.

Maybe this helps, maybe not. I once had a weird spark situation related to excessive spark plug gaps on a few plugs.. In the end, my conclusion was if I had too big of a gap, the spark would rather arc someplace else. Removing the spark plug from the cylinder and cranking showed a nice fat bright arc, but under the pressure of the cylinder, it would choose to arc thru the wires or across the cap to another plug rather than jump that arc.

Just a thought,
Chuck.H
'89 M491 Targa, 439k miles

I was thinking more about your issue. What strikes me as odd, if you do have an ignition problem and the fuel system is OK, then why are your A/F ratios so lean? Certainly if there is an ignition malfunction, the unburnt fuel entering the exhaust stream should be showing up as rich on your wideband. Something is not adding up here.

update: intake gaskets

INTAKE GASKETS !!!

finished replacing earlier this afternoon. rock steady idle at 1500 rpm. AFR showing at 11.5
will let it warm up a tad in the morning and then creep in to where I need to be as far as AFM & speed at idle.

gaskets were only two years old. spraying starting fluid right at them and the injectors did nothing. upon inspection, it was obvious which ones were leaking I found fuel that looked sorta orange-ish and sticky!

guys, thanks for all your help and advice.

~Chris

OMG. Great you found it. So it was leaning out mixture enough to make it not fire, hm.

Glad you found your problem. Now the lean A/F adds up. From my experience, I suggest adding torque checks of the intake manifold bolts be part of a 3.2 routine maintenance.

If there is no ignition, unburned fuel shows up as lean on AFR. The oxygen rich air is not consumed and turned into inert gasses because there is no combustion.

Because all the injectors fire at the same time the effect of a vacuum leak at the manifold gasket can be different on different cylinders. If the port is one that fires right as the valve opens (or just before) the vacuum leak won't do much at idle. The charge will still end up in the cylinder.
But if the port happens to be one where the injector fires right after the exhaust valve closes, the vacuum leak can allow the charge to be pulled back out of that runner into the plenum where it will end up in one of the other cylinders.

At idle the engine will run badly but at full throttle there is no vacuum in the manifold so it will run with no ill effects. It makes it a bit frustrating to troubleshoot.

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BTW - Did you change the manifold spacers or at least carefully inspect them? They tend to be crumbly junk at their age. Having to redo a job really sucks.