Car is a 1986.5 auto. I have had a running issue for quite some time and have been slowly trying to work it out. It idles very rough between 600-800 rpm. When cold it will most likely die after firing the first or second time. After that it will continue to run on it's own. If throttle is applied carefully it will rev up and above 2000 it begins to smooth out. I have replaced Temp II, rebuilt MAF, swapped EZF and LH with known good ones, done the intake refresh with new ISV, checked cam timing with Porken's tool. Plugs are WR7DC and I have verified gap. New caps and rotors, new plug wires, new o2 sensor. Fuel pressure on the rail is 36psi, fuel pressure regulator and dampers are not leaking fuel when I remove the vacuum fitting. I put a long screw driver to the injectors and can feel and hear them clicking. I began pulling plugs and noticed the drivers side bank looked cleaner, and slightly wet. I pulled one of the plug wires off that bank and there was no difference in the way it ran. I pulled the plug, grounded it and verified there was spark. Hooked up an inductive timing light and again showed spark. i removed one of the ignition modules / amplifier at the front of the car and there was no change in running condition but the timing light showed no activity for that bank of cylinders. I plugged that ignition amp back in and disconnected the other and the car died immediately. Cylinder compression is 165. i have not replaced the 4 relays that are often referenced on rennlist (ignition, and 3 others) because I'm not certain they have control over the issue I have. If so please inform me and I will replace. I am just stumped. It appear I am getting fuel, I am getting spark yet half of the cylinders are dead. I have also cracked the fuel line fittings all around the engine to verify it is flowing through everywhere and it is. Fuel pump is new also. Any suggestions?

 

Weak ignition coil or high resistance/spark jumping on the coil wire leading to the cap. Some of the replacement wire sets have very poor coil wires. Also be aware that there are two different styles of the coil wires, depending on which version coil you have.

 

deleted - not relevant

 

Put that back up there....it was relevant....and a great point!

Nothing anyone is going to post is going to make perfect sense.

If he has compression, spark, and fuel...it runs!

 

Your car has basically two independent ignition systems, with each feeding two cylinders on each bank. As Greg pointed out, the coil wires are the most common problem.

Since you have a timing light (hopefully with an inductive pickup), clip the pickup onto the coil wire and see if you have voltage there. If so, go to the distributor cap and rotor button.

If not, check the coil wire for corrosion, and for correct contact. Look it over very carefully in good light for any tiny burned spots or pinholes. Make certain that the coil wire doesn't touch any metal or wire harnesses.

You can swap ignition amps (just the cables), coils etc. Should be pretty easy to find the problem.

 

I will also add that I have cleaned ALL grounds on this car. Including the coil to head, under air box, and up by the headlights. Now I am going to do the tests that you two just suggested. Did anyone catch Bill's post before he deleted it?

 

OP Says:"i removed one of the ignition modules / amplifier at the front of the car and there was no change in running condition but the timing light showed no activity for that bank of cylinders. I plugged that ignition amp back in and disconnected the other and the car died immediately. "

Then I would think the ignition modules / amplifier at the front of the car is knackered. Test with an old plug against the block to isolate which distributor cap is at play.

I went through this with my 87. Replaced the ignition modules / amplifier at the front of the car.

If you are only firing on one module you are pouring raw fuel into the cats. you should pull the fuel pump fuse until you resolve the spark issue.

 

Put inductive light on the coil wires and the light pulsed very rapidly on each coil wire so presuming that works. Then I replaced the new coil wires with the old in case I did have the incorrect wires as stated- no change. I swapped ignition amps and it was harder to start but once it started it ran the same and the same plugs were still slightly wet which I find puzzling. Makes me wonder if cam timing is off and it's not firing at the correct time on that bank. Yet I have checked the cam timing three times now.

5Tiburon- you wrote, " Then I would think the ignition modules / amplifier at the front of the car is knackered" - But I have spark there??? If it was knackered wouldn't there be no spark for that bank of cylinders? And I realize fuel may be dumping in the cats so I am only running it for a few seconds at a time and just at idle. You're right, I need to check spark at every lead. I did on two of drivers side and both had a strong spark yet when I unplugged those two there was no change in the way it ran, like the car didn't even notice.

Thanks for the knowledge and ideas, keep them coming. I have thrown so many parts at this thing I think I'm running out of items to replace.

 

Try the timing light on plug wires, especially on the ones you think are not firing. That will tell you for sure whether there's an issue with no spark to the plugs.

If you find the same firing of of the timing light on the questionable cylinders as on the good ones, then the next thing I'd double check would be that the wires for those cylinders are running to the correct terminals on the distributor caps.

 

"Try the timing light on plug wires, especially on the ones you think are not firing"
I did and it shows they are all firing. I did check that the wires are going to the correct plugs but I am beginning to second guess myself on everything I have already re-verified.

 

Bill made the very valid point that each coil fires two cylinders on one side of the engine and two cylinders on the other side of the engine....so if there was a coil or main coil wire problem, it would not effect all the spark plugs on one side of the engine. Extremely good point.

He then went on to suggest that the injectors are "grouped" together from one side to the other and that you should be looking for a crossed wire/short in the injection loom.

I think he must have realized that you had been listening to the injectors...but as I said....if you really had spark, compression, correct cam timing, and fuel, you wouldn't have a problem.

 

If you have spark on all plugs that would me the amps are ok and your car will start. I just got confused when you mentioned pulling one amp and the car died.

 

Tiburon- I believe the car died when I pulled the other amp because 1/2 the cylinders were already not firing.

I have spark on all cylinders so now I will concentrate on the injectors harness. Any pointers where / how to check? Pull each injector harness and check for 12v when they pulse?

That is a good point that Bill made. So I need to determine if one entire bank is not firing or if it is 2 on each side. More work to do, I will post results.
Thanks.

 

If your miss fire is one bank and you have fuel then camshaft timing needs to be checked.

 

I thought I was onto something until I re-read his description. It didn't fit at all, at least if his description was accurate.

My point was that is if one has an 86 with one bank of cylinders not firing, it's not the ignition system, as each of the two coils serve a mix of cylinders from both sides. However, the injector wiring is broken into two 4 cylinder sections that do match the cylinder banks. So, in that case I would look for a continuity break in the harness from the LH to the dead injectors or from the CE panel to the injectors. The wiring diagrams illustrate this.