: Intermittent spark loss on random coils 94' STS

07-16-08, 01:24 PM
Okay soo I'm trying to sell my customized 94' STS and I don't think it wants to go without a fight. It has recently been running rough and now even worse. It is def a spark issue as confirmed with a inline spark tester tool. It is randomly running on 6cyls or 4cyls. No rhyme or reason to it. It has a recent tune up with plugs(iridiums) and wires(aftermarket cheapies). It has a totally new coolant sytem and catalytic converter with 02's. We also had the ECU replaced about 1.5 years ago. That was all before this new problem. I cleaned the TB out really well also. I bought 2 extra ICM's from the bone yard along with an extra set of coil packs. I also purchased some Accel coil packs and some parts store coil packs soo I have 12 coil packs total 2 mounts and 3 controllers. I have tried swapping through all of them and cleaning out all of the connectors on the ICM. its either going to weak spark or no spark on random packs. I have completely cleaned up all the mounts ground points and even cleaned off the mounting bolts for the mount and packs. Do I need to put some kinda electric compound between the controller and the aluminum mount or the packs? What else could cause soo much trouble? I'll rerun the codes tonite to see if anything is coming up. It will barely start when not run in awhile, then when it does it's on 4cyls.:thepan::rant2: Please help guys this car is leaving a bad taste in my mouth and a gaping hole in my bank account.

BTW before this spark issue the car ran like a bat outta hell.

07-16-08, 01:30 PM
You may have the wires in the wrong places. (wrong firing order)

But you say theres NO spark coming from some of the coils?

Anyway, otherwise you could have the firing order wrong. Ill go do a search to see if i can find the fireing order ''chart''. If i dont find it first. Somone else will more than likly post it up.

07-16-08, 01:35 PM
Okay soorry forgot to say that. The firing order is correct as I wrote it down first and labled the plugs. It will randomly run great then next time you turn it on it's running like poop.used to run great when started for the first time that day. Then when you turned it off for a min then back on it was on 6cyl's. Now it's mostly running on 4cyls. You can literally pull a plug wire off while its running like poop and it won't change. Pissing me off 1 key turn at a time. I would appreciate that firing order sheet though for future reference. I need this car sold soon soo I can buy a 4wheeler(ATV).

07-16-08, 01:49 PM
Ok, So you say you checked the spark with a tester. So that means there is no spark coming from the coil. or there could be a break in the spark plug wire.

Have you tried putting the some of the old wires in the place of the wires that are misfiring? That is if you still have the old wires.

Also did you make sure when you replaced the coils that there was a little rubber gasket like thing around the socket plug for the coil on the car? Could be arching if not..



Ive bought bad coils in the past. Did You try putting different coils in different places to see if its the coil? And did you make sure the coil is seated good?

07-16-08, 01:56 PM
Yup the rubber gaskets are in place, the coils are propperly seated each coil has played musical chairs multiple times, The old wires are MIA as of 2 years ago. I hope the newer wires are broken. Don't feel like shelling out money for more new wires. Specially not the $150 AC Delco ones.:want:

Think it might be a loose or broken ground wire? Anybody know the ground locations on this motor?

07-16-08, 02:50 PM
You might look into making your own set of wires. It cost me less than $50.


07-17-08, 06:31 PM
OK - sorry but I couldn't resist:

Are you sure this is not a V8-6-4 engine?

07-17-08, 08:39 PM
It has a recent tune up with plugs(iridiums) and wires(aftermarket cheapies).
This may be your problem. Also, I'm not sure how much difference it makes, but the plugs are supposed to be Dual Platinum tipped, not Iridium.

07-17-08, 10:41 PM
At this point, I would start to suspect the crank sensors. You've taken care of everything else it could be. Not saying it couldn't be a chafed wire intermittantly grounding, but it would be the next logical parts to check.

07-21-08, 06:40 PM
Are these the propper Crank sensors for my 94'? They look simple to change but do the have any problems coming out of the block? Do they need to be sealed to the block? Will I be able to swap them from below without dropping anything else? Not really wanting to remove the oil filter adaptor assembly. Would one of them going bad throw off certain coil packs?


07-22-08, 06:49 PM
I don't think that is the problem - the N* has two crank sensors and 1 cam sensors - it will run on as few as 1 of the above.

Have you actually checked for missing spark? A fuel injector that is not firing will cause the exact same miss as an ignition problem - no fuel or no spark means the same result.

07-23-08, 10:36 AM
Yes I have tested for no spark with a simple inline spark tester where you can watch the spark hit. It fits between the coilpack and the plug wire. You can see some coils fully sparking and some are really weak or non exsistant. Thats why I was asking about intermittent spark.

08-05-08, 02:00 PM
Okay soo now the car wont start at all. Is that a sign of dead Crank sensors? It just isn't firing on any coils. I pulled them all off again recleaned all the contacts and mounting/grounding points sprayed contact cleaner in all of the controllers connectors and plugs. It just cranks and cranks.

08-05-08, 03:00 PM
Okay soo now the car wont start at all. Is that a sign of dead Crank sensors?


I'm surprised you didn't replace them already.