cylinder not firing

[GotGas8668]

Sorry, this is the first post here, forgive if it has already been discussed.

Alright, sitting at a stop light the other day, car has been running great (86 GN). I notice that the car is idling somewhat low (650-750 when it was set about 750-850). When I start to drive down the street, I notice that the car is running pretty sluggishly, no power, turbo is spooling at low throttle increments and the car is kind of making a "put-put" noise. Well, I immediately pull over and check all my connection and wires/vacuum lines. I am not getting any codes at all and the engine is rocking from side to side. I take it to a friend's house, we change MAFs, still nothing. We then check the coil pack, everything seems good here, but ew have come to the conclusion that the car is missing. I take it home, and according to John Pearcy's instructions, I place 2 inch pieces of 1/4 inch vacuum tube on every terminal of the coil pack, then put the plug wires ack on top of the tubing. I start the car and ground out each individual tube to see which one doesn't make a difference in how the car runs. I show that cylinder 6 is not firing, so of course I change the plug wire, no difference and then the spark plug (which looks a little rich), still no change in the engine. I checked the compression on every cylinder (No. 1=130, No. 3=130, No. 5=134, No. 2=126, No. 4=124, No. 6 =122), so things seem to be close. I took off the valve cover, everything looks fine. I also put a different injector on the No. 6, still no change. I tried 3 different chips, no change. Took off the spark plug wire on No. 6 and put a plug in the end of it, getting ignition to this point. I then disconnected the Cam Sensor while the engine was running and I didn not notice any big difference, but the car does try to die with it unplugged (and of course I get Code No. 41 when the Cam Sensor is unplugged).

I am kind of at ends here, I cannot think of anything else. The car is getting fuel, air and spark. It has compression, is not overheating, but there is no combustion on the No. 6 cylinder. Can anyone give me any ideas?

The car is an 86 GN, pretty much stock. Stock turbo, stock injectors, accufab 3" downpipe, electric exhaust cut-out, aerochamber exhaust, new valve springs, red armstron fuel pump, racetronix fuel pump hotwire kit, k&n 9" air filter, chrome MAF pipe, adjustable FPR, rjc powerplate, smc dual nozzle alcohol kit, all the free mods, good supply of gauges and scantools ad probably something I forgot for the time being.

Any help would be much appreciated.
Feel free to email at WildKarde79@aol.com

 

[jastrckl]

coil/module might be good enough to fire off a plug not under compression, but when you put it in the cylinder, it's too weak a spark to light off the gas. I have -no- clue why it takes more energy to fire off a spark plug that's under compression... it's a myth of much intrigue to me, why do the electrons care? Anyway I'd still be looking very carefully at your coilpack/module. What do the #6 plug wires you've tried ohm out to?

 

[1970gsx]

I know you changed the injector, but did you check the injector wire? Make sure the wire has juice to the injector, it may have broken or been pinched.

 

[billsgn]

Good point, but since he mentioned that the #6 plug was wet, it sounds more like a spark issue.

 

[GotGas8668]

well i put a NOID light on the No. 6 injector harness, looks to be good. The car is running very rich right now, lots of black moisture coming out of the tailpipes. I'm thinking it is getting fuel, and it seems to be getting spark. I just made new spark plug wires, but the car is running exactly the same. Could this be an ECM problem? Or is it still feasible that the Coil pack or ignition module is not running right? I did put the coil pack tester on there, looked good but still seeing the same problem.

 

[Russ Merritt]

Your sure ALL the valves are opening up right? Poss camshaft.

 

[GotGas8668]

That's a good idea, I have another injector i can test with for fuel flow. I'm pretty sure is flowing though, because it is running really rich. I seem to have spark, but still no combustion. I don't think I would have fairly equal combustion on all cylinders of a valve were sticking or there was a problem with the camshaft. But, then again, that's what I've been told. John Pearcy told me that I need to do a leak down test to see if a have a burnt valve causing my problems.

 

[GotGas8668]

Took off the upper intake plenum looking to see if something was blocking air flow to No. 6. Nothing seems to be in the way. I also took off the bell on the turbo, spindle looks fine. Went to the local parts stora and had the ignition module checked on their diagnostic machine (just for personal satisfaction), everythign checked out good there, too. Still at a loss?

 

[Russ Merritt]

If you had equal combustion you wouldn't have a miss. I think you were trying to say compression. If a lobe was gone the compression would be good, it just wouldn't have anywhere to go. Does the car run ok WOT? Pull that valve cover and turn it over and watch the valves. Make sure they open all the way.

 

[GotGas8668]

Everything seems to be opening and closing all the way from a visual point of view. Nothing was evident in the intake that would cause it to be starved of air.

The one thing I have noticed the entire time is that at the coil pack, No. 6 is getting a lot less spark. When I say this I mean that I am doing what John Pearcy told me to do. I pull off all plug wires from the coil pack, place a 2 inch long piece of 1/4 inch vacuum line on each terminal and then place the plug wires on top of the tubes. I can then start the car, and with a test light I touch each individual tube, which in turn cuts spark to that certain cylinder. When I touch any tube besides the one on No. 6, I am seeing a lot of spark arching to the grounded test light. BUT, when I touch it to the tube on No. 6, you hardly see any spark as a result arching to the test light, you actually have to touch the tube before you see any sort of arching. This is telling me that for some odd reason I'm not getting a lot of voltage to the plug.

Could the spark be put out when the cylinder is building compression?

What determines how the coil fires to each individual cylinder? Is the ECM saying fire, fire, fire, or is it in the ignition module? I just had the ignition module tested, it showed good. I put on another coil pack that I know has a miss in the upper RPM range, but I still got the same results.

I have a friend coming over tomorrow to let me borrow his ignition module and coil pack for further testing, but does anyone have any ideas so far?

 

[GotGas8668]

Guys, let me know. Am I giving enough information to give you a chance to try and diagnose the problem? I know john wants me to do another compression test with a different gauge and also a leak down test, does anyone else have any questions about something I might have not said?

 

[GotGas8668]

Could this have anything to do with the ECM, the wiring harness to the ignition module or the Cam Sensor? those are the only things I can really draw any of this down to. I put a timing light on the No. 6 and showed current flowing through it, but like I said earlier, I am not seeing a lot of spark when grounding out at the coil.

????????

 

[jastrckl]

It's very odd that only #6 wouldn't get enough spark. On a DIS, two plugs are fired at once, one anode to cathode and one cathode to anode. The wasted spark is when the other cylinder is on the exhaust stroke, so you don't notice it really, but I would still imagine you'd have a problem in -two- cylinders if a coil or part of the module went bad. You can douse a spark with too much fuel, never heard of compression doing it. Once the spark is weak enough though, fuel will eventually pile up in there and make dousing the spark likely. As far as what signals the coil to fire, it depends on the conditions of the motor. If you are cranking the motor, the module controls timing up to something like 400rpm if I remember right, and then goes into a bypass mode and the ecm starts telling the module when to fire the plugs. My money is on a bad coilpack, but I still don't know if I would trust the module tester that was used to test your module. Blow like $100-150 on a new coilpack and module, and at the worst you'll have spares, at the best, you'll have fixed your problem.

 

[1970gsx]

You could try and switch the plug wires at the coil on cyl 6 and it's corresponding terminal (the one that shares the same coil pack, I think it's #3) and see if the problem moves to that cylinder. Then you'll know it's not something in the combustion chamber itself. If it moves than it has to do with the coil pack and or module.

 

[jastrckl]

There are only three coils on a DIS. swapping which cylinder's plug wire with it's opposite will do nothing, only cause the cylinder that used to fire anode to cathode to fire the other way, cathode to anode, but it will still fire at the same times. if the problem follows, you would've just narrowed it down to the CABLE.

 

[1970gsx]

jastrckl exactly. What I'm trying to help him do is eliminate systems. If he switches wires and it does NOT follow, he can pretty much eliminate the coil pack/ ign. module out of the loop.

 

[jastrckl]

If there's a problem, it's going to be in both. It's not a matter of following. Both plugs fire at the same time if they fire at all. You just notice the one that's firing on the power stroke. It would tell him nothing about the condition of his coil or module by doing that test, only would tell him whether or not his cable was bad.

 

[1970gsx]

Could there be an internal failure where the terminal is connected inside the coilpack?

 

[GotGas8668]

losing patience

Okay, I swapped coil packs and ignition modules with a friend, nothing. I did a leak down test on No. 6, 19%. I swapped computers with a friend, nothing. I pulled the valve cover off and double checked to see if the rockers were moving, no problems here. I put another wire on No. 6 at coil pack and watched the spark, getting spark. I tried it with No. 4, and 2 and all the odds as well, noticing a lot more spark out of them than from No. 6. Still no clues. Car is seeming to run realy rich right now. I replaced O2 Sensor and IAC. I reset the IAC. While test driving it to reset the IAC, the car was bucking and backfiring. Acting like a MAF, tried swapping those, nothing. I'm lost.

 

[GotGas8668]

I don't know if this is a good or bad idea, but I'm planning on taking the car to the Buick dealership. I'm hoping they have some way of testing the areas I have not hit. I know I need to check the ground wires one last time, and I'm really concerned that this may be a wiring harness problem. I don't know anymore, I feel like I have checked everything without breaking down the engine. Any ideas?