Cylinder not firing, completely stumped!

[invain]

This fall my 98' 240sx started running on 3 cylinders randomly. Somedays the car would be fine, other days it'd run like s***. For a while I thought the ecu just needed to be retuned, but one day while the car started running like s*** I pulled off to the side of the road and started pulling plug wires. Come to find out, cylinder 2 was dead. At the time the problem was very spontaneous, and it seemed like everytime I wanted to work on it things would be running normally again.

A couple months later and the randomness stopped and the car has been running on 3 cylinders ever since. I drove home a couple times and spent hours checking things over trying to diagnose the problem. Plugs/wires/distributor are all farily new, spark tested fine for that cylinder numerous times. Compression test was fine. Injectors are all farily new but we swapped injectors from clinder 2 to cylinder 1 and tested impedence of all injectors - all 4 are working fine. We checked the voltage at the injector plug for cylinder 2 and it was pretty low. We tore into the wiring harness and found some pretty s***ty wires. Put in lots of new wire, voltage is now good at all 4 injectors, however the cylinder was still not firing. Since voltage was good we then checked the ground signal from the ECU, and found that the signal for injector 2 was not pulsing. We tested the impedence of the ground wire to the injector plug for cylinder 2 from the ECU harness and found no problems. Since the wiring appears fine, the only other option left was the ECU its self. I had a second stock ECU that came with the car, so we swapped that in. Cylinder 2 was still not firing.

This is pretty much as far as I've gotten. I'm at school so the car has been sitting most of the winter. Now that it's spring and I'm almost done with class I need to start working on this again as I need the car for my summer job. At this point however, I'm completely stumped. Everything we've tested/checked as turned out normal. I was sure it'd turn out to be injector drivers in the ECU or something until we swapped in another ECU. I've even been in contact with the guy that tuned the first ECU and after describing everything I'd done he doesn't believe the ECU is the problem either.

What the hell else is there to check? I know there's voltage at the injector plug, it's just not getting a ground signal. I've checked the ground wire multiple times, but maybe there's some really small short I'm not detecting? I've thought about just running a new ground wire from the plug to the harness. If that doesn't work however, what would you guys do next? I'm completely stumped.

[invain]

Forgot to mention that the car is turbo'd. The strange thing is, the car runs almost perfectly even on just 3 cylinders. Of course there's a huge loss of power but if somebody that didn't know the car were to drive it they'd probably never guess it was missing a cylinder. Runs/idles fine, never had any problems with stalling.

[the converted]

Spark problems can be really hard to find. Check the resistance from one end of the plug wire to the other and the condition of the distributor cap. Sometimes a weak spark will show you spark but not enough to actually light off in the cylinder.

[90 S13 VG30ETT]

hmm that sounds like a really fustrating problem to find.its definaly electrical. try a noide light? for the injector sure its not a spark problem?or even a compression problem?

[invain]

Just got home from college today and worked on the car a little this evening. I spliced in a whole new signal wire for injector 2. Still nothing.

This is driving me f***ing nuts. We changed plugs around again, checked voltage at the injector, swapped in another ecu, no change.

Is there anyway the CAS could have anything to do with this? I'm pretty sure I asked before a while ago and was told if the CAS was acting up it wouldn't effect just one cylinder.

I'm gonna go buy a noid light from autozone tomorrow just to make sure there isn't a signal.

[invain]

Bump. I really need some help. I dont even know what I should do next. I'm so sick of driving this damn car on 3 cylinders.

[airman86]

i mean physically if you have air, fuel, compression and spark - the piston will fire. have you pulled the injector out and check the spray on it? it could be spraying poorly and not misting well enough.

like the converted mentioned it could be a weak spark as well. i know these problems can be hella frustrating - it should be something simple lol

[invain]

I haven't checked the injector spray out, but we did swap injectors with a working cylinder so I don't think that's the problem.

I can't find a noid light anywhere close for a nissan so I'm taking the car to a shop tomorrow to have some diagnostics run and the injector checked out. Hate having to take it to a shop but I'm running out of options.

[quars]

just started getting the same prob as you and found this on another site not sure if its of any help

worn timming chain or belt (this is usually not consistant toward dropping one hole instead it will effect all at once or the cylinder that is dead will be good one second and bad the next)

http://answers.yahoo.com/quest...f0lrl