This misfire is killing me!

[DriftingisLame]

Okay guys, facing the worst misfire I've had since I got this motor 5 years ago.

I've faced non stop ignition misfire problems since I bought the motor. I've replaced 4 stock coils with Q45 coils, where I used to buy them from jacked up the price 3 times what I had been paying.

I decided to wire in '01 maxima coil packs that I had laying around the dealership. These coils have individual power transistors on them so I was able to eliminate the ignitor. This ran my motor fine for about 6 months until I parked the car for a year.

I just got the thing running again but have a misfire that I CANNOT find!

Here's the facts:

Fuel Pressure at 44 psi with vacuum line offCompression within 5 psi across the boardNewish Bcpr6es's gapped at .9mmHave continuity through my home made ignition harnessPlugs all look normal, with a little white on the electrode, EXCEPT cylinder 2 which is black.

The car seems to run fine without a misfire until you exceed 20% throttle (roughly), then misfires. It sounds like its misfiring on 1 maybe 2 cylinders past 3000.

I've grabbed a brand new coil out of parts and swapped it in place of each and every coil and it never makes the misfire better.

I've put a stethascope (sp?), it was actually a long screw driver, up to each injector and they all click consistantly.

I could use an idea or two if you guys could share with me some issue's you may have seen.

Thanks-Max

[DriftingisLame]

Reply before I put a KA back in this damn car.

I'm so sick of it not running right I dont care if I have 250 hp or 100 hp.

[ka24eracer]

Im throwing something completly random but cleaning the maf never hurt !

[virus77]

Try hard-wiring the power to the coils (big white wire) through a relay instead of through the harness, this fixed my misfire issues....

[ka24eracer]

+1 easy to do and it cant hurt

[DriftingisLame]

Not to discredit your idea, but I cant imagine needing to modify how it was designed from the factory to make it work properly. Something must have been broken for that to have fixed it.

How did you do this exactly? I may try it if I find no other option.

[Yellow4g63]

Tested for any boost leaks?

[DriftingisLame]

Yep, pressure tested right after I made my FMIC piping.

I'll order a pizza for whoever comes up with the winning answer.

I'll give it a week and then this motors going in the dumpster, and I put a motor that pisses me off less in the engine bay.

[eh?]

Change or swap #2 injector with another. See if it follows.

Does it do this only when driving or can it be replicated in neutral?

[DriftingisLame]

I can duplicate the problem with a static rev.

I'll change the injector in the morning and see if that changes anything.

Thanks for the replies everyone, and trying to restore my faith in the RB engine!

[eh?]

To be sure which cylinder is misfiring:Have someone rev the motor until it misfires. Unplug each coil pack one at a time until you don't hear much of a change in engine noise. That will be your bad cylinder.

[robbie2883]

just to toss it out there but have you ran separate ground to the igniter and the coils?

[DriftingisLame]

To be sure which cylinder is misfiring:Have someone rev the motor until it misfires. Unplug each coil pack one at a time until you don't hear much of a change in engine noise. That will be your bad cylinder.

Holding at a constant RPM the motor usually doesnt misfire. It seems it will only misfire under stabs of the throttle or under load, perhaps because its in boost. Its hard to just hold the motor in boost you know lol. I'm pretty sure the black spark plug of cylinder 2 means its probably there, now I'm not 100% sure, I've seen more dumb things than this. My theory is a stuck open injector on that cylinder, although I've never seen it... it would cause a rich misfire on that cylinder and a black spark plug, even if the ignition system were working properly. I cant imagine anything else causing a misfire and still ending up with a black plug.

just to toss it out there but have you ran separate ground to the igniter and the coils?

Read the original post, there is no ignitor, but yes I've grounded the harness in many places to be sure that it is good.

Thanks guys-Max

[S14-NEO]

if you have a multimeter, check the resistance values across all six injectors...all you need to do is to measure across the two terminals in each injector..it will give you a good indication if you have an injector that is starting to flake out on you...

[Ramius83]

if you have a multimeter, check the resistance values across all six injectors...all you need to do is to measure across the two terminals in each injector..it will give you a good indication if you have an injector that is starting to flake out on you...

This is a good idea, but it still doesn't mean that he doesn't have an actual mechanical problem in the injector itself. All you are doing here is checking the "coil" side of the injector. This does not test the actual opening/closing of the "plunger" inside the injector. But nonetheless, it is a quick and simple check that needs to be done, just not as conclusive as it is thought to be.

To rule out any possible harness issues, try running six jumper wires from the ECU to the actual coil packs. It takes a few minutes to set up and do, but it will give you a quick and easy answer if the problem lies in the harness.

[robbie2883]

Read the original post, there is no ignitor, but yes I've grounded the harness in many places to be sure that it is good.

Thanks guys-Max

missed that part...sorry...but i wasn't talking about grounding the harness. i was referring to grounding the actual body of the coil pack. you'd be surprised what a coil pack can do if it's not grounded properly. just a suggestion

[dfddfd2]

Plug gap at .9mm might be the problem. Try .7mm.

[Eikon]

Plug gap at .9mm might be the problem. Try .7mm.

I'd go to .8mm first and see how that goes.. that's the commonly accepted sweet spot for RB motors.

If you parked the car for a year without startup.. how's the fuel? Stabil before you left it sit for so long? Perhaps your gas has gone stale and isn't igniting very well?

[DriftingisLame]

Sorry I havent made it back to working on the misfire guys. I've been sick of dealing with it for the past few days so I decided to put on my 5 lug conversion and new wheels.

I'll be back at the driveability issue tomorrow morning, you can be sure of that!

Here's the new wheels, its not a factory color in case anyone was thinking it was. These are stock 350z tires, 245/45/18's, I wont be running tires that tall for the record.