Symptoms:
At low rpms, if you step on it, *sometimes* it misfires once or twice, sometimes it misses a lot and looses a lot of power unless I downshift, other times its fine. Usually happens when I'm going uphill. At this time I have no check engine light.

I checked the front plugs and they all look ok, like they've been replaced at some point. I went through the front bank of coils, replacing them one by one to find the culprit, still misses (I used the same coil and just rotated them out, it was a used OEM coil I found on ebay.) Should my next step be to get to the rear bank and replace all three coils, or should I try something else before I go to that extreme? Thanks for any and all input!

 

funny you say your not getting any code, at the very least you should have a 1320 code ignition primary . did you buy this car used recently ?

 

I would first try to pull the pending code when the miss fire occurs. (you might not need a cel to be on to pull pending codes).

Replace all 6 sparkplugs with double platinum's. if the front bank coils are fine, I would swap them to the rear bank and proceed with the coil diagnosis.

A random misfire usually is a coil and not a spark plug.
Also to note, a faulty or clogged fuel injector will cause a misfire.
A bad intake gasket will cause rough running/misfire.
Bad maf might cause a misfire.
If you are having any issues with the timing, like a clocked variable timing solenoid, it will also cause a rough running/misfire.

good luck.

 

Good input, thanks! I did buy the car used recently. It's worth it to mention I did the timing chain tensioners as soon as I bought the car, but the misfire was occuring before I even bought it.

 

Was there a problem with the tensioners? I don't think it's necessary on virtually any '02-03 vq35.

I vote maf or leak.

 

Scan your codes first. There might be some pending ones.

 

if its missing that bad then you should by now have a code as to which cylinder it is . i just had a code on my gfs 2000 max it had a 1320 code ignition primary after taking a 15 min ride and having it missing a lot and the check engine was flashing coming up a hill when i got home i checked the codes and it said cylinder 6 missfire . put in used coil that i had from junkyard and missfire was gone

 

Yeah no code yet. Weird huh? Maybe I get myself a MAF from a junkyard before I go through the trouble of taking the intake collector off and spending God-knows-what on coils. What do you mean by leak?

 

had some similar issues about two weeks ago and finally got a P0300 code (random cylinder misfire). i changed the plugs to start and it was fine for about a week until i got a P102 code (MAF low circuit input). swapped in a new MAF sensor today and the code is gone (for now). still idles a bit rough and there is an occasional misfire/exhaust 'pop' when given gas at idle as well as coasting/decelerating.

 

I ordered a new MAF today because that seemed like the next logical step, hopefully that will take care of it for me. It sounds like coils are the only thing you haven't done, maybe that's your next step.

 

Let me know how this goes, I've been fighting a PO300 for a long time.. I've tried many thing but still no luck!

Here is a list of things from the FSM that can cause a misfire.

I Improper spark plug

I Insufficient compression

I Incorrect fuel pressure

I The injector circuit is open or shorted

I Injectors

I Intake air leak

I The ignition secondary circuit is open
or shorted


I Lack of fuel

I Drive plate or flywheel

I Heated oxygen sensor 1

I Incorrect PCV hose connection

I'm about to get a fuel pressure gauge and try that step.. Well see.

Any thoughts please say.

 

Just want to throw this out there, not sure if it would help. I have a thread around here about an Android app that you can advance your timing with, Car Gauge Pro. One of the features in the app is an Active Test. You can turn individual cylinders on and off when in this option. The app is $6 and a compatible bluetooth elm is anywhere from $10-$20 on eBay (I use the VGate).

Chances are it's a coil pack. Maybe that app can help you figure out which one is bad. Clear the code, turn a cylinder off, hit the throttle a few times... and move on to the next.

Ever since this feature was added I thought it would be perfect for this type of situation. Luckily, have not had to deal with it though.

 

Its not always coil packs, there are many variables. kinda sucks there isn't an easier way to diagnose these problems.

 

Just put in the maf... Still have the misfire and no code to show for it. How frustrating! Part of me just wants to wait for a code. I am also paranoid that the new MAF might be bad. It wouldn't be the first, or second time I've gotten a brand new part that turned out to be faulty.

 

I doubt your MAF is causing the misfire. If its a random misfire then it has to be your ignition coils. The used ignition coil you recieved on ebay could be bad. Its also possible you have more than one bad coil. There is a FSM that shows how to diagnose the ignition coils by using a volt meter.

 

Thanks Bullet, I had no idea that there was info on it in the FSM. But since it is random, will the volt meter test work definitively?

 

The volt meter test may not always work, because in your case the coils are going out intermittantly. When you test the coils they may be fine when they are cool, but may not work right when they are hot. You may have to replace all 6 of them if you can't find out which ones are bad or wait till one of the coils fails completely.