(Y33) Dreaded P0300 Misfire

[TrizzyDizzy]

Hey Nico Club, been a long time since I've been here. Yall mind helping me diagnose a problem?

So starting earlier this week while sittin in my car, my Q went from a normal idle to a violent shaking rumble. Previous automotive experience helped me assume that the engine was misfiring. I took it to a local auto parts store to have it scanned. P0307 (#7 Misfire) code was up as well as P0330 (Knock Sensor). Common instinct is to replace the spark plugs and do some routine cleaning of various parts.

After the spark plugs and cleaning, the problem persisted. Did a little research to verify my assumption, then bought a single coil pack to replace for cylinder 7. After the install, problem continued to persist. Took the car back up to an auto parts store and the scanner spat out the same P0330 code, but instead of the P0307 (#7 Misfire), I get P0300 (Multiple Misfire).

So apparently the problem exists beyond just cylinder 7. Two days of research across various sites point to replacing all the coil packs and praying it works. I do not have the luxury of shelling out $600+ for a handful of hope. Do I have any other alternatives to narrowing down this problem? Have there been any new findings in this seemingly common problem? Does cleaning of the connectors/sensor often prove positive results? How would I narrow down an injector problem?

Claimed Common Fixes
- Replace ALL spark packs (Done)
- Replace ALL coil packs (1 of 8)
- Clean connectors and Sensors
- Force out carbon build up
- Injector cleaner

Disclaimers
- Prefer not to spend excess if possible
- Prefer not to take it to dealership (previous work doesn't highlight their experience well)
- I've use all OEM replacement parts
- I do have the copy of the FSM
- I do not have a have a personal scanner tool

[Lokim]

Start the engine.

Disconnect then re-connect each coil one at a time.

Note which cylinders cause the idle to drop significantly versus those that do not seem to effect the idle.

Those that do not effect the idle speed are the dead cylinders.

To isolate whether it is spark or fuel, swap a coil from a cylinder that is working to a cylinder that is not working.

Repeat the test on the two cylinders on which the coils were swapped..

If the problem moves with the coil, you have a bad coil.

If the problem stays on the original dead cylinder, you have an injector issue or a mechanical issue on that cylinder.

Good luck, and keep us posted!

[TrizzyDizzy]

Thank you Lokim, that is exactly what I was looking for to troubleshoot.

Now, before I do this, I will still be able to differentiate between good/bad cylinders regardless of the MAF being disconnected, correct? Just want to clarify.

I've got all day to work on it, so hopefully you'll hear back of some results by the evening, but before football... hopefully.

[Lokim]

Find a way to keep the MAF functional. That will yield the best results. Try taking the cover off the coils and reinstalling the intake tube. Work around it with pliers or whatever it takes. If it proves impossible, disconnect the MAF and let the car run until the idle stabilizes, then perform the test. The computer should enter fail-safe mode and will substitute a value for the MAF based on TPS and O2 sensor readings.

One more thing - ignore any codes set during this diagnostic procedure as all this disconnecting and re-connecting will set a plethora of codes.

If you're planning on DIY-ing stuff on this car, I would suggest investing in a good OBD2 scanner with live data capabilities. It will really help with diagnosis, and they're not super expensive. You can likely get a decent one new for under $250, and a used one through ebay or craigslist for considerably less. I prefer Auto XRay or Actron brands if you can't afford a professional scanner (Snap-On, Launch, etc.)

[TrizzyDizzy]

OK, cool. Was wondering if I could do that.

I am considering a scanner tool from autozone. Its only $80, unsure of the brand though. Do you really get what you pay for with those things, or am I safe buying a basic one?

[TrizzyDizzy]

By the way, how the hell are you supposed to get those damn green connectors off? Like I've taken them off 3-4 times each, but everytime it seems to be more and more difficult. I would think the opposite.

Is there a secret to get these off? Logic would simply tell me to press the green thing in, and pull them off. But it seems thats never the case. Even when fully pressed, and clicked into place, they refuse to budge. They just decide when to come off on their own.

[Lokim]

Any scan tool is better than none, but again, I definitely recommend one with live data streaming. This will allow you to look at the engine data (O2 sensor voltages, misfire counters, TPS voltage, etc.) which is EXTREMELY helpful for diagnosis.

As for the connectors, try pushing them IN a bit before trying to depress the button. That should unload the pressure on the tab and they should slide right off.

[TrizzyDizzy]

Yea, that was the problem with the connectors.

Ok, so check this. Plugged the vacuum lines for the intake, reconnected the two sensor connectors, and put a filter over the throttle body, thats it. Didn't undo any of the plugs/coils at all. Now the car will turn over, then die shortly. It won't stay running long enough to troubleshoot each cylinder. Ideas?

[qship96]

"put a filter over throttle body".....are you saying the air intake tube between air filter box/MAF and the throttlebody was disconnected???? IF YES, thats your problem, as engine airflow is not being measured thru the MAF...leading to stalling motor.

[Lokim]

Yeah, looks like you'll need to have the MAF hooked up.

[maxnix]

Look, I hate to break it to you, but the coils in short order will fail sequentially. I replaced 3 until I gave up chasing the next failure and replaced all eight and kept two good ones as spares. Never a problem since.

My best deal was Hitachi OEM from FCP Groton off eBay. They have an all Japanese website now, I believe.

Oddly enough, the coilpacks for my BMW are about have as much, but everything else seems to be at least twice as much.