martha stewart

I have a 99 Z28 with intake full headers and other bolt on stuff, with high flow cats and the rear 02's deleted/ removed. Just recently it started running really ruff. It has a skip and does not accelerate for crap. Got codes p0300 and p0304. It shows it is a random misfire as well as #4 misfire. I tried doing the following.

1. swapping plug, wire, and coil with the #2. I reset the codes and started with still the same codes coming back.

2. felt the injector and it still vibrates as the others do and the fact that the plug actually has a little gas on the plug when I pulled it makes me believe the injector is good.

3. did a compression test on that cylinder and it showed 140psi. (I did it with all the other plugs in and just for compairson I did #2 and that one had 150psi).

4. left the plug out of #4 while it was attached to the wire and turned over the car. The plug has spark.

Anyone have any clue what could be the problem or what else to check?

KosoKustomz

Often Times the computer will toss a random Missfire code along with one that pinpoints a Cly. When you switched could packs, did the SAME P0304 come up or did it move to Cyl. #2 ( P0302 )? If it stayed at #4 Cly. Then you have a problem there, How many miles on the car? A headgasket that only drips coolant down there under WOT could cause it. How old are the plugs, what are the plugs gaped at? is #4 the same? Try switching plugs with #5 and see if that fixes the miss fire or if it moves to #5. Check and report back.

martha stewart

yeah that was what I did with #2. I moved the plug, wire, and coil all from #4 and swapped it with #2. I still get code 300 and 304. So that tells me its at #4. I dont think it is a head gasket, since i am not loseing any fluids, it does not smoke, I have decent compression in that one and I dont see anything dripping.

KosoKustomz

Change your plugs around.

martha stewart

I did swap #2 with #4 and not go still the same code. I am wondering if the 3600 stall I just put in 300 miles ago might be the problem. Just read something about desensitizing the knock sensors.

KosoKustomz

Well it will not cause a miss fire but will cause false knock and retard your timing.


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rwb

Did you swap the correct coils. #2 & 4 are on the passenger side of the motor. I have seen that done enough to know that sometimes people make the easiest mistakes.

martha stewart

I swapped them as in I unplugged them both and put one in the others place, so the wires/ firing order stayed the same, just the coil changed.

It's not looking too good. Just did a quick test of desensitizing the knock sensors and started it up. Now I hear a loud knock coming from the #4 area of the motor that was not noticed before. I didn't give it any gas or drive it, I don't want it to mess anything else up. What to check next? Sounds a little higher in the motor/head.

I am not getting a good feeling about this.

KosoKustomz

Hummmmmm.


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martha stewart

I'm lost here with this now. The knock is gone and just a little smoke is coming out the right exhaust. I just swapped injector from #4 to #2 and also disabled the 02s so it was only running off the MAF. Still getting these same two codes.

All this eliminates problems with plug,wire, coil, injector, o2. Where does that leave me????? Lifter valve or rod?????

KosoKustomz

What did that plug look like when you pulled it? What color smoke ?


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martha stewart

Plugs looked like a nice tanish ( like its burning good) however the plug in number 4 did have a little fuel on it (plug was slightly wet). Smoke was a darker smoke (not a really thick black just slightly grayish black and not much of it though).

Marc 85Z28

Remove the valve cover and have a look. Inspect the springs, rockers, and pushrods. If you find nothing obvious, get a scanner that will show misfire data, then monitor ALL cylinders.

martha stewart

Not a good day..... Missing the intake pushrod. Time for a head/cam upgrade!

AL SS590 M6

What do you mean missing???

If it's just a bent pushrod then why not change it and see what it runs like after?