marthastewart

iTrader: (1)

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?

blade2222

Still can be a bad injector, I've also had a random misfire from a failing o2 sensor that wasn't throwing a code.

DaddySS

Without more information, I would go with the probable causes - injector issue or bad 02 sensors.

When did the problem start - did the weather get colder, did you recently fill the tank, etc.

I would try GM injector cleaner and /or replace the 02 sensors.

marthastewart

iTrader: (1)

Thanks guys. I will look into some injector cleaner. I have HP tuners so i can always run in open loop S/D off the MAf, so I guess that will see if its the 02 sensors or not.

I could see the 300 code coming from the 02 sensors, would the 304 really come from those? I was thinking it was a lifter or valve ( along those lines) and that was making me worry. There is no knocking though so I would think if it was one of those I would hear something.

I guess tomorrow I will start with

1. Runing it off the MAF to see if its the 02.

then

2. swapping injector from #4 to #2 and see it that changes.

marthastewart

iTrader: (1)

Just did a little research and what do you guys think, could this have anything to do with the new tranny we just installed with a 3600 stall? Ever since the install the car has not had much power. After about 300 miles of driving were when the SES light came on? Think that I might need to disable the p0300 code or what to do. I found someone posted this....

"ITs the torque converter...* you need to disable misfire detection.* The torque conveter weighs less and the computer dosen't know how to calculate for it.* Do a seach for converter randomly unlock"

marthastewart

iTrader: (1)

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.

marthastewart

iTrader: (1)

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?????

marthastewart

iTrader: (1)

Not a good day.....