Thread: GTP cylinder 4 misfire

Hi everybody, I am new to this forum, but have been on here many times you guys are great. I have a 2002 gtp 40th anniversary that I bought for a good deal from a local credit union that was a repo. I drove it off the lot was able to get the car emissions, everything was fine. After driving it for a day my check engine light came on, turns out it was a O2 sensor bank 2. I replaced the O2 sensor, spark plugs (OE style), spark plug wires, cleaned mass air flow sensor, and fuel filter. Car still had check engine light. I reset light now it is a P0304b code cylinder 4 misfire. the car runs a little rough at idle, and gets worse gas mileage than my 2001 by three mpg (yes I love these cars I have two ). I checked spark on #4 coil it is weaker than the rest. I replaced with a coil off of my 2001 gtp the spark was still week. I bought a new Ignition control module, still the same. I thought to check the fuel injectors so I replace #5 with #4, still have the problem. I than did compression test it was fine. So because I love the power of these cars I wanted to see how they do performance wise against each other (the 2001 against the 2002). we raced with equal weight the cars are side by side hmmm. Anyways engine is strong at full power. Next I did a leak down test that was less than 10%. I than did a smoke test to see if maybe the intake was leaking it is not. I was watching the misfire on the test computer it goes away at 1600 rpm. I hooked another computer to it, that does 3x and 18x for the cps, I dont really understand it but at idle or up to 1600 rpm the computer graph was going up and down. Above 1600 it stayed in a straight line. I was thinking that maybe something is not right with the crankshaft position sensor, maybe the fin for #4 is bent or something. What do you guys think. The car is in mint condition the carfax shows that the guy that owned it for the first eleven years maintained it very well didn't miss a maintenance interval. the guy that owned it the last two years didn't have maintenance on carfax, but doesn't mean he didn't maintain it. thank you for any help you may be able to give me.

Originally Posted by BillBoost37

I'd do a crank learn.

Does anybody know step by step instructions on how to do a crank relearn?

Thank you,
I am going to check my cxp sensor to make sure something isn't wrong there. After that I am going to have to find someone to do a relearn. I only have a snap on tester, and cornwell tester that don't have the relearn option.

So since I have been on here last, I tested both the crank and cam sensors. I also put new plugs in one and four, also checked ohms on the brand new wires everything was fine. I was told to take the wires off battery than hook them together with vise-grips, this makes computer go stupid so that it has to relearn itself. I drove it for three days, car ran fine after that it went right back to the p0304b misfire. I decided that maybe I will try to put a new computer in it. I got in touch with intense racing and ordered a computer, figured if this doesn't fix it oh well I will have a better computer. I will make sure I let everyone know what is going on.

Update:
I did another compression test all cylinders are between 140 and 150 psi. Replaced the plug, and wire again. Crank relearn after I bought a new computer from intense racing (i love the shifting points on the new computer). This is what is so irritating, I drove the car for five days (150) miles, it ran like a dream. You guessed it, the light came back on and it is running rough. I am lost.