Gtp/130 compression#4cyl/150othercyl/misfire#4

[darin4fun]

I have 02 gtp I have done everything possible to fix this car: injector, oem plugs, oem wires, lim gasket, computer, coil, icm, leak down test, #4 cylinder 130 psi, the rest closer to 150. The dealership told me it is because of the lower compression. They said they checked wiring everything ok. They also said leak down test was ok. How can leak down test be ok but not compression? Car misfires under 1600 rpm over that no misfire. Snap on scanner confirms that. I am in this car 1200$ don't want to go any more from assumptions. Any advice would help thanks folks

[Scottydoggs]

so its cyl 4 thats got the mis? what code you getting?

it could be a worn wire near the pcm. or even a bad crank sensor or its harness. crank sensor hardly ever sets a code, but can cause it run poorly, same with a cam sensor. never know when you seem to have done all the logical stuff already.

[darin4fun]

Ya #4 . I can't remember the # but it is #4 misfire for sure. The dealership checked all the wiring, I am not much of a wiring guy. I did the ohm test on crank and cam sensor they both seem fine. Plus aren't those sensors on /off; what I mean is there will be more problems than just 1 cyl.

[Scottydoggs]

this just started one day? or was there any work done then it started up?

you could also try a crank learn, not sure if the snap on scanner can pull that off or not. you'll have to look through it to see.

[Scottydoggs]

clogged cat comes to mind too.

dont think the low comp of 130 would cause a misfire tho. most are 150 give or take some.

[darin4fun]

No I can't on this scanner. Do these cars need that? I own an 01 gtp I replaced the cxp sensor and didn't need a crank relearn.

[darin4fun]

By the way cat was replaced yesterday

[Scottydoggs]

never know. it cant hurt if its free. thats for sure. ive heard of cars running poorly and got a crank learn and ran fine afterwards, but they were worked on. pcm tuned mods installed likely.

why i asked if any work had been done to it before this started acting up. one thing can trigger another sometimes. and you dont know it.

like what plugs did you install? not plats i hope, cause that could be the issue right there.

[darin4fun]

No no I put oem. I bought the car in January. I bought it from a bank no check engine light until i drove it off lot. My kinda luck. This car is perfect example of don't judge book by its cover. It is 40th anniversary great condition, but runs like ****. My 01 with 40 thousand more miles runs perfect

[Scottydoggs]

oem means nothing. parts stores are dummys.

it wants iridium plugs, or copper core plugs work best, but only last 15,000 miles. most use trk or ac plugs.

[darin4fun]

Ya they are iridium ac Delco

[J57ltr]

Are these older cars just slap worn out or what? I have always gotten much higher numbers on low compression engines especially if the engine is in good condition. As long as the rings aren't gapped like a picket fence they usually have higher compression. That wouldn't seem to be the case since a lot of the L67's seem to but the ring lands together and chip pistons. Just wondering why so low?

Jeff