So my ap1 s2k is still having misfire issues! Things I've done so far

1.Valve adjustment
2.new injectors
3. new coil packs and plugs
4. new MAF sensor
5. New knock sensors
6. Used about 40 gallons worth of chevron/shell premium and various fuel additives such as chevron fuel system cleaner
7. fuel pressure is normal
7. compression test is 218-220-220-218
8. new air filter
9.Icv Cleaned
10.grounds cleaned

and to add to the madness I DONT GET check engine lights!!! But i know my CEL light works because i pulled a sensor off and it shows the CEL right away and when i put the code reader on it with no check engine light on it will still show the misfire code p1399 it just dosent light up my dash. Note: I've reset the code a few times and driven the car 80+ miles and no CEL BUT it will be there if i hook up the code reader.

Its a small misfire i believe because i have to power drain and it runs great all the way to 9k rpm at side or at various rpm like 2k or 4k for example. it will pop every few seconds i can hear it from my muffler. Im stumped what the heck is this cars problem lol


If someone solves this for me ill buy them a steak and lobster! haha

 

You are not throwing a CEL now but down the road you will. Our cars have the ability to compensate a great deal but eventually the problem will over come the car's abilities to compensate for the ransom misfire.. Prob nothing a nice set of Ferrea stainless valves won't cure to replace those burned OEM ones. Good luck buddy.

 

You think it could be valves? Ill have to delve into the subject more but id think compression tests would show if its a valve right? All my spark plugs are a cocoa brown with i live to be normal. Im going to clean up the piston heads with some seafoam though since they are black.

 

Try an ecm. You should be able to get one from someone off of here in the classifieds. There are a lot of folks out there with stand Aline's that have their old ecm's taking up space in the garage.

I know that's a long shot, but it's a fairly cheap part to throw at it.

So, no cylinder specific misfire, just the 1399??

 

could be a sticking valve. works most the time with a occasional miss. I know airplane engines are notorious for this. car engines aren't no different. its possible. compression check would not detect this. but could be a valve issue. add a little marvel mystery oil to your oil. helps with sticking valves. worth a shot.

 

Find a tech with a picoscope

 

My bet is on some burned exhaust valves. Hit me up if you want some prompt outpatient same day surgery if you're semi-local. I can also do a leak down to make sure that is indeed the issue.

 

Would a car still have decent compression like that, with burned valves? I have the same misfire(occasional puff on idle), and I've had my head reconditioned, it does it more or less depending on the weather and the humidity. Valve adjustment is dead on, checked it this weekend, compression is perfect, leak down showed no obvious leaks. One thing I haven't done is check the fuel injectors, I have added some fuel cleaner, and it definitely helped my low rpm throttle response. Other than the occasional puff which practically goes away once the car is at operating temperatures it idles perfectly. I don't get a CEL at all.

 

I've had plenty of cars come in with "good" compression results but not so good leakdown results pointing towards a burned exhaust valve. If both compression and leak down are giving good results, then a burned valve definitely isn't your issue, nor is any sort of valve issue other than possibly valves out of adjustment.

 

Does the car have an aftermarket header on it? If so retorque all header mounting bolts to 23 LB-ft per the Helm Manual. If you have the OEM header ignore my suggestion. I won't get into specifics as to why I am suggesting this as it will be long and over the head of most here. If it works for you post up and I'll explain what was going on.

Utah