I have a misfire on the number 2 cylinder on my 97 Nissan Maxima 5spd. The computer has been changed 3 times, and it’ll work for a short time after the new computer is installed, but then the problem resumes. What would cause this to happen? The coil has also been changed.
For what reason was the computer changed 3 times? Was something verified to be wrong with it, or did whoever change it just start chucking parts at it hoping something would stick?
Other than the coil you’re going to have to tell the rest of the story.
It is possible for a bad ignition system component to damage the PCM. Its also possible to assume that the PCM is bad after one thinks that they have eliminated other possible causes of a misfire…and then continue to replace them.
So you need to lay out the whole story if anyone is to say anything intelligent. (E.g. Great - you changed the coil. How about the plug & wires? Has anyone checked the compression? Fuel injectors?)
compression is fine on all cylinders, plugs have been changed, all coils are known good, knock sensor has been replaced, injectors are all working fine (#2 was replaced)(clicking under a scope), shops told us the computer was bad (three different shops). battery is good. the problem started after the head gaskets were replaced. timing has been adjusted. some sea foam was run through the brake booster line to see if it affected anything. After the most recent new computer was installed, it ran/drove for about a half hour before the misfire started again. now the check engine light is blinking, but we havent ran the code yet so dont know what it is for yet.
Its hard to know where to start only b/c in all of the stuff you mention there are further questions. E.g. if an injector is clicking that only means that power is showing up. It doesn’t mean it is delivering fuel correctly. Why was the #2 replaced? Was there something wrong with it or was it a guess about the misfire? Do you know what the actual compression numbers were? And did the same shop that did the head gasket check the compression? Their idea of “fine” might not be. When the head gaskets were done was anything done to the head? Any valve work? How do you know the coils are good? If you do keep frying the driver circuit in the PCM the most likely cause is from a bad coil. If the coils were actually tested in some way, were they tested hot? The heat changes everything in terms of the resistance.
Anyway, who is doing all the work? You? Same shop? Maybe its time to have someone else take a look.
OK- heads were shaved during the headgasket replacement, no other machining work was done. Injectors were all checked, and all sprayed evenly and consistently. Everything would work except that for some reason the #2 cylinder wouldnt fire. checked and ran a different ground, checked and confirmed power, and confirmed signal from the computer. So the wires are good… but no spark. And no misfire code. I did the work with help from mechanic sons, and we sent it to detroit lakes votech… along with some “certified” shops.
Once, unplugging the old pos crankshaft sensor caused it to run perfect, no misfire for a few minutes, then it died. that trick doesnt work anymore. We thought that we kept getting bad computers- but if they all work the same they all cant be bad can they?
Back up a step. You state the compression is fine. People routinely post on this board all of the time stating that such and such a number if fine when nothing could be further from the truth. Even many mechanics stated lousy numbers were in fact good.
What are the compression numbers on this engine, especially cylinder 2?
Changing the computer 3 times is nothing but WAGing.
Compression checks out fine, all cylinders between 130-140. #2 was at 140. Now we think its a TPS- did a resistence and continuity check, but did not have any numbers that made any sense… no continuity at all, either. monkeying with the idle set screw, and we couldn’t get the car to idle in between 650 and 1300rpm… either above or below. at normal operating temp.