Car misfires 5% of the time
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Car misfires 5% of the time I seem to have a really random misfire, and it wouldn't throw any codes despite it happening 8 times now. It only happens for 5-10 seconds in the middle of hours of driving. The car isn't getting over 210F ish. The only code I got was a "slow response" passenger O2. So, I fixed that, and I'm STILL getting the misfire. (I monitored O2 activity after replacing, and both seem to be working super fast/well, now that I replaced the passenger one.) I already cleaned the MAF a month ago, but I did it *again* just to be safe. If it would show me a cylinder # in the codes, I could obviously check plugs/wires/coilpack. But it's not giving me any kind of misfire code, not even a "random misfire" code. It drives super strong the other 95% of the time.
It takes a certain minimum number of misfire counts to set a code. Don't remember the criteria off the top of my head, but it's entirely possible you have a miss that's not bad enough to set a DTC.
If you have a scan tool (guessing you do, since you mentioned monitoring the O2's), I'd take a look at fuel trims and misfire counters, preferably while driving so you can save the data. If it's been a while since the plugs & wires were done, that's also a cheap fix to throw at it and see what happens.
If you have a scan tool (guessing you do, since you mentioned monitoring the O2's), I'd take a look at fuel trims and misfire counters, preferably while driving so you can save the data. If it's been a while since the plugs & wires were done, that's also a cheap fix to throw at it and see what happens.
In my line of work (auto tech) spark plugs are about the only item that will cause a misfire to come and go. Fuel components and mechanical engine components 99% of the time are either good or bad and don't come and go.
Ignition coils 99% of the time are either good or bad, they don't usually come and go.
A funny plug or plug wire though, I have seen many times come and go.
Ignition coils 99% of the time are either good or bad, they don't usually come and go.
A funny plug or plug wire though, I have seen many times come and go.
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I use Blue Tooth OBDII adapter with Torque Pro app. I didn't think it had an option for misfire detection, but after your post I looked and apparently you just have to enable advanced GM options. So far I haven't been able to reproduce the problem, although I saw the very occasional miss on 8, 7 and 6. I guess I might as well do plugs and wires like both of you are saying. Are they only supposed to last a couple years?
Very occasional misfires happen. Not necessarily a cause for concern. While it's nice to never have any focus on the cylinder that has the most and inspect the components on that one.
There are many things that can cause an occasional misfire like build up on valves, old injectors etc so that's why I said some of it isn't necessarily a concern.
Plugs and wires should last longer but things happen and sometimes you get a crappy plug. Happened to me this year with my truck. I put in brand new NGK plugs and right after I had a misfire at heavy throttle on cylinder 5. Had to swap that plug with another new one and went ahead and did new plug wires just because.
There are many things that can cause an occasional misfire like build up on valves, old injectors etc so that's why I said some of it isn't necessarily a concern.
Plugs and wires should last longer but things happen and sometimes you get a crappy plug. Happened to me this year with my truck. I put in brand new NGK plugs and right after I had a misfire at heavy throttle on cylinder 5. Had to swap that plug with another new one and went ahead and did new plug wires just because.
