Random Misfire Code

[Forty61]

Just poking around for ideas or experiences people have had similar to mine.. plus something to talk about right?

So I have the "Random Misfire" code coming and going on my car. It came on maybe 3-4 months ago, cleared it, didn't come back until yesterday. CEL was on when I pulled up at home, back off this morning when I left, back on now after I ran out to get lunch.

Car has JLT intake, Hot Rod cams and LT's so nothing too wild or different. Plugs are less than a year old, COPs are factory originals. Being random means obviously I have no clue what is tripping the light but the car runs fine, pulls like normal and I don't feel any misfire driving around. The only exception to smoothness is that occasionally taking off from a stop the car will kind of buck a little bit at low RPM or if you go from closed throttle to part throttle at low RPM in first it'll do similar. I always chalked this up to the cams though.

So are there any things I could investigate that may create an erratic misfire? I had read about possibly the alternator starting to go (need to find my meter), bad grounds (cleaned factory grounds) or a failing COP but I would think if it was that I would get a more specific code.

Any and all feedback or input is welcome!

 

[Juice]

If there are absolutely no mechanical or electrical issues, it has been my experience a borderline lean condition can result in random misfires. Or just bad sparkplugs.

 

[DieHarder]

You won't necessarily get a code. I had two bad COPs and had to get an analyzer to ID which ones. If you changed spark plugs in the not too distant past and started getting random misfires that's likely the issue. After changing spark plugs the ends of the coils often get pushed too far up into the boots making the spark jump a gap which shows up as bogging/bucking/choking/etc. If you can get it on an analyzer that would be best to ID exactly which ones are causing the problem.

I'd check for that first. Then, look for connector issues/bent cabling/etc.

 

[StockishS197]

What misfire codes specifically? P0300/P0316?

I recently chased this issue with the same mods and it was tune related. Not 100% which what caused it, but my tuner at the time was using a different strategy code that was causing some weird issues. Switched tuners and they are using the factory strategy code and runs a lot better with no random misfires.

YMMV

 

[Pentalab]

I was getting misfires on my 2010 GT auto years ago. (Roush M90 blower, LT's, FRPP twin 62mm TB). Swapped plugs to Brisk, with a .035" gap...and never got a misfire since.

 

[whitmanink]

i kinda had an issue you are saying,,
in lower rpm when cold , if i gave it gas , sometimes it felt like it was falling on its face and missing or sumthing,
i also chalked that up to my mutha thumper cams,,.

about a week ago i was gonna go to the gym ,,
i noticed sometimes when starting the car,, it seemed like it was slightly off, but again , i thought maybe cams,,,
and then a day or so later , again heading to the gym, i started my car, it seemed slightly off here and there.,.... then i got a blinking cel for a moment,

i changed my plugs about a month ago ,, partly due to this problem i was noticing ..

got new set of cop (mine were 150,000, original )
and now it seems to run just fine,,,,,

the two main differences between and electrical failure and mechanical?

a mechanical failure will always be broke , once broke,, ie timing chain, cam follower,
ect ect.. so no matter when u start the engine (hott or cold) it will always be broken ,,

and electrical failure is a bit funny,, sometimes the electronics' will work fine until exposed to a little moisture ,,, or once they get above a certain temp they start going wonky,, or sumthing as small as a wire moving slightly one way to kind and break it internally and will momentary work until vibration or sumthing moves the wire again causing a short..

hence why i hate chasing ghosts with wiring problems

 

[Forty61]

What misfire codes specifically? P0300/P0316?

I recently chased this issue with the same mods and it was tune related. Not 100% which what caused it, but my tuner at the time was using a different strategy code that was causing some weird issues. Switched tuners and they are using the factory strategy code and runs a lot better with no random misfires.

YMMV

It's the 0300, just cleared it again this morning, hasn't returned yet.

i kinda had an issue you are saying,,
in lower rpm when cold , if i gave it gas , sometimes it felt like it was falling on its face and missing or sumthing,
i also chalked that up to my mutha thumper cams,,.

about a week ago i was gonna go to the gym ,,
i noticed sometimes when starting the car,, it seemed like it was slightly off, but again , i thought maybe cams,,,
and then a day or so later , again heading to the gym, i started my car, it seemed slightly off here and there.,.... then i got a blinking cel for a moment,

i changed my plugs about a month ago ,, partly due to this problem i was noticing ..

got new set of cop (mine were 150,000, original )
and now it seems to run just fine,,,,,

the two main differences between and electrical failure and mechanical?

a mechanical failure will always be broke , once broke,, ie timing chain, cam follower,
ect ect.. so no matter when u start the engine (hott or cold) it will always be broken ,,

and electrical failure is a bit funny,, sometimes the electronics' will work fine until exposed to a little moisture ,,, or once they get above a certain temp they start going wonky,, or sumthing as small as a wire moving slightly one way to kind and break it internally and will momentary work until vibration or sumthing moves the wire again causing a short..

hence why i hate chasing ghosts with wiring problems

I'm leaning towards an electrical issue but so minor and intermittent it's going to be tough to find.

Measured from positive battery terminal to chassis ground and have just over 14VDC at idle, switched it to AC and for a split second when I touch the leads it'll show voltage but immediately settles to .01-.02 so I think I can most likely rule out the alternator.