Random Misfire

Saleen304 · Oct 19, 2016

boomer9999 said:
If it's true that the misfires are limited to one bank and are random on that bank, indeed the +12 to the coils AND injectors are are good culprit. I would also not rule out the O2 sensor nearest the engine on that bank and also the VVT and associated components.

In my 30 years experience, weak ignition shows up at high cylinder pressures under high load. Bugged up fuel injectors usually result in bad idle and misfires at high RPMs.

What do the fuel trims look like on that bank? An exhaust leak before the first 02 sensor and cat will richen the mixture causing large fuel +fuel trims (since the 02 sensor is reading too much oxygen, the computer adds fuel). If it gets over 20% extra or so a code will be set.

And another thought, the dreaded alternator difficulty with these cars can cause all kinds of problems. Usually i see cam position problems, but who knows what else it can effect.

Sorry for your problems, but this is a good thread. Please keep us posted.

I have data logged while misfiring and sent the information to Lito and he has not noticed any issues. Also, I unplugged VVT solenoids to remove it from the equation and the misfire was still present. Also wanted to note that the majority of the time it's cylinder 5, but I have seen it on the other bank as well. Just not very often.

redfirepearlgt · Oct 19, 2016

Well boss, I'm spent. I concede defeat on this one. My only rational at this point is to conclude the PCM is still fritz. Since misfires are not common to one cylinder or bank the only common thing in the system to cylinders 3,4,5,6 would be the PCM relay, the alternator providing the voltage through the PCM relay to the COP's, or the PCM which sinks the COP's low when commanded to fire by the PCM. Sorry I sent you on a goose chase with the Caps because I was thinking this was still a one cylinder or one bank isolated problem after getting the PCM back. I would doubt O2 sensors as well but you could pull the plug on both and see if the misfire goes away and only O2 CEL's pop up possibly, but I have never tried that. I assume the car would go into limp mode but not have the 303,304,305,306 misfires.

As a last thought and you have likely already done this. Try reseating all of the plugs on the PCM and as a last resort you could check teh grounds on this portion on this system which are C175E pins 47,48,49,50 to frame ground. They should read less than 2 ohms from each pin (isolated from the PCM) to good chassis ground. Good luck. Sorry I have been of no help at all.

redfirepearlgt · Oct 19, 2016

redfirepearlgt said:
Well boss, I'm spent. I concede defeat on this one. My only rational at this point is to conclude the PCM is still fritz. Since misfires are not common to one cylinder or bank the only common thing in the system to cylinders 3,4,5,6 would be the PCM relay, the alternator providing the voltage through the PCM relay to the COP's, or the PCM which sinks the COP's low when commanded to fire by the PCM. Sorry I sent you on a goose chase with the Caps because I was thinking this was still a one cylinder or one bank isolated problem after getting the PCM back. I would doubt O2 sensors as well but you could pull the plug on both and see if the misfire goes away and only O2 CEL's pop up possibly, but I have never tried that. I assume the car would go into limp mode but not have the 303,304,305,306 misfires.

As a last thought and you have likely already done this. Try reseating all of the plugs on the PCM and as a last resort you could check teh grounds on this portion on this system which are C175E pins 47,48,49,50 to frame ground. They should read less than 2 ohms from each pin (isolated from the PCM) to good chassis ground. Good luck. Sorry I have been of no help at all.

You may wish to PM 05stroker as he sent his PCM in for repair and got it back to only find it still had issues. He ended up sourcing a used one which resolved his problem which is pretty similar sounding to the one you are having. It may be time to go junk yard hunting.

06monera96 · Oct 20, 2016

Try covering half your air filter and drive it (y)
Colder air is causing major issues over here with tunes and such (y)
05 are super sensitive to temperature change

Boone · Oct 20, 2016

I had the random cylinder 5 misfire code that would show up during cold start. If I cleared the code and let the car warm up for 10 minutes, I could baby it for a little while and avoid the codes (cyl 5, random misfire, maybe others).

This was my issue.

Replaced the Livernois Stage 3 NA cams and the followers on cyl 5 and 6. No more codes.

Saleen304 · Oct 20, 2016

06monera96 said:
Try covering half your air filter and drive it (y)
Colder air is causing major issues over here with tunes and such (y)
05 are super sensitive to temperature change

I have been having issues all year. Hot or cold weather.

Saleen304 · Oct 30, 2016

Update: Decided to get a used 2005 PCM and installed it yesterday along with an updated tune from Lito to disable PATS. Unfortunately I still have a misfire on cylinder 5. Swapped cyl 5 coil with cyl 1 just in case the new coil was defective. Still have misfire on cyl 5. Ugh, I am about out of ideas. Oh if anyone wants to buy an 05 PCM, I have one for sale.

redfirepearlgt · Oct 30, 2016

So about everything on the COP side has been ruled out. I assume you have also swapped fuel injectors but am too lazy to read back through to see. This then leaves the mechanical side of things that BOONE points out. Sorry you have failed to isolate it but I do give you props for sticking with it.

06monera96 · Oct 31, 2016

Saleen304 said:
Update: Decided to get a used 2005 PCM and installed it yesterday along with an updated tune from Lito to disable PATS. Unfortunately I still have a misfire on cylinder 5. Swapped cyl 5 coil with cyl 1 just in case the new coil was defective. Still have misfire on cyl 5. Ugh, I am about out of ideas. Oh if anyone wants to buy an 05 PCM, I have one for sale.

ill grab that 05 ecu from you
GT, federal, Manual right?

06monera96 · Oct 31, 2016

pull the valve cover check if the lifter , rocker or maybe even cam is damaged

06monera96 · Nov 10, 2016

Got the ECU today, thanks (y)

Saleen304 · Nov 10, 2016

06monera96 said:
Got the ECU today, thanks (y)

Great! Hope it fixes your issues.

Saleen304 · Nov 15, 2016

Doesn't look like a cam issue.

06monera96 · Nov 15, 2016

is your misfire physical or do you have a device like areo interceptor that reports misfires?
Could it be that your tune is out of wack of the injectors are leaking?

Saleen304 · Nov 15, 2016

06monera96 said:
is your misfire physical or do you have a device like areo interceptor that reports misfires?
Could it be that your tune is out of wack of the injectors are leaking?

I feel it and my CEL flashes. Lito has been over tune many times. I have also swapped injectors out. Tried smaller ones and switched positions.

redfirepearlgt · Nov 15, 2016

Saleen304 said:
Doesn't look like a cam issue.

I'd scope the cylinder next. Have you done a compression check and or leak down test I can't remember if you said you have or not. Man I hate this for you.

Saleen304 · Nov 15, 2016

I've run compression tests and they are all between 195 and 210. Ran 1/4 mile a couple weeks ago and was running 10.6@132. Took to dyno last week and the graph was weird. I have Lito going over logs, but it looks fine to me.

redfirepearlgt · Nov 15, 2016

Just read back through and saw you mentioned the compression in the opening. Is the sheet above typical of a WOT pull you had prior to this problem? Something just looks a little odd 4200-4600 to my novice eye. Would like to have seen AFR plotted as well being you said you noticed a lean out when the misfire was taking place. Maybe we have been looking at the wrong end? Could there be a fuel pump or FPDM issue? Something flaky causing the fuel pump system to sag intermittently and cylinder 5 just happens to be the most susceptible to this? I am just brain storming at this point in hopes it might jog a thought from someone following the thread. If I am muddying up your diagnostics just say so and I'll just follow and hopefully see the end result. Just trying to think outside that box, because this seems to be one of those, "anything could be possible issues".

deebo05 · Nov 16, 2016

How did fuel pressure look on that dyno pull?

can you post a log?

Saleen304 · Nov 16, 2016

deebo05 said:
How did fuel pressure look on that dyno pull?

can you post a log?

Data log attached. Includes air/fuel ratio and boost as well.

Random Misfire

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