Hi all,

I decided to check the "Misfire" section of my GM Tech2 tool on my 2004 C5 Corvette Base +A&A procharger. The vehicle drives fine no indication of misfire, no DTC codes no Check Engine lights. The tool however indicates random misfires as I increase the RPM both in neutral and under load. I am unable to find any reference as to if this condition is normal or not.

Can you guys please take a look at the attached image/video and let me know if this is normal?

Thank you in advance,

Mike

 

Welcome to the Forum !!!…If you are seeing misfires on the Tech 2 but you can’t feel any do the “crankshaft variation learn” using the Tech 2 !!…should be under special functions and remember to keep your left foot on the brake when you do this procedure !!…let us know if it works !!

 

I have an older Diablosport hand held tuner that contains 2 tunes, can reset codes, and also can read all engine parameters in real time. Even though my car was running great, I thought it would be cool to check the engine parameters readout in real time. After I installed a healthy cam, this message appeared on its readout:
"Random multiple cylinder misfire, cause unknown"!! Living proof we know more than electronics!!! The cam was the obvious cause of the 'random multiple cylinder misfire, cause unknown'.

 

Thank you so much for this suggestion. I followed your advice and preformed the crankshaft relearn procedure however the problem still persists. I am going to replace the original 20 year old coil packs next.

Any comments on my next step approach?

Attached is the latest misfire graph. This is from a 15 minute drive cycle.



Thank you all and God Bless!

 

Probably not coill packs before I started changing them I would look at the spark plugs and wires. Cylinder #6 looks to be the worst. You can remove the plugs and check the gaps and see how they are running. You can also pull the worst misfiring wire at the coil and sée what the spark looks like when it's running. Should be nice and blue. I would use dielectric grease on the boots

 

Seems like #6 is the misfiring cylinder…do you feel a misfire ??…you can take a dollar bill and hold it up to the exhaust pipe…if the bill gets sucked into the tailpipe momentarily it’s misfiring !!…coil packs are super reliable on these engines so save your money…do you have a P0306 or a P0300 or still no DTC’s showing ??…there may not be enough misfires occurring to illuminate the MIL yet….what do your long term fuel trims look like ??…if ignition related bank 2 fuel trims should read maybe 5-8 %…if injector related maybe 13-16% or so…there is a lot of unburned oxygen in that cylinder…just to rule out a coil pack if that is a concern you can swap #6 with another and then see if the misfire moves to the other cylinder…if it moves the coil pack is faulty…if anything I’d change plugs and wires first…if we suspect #6 injector is bad you can do an injector balance test with the Tech 2 however you will need a fuel pressure gauge…you can take a long screwdriver and touch it to the injector…do you hear it “clicking”…not the best way to check if you don’t have the right diagnostic equipment. It may be something mechanical too (broken valve spring or sticky valve) so that can’t be ruled out !!…what part of the country you located ??

 

Before you buy any new coilpack , try to switch coilpoack 6 with number 8 and check if the misfire rate moves from 6 to 8 .
If not you should also try to switch ignition wire and plug to also to verify same issue

 

?????? Why 6 8 can it be done swapping any 2????

 

You can swap any coil pack !!

 

Nunber 6 has multiple misfires and should be swapped with another coilpack to confirm if the mhigh number of misfires move .
Number 8 has none and is close to number 6 and the one I would personally swapped coilpack with.
The issue is to confirm if misfire numbers move along with the component movement.

Swapping coilpacks with similar misfirenumbers confirm nothing to me

 

You’re right !!…looking at the misfires and #8 has none…use that one…excellent !!