E40 GTO miss. No codes. Restart "fixes" it?!

[twoutes]

Hey guys, I have a 2005 GTO, T56. It is driving me crazy with this random miss that seems to appear after a prolonged hot idle. Like sitting at a light, in traffic, etc. It is SD mode, so I cant log misfires by cylinder. No other codes besides the MAF code pop up. If it starts missing, it will miss all through the rev range, including at WOT. If I turn the engine off and restart it, it is immediately "fixed" until the next long idle...

I have changed plugs and wires with no change. Currently plugs are BR7 gapped at .025. I also added a large ground from the engine to the chassis and resistance is .2ohms or less.

Will failing coils behave like this?

TIA for any help

[twoutes]

And here is another log that was just idle and revs in the driveway.

[GHuggins]

Are you sure it's dropping a cylinder? I only ask because both of those logs show fueling off sure, but bank to bank is staying really close and showing no signs of a misfiring cylinder.

[twoutes]

It's for sure dropping one. It's a dead miss. I did get an infrared thermometer and found that #7 is 100? cooler than the rest of the bank though, so I'm going to do some more testing and see if I can confirm that hole is the problem.

[GHuggins]

If it's only doing it under load then either coils, plugs, wires, possibly injector or even cracked or broken valve springs can cause it. I've even seen water in an ecm's connector and trash in the intake cause it.

[twoutes]

If it's only doing it under load then either coils, plugs, wires, possibly injector or even cracked or broken valve springs can cause it. I've even seen water in an ecm's connector and trash in the intake cause it.

Thanks for the ideas. It does it even free revving, so not load dependent. I have changed plugs, wires, and injectors with no change. It has new pac springs, and because a restart fixes it, I was thinking a spring was unlikely? Also carefully inspected all ecu pins and connector sockets. I have not changed coils yet and that may be the next step. I should have time this weekend to dig further into it. I appreciate the help!

[Alvin]

Have you tried another ECM? I've had them fail in all sorts of weird ways.

[Lakegoat]

Under DTC's, P0101, 102,103 should all be Mil on First error. Under airflow --Map sensor, LinearB should be 66.66 and Offset should be 8.00. What injectors are those? Do you have a boost referenced regulator or stock pump system? I see you are getting into boost, but your boost fuel table is not tuned. I don't see your Wideband input either.

[twoutes]

Have you tried another ECM? I've had them fail in all sorts of weird ways.

I considered that as well. I don't have another to try and it's a very expensive guess

[twoutes]

Under DTC's, P0101, 102,103 should all be Mil on First error. Under airflow --Map sensor, LinearB should be 66.66 and Offset should be 8.00. What injectors are those? Do you have a boost referenced regulator or stock pump system? I see you are getting into boost, but your boost fuel table is not tuned. I don't see your Wideband input either.

Thanks for that! Someone is helping me base tune it remotely while I wait for the dyno to open up, so it's a mild street tune just to get it to the shop. Injectors are ID1050X, fuel system is an aem 340 feeding a surge tank with twin 340s. Regulator is Aeromotive, boost referenced.

Just FYI, the car has been doing this since before it was tuned at all. When it was NA and cam only, and the ecu still thought it was auto and it was running a maf. None of the changes to the fuel system or ecu have changed the miss behavior.

[TheMechanic]

Re-enable misfire back to stock in 14014. You can find out better what cylinders etc.

[pannetron]

You could swap two coils between cylinders to see if the misfire follows the coil...

[GHuggins]

Do what the Mechanic said and re-enable misfires. I bet your going to find it's missing enough that it's shutting the cylinder down for that ignition cycle. In fact if you have a cam, you might even want to try completely disabling your misfire counter section by maxing it all out to see if the problem is still present. That's if it only started after the cam install...

If that doesn't pinpoint it and If it will indeed do it free revving, then get it to shut down the cylinder and allow it to run that way for 5 or 10 minutes at an idle then hit it with the thermometer. One cylinder is getting shut down for safety by the ecm if it's not actually a bad ecm dropping out a driver.

[twoutes]

Thanks all. I'm running a SD tune, so I can't enable misfires. At any rate, I am going to try a new PCM since it's relatively quick and easy, and the e40s are notorious for failing.

[Lakegoat]

Thanks for that! Someone is helping me base tune it remotely while I wait for the dyno to open up, so it's a mild street tune just to get it to the shop. Injectors are ID1050X, fuel system is an aem 340 feeding a surge tank with twin 340s. Regulator is Aeromotive, boost referenced.

Just FYI, the car has been doing this since before it was tuned at all. When it was NA and cam only, and the ecu still thought it was auto and it was running a maf. None of the changes to the fuel system or ecu have changed the miss behavior.

I was trying to help you clean up a few things that were not correct. Always helps to have the right info for the computer. Also, if you have a return fuel system, your IFR and VAC tables are incorrect under FUEL. If it is a BASE tune, don't go WOT---BOOM

[twoutes]

I was trying to help you clean up a few things that were not correct. Always helps to have the right info for the computer. Also, if you have a return fuel system, your IFR and VAC tables are incorrect under FUEL. If it is a BASE tune, don't go WOT---BOOM

For sure. Thank you very much for all the help!

[Snowman1987]

Very strange one, indeed. Speaking of E40s, anyone have a way to log a misfire data in SD mode for the E40s?