M182 Intake Backfire - Rod Bend

[ckassen]

Hi - I am working to diagnose an intake backfire when using the M182 for a gear shift ignition cut. The vehicle is a newer model GM LT4 with both direct and port injection. Car is running a blower, 24psi of boost, ~E80, and running plugs more than cool enough for the application (Brisk RR12s). The backfire has now resulted in two separate rods being bent, both in cylinder #2.

Attached you will find two separate logs, one showing a 50% ignition cut without an intake backfire, the second with a 60% ignition cut and an intake backfire. This shift resulted in a 2nd bent rod. Prior to the 60% cut run, there were 6 shifts at 50% cut without an intake backfire. No fuel cuts occurred on these events.

The first bent rod unfortunately I have limited data available (log corrupted). The shift was using a 60% ignition cut, 60% fuel cut timed at -50ms (reintroduce fuel prior to ignition restarting). My logic on the first bent rod was a lean condition and subsequent detonation, likely incorrect given the most recent occurrence.

My questions include:
-Are there any red flags in injector timing data that would indicate a potential tuning mistake?
-Are there any red flags in the spark timing or cut data that would indicate a potential mistake?
-Is there any coil or injector data/voltages that look odd that could indicate a wiring short, or fault potentially resulting in the issue?

If nothing is found and there are no other ideas, wiring and harness will begin to be unwound/tested to verify integrity. The challenge is logically it seems odd that the issue would only occur the brief period during a 60% ignition cut and not be more noticeable during regular operation.

Note that early in testing, prior to the first rod bend, we did try an 80% ignition cut and 100% ignition cut, both with intake backfires occurring. The only thing that kept an intake backfire from occurring was a significant fuel cut + ignition cut, or ignition cut at or below 50%.

I apologize for the long winded email. Please see attached logs for reference.

[stevieturbo]

Ignition cuts can be violent. Always safer to use a fuel cut

Although it is an odd one

[bing]

Maybe upload you calibration here we can have a look.

[NathanB]

Maybe upload you calibration here we can have a look.

The Config is attached - you can retrieve the config from logging

[bing]

I think you should to reduce Primary Injection Start Limit to 300 degree BTDC, also primary timing to less than 300 deg BTDC, since your fueling are not limited to DI only.
Increase Fuel Primary Timing load axis to 350kpa as well.

My questions include:
-Are there any red flags in injector timing data that would indicate a potential tuning mistake?
-Are there any red flags in the spark timing or cut data that would indicate a potential mistake?
-Is there any coil or injector data/voltages that look odd that could indicate a wiring short, or fault potentially resulting in the issue?

[ckassen]

So essentially move the DI timing further from EVC point and ensure there is no flame in cylinder prior to starting fuel injection. Good thought. Anything else stick out in your mind? I am considering upgrading to higher frequency logging to try and find any signal or voltage anomalies, however am not certain it is going to tell me much.

One other piece of information, after pulling the engine apart it turns out it was not a second cylinder #2 rod bend. #2 occurred the first instance, #8 occurred the second instance. I am not certain it changes anything other than minimizes cylinder #2 specific items such as injectors, coils, etc. Not to mention DI injectors are relatively new at ~1000 miles. They were replaced due to B1/B2 deviation after installing the new ECU.

Lastly, after the first failure I completed a cold bore leakdown with all cylinders less than 4% with the exception of number 6 at 5%. Which ruled out any leaking exhaust or intake valves. I suppose there could be a sticking or floating intake valve if a spring is getting weak, however it feels like a bit of a stretch.

 

I think you should to reduce Primary Injection Start Limit to 300 degree BTDC, also primary timing to less than 300 deg BTDC, since your fueling are not limited to DI only.
Increase Fuel Primary Timing load axis to 350kpa as well.

[bing]

I don't normally think you can get wrong timing, if anything timing issue always refer back to Ref/Sync State from logs.

Well you need some kind of ignition source to ignite fuel in intake manifold, it can be incorrect timing, bend inlet valve, EGR etc.. in this case i suspect the direct injection timing with overlap of camshaft combine high exhaust manifold pressure from Ignition cut.

Also you could have exhaust valve floating from high back pressure.