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Fredk20716 · 10-06-2019, 12:21 PM

Okay all you smart people out there, here's a puzzle. I have an 8.1 L also known as a 496 cubic inch GM engine in my MH. Immediately after replacing the AC Compressor I have been getting a check engine light; checking it shows error code P0356 indicating a problem with number 6 cylinder. I have replaced the ignition coil replaced the spark plug replaced the PCM (shop test indicated bad drive) and I continue to get the error code. The code only comes on at start up and after running about 45-60 seconds. After I clear the code the engine runs fine no missing or codes while running. Popular consensus is there's a wire somewhere that is grounding or has grounded causing the error code. Not sure if the removal of the AC compressor and replacement of it had anything to do with this problem (wire grounding). Any suggestions?

HELP.... and thanks.

vettenuts · 10-06-2019, 06:08 PM

Since you replaced the coil, did you look closely at the coil connector and wiring? Any corrosion or maybe the contact is deform.

Fredk20716 · 10-22-2019, 08:53 AM

UPDATE; It looks like the problem has been solved. I swapped out all 8 plugs and plug wires and the code disappeared (actually disappeared after install on cylinders 2-4-6-8). Removed the Denso TJ14R-P15 and replaced with AC-Delco 41-101. It appears the Denso are not the best plugs for a Workhorse with a GM 8100 engine according to all the RV forums. I’m not sure how long ago they were changed out but they were chipped and fowled. I also replaced what appears to be the original AC Delco plug wires with Ultra-Power Magnum SPW8100 plugs. No more Check Engine OR Service Engine Soon light or the P0356 code.

Keeping my fingers crossed!

Arch Hoagland · 10-22-2019, 10:57 AM

Thanks for the update, always good to hear the solution.

While you are at it may I suggest you clean the MAF.

Fredk20716 · 10-22-2019, 07:39 PM

Quote:

Originally Posted by Arch Hoagland

Thanks for the update, always good to hear the solution.

While you are at it may I suggest you clean the MAF.

Waiting on a new gasket to be delivered via Amazon and it is next on the list.

Fredk20716 · 10-18-2020, 08:27 AM

Well a few months ago the check engine light came on again and all my limited magic could not get it to stay off as it was intermittent. Well took it to my trusty repair facility and he rewired the ground coming from the ECU to cylinder #6 and voila, it is repaired.

The prior repair facility monkey's when replacing the faulty AC compressor crushed the wires causing a shortage. This after I asked that they stay off the wiring harness and its clamps. So if you have an 8.1 or similar, I suggest you take precautions when working around the harness. The new mechanic said this is a common problem with these GM 454/7.4L and 496/8.1L engines.