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That 's a tough call. Best bet is borrow a FICM from someone to see if that fixes problem. My truck is running perfectly on it's 3rd FICM including original, so they are a weak link IMO.
 

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What degrades in an ficm? Is there potting inside that's broken down by heat, or a circuit board, or? Also, which of the main C1/C2 connectors contains the ficm wiring, the top or bottom connector?

Odd thing: may start & run fine, idle for forever, then throw it's fit. Shut it off, restart the truck and it may run fine again. The fuel gauge zeroing out when it throws

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What degrades in an ficm? Is there potting inside that's broken down by heat, or a circuit board, or? Also, which of the main C1/C2 connectors contains the ficm wiring, the top or bottom connector?

Odd thing: may start & run fine, idle for forever, then throw it's fit. Shut it off, restart the truck and it may run fine again. The fuel gauge zeroing out when it throws

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My #2 defective FICM had no visible defects in circuit board on top. The circuit board is bonded into the lower case. I didn't cut it out to look at the bottom because it still worked most of the time. Hitting it with a screwdriver handle did allow truck to start after stalling out on 100* days, usually after freeway driving. No surprise to me after 15 years of shake and bake on top of the valve cover The air vent in the FICM not being waterproof doesn't help either.
 

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My #2 defective FICM had no visible defects in circuit board on top. The circuit board is bonded into the lower case. I didn't cut it out to look at the bottom because it still worked most of the time. Hitting it with a screwdriver handle did allow truck to start after stalling out on 100* days, usually after freeway driving. No surprise to me after 15 years of shake and bake on top of the valve cover The air vent in the FICM not being waterproof doesn't help either.
Interesting you say that about the vent not being waterproof. I'm in southern Missouri, so humidity is a constant, but for the better part of a week I've had these issues and it's been rainy & overly humid. Granted, humidity/moisture will cause the same results with a nicked wire, but I cant find any other bad wires and this thing is still out of commission.

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Just an update, maybe it will help someone else: I basically retaped the harness on the passenger side, added some wire conduit, cleaned all of the connectors, and wire tied the harness back to the alternator bracket. Since then all has been good.

The only other thing: while fighting this I noticed the primer bulb is slow to return when you prime it, you practically have to pull it up. I've put a rebuild kit in this filter head before, but does the spring go bad, or is something else going on?

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Just an update, maybe it will help someone else: I basically retaped the harness on the passenger side, added some wire conduit, cleaned all of the connectors, and wire tied the harness back to the alternator bracket. Since then all has been good.

The only other thing: while fighting this I noticed the primer bulb is slow to return when you prime it, you practically have to pull it up. I've put a rebuild kit in this filter head before, but does the spring go bad, or is something else going on?

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The seals can chafe if you do not lubricate them when installing and can cause a leak.
There are some poor quality kits out there..
Did you clean the filter head before the install?
 

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It's been years since I did it, so I'd be lying f I said I remembered. The truck has 350k+ on it now, and probably ~100k miles since I rebuilt the filter head, so I can't complain. It holds a prime fine, just when my wiring issues first appeared I thought i needed a filter change but when i went to prime it the plunger was really slow to come back up. It pushes down fine and primes normally, but even my buddy commented out of the blue watching me work the plunger. Not a big deal, I just dont want to lead to something else. I also need to throw on some new rubber lines from the filter head as they're pretr weather checked.

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I spoke too soon...

The truck had no issues until my dad borrowed it to pull a trailer last night, and of course it quit him in the middle of a blind curve in the dark.

Which of the big connectors on the drivers side has the ficm wires? Or do both have ficm wiring?

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Lol, no, its throwing the same ficm wiring codes as before. So I'm digging back into the wiring harness.

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After sitting in the shop all night the thing wont start. Always before it would start but run on 4 cylinders but now it's not having it. A couple of times I tried it hit for about 1 second then died, but the majority of the time it simply wont start. I've spent all day tearing the harness apart and going over it, icepicked 2 & 7 for good measure, but nothing. Does the fact that the "Group A" P2146 is the only one faulted but the rest are pending mean anything significant?





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I think the others are pending only because the truck hasn't been able to run long enough or the specified number of start cycles hasn't occurred for the codes to set as hard codes.

Last year I performed a "chiropractic" type of operation of flexing and tugging on the engine harness to see if that helped my intermittent stalling. It didn't. Also looked at every pin on both ends of the engine harness from the FICM connectors to the large bail connectors on the left top of the engine. Bent pins happen..

A new FICM seems to have fixed mine. Not one misfire out of it since installed 12/2019.
 

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Gotcha, thanks. I'd like to try and track down a used ficm and try it, any idea which years will work on my 2004.5 LLY?

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Looks like 2004.5 - 2005 LLY is the interchange for the FICM.

97303751 is the GM part number I received from my local dealer for my 2005 LLY. Also (4) fuel connector seals on the FICM # 490549. Better confirm the seal part numbers for your own vehicle. I reused the fuel line seals a number of times previously while troubleshooting, never had a leak.

This appears to be the same as what GM dealers are selling:

 

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Here's the failed FICM I removed 12/19 with an earlier part number. This was originally installed about 2007 by the dealer under warranty on my 2005 LLY. This is what you may find in a recycle yard for 2004.5-2005 LLY.
IMG_2126 (1).jpg
 

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Had similar issue then was told it was definitely FICM thank God I waited ended up being bad ground on passenger side down pretty low on block Towards front . Tricky to find. Two smallish gauge wires think both were black. Took them both off sanded and cleaned, Connectors and where it touches block,they were rusty, Put back snugged them down and fired right up stayed running no issues since, it鈥檚 been 6-8 months, so ...
 

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Ended up sending my FICM to vehiclemodule.com and getting it rebuilt; they said it had "multiple codes". I put it in and truck fired right up and hasnt missed a best since. I'll report back in a few weeks but so far so good.

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That's good to hear; did they give you any detail on what was actually wrong or what they did to repair? Having multiple codes isn鈥檛 the base problem it鈥檚 just the unit recognizing that something is out of predetermined parameters. I guess my question is what was base problem that caused codes to be set? And what besides clearing codes was done to correct. If only the codes were cleared can鈥檛 his issue just come back? And what codes exactly?
 

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I went back and read what I posted and what they actually said was "multiple faults". I dont think the ficm stores codes, so my guess is there was something physically wrong with the unit (short, bad circuit, bad potting, etc.) that was causing the issue.

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