Few things I want to fix before PCM swap.

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Orpedcrow

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97 Silverado 5.7 4l60e 2wd unknown mileage. Engine harness has been gone through and repaired and re-taped/loomed. Verified all connections. The following issues were present before and have not changed after. This all may very well be PCM related. I don’t know the history of the truck before I bought it but I have seen signs of it being a rough past. When I had a Snapon scan tool the PCM showed it being a 5.0. The vin matches but the engine was a 5.7 (I have since replaced with another unknown mileage 5.7) the transmission has a GM Goodwrench sticker on the top of the bell housing.

So there’s a few things I’d like to take care of before I do the 411 swap. I’ve spent days scouring through posts and my eyes have glazed over.

EDIT: I found the hummingbird gauge thread, I’ll either fix or replace all 4 motors or just get a new cluster

Fuel level, volt, coolant temp and oil pressure gauges bounce, flutter, buzz sway, tick and every movement in between while driving and sometimes at idle. Part of proactive maintenance I have replaced Oil pressure and coolant temp sensor (issues were present before and after) fuel pump and sender have been replaced. Alternator replaced with AD244.

This second thing is really weird and very random/seldom. I know it does it during the day but it’s noticeable at night.

So it’s like a glitch in the matrix, ALL gauges drop and lights flicker off but it’s only for less than half a second. Actual engine RPM does not appear to drop.
I’m unable to duplicate it. I’ve done the wiggle wire dance, I’ve hit bumps and wash boards, I’ve smacked the PCM. Like I stated earlier this issue was present before repairing the harness and has not changed after. For the longest time I thought I was falling asleep or having a seizure or something.

Let me preface this third thing by saying I live out in the country and have a half mile “driveway” that I idle the entire way down.
With that being said, every once in a while when coming to a complete stop after idling the engine RPMs will drop to below 400 for a second then come back up to 750.

Lastly most of the time but not always, when the engine is cold and I put it into gear, the engine revs up to almost 1500. Like my foots on the gas accelerating, it will shift into second at idle. I’ve spun the tires on wet concrete at idle. I’ve read the IAC could be an issue (it’s been sprayed out with carb cleaner a few times) and I’ve read the PRNDL switch could be the issue (I remember having a really hard time getting the harness unplugged from it when I pulled the engine out, like the connector was glued in)

I know it’s a lot to read and I appreciate y’all taking the time to help a brotha out.

Here’s some random pictures to look at
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L31MaxExpress

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Not sure why so many people think the PCM has anything at all to do with the gauges. The only thing that runs through the PCM is the speedometer on a 97 and 98+ added the fuel gauge. Temperature, Oil pressure and Tach are all picked up directly from their sources. My guess is the dampening silicone has left the air core motors and now the gauges are fluttering.

My 97 had numerous driveability quirks that went away when the black box made way for the 0411. If the weather changed 50F cooler suddenly it would flood when you tried to start it. The idle was always horrible and the throttle follower had a mind of its own. No tach on my 97, but it would sometimes idle so low after coasting along at idle that the oil pressure gauge would drop to near zero and the check gauges light would come on, then activate the stall saver. On cold starts it would often run so rich it would burn your eyes. Keep in mind this was all back in the late 90s and early 2000s these hiccups showed up. The older black box programming was garbage.

As for your electrical flicker, probably corrosion between the two halves of the positive battery connection. I replaced the positive cable on my 97 years ago with the AC Delco upgraded 1 piece cable. It would lose connection randomly to the point of stalling the engine when the underhood fuse block lost power. Then it would fire back up and run like nothing ever happened.
 

Orpedcrow

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Thanks for your input, sounds like similar issues…
My guess is the dampening silicone has left the air core motors and now the gauges are fluttering.

I think I saw a post about filling the gauges with oil? I guess I thought they were stepper motors, I’ll dig around in the search bar again.

Yea the random flicker is really strange. I’ve checked every main 12v connection I can think of. New cables, new terminals, new battery.
 

Orpedcrow

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@Orpedcrow, any updates on these issues?
The only update is I have confirmed the original pcm in the truck is for a 5.0, I dont know if that would cause any of these issues.

My current plan is to do the pcm swap this weekend and see what happens. I’m ignoring the gauges and looking for a functioning 120mph Denali unit
 

1998_K1500_Sub

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The only update is I have confirmed the original pcm in the truck is for a 5.0, I dont know if that would cause any of these issues.

One can fix the hummingbird gas gauge on the later GMT400s with a simple change to the tune in the ECU, FYI. This applies to those whose gas gauge is controlled by the ECU.

My current plan is to do the pcm swap this weekend and see what happens. I’m ignoring the gauges and looking for a functioning 120mph Denali unit

Keep us informed!
 

Orpedcrow

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One can fix the hummingbird gas gauge on the later GMT400s with a simple change to the tune in the ECU, FYI. This applies to those whose gas gauge is controlled by the ECU.
I did read about that but, I’ll eventually get setup to do my own tuning… maybe but don’t have any body local (at least not within 2 hours) that I know if that does any tuning. :shrug:
 
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