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PCM 5.7 bogs down at high rpm

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Quickstep192

New member
My 2001 PCM 5.7 is having an issue if I try to go over 4800 rpm.

It runs like a top at lower rpm, but as soon as you try to throttle up past 4800, it suddenly loses power. And I mean suddenly.

If I throttle back down, it’s back to running fine again.

This happened couple of years ago and the final solution was to replace the ignition module in the distributor. I replaced that module this morning, but the problem persists.

It almost is behaving like a rev limiter in a car. Everything is fine and you hit a point and power is lost. It’s abrupt and feels like someone’s hitting the brakes.

Hopefully my desciption is clear, but feel free to pepper me with questions.

Any ideas?
 
Not real familiar with PCM models but most 5.7's topped out at 4800 rpm.
That said, if your tach is not 100% accurate then it could be your above 4800 and it is hitting the rev limiter
 
Does it have fuel injection (ECM) or a carb?

The little bit of PCM data I have from that vintage suggests an ECU controlled engine should be able to run at 5000RPM - so verify the tach like AllDodge suggested. The owner's manual recommends cruising at 4000RPM max, assuming the engine is propped to reach 5000 RPM with a full load.
 
I was mistaken, the engine starts bogging below 4400. Sometimes even lower than that.

It’s a TBI engine.

Any ideas?

BTW, what is this connector for? Could it provide diagnostic information ?
 

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Quickstep192 said:
I was mistaken, the engine starts bogging below 4400. Sometimes even lower than that.

It’s a TBI engine.

Any ideas?

BTW, what is this connector for? Could it provide diagnostic information ?
Click to expand...
Not a connector, looks like fuse and cover, most likely there are 3 fuses
Take the cover off and look under it
 
have you checked the fuel pressure at WOT?

Its a pain on the TBI units - there's an aftermarket version but not everybody carries them...
 
Thanks for the info. Do I correctly understand that there’s no diagnostics like OBD on these engines?

Any ideas on where to look? This sure feels like an engine control issue, but I’m really not well versed.
 
Quickstep192 said:
Thanks for the info. Do I correctly understand that there’s no diagnostics like OBD on these engines?

Any ideas on where to look? This sure feels like an engine control issue, but I’m really not well versed.
Click to expand...
Being a EFI motor it should have a diagnostic connector, but as before I'm not well versed on PCM systems.

There should be a ECM on top the motor, and next to it should be the connector, and the connector will have a cover cap on it
 
PCM used the baseline GM parts for their TBI engines...and the MEFI ECUs...probably an MEFI-2. The harness will have the standard 10 pin DLC connector. Once you find the DLC, you can rig up an LED to read the codes it may have...that said, if the issue is in the fuel supply subsystem, there won't be any trouble codes as the ECUs in that era didn't monitor that subsystem.
 
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