No start 2001 chevy 8.1 fixed

nickb2

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#16
I hope this pdf will help. I am using different software, more printer friendly.

You could always try to add an engine ground, they tend to fritz up I have encountered this often on these chassis. All engine series use same chassis ground. All pcm grounds route through the right hand firewall/wheel well.
 

autojoe

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#18
Thanks for the wiring schematics. I have alldata and hate it. Miss information at times.
 

grcauto

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#19
Thanks for the wiring schematics. I have alldata and hate it. Miss information at times.
We call it SomeData and some of that data is bad data. They can't blame it on the writers of OEM material since Mitchell gets it right much more than AllData.
 

autojoe

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#22
Have crank counts on scan tool but no cam counts but I think it only needs crank input to start. No spark or injector pulses or fuel pump prime. Thanks guys. Like beating a dead horse. Was thinking of scoping crank signal at pcm but scan tool showed crank counts and no spark or injector pulses or fuel pump prime.
 

billr

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#23
Nickb2, do you have a schematic showing the ignition switch itself?

OP, the lack of key-on FP operation has nothing to do with the CKP or CMP signals (or spark/injector pulses). I would get the FP issue resolved before fussing with anything else. I would also get the PCM out and powered on the bench. Use common RS232-type sockets to connect test leads to the PCM
 

autojoe

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#24
I found it once on my alldata but couldn't find it again. Have 12 volts to all coils and injectors from ignition relay.
 

billr

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#25
Do you understand that the ignition switch has multiple "hot in run and start" contacts? Having 12V to the coils and injectors does not ensure that the PCM is being powered-up properly, or that all its 5V supplies are coming up properly at key-on. the only "hard" symptom you seem to have is that the FP doesn't run at key-on, so that's why I am focused on that. It is easy to test the FP output function on the bench, and if the PCM won't even do that, then the PCM must be bad in at least that regard.

If you do do bench-testing of the PCM FP output, let me warn you that it may not be a "solid" 12V output. On my Saturn PCM that FP signal goes solid to 12V for about 1 sec and then becomes a high duty-cycle pulse train for the remainder of the key-on run. You may see this using a scope, and it may be perfectly normal for your PCM; same as it is for the Saturn
 

autojoe

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#26
Thanks Bill. All ignition inputs to the board show 12 volts. No fuel pump control and no coil or injector control. Pcm is receiving a crank signal.
 

grcauto

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#27
Have crank counts on scan tool but no cam counts but I think it only needs crank input to start. No spark or injector pulses or fuel pump prime. Thanks guys. Like beating a dead horse. Was thinking of scoping crank signal at pcm but scan tool showed crank counts and no spark or injector pulses or fuel pump prime.
I'm thinking the vehicle will continue to run if it loses the cam signal but will not start without it. I'm going by memory but it seems this was true with some GM platforms of that era.
 

autojoe

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#28
IMPORTANT: A missing Camshaft Position (CMP) sensor may cause a long crank condition.

The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM can determine when a cylinder is on either the firing or exhaust stroke by the 24X signal.
Now it is showing cam and crank counts and rpm. No spark or injector pulses.
 

autojoe

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#30
Going to check all ignition switch inputs and grounds before I make the call. Thanks.