No start 2001 chevy 8.1 fixed

autojoe

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#1
Make
Gm
Model
Silverado
Year
2001
Miles
90000
Engine
8.1
No spark... No injection pulses..... No fuel pressure....when first no start there was fuel pressure 38 psi but no spark or injector pulses. Now no fuel pressure don't even have koeo fuel pump prime for two seconds. Can take a test light on fuel pump relay control wire at pcm connected to battery positive and the fuel pump relay will energize and fuel pump will pressurize the rail 38 psi. Before I was leaning towards faulty crank sensor with no spark or injector pulses but the fuel pump should still run koeo to prime the rail. If the pcm doesn't see a rpm signal it will shut down the fuel pump relay or not even energize it correct? But not getting the two second koeo prime. And before when it was priming rail 38 psi there was no spark or injector pulses. Battery voltage to all coils and injectors but no control. Thinking bad pcm. Happened all of the sudden. What input is the pcm looking for from ignition switch to energize the fuel rail koeo? There is a orange wire from ignition switch to pcm that has battery voltage koeo. Sorry so long.
 

grcauto

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#2
Check the ignition switch in the start position and see if you still have 12 volts.
 

autojoe

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#3
Ignition relay powers the coils and injectors and all have battery voltage koeo.
 

billr

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#4
OP, are you familiar with how to back-probe connectors, and how to use a multimeter in general?

We need schematics posted.

Live-data could help a lot; consider getting a scanner or ELM327-type link that will provide live-data.

Agreed, the key-on failure of the FP is probably the most important clue. I, too, would have been suspecting the CKP sensor if it wasn't for that FP problem. And I, too, am suspecting the ignition switch/wiring.
 

autojoe

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#5
Battery voltage in crank run position. I been doing diagnostics for 30 years. I have electronics training. I have fluke meter snap on scan tool and Pico scope. I have seen many many times no spark or injector pulses and use scan tool and scope faulty crank cam sensor or wiring issues but not fuel pump prime issue. Going to scope crank sensor. I know that if you turn the key to on position the pcm should energize the fuel pump relay for two seconds to prime the fuel rail..... Then if cranking no rpm signal is seen then pcm will not energize the fuel pump relay safety issue in case of a vehicle accident but in this case no prime is happening. I am wondering if there is a input to the pcm from the ignition switch I am missing. I seen circuit 1020 orange wire from ignition switch to pcm. Don't know if it is the main input. Koeo the ignition relay is energized because I have battery voltage to coils and injectors. Trying to figure out. Thanks for the help. Joe
 

billr

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#6
I'm sure there are two wires supplying 12V to the PCM. One "always hot" from the battery/fuse-panel and one switched from the ignition switch. We need a schematic so you can check that switched one at the PCM connector. Do you have live-data? If so, do you get rpm when cranking? Does the scanner even connect to the PCM at key-on and display things like ECT, IAT, TP, etc correctly? If the PCM does connect, then I think it is pretty likely that switched supply is OK; no need to even probe at the PCM connector.

I am a bit confused about how you checked the FP circuit with a test light. I think you energized the FP relay coil by grounding it through the test light, and the light is low enough impedance relative to the relay coil that the relay pulled-in and the FP ran; is that correct? At key-on, what does a meter show that coil terminal doing, does it go nearly to ground? Next step would be back-probing at the FP pin on the PCM connector. Again, we need a schematic, and one will be posted soon, I'm sure.
 

autojoe

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#7
The fuel pump relay is power side switched. The pcm supplies battery voltage on control circuit. The test light is connected to battery positive at pcm control wire doing what control circuit should be doing. I am going to look vehicle again. Will keep you posted. Thanks. Scanner will connect and all sensors have 5 volt ref. If the crank circuit is good input to pcm and no control I will probably replace pcm and flash. Thanks for the input. I will keep you posted.
 

billr

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#8
Yes, I can believe the FP relay drive is 12V, not grounding. I recently went through a PCM problem with an old Saturn and that's the way it is too; not "grounding" drive like injectors or spark coils commonly are.

I don't want to send you "in the weeds", but pay particular attention to the 5V reference supplied to the TPS. My problem ended up to be that the 5V in the PCM was flaky. Sometimes it would come up slowly to about 3.5V, then after several minutes finally creep toward 5V. That was enough to confuse the whole key-on boot and prevent the proper key-on FP operation (as well as a bunch else!)
 

grcauto

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#9
Apply B+ to the gray wire of the FP relay and listen for the pump.
 
Last edited:

autojoe

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#10
Thanks for advice. Will test 5 volt ref again and see if it is different. The fuel pump will run if fuel pump control circuit is manually energized.
 

grcauto

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#11
I'm wondering if the start signal is being sent. Going by memory (not a good thing) I thought the theft would disable the injectors but I may be mixing this up with Chrysler. At any rate I do believe you will see a crank signal in the BCM and it will tell the PCM to, 'YES' good to start or 'NO' do not allow. There should be a PID in the datastream for this. Your Snappy will have this pid available.
 

autojoe

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#12
Thanks I was thinking that also if there was no crank signal received by the pcm then the pcm would not energize the starter relay. The starter motor turns Cranks no start. Gm is usually start stall disable injectors. I will keep you posted. Thanks again. Wanted to mention that at the beginning of this problem there was only 6 volts bias on the fuel pump relay control circuit with relay removed normal on power side switched circuits now no bias voltage on control circuit also I think there was a fuel pump relay control circuit fault code. I think it is going to be a faulty pcm.
 

grcauto

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#13
Sounds like the PCM may be the problem. Before condemning it be sure the powers and grounds to the module are good.
 

autojoe

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#14
Thanks.... I always do that first. No crank or cam counts on scan tool. Going to verify 12 volt ref from pcm. Will keep you posted.