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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 years experience.
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My name id My issue is a no start on a 1996 chevy 3500 7.4

Customer Question

Customer: hello my name id dave My issue is a no start on a 1996 chevy 3500 7.4
JA: Thanks. Can you give me any more details about your issue?
Customer: Have tested coil, cam sensor, crank sensor and control modual. Have power but no trigger signal
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Submitted: 12 months ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 12 months ago.

hi there, I am Cam. With your issue, you get no spark from the coil?

Customer: replied 12 months ago.
correct
Expert:  GM Tech (Cam) replied 12 months ago.

Ok, do you have access to the scan tool live data?

Customer: replied 12 months ago.
not at the moment
Expert:  GM Tech (Cam) replied 12 months ago.

Ok, that’s going to be the key. We need to see if there is a crank signal being read by the PCM. You replaced the sensor, is there power to the sensor, ground? Wring damages? If you unplug the cam sensor, does it spark?

Customer: replied 12 months ago.
I have power to the sensor yes ground checks good have not unplugged the cam sensor
Customer: replied 12 months ago.
hooking scan tool up now
Expert:  GM Tech (Cam) replied 12 months ago.

ok

Customer: replied 12 months ago.
scan tool reads cranking rpm at 132 everything else checks ok
it does pull up 3 codes 0154, 1351, 1406
Expert:  GM Tech (Cam) replied 12 months ago.

P1351 is the one of concern. That is the timing wire between the ignition module and the PCM. It’s the white wire. Trace that wire down. If you find no issue, then the PCM is bad as you have replaced the ignition module already.

Customer: replied 12 months ago.
ok I will start tracing that wire now. yes I have replaced ing mod, cam sensor, crank sensor and coil.
Expert:  GM Tech (Cam) replied 12 months ago.

Ok, let me get the code chart for this so you can follow it.

Customer: replied 12 months ago.
can this be caused by a bad ing switch
Expert:  GM Tech (Cam) replied 12 months ago.

Here it is.

Yes, it could if its not sending power properly. Follow through the document and it should get you there.

Customer: replied 12 months ago.
thank you I will let you if it works
Expert:  GM Tech (Cam) replied 12 months ago.

Please bookmark this page so you can easily navigate back to it so we can continue the discussion. This is done by pressing (CTRL D on PC and CMD D on Mac). You can reply at any time for follow up information regarding this issue, even after you rate the site and I will reply.

Customer: replied 12 months ago.
white wire from modual to computer is fine and test clear.
Expert:  GM Tech (Cam) replied 12 months ago.

Ok, so we may have a problem with the PCM, did you make it through the diagnosis in the document I posted?

Customer: replied 11 months ago.
I did every single test on that list, Everything checked out perfect. But I still get no trigger signal
Expert:  GM Tech (Cam) replied 11 months ago.

I am going to see if any other experts have an idea of whats going on.

Customer: replied 11 months ago.
Right now it has a new coil, cam sensor, crank sensor, ing modual, and new computer. and no spark.
Expert:  GM Tech (Cam) replied 11 months ago.

I guess they don't. So i have a question, you went through the code chart for ignition diagnosis that I posted. The steps to the end list what to do if its running, but you did not get it running. How could you complete those steps if it was not running?

Customer: replied 11 months ago.
Cam Here is what the test results are as of today. Everything is different now. Step 3 ignition coil module terminal B voltmeter to ground Crank Engine reading 0.012 Not 1 to 4 volts. Step 4 check resistance from coil module terminal b and vcm reading 00.0 checked connection at vcm no problem found. Next said to replaced vcm and did but still to voltage on terminal B at coil?
Expert:  GM Tech (Cam) replied 11 months ago.

Did you have it on AC volts or DC volts?

Customer: replied 11 months ago.
ac
Expert:  GM Tech (Cam) replied 11 months ago.

Then your issue remains your VCM. There is no way around that. If the voltage is not being sent then its bad provided everything else shows up properly.

Customer: replied 11 months ago.
those readings are with a brand new vcm installed
Expert:  GM Tech (Cam) replied 11 months ago.

New or reman?
What source?

Customer: replied 11 months ago.
New from Orielly auto parts
Expert:  GM Tech (Cam) replied 11 months ago.

I would talk to them. Let them know your results and proceed from there.

If it waddles like a duck and quacks like a duck......

Customer: replied 11 months ago.
ok I will have them get me another one
Expert:  GM Tech (Cam) replied 11 months ago.

ok

Customer: replied 11 months ago.
Hi Cam, Ok I got another computer from the factory, Had them flash the computer there. Installed new vcm. cleared all codes.. Ran a code check all clear. Cranked the engine 15 seconds and the code 1351 came right back and still no spark.
Expert:  GM Tech (Cam) replied 11 months ago.

That code is specific then, VCM, Ignition module or wire. Is there a pin fit issue on the wire at either end? Anything spliced into that wire where it should not be?

Customer: replied 11 months ago.
I have actually traced the white wire from the Ignition module to vcm. Not broken nothing spliced into it. Before we got 3 codes now the only code that shows is 1351. I do still have power to Coil, Crank shaft Pos sensor and Module both with key on and while cranking. I have checked pins for any damage and do not see any. What can I be missing here.
Expert:  GM Tech (Cam) replied 11 months ago.

The voltage signal of 1-4 volts ac is vital for operation of the cool.

Customer: replied 11 months ago.
that I do not have.
Expert:  GM Tech (Cam) replied 11 months ago.

OK so with that we need to go back to the VCM. You replaced it so lets test the voltage at the VCM with the engine cranking. If you get voltage then your wiring is bad.

Customer: replied 11 months ago.
Ok test Voltage at the Vcm on the white wire going to Ignition module I will try that. Is there a power wire to the Vcm that should be checked also???
Expert:  GM Tech (Cam) replied 11 months ago.

Terse is an orange in the grey connector, pink in the blue connector and a pink and brown in the black connector. Orange is battery and the other is ignition. Make sure those have power. Then black white wires in the grey connector are ground.

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