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JFN1
JFN1, ASE Certified Technician
Category: GMC
Satisfied Customers: 4618
Experience:  GM Master Technician
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2005 GMC Denali 6.0 Engine turns over but won't start. No

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2005 GMC Denali 6.0 Engine turns over but won't start. No power at the CRNK fuse key on, but powers while cranking. This is a rebuild initial start up. Fuel 55psi. Every once in. A while it will act as though it's going to start.

Looking at a scan tool, when it's cranking, does the RPM go up or does it stay at zero?

Customer: replied 4 months ago.
Best I can tell it stays at zero. Injectors do have power but no spark for sure. Put in a new Crank sensor it has a good ground.
Customer: replied 4 months ago.
Coils do have 12v and a good ground

If the scan tool RPM is staying at zero when cranking, there is a problem with the crank position sensor circuit that needs to be corrected. Computer may not pick up on this and set a code, because it doesn't know whether the engine is cranking or not until it monitors things for awhile and determines that things aren't working like they should.

You don't seem positive about the zero RPM, though, can you recheck that?

Customer: replied 4 months ago.
I preformed these test. http://troubleshootmyvehicle.com/gm/4.8L-5.3L-6.0L/how-to-test-the-crank-sensor-1Ground pass
Signal pass
12v w Key On Engine Off pass

All of the circuits pass, so the question is whether there is actually a signal being received at the ECM.

Do you have a scan tool that reads data?

Customer: replied 4 months ago.
Actron 9690

And you've verified that there is zero rpm while cranking, yes?

Customer: replied 4 months ago.
Correct

OK, reading back in the thread, I just wasn't certain that we actually got an answer on that, so I apologize for being redundant.

If the circuits test OK from end to end, there are other possibilities. One is that one of the CKP wires is grounded, and this wouldn't show up as irregular if you are using an ohmmeter to test from end to end. The wire can be connected at both ends, AND be touching ground somewhere, and if this happens, it will kill the CKP signal. Careful inspection of the wiring might reveal this, and you can also use an ohmmeter to test continuity to ground on the 5v and the sensor return circuits, they should NOT have continuity to ground in any fashion.

It's possible that the wires are broken right at the connector, this happens occasionally, and when you unplug it to test it, it makes the connection, but breaks the connection when you plug it back into the CKP.

It's also possible that your ECM is faulty, though this is a lower probability. ECM's are pretty high quality. I suspect a wiring issue, and just a careful visual inspection might reveal where this wiring is touching ground.

Customer: replied 4 months ago.
Could the cam sensor cause the same issues

No. The only thing that causes the RPM to read zero is a failure of the CKP circuit. This engine will actually run without a cam sensor.

Customer: replied 4 months ago.
Thanks for the help!!! We are running like a top!! The ground wire on top of the engine on the passenger side near the #8 cyclinder was not grounding good. Even though the CRK sensor had a good ground.

Excellent!

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