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99 Chevy Tahoe 5.7l. No start.

Carla Jean simmons

By Carla Jean simmons
in Ask A GM Technician

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Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted
16 hours ago, Carla Jean simmons said:

Is there anything anyone can think of a sensor or anything that would cause the icm not send signal to the coil

How much is the ICM?  I know you said it checks out fine, but, sometimes things check out, only to be just a little bit bad.  You keep going back to that part.  I always look at how the part is that is likely is, and if it is less than an hour of my time, just replace it.

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riverbanks Senior Enthusiast

riverbanks

Posted
Posted

Time to look further in?while cranking test pcm fuse for battery voltage, sometimes spark and sometimes not,a feed is compromised?

Carla Jean simmons Enthusiast

Carla Jean simmons

Posted
  • Author
Posted

the computer is reciving signal and sending signal to the icm but i have no signal coming out of the icm. I have put 5 different icm on it. I dont understand this at all

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Either there is something wrong with the computer signal that you won't be able to see without a scope, or there's something missing at the ICM - a power, ground, or something else.

 

This page refreshed my memory - I was thinking you had a completely different system. This might help: https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/how-to-test-the-icm-2

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Too low is bad, so for me, anything above 1 ohm would work. Couldn't tell you what the spec is.

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Here's something I should've thought of long ago in this thread - can't recall if it was brought up before or not ... but how is the crank position sensor? Is there an aftermarket one in there? Did the no start happen not long after it was replaced?

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

You didn't answer my question - how is the crank position sensor? Is it sending the proper square wave signal to the engine computer? New, OE, aftermarket ...???

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Reason I ask is, I've seen many parts store units (like Advance Auto, Auto Zone, O'Reilley's, etc.) have stuff not work, or fail shortly after taking it right out of the box, brand new. Most of the time you'll never know they're bad without a scope.

 

Same goes for OE - lots of GM's parts are made in the same places that the aftermarket stuff is. Every so often you'll get a batch of bad ones. Gonna be hard to condemn that part without a scope, though.

 

If you can get ahold of a known good one - one that came off a running truck, that would be the best way to test it without a scope, just by playing swaptronics.

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Have you tried back probing the white wire on the ICM, and touching it, key on engine off, with a test light connected to ground? Does it spark then? IF you can make it spark consistently this way, the problem lies somewhere between the ICM and CKP sensor, and engine computer.

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