No Start No Spark

[THase89]

96 C3500 w/ 454 Vortec

Problem Summary: Randomly completely turns off ether driving or idling but would restart immediately. Truck still has power. Did this for a couple months. Now truck will not start at all. No spark at the plugs.

New parts 6 months ago:
Distributor, rotor and cap.
ICM
Coil
AC Delco plug and wires

New parts trying to diagnose issue:
Coil, ICM and Crank sensor.

Diagnostic activity:
12v power to ICM, Crank sensor and coil good.

Ground wire to ICM good. ICM is getting signal from PCM.

Coil is getting signal from ICM. Dash command app is showing rpm when cranking over.

Coil wire has continuity. Rotor and cap also tested good.

Confirmed no spark at plug. Also checked fuel pressure to be at ~55-60 during cranking.

Truck shows zero signs of firing. What am I missing?

 

[stutaeng]

Puzzling...Have you checked for spark at the coil? If not, then coil is likely bad (stuff fails regardless of age.)

Have you checked injector pulse? Do the spark plugs smell like gas? Just some additional information that may help.

Does truck have any rust? May a loose/corroded wire not making full contact?

 

[THase89]

Truck is getting gas. Surprisingly not rusty. I’ve checked all ground connections as well to rule them out.

Coil was replaced but both old and new tested ok.

Only thing I’ve not checked wiring wise is crank sensor to PCM but with the scanner showing RPM, I assume that means it’s getting the reading

 

[Erik the Awful]

Sidepost battery problems. No matter how tight I tightened mine I had this problem. I chopped them off and went top post and never had that failure again.

 

[Schurkey]

I don't know how the battery terminals can be a problem if the engine still cranks normally.

 

[Erik the Awful]

Intermittent contact. My Suburban would die while driving down the road. It would crank back up just fine. When I got home I cranked the terminal down and it would tighten up a smidgen and run fine for a couple months, then it would act up again. When it was "loose", you could fire it up and wiggle the positive cable and duplicate the problem. I know you like to disbelieve that side terminals are garbage, but in my experience they are.

 

[Nad_Yvalhosert]

Restart at the basics. All fuses good?
Do you have a crank reference signal on a scan tool?

 

[THase89]

Nasty storms today but will go back though everything probably this weekend. Just got a new brass style cap and rotor in today just to change out for peace of mind.

By crank reference signal, I am getting RPM reading with scan tool if that’s what you mean?

So far, I’m confident ICM, Coil and related wiring is good as is spark plugs and wires. I put a new crank sensor on with no change. One of my next steps is to follow the wires for that. Scan shows RPM, but not sure where it get that’s information from.

 

[THase89]

P0336 code popped up. Truck has had crank sensor replaced during all of this. Just ohmed out the signal wires to the VCM and both come back good. Odds of a bad new sensor? Any place I can find an OEM sensor as the one I took out is different color / design that one I put in but is correct p/n according to rock auto.

What else to look at or check?

 

[Schurkey]

Connect scan tool, verify signal strength. Signal strength varies with gap between sensor and trigger wheel. Big gap = low voltage.