Chevy 5.3 no spark?

SLKELTIC

MEMBER
2003 CHEVROLET SUBURBAN
V8
2WD
AUTOMATIC
220 MILES

Ive got a 2003 5.3 flex fuel suburban. Problem started about 3 weeks ago. The truck would shut off occasionally at stop lights with no "stumbling or miss fire". Then it proceeded to start dieing while driving, just shut off with no stubling or hesitations. I thought fuel filter, replaced it, it was dirty, then replaced it again about 1 week later. Problem went away for a few days. Then the same thing started happening again. I pulled the injectors, fuel rails and throttle body and checked / cleaned everything. Problem was gone for 2 days. It started dieing again today so I dropped the tank and checked the screen, its perfectly clean, pump was replaced about 9 months ago. Went out this afternoon and it wont start at all. 50 psi at the fuel rail, but now no spark to any of the di coils. I disconneted the mass air flow and checked all the fuses. Still no start. During all of this I have not gotten any trouble codes. Any ideas?

1 Reply

AL514

MECHANIC
4,793 POSTS

Hello, do you have an automotive 12v test light? Since this vehicle has a 12v Crankshaft position sensor, you could check for a dim pulse on the test light while back probed into the crankshaft position sensor harness plug. You'll have to have someone crank the engine for you, it will also tell you if you have power to the crank sensor and if you use the sensors ground you can verify the ground is good all at once, It sounds like the sensor is getting hot and failed, that or the cam sensor, but if your fuel pressure is holding up (spec is 48 to 54psi) and not dropping off during cranking. I would check the crank sensor next. We can post the wiring diagrams for you. Check your fuses too. Does the Check Engine light come on at key On? It should for about 2 seconds,

Hello, do you have an automotive 12v test light? Since this vehicle has a 12v Crankshaft position sensor, you could check for a dim pulse on the test light while back probed into the crankshaft position sensor harness plug. You'll have to have someone crank the engine for you, it will also tell you if you have power to the crank sensor and if you use the sensors ground you can verify the ground is good all at once, It sounds like the sensor is getting hot and failed, that or the cam sensor, but if your fuel pressure is holding up (spec is 48 to 54psi) and not dropping off during cranking. I would check the crank sensor next. We can post the wiring diagrams for you.

The crank sensor is on the passenger side of the engine, in the rear of the engine block near the bellhousing. Check the connector to for any corrosion or oil leaking on it, its not in a great spot.
Do you have a scan tool? Along with watching for a check engine light, during cranking you can watch the Tachometer, it should be jumping alittle during cranking. If the check engine light doesnt come on at key On, then the ecm is not powering up, and it might be a relay failure or fuse.
If you do have a scan tool, pull up live data and watch for an RPM signal (engine speed) data PID.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

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