Cant get spark. Help!

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Oct 1, 2018 | 08:47 AM

Stepsidestatus

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Cant get spark. Help!

I have a 2004 Silverado with a 5.3 lm7. I pulled the motor and sent it off to get new bearings, rings and all new gaskets. I put an LS9 cam and moved the cam position sensor. I put on milled and P&P 243 heads. Anyways I put the motor back in the truck and assembled everything. I am not getting spark. Or a very very weak one. I can’t get it to fire at all. The coils were changed before I rebuilt the motor. I put on new plugs and wires. New crank position sensor. I attempted a new PCM (Didn’t help) I unwrapped the wire harness where it rests over the top of the intake and checked all of the wires and grounds. The grounds are on the back of the block. We have 12 V going to the coil plugs. But when I crank it it won’t fire. I’ve done this exact cam swap before and I should have plenty of experience with troubleshooting these LS motors by now. But me and my other mechanics are baffled. Does anyone know what could be causing this?

Oct 1, 2018 | 09:44 AM

fst100

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From: lancaster, pa

so what exactly happens when you turn the key to ace and run? fuel pump primes and all lights on the gauge turns on correct? when you fully turn it to run, what happens then, does the starter engage?

Oct 1, 2018 | 10:12 AM

Philhippy45

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I'm having similar issues car cranks and seem sensors habe power as I can hear the iac motor. But no spark or fuel. Fuel pump starts and is sending it to fuel rail. I'm thinking maybe not enough grounds could be our issue.

Oct 1, 2018 | 12:30 PM

Stepsidestatus

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Quote:

Originally Posted by fst100

so what exactly happens when you turn the key to ace and run? fuel pump primes and all lights on the gauge turns on correct? when you fully turn it to run, what happens then, does the starter engage?

yes everything works properly and the motor Cranks. But that’s all it does. Out of the countless number of tries we have had one cylinder fire once and that was it, just a pop. My compression is good too. We’re just not having to park coming out of the coils very well

Oct 2, 2018 | 08:05 PM

jetech

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From: Dade City, Fl.

Did you check the wiring for the newly positioned cam sensor ? Sounds like the PCM isn't receiving all the info it needs BTW... You are using a 1X cam gear for the ls9 camshaft not the original ls9 4X cam gear, right?

Oct 2, 2018 | 09:08 PM

Stepsidestatus

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Quote:

Originally Posted by jetech

yes I have the correct sprocket and sensor. I used the Brian Tooley racing Wire harness extension to relocate it. But even thenThe camshaft position sensor only times the injectors. I replaced the camshaft position sensor. it was reading an RPM, but it had a fried pin In the connector. But the crankshaft position sensor is what times your spark. I’ve done this exact cam swap on several other trucks and cars and cars but never had something like this happen
I might be going tomorrow to takeoff my intake and double check my grounds again.