Crank - No Start Intermittent Pulse - Injector & Coil

WDC

New member
Vehicle: 2007 Jeep Grand Cherokee 3.7 L

Recently rebuilt top side of engine after fire. We are getting an intermittent pulse on injector and coils. When cracking engine, (testing with noid lights on spark and injector) systems get normal pulses, engine tries to start, then pulses stop. Continued cranking gets intermittent on/off pulse signal surges. We get a blast of pulses the engine might turn two revolutions and then another blast.

We are seeking help and answers to what would cause intermittent pulse signals on the coil and injector circuits.

Useful Information:
• ASD auto shutdown relay working normal i.e relay closes for 2-3 seconds, if engine is cranking stays closed. If you stop cranking relay opens 2-3 sec (normal). Because it is working normal we assume the ECM is providing ground.
• we have a problem with no ground on Starter Relay. Likely problem with internal transmission NSS. With ground jumper on relay it works fine. We get 12V pilot but no ground. Will address the NSS problem once we solve the no the start problem.
• Engine wire loom was switched out with matching vehicle/loom (plug-in replacement).
• Two ECM were tried (original & and donor vehicle matching the loom)
• all other functions work (to the best of our knowledge)
• I should note we rebuilt the heads i.e. new timing chain, but we have checked the timing marks a number of times.

Can anyone recommend what would cause a intermittent coil and injector circuits pulses?

Your help is greatly appreciated.
Will

PS also looking for a PIN-OUT diagram for the 3 ECM plugs in order to trace grounds from the under hood relay boxes to ECM.
 

Crank - No Start Intermittent Pulse - Injector & Coil

IDK.

I could only ask if there is or was a SKIM unit on the vehicle. That and the CKP. Or crank sensor will allow turning but no firing.
Also many electrical systems on the jeep switch on the ground side. So your no ground on a relay may be a condition not met and the ground is not closed.



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