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Is this a PCM wiring issue?
Posted: February 29th, 2016, 10:32 pm
by DaemonForce
I have a 4.7L stroker with the 99 intake, Neon injectors and a Precision fuel pump. I'm attempting to use a minimal harness from a LATE 96 XJ(the one with bubble connectors) and my first issue is when attempting to start it from the ignition side. I connect the IGN/SW OUTPUT circuit to a 12V (B+) connection to bring it to the Run/Start position and the immediate behavior is all three relays(Starter, Fuel Pump, ASD) all activate then shut off after what is maybe a ½ second.
Since I am unfamiliar with the 4.0 in every form, I'm wondering if this is the common behavior of a bad PCM circuit or something else that I need to check. Is there any way to check what's going on?
Re: Is this a PCM wiring issue?
Posted: March 5th, 2016, 11:55 am
by DaemonForce
Wow, no response? I guess turning the ignition key from OFF to the RUN position is beyond everyone here.
Re: Is this a PCM wiring issue?
Posted: March 5th, 2016, 2:08 pm
by jsawduste
Verify you have 12v in both crank and run.
The ASD/Fuel pump share a common 30 and a common 85/86. The ECM grounds both the ASD/FP.
If the ECM doesn't see an ignition signal it shuts off the ASD/FP within a few seconds via the ground to the relay.
Re: Is this a PCM wiring issue?
Posted: March 5th, 2016, 2:32 pm
by DaemonForce
jsawduste wrote:Verify you have 12v in both crank and run.
My bench is using a +12V circuit direct from the battery for both the IGN/SW RUN and START positions.
jsawduste wrote:The ASD/Fuel pump share a common 30 and a common 85/86. The ECM grounds both the ASD/FP.
The common 30 for the ASD is a red wire that comes off of Black connector A22 and the Common for my FP goes to Battery (+).
jsawduste wrote:If the ECM doesn't see an ignition signal it shuts off the ASD/FP within a few seconds via the ground to the relay.
Meaning it breaks the circuit? That would explain the behavior but I have no idea what to do about this.
Re: Is this a PCM wiring issue?
Posted: March 6th, 2016, 4:20 am
by jsawduste
Yes it breaks the circuit and shuts the 12v down by ungrounding the relays.
Look to see if you have spark.
Re: Is this a PCM wiring issue?
Posted: March 26th, 2016, 7:42 pm
by DaemonForce
I've come a long way this month. :/
New flywheel, new crank sensor and new distributor. Now attempting to start on 91 grade premium.
Today I setup the radiator and hooked up the main plumbing. It cranks over barely a rotation to get started but dies unless the throttle is halfway open. Is this the famous security module issue and if so, does this mean getting yet another ECM? What should I choose, a 97 Cherokee PCM?
Tomorrow I hope to figure out the pilot bushing for the crank. I'm a hop and a skip away from bolting up my rebuilt T-5.
