New Engine Install - Rough start then Stalls

[mwilk012]

In addition to the previous fuse and relay checks, pcm connector check, and PDC connector check, I ran the Ignition Off Draw (IOD) parasitic test. After waiting for the modules to shut down, the system only had 12 ma of residual draw, which is well within the 50 ma limit. Passed.

The Power Control Relay is not stuck in the open position. Normal for the PCR is closed (connected). Passed.

I put in my SGW bypass harness and hooked up the Autel MP808S with the ignition in the "ON" position, engine not running. Tried to get it to read the VIN and that failed. I manually entered the VIN and it confirmed the make/model/year correctly. When I had it check for codes it said there was no communication with the PCM. Fail.

I installed the wireless BT bridge in the SGW bypass harness and opened JSCAN. Ignition "ON" engine not running, cleared codes, JSCAN gave me a U0100 code "lost communication with engine control module/power control module. Fail.

It sounds like that is the problem. No comms with the PCM.

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[alphawolff]

It sounds like that is the problem. No comms with the PCM.

Which is what I've been saying two weeks of chasing tails when the problem was obvious from the start. I know communication faults is well outside the normal scope of standard DIY'ers but it's an important part of modern diagnosis.

 

[roaniecowpony]

Which is what I've been saying two weeks of chasing tails when the problem was obvious from the start. I know communication faults is well outside the normal scope of standard DIY'ers but it's an important part of modern diagnosis.

I knew it wasn't communicating. You told me that a week or so ago, and I've been looking for why. I've been trying to find a bad wire or connector, short, etc.. No luck on finding anything. I pulled the PCM today and sent it off to be checked by Mark at WranglerFix

 

[alphawolff]

I knew it wasn't communicating. You told me that a week or so ago, and I've been looking for why. I've been trying to find a bad wire or connector, short, etc.. No luck on finding anything. I pulled the PCM today and sent it off to be checked by Mark at WranglerFix

You need to just check it for power, ground, and communication. You'll have 2 power wires (fused ignition and always hot B+), 3 grounds wires, and 2 can c+/- wires. The can C wires should be roughly 2.7v on can+ and 2.3v on can-. They should add up to equal 5, but not be identical and be around those values. Test with key on.

Could just be a spread terminal, so make sure you test pin drag

If it has all the above it's a dead module, which is rare.

I'm putting money on a spread pin for the fused ignition output circuit at the PDC. Seen it a handful of times

 

[roaniecowpony]

You need to just check it for power, ground, and communication. You'll have 2 power wires (fused ignition and always hot B+), 3 grounds wires, and 2 can c+/- wires. The can C wires should be roughly 2.7v on can+ and 2.3v on can-. They should add up to equal 5, but not be identical and be around those values. Test with key on.

Could just be a spread terminal, so make sure you test pin drag

If it has all the above it's a dead module, which is rare.

I'm putting money on a spread pin for the fused ignition output circuit at the PDC. Seen it a handful of times

This fused ignition output of the PDC, is that an internal board fuse? None of the replaceable fuses are blown.

Since the PCM is out and I don't have any dimensions available for making a pin drag gauge, I'll probably be waiting a week or so to get to that test, pending the outcome of the PCM check, unless you have one you use and can provide some dimensions. I have a full machine and fab shop available to use, so making one from scratch is easy enough. Thickness and width would be all I need.

I really appreciate all the time you've taken to give on this.

 

[alphawolff]

This fused ignition output of the PDC, is that an internal board fuse? None of the replaceable fuses are blown.

Since the PCM is out and I don't have any dimensions available for making a pin drag gauge, I'll probably be waiting a week or so to get to that test, pending the outcome of the PCM check, unless you have one you use and can provide some dimensions. I have a full machine and fab shop available to use, so making one from scratch is easy enough. Thickness and width would be all I need.

I really appreciate all the time you've taken to give on this.

It's a BCM controlled relay at the PDC. When the key is placed in the on position the BCM energizes a relay to turn all the other modules on. There's 2-3 different run/start relays for this purpose. Check for the proper voltages & ground at the PCM connector before chasing down pin drag issues

 

[roaniecowpony]

It's a BCM controlled relay at the PDC. When the key is placed in the on position the BCM energizes a relay to turn all the other modules on. There's 2-3 different run/start relays for this purpose. Check for the proper voltages & ground at the PCM connector before chasing down pin drag issues

Is it safe to energize the system with the PCM unplugged? I don't currently have the PCM available. It's off to a PCM shop for testing.

 

[alphawolff]

Is it safe to energize the system with the PCM unplugged? I don't currently have the PCM available. It's off to a PCM shop for testing.

Yes, feel free to turn the key on. You'd be testing it with it disconnected anyway

 

[Mx5red]

Jesus Christ you guys are smart.
I somehow take 2 hours to clean my air filter

 

[Bill_BCNtoNY]

Jesus Christ you guys are smart.
I somehow take 2 hours to clean my air filter

I’m with you - following this thread to watch&learn

I’ll get the popcorn!

 

[roaniecowpony]

I’m with you - following this thread to watch&learn

I’ll get the popcorn!

You're going to need survival rations.

 

[JLfromCA]

Great thread, hope you get it sorted.

 

[roaniecowpony]

You need to just check it for power, ground, and communication. You'll have 2 power wires (fused ignition and always hot B+), 3 grounds wires, and 2 can c+/- wires. The can C wires should be roughly 2.7v on can+ and 2.3v on can-. They should add up to equal 5, but not be identical and be around those values. Test with key on.

Could just be a spread terminal, so make sure you test pin drag

If it has all the above it's a dead module, which is rare.

I'm putting money on a spread pin for the fused ignition output circuit at the PDC. Seen it a handful of times

I discovered some various fuses use the same size (width and thickness) pins as the PDC. I had to narrow one down to make the gauges. Did the pin drag test on every socket. No problems found. Waiting on the PCM test results.

 

[alphawolff]

I discovered some various fuses use the same size (width and thickness) pins as the PDC. I had to narrow one down to make the gauges. Did the pin drag test on every socket. No problems found. Waiting on the PCM test results.

Just confirming here, you didn't put a multimeter on them and confirm the proper voltages and grounds?

I've attached the pinout for the PCM C1 connector for a 2018 JL 3.6L.

With the key on, perform the following tests:

Pin 57, CAN C(+) - ~2.6-2.9v
Pin 33, CAN C(-) ~2.1-2.4v
Pin 23, Fused ignition output equal to battery voltage (~12v)
Pin 96, B+ supply, equal to battery voltage (~12v)


Pins 52, 53, and 72 are grounds. Should be 3 ohms or less between pins and chassis ground.


I suspect pin 23 , the fused ignition output, is going to read low or zero. That's just my gut feeling, though. Sometimes I forget people don't have access to the proper scan tool and wiring diagrams that we do. To diagnose something like this my scantool would've shown the PCM offline on the vehicle's network, then I'd just do the above tests to confirm a wiring issue or a PCM issue and go from there. If all the above circuits check out OK than the PCM is indeed failed. Also do be careful, these old gpec 2 PCM connectors are fragile and the locks like to break off. If that happens you might not fully seat the connector when you go to connect it back up

 

[roaniecowpony]

Just confirming here, you didn't put a multimeter on them and confirm the proper voltages and grounds?

I've attached the pinout for the PCM C1 connector for a 2018 JL 3.6L.

With the key on, perform the following tests:

Pin 57, CAN C(+) - ~2.6-2.9v
Pin 33, CAN C(-) ~2.1-2.4v
Pin 23, Fused ignition output equal to battery voltage (~12v)
Pin 96, B+ supply, equal to battery voltage (~12v)


Pins 52, 53, and 72 are grounds. Should be 3 ohms or less between pins and chassis ground.


I suspect pin 23 , the fused ignition output, is going to read low or zero. That's just my gut feeling, though. Sometimes I forget people don't have access to the proper scan tool and wiring diagrams that we do. To diagnose something like this my scantool would've shown the PCM offline on the vehicle's network, then I'd just do the above tests to confirm a wiring issue or a PCM issue and go from there. If all the above circuits check out OK than the PCM is indeed failed. Also do be careful, these old gpec 2 PCM connectors are fragile and the locks like to break off. If that happens you might not fully seat the connector when you go to connect it back up

I just completed the pin drag test of the Power Distribution Center connectors. I have not done the PCM harness meter test yet. Moving slow here. Wrenched my back last weekend.

To be clear, which is the C1 connector?

Forward connector.

Rear connector.

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