I think the PCM is dead

[All 4 Wheelin']

Last fall I replaced the spark plugs in my 4.0. Not because any real issue but because I haven't since I bought the tj in 2018. What I removed were some kind of Bosch plugs and they definitely needed replaced. New autolite double platinums in and buttoned up. Went for test drive and it ran like shit. Threw a code for missfire cyl 3&4. Figured it must be the coil pack. New coil pack. Test drive still ran like shit and threw a pre cat o2 code. So off with drivers fender and all new o2 sensors. Since the fender was off I figured it was a good time to install the GR aluminum fenders I've had sitting around for a year. That led to other things cause, you know, the snowball effect. Well I have everything back together and go to start the tj today and no start. Cranks fine no fire though. Turned the ignition off then turned it to run and got 12 flashes from the cel with no repeat. Pluged my code reader in and got no communication from the ecu. So I'm thinking wranglerfix unless someone has an idea.

 

[ColoJeep]

Last fall I replaced the spark plugs in my 4.0. Not because any real issue but because I haven't since I bought the tj in 2018. What I removed were some kind of Bosch plugs and they definitely needed replaced. New autolite double platinums in and buttoned up. Went for test drive and it ran like shit. Threw a code for missfire cyl 3&4. Figured it must be the coil pack. New coil pack. Test drive still ran like shit and threw a pre cat o2 code. So off with drivers fender and all new o2 sensors. Since the fender was off I figured it was a good time to install the GR aluminum fenders I've had sitting around for a year. That led to other things cause, you know, the snowball effect. Well I have everything back together and go to start the tj today and no start. Cranks fine no fire though. Turned the ignition off then turned it to run and got 12 flashes from the cel with no repeat. Pluged my code reader in and got no communication from the ecu. So I'm thinking wranglerfix unless someone has an idea.

@Wranglerfix is your best resource . I've only heard good things said of him.

 

[CharlesHS]

I would check thru the fuses in the PCM and Fuse box behind the glove compartment.
Check the (3) 32 pin harness connectors that plug into the ECU looking for oxidized or burned pins or clips.
Reinsert the connector and test for ECU communications.

 

[Chris]

@Wranglerfix is the man!

 

[JKP]

Fuses, ASD relay, fuel pump, crank sensor...

Swap ASD relay with horn relay after verifying the horn works.

If you spray starting fluid in it and no start, I would suspect no spark due to crank sensor.

Verify you have fuel pressure.

Disconnect battery to reset PCM and verify no comms.

 

[Wranglerfix]

@All 4 Wheelin' What year is your Jeep?

 

[All 4 Wheelin']

I would check thru the fuses in the PCM and Fuse box behind the glove compartment.
Check the (3) 32 pin harness connectors that plug into the ECU looking for oxidized or burned pins or clips.
Reinsert the connector and test for ECU communications.

Did that

 

[All 4 Wheelin']

@All 4 Wheelin' What year is your Jeep?

02

 

[All 4 Wheelin']

If you spray starting fluid in it and no start, I would suspect no spark due to crank sensor.

Verify you have fuel pressure.

As I explained at the initial post, was running fine until I put in new plugs. Old plugs were worn anywhere from .045 to .068 and was running fine.
I have fuel pressure. Verified at pressure relief valve.

 

[ItchyDong]

If I’m not mistaken, I’m pretty sure the DLC shares its 12 volt supply from the cigarette lighter fuse. Be sure that’s not popped.

Or verify you have power at the cigarette lighter.

 

[All 4 Wheelin']

If I’m not mistaken, I’m pretty sure the DLC shares its 12 volt supply from the cigarette lighter fuse. Be sure that’s not popped.

Or verify you have power at the cigarette lighter.

My code reader is BT and is powered by the DLC and has leds to indicate power so yes the DLC is working.

 

[Wranglerfix]

Have you bypassed the ignition switch to make sure that it’s good?

 

[JKP]

As I explained at the initial post, was running fine until I put in new plugs. Old plugs were worn anywhere from .045 to .068 and was running fine.
I have fuel pressure. Verified at pressure relief valve.

Well, for spark you need the crank sensor, the PCM and the coil.

 

[JKP]

And I always forget, I think the older TJs need the cam sensor input or no spark or possibly they don't fire the injectors.

 

[All 4 Wheelin']

Have you bypassed the ignition switch to make sure that it’s good?

Like I said in OP, it cranks just fine, just no spark happening. And again, no communication between BT code reader and ECU. And yes the dongle has power.

 

[ItchyDong]

You need to test the coil driver or drivers (based on year) for control with an incandescent test light.

Give me the details of your jeep.

Edit: found it in your profile.

 

[ItchyDong]

With key in run position, connect incandescent test light to battery negative. Back probe coil pack pin 2 DG/LG wire with t pin. Touch t pin, test light should illuminate. Crank engine and be sure test light stays illuminated.

Switch test light to battery positive. Back probe coil driver 1 wire, pin 1 GY. Touch test light to t pin and crank. Test light should flash. Repeat test on 2 remaining coil driver wires.

 

[ItchyDong]