Troubleshoot a "once fire" and now "no-fire" scenario"

sierradmax

TJ Addict
Supporting Member
Joined
Jan 1, 2020
Messages
1,062
Location
RI
I swapped a running & driving 03 5-speed donor into another jeep. Everything except the tub, transfer case, frame, and axles are from the 03. Dash, ignition, fuel, PCM, wiring harness, etc. is all from an 03.

At crank, it started, ran rough for about 5 seconds then died. Following, a crank but no start. Fuel pressure at the rail is 45 psi. I have 5 volts at the crankshaft position sensor and 5 volts coming out whenever it's cranking. I have ZERO volts at injectors whenever cranking. Injector relay in PDC is good.

The 03 was, and still is a SKIM vehicle. Spraying starter fluid in intake turns it over briefly.

Any help? Thank you.
 
Last edited:
  • Like
Reactions: Wranglerfix
I swapped a running & driving 03 5-speed donor into another jeep. Everything except the tub, transfer case, frame, and axles are from the 03. Dash, ignition, fuel, PCM, wiring harness, etc. is all from an 03.

At first crank, it started, ran rough for about 5 seconds then died. Following, a crank but no start. Fuel pressure at the rail is 45 psi. I have 5 volts at the crankshaft position sensor and 5 volts coming out whenever it's cranking. I have ZERO volts at injectors whenever cranking. Injector relay in PDC is good.

The 03 was, and still is a SKIM vehicle. Spraying starter fluid in intake turns it over briefly.

Any help? Thank you.

Did the Jeep crank and run for a few seconds twice before the crank no start? It sounds like the skim could be active. Does the vin in the skim module match the vin in the ecm?
 
  • Like
Reactions: macleanflood
Yes it does. The SKIS indicator flashes on start up for bulb test then goes off after a few seconds. It's my understanding that if flashing or remaining on, it's an indication of SKIM fault, right?
 
  • Like
Reactions: Wranglerfix
Did a gauge cluster test. "Bus B1", "Bus B8" and "Panel Open"..
b1 is SKIM - SKIM Message, b8 is ACM - Airbag Message, Panel Open is Panel Sense - Open Circuit (related to the panel lamps dimmer circuitry of the left multi-function switch on the panel lamps dimmer signal circuit)
 
Yes it does. The SKIS indicator flashes on start up for bulb test then goes off after a few seconds. It's my understanding that if flashing or remaining on, it's an indication of SKIM fault, right?

The bulb can stay on even if no skim is present. The only way to kill that bulb is by unsoldering it. I do not believe your pcm is bad. You can send the pcm into us and we can test it for you if you would like.
 
Did a little bit of troubleshooting. Zero power to injector fuse and O2 fuse in PDC. I now understand this is powered thru the ASD relay. ASD relay fuse is good and constant power is present at the relay. Ignition power is present at opposite end of coil terminal for ASD relay, when ignition is in run position. I traced PCM ground to PCM terminal #3 at the plug #1 (closest to fender) and there was continuity. My next step is to test PCM ground while cranking engine which, correct me if I'm wrong, would result in..

1. Issue with ignition (SKIM?).
2. Issue with wiring from ignition to PCM. (rule out via continuity test)
3. Issue with crankshaft or camshaft position sensor. (rule out via replacement)
4. Issue with crankshaft or camshaft position sensor wiring. (rule out via continuity test)
5. Issue with PCM.

If there's anything else to look for, input would be greatly appreciated.
 
A short on any of the sensors that share the same 5V/ground can give you trouble like this.
 
A short on any of the sensors that share the same 5V/ground can give you trouble like this.

True. I wonder how many sensors share the 5v circuit & ground as the cam/crank sensor? Looks like more FSM book time..
 
True. I wonder how many sensors share the 5v circuit & ground as the cam/crank sensor? Looks like more FSM book time..

off the top of my head: crank, cam, tps, oil pressure, MAP, speedo sender, clockspring. Possibly others. They all share the same 5V reference signal from the PCM, and all share the same ground at the PCM.
 
  • Like
Reactions: Rickyd
3/30 UPDATE:

ASD relay is working. PCM closes ground, ignition provides 12V and closes the relay to power injectors and O2 sensors, when cranking. Still no start. Crank & camshaft wiring from PCM to sensors checks out good. Back-probed signal relay from Crank sensor and was getting 1-2 volts. I suspected this was the culprit as the camshaft sensor was reading 3-5. I replaced both, nonetheless. Still, crank no start.

I traced each injector ground back to the PCM, back-probed the pins and the PCM and teste to positive source. The PCM is not closing the ground circuits to the injectors.

I feel its a PCM or SKIM issue..
 
  • Like
Reactions: macleanflood
probing the signal on a normal meter is hard because it’s an oscillating signal. The best way to check that is on an oscilloscope or one of them Mack daddy scanners.