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Discussion Starter · #1 ·
guys i am banging my head against the wall trying to help a fellow jeeper out.



His 1998 TJ was driving, then died and now it will not start.



Let me review what i have checked and see what maybe i have missed or someone can suggest, but i have ruled a lot out already.

at first thought oh maybe CPS - replaced it no change (one on jeep was 2 months old

then changed Coil Pack - No Change

Tested Ignition Coil wires -
a) only .1v registers on orange/green

1) Key to on position
a) ASD kicks on and fuel pump does
b) No +12v to Orange/Green wire for 2s (more like .1v)

2) ASD
a) tried swapping ASD relay with horn relay - no change
b) tried jumping pins 87-30 of ASD - no change still no power to ignition wire

3) Fuse 6 and Fuse 11 are both good

4) checked all ECU connections

5) Tried to jump +12v to Orange/Green - got an arc

6) Tested Orange/Green for continuity to ground = 0 (no resistance path)

7) tested +probe to battery and - probe to Orange/Green = got 12v as if this power wire is grounding out?

8) checked for + voltage at injectors (during 2s key on and cranking) only get like .1v

9) visually inspected harness but cannot see any issues

10) tried unhooking ECU and wiggling harness while multi meter was on the orange/green, never could break what appears to be a ground


I don't think its the ignition switch pin because if that was the case, fuel pump should never kick on.


i am starting to think that there is an issue with the harness grounding out the power somewhere???


Or this is a bad PCM. i found this guys post and he describes a lot of the same issues, and his fix was a new PCM


if anyone has any thoughts please let me know, i took today off to help him but i can not seem to find what the root cause of this is???
 

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I need to find the thread I started last year, but basicly, if I remember MY problem (yours can and probably is different) add relay was not getting power, a fuse in engine compartment was also not getting power, a fuse in cabin was blowed. In the beginning the tpc wire had melted/shorted and engine died, no warning. I had no communication between my scanner and the computer.

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If the orange/dark green wire is shorted as it seems from everything you tested, fuse 21 is probably blown but you will have to find the short. Besides the coil & injectors that fuse also powers the O2 sensor heaters. That is the most likely place for a short. Check the harness there for damage like melting from getting into the exhaust pipe.
 

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Checking the fuse for continuity is good but do the fuses get power ?

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Discussion Starter · #8 ·
thanks everyone i ended up figuring out the problem!

The F21 fuse was blowing, killing the ignition circuit.

after some more troubleshooting and isolating, i ended up figuring out the pre-heat in the O2 sensor for the back CAT ( near the trans) was bad, thus causing a short and blowing the F21 fuse and killing the ignition circuit.

unplugged that sensor, and fired right up. replaced sensor cleared codes and all is well now.
 

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thanks everyone i ended up figuring out the problem!

The F21 fuse was blowing, killing the ignition circuit.

after some more troubleshooting and isolating, i ended up figuring out the pre-heat in the O2 sensor for the back CAT ( near the trans) was bad, thus causing a short and blowing the F21 fuse and killing the ignition circuit.

unplugged that sensor, and fired right up. replaced sensor cleared codes and all is well now.
Good to hear you got it to run !!!!

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Discussion Starter · #11 ·
it was a tricky one to hunt down

browsing the forums a lot of people ended up replacing the computer and that fixed it.

others found wires rubbed, or wires corroded in the harness etc.

never did i find one that said oh check the O2 sensors as they short and can kill the circuit.


however i believe only the 97-99 this applies because they changed the ignition in 2000 and then again in 2003.
 

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Yeah. That fuse in the Starting Circuit behind the glove box is usually missed.
Who ever said Jeep Wiring was great!
 

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it was a tricky one to hunt down

browsing the forums a lot of people ended up replacing the computer and that fixed it.

others found wires rubbed, or wires corroded in the harness etc.

never did i find one that said oh check the O2 sensors as they short and can kill the circuit.


however i believe only the 97-99 this applies because they changed the ignition in 2000 and then again in 2003.
That is a first for me. That is why troubleshooting is important but you never know where it will lead. Posting results is important as we all learn something & help others too.
 

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Discussion Starter · #14 ·
Yeah. That fuse in the Starting Circuit behind the glove box is usually missed.
Who ever said Jeep Wiring was great!

it wasn't the fuse 11 in the glove box that energizes the ASD, it was the F21 fuse in slot 21/22 in the PDC under the hood.

the ASD was working fine, and energizing the fuel pump and ignition circuit.

but the pre-heat on the O2 was fried shorting the ignition circuit blowing F21
 
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