subparEngineer

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Minneapolis
Hey all,

First post. Have lurked quite a bit, thanks for all your insight over the years.

I have an 05 TJ Rubicon. A while back, I noticed I was low on gas, hesitated to start later in the day but figured it wasn't due to low gas (gauge read 1/8 tank, and I know there's a reserve). Got it started, filled up, washed him off. Noticed a CEL, so stopped by autozone on the way home. P0508, IAC system circuit low. Now the jeep will crank, but won't start, even with added throttle.

Relevant history (maybe): Had a PCM issue a while back (~4 years, low mileage). The shop I took it to fucked it up a few times. Finally found a new PCM, but they programmed it for an automatic FWD. They corrected this after taking it to a different shop to check their work. Has run fairly well since then, besides maybe some idle issues but never any stalls or difficulty starting. Also recently soldered on a new wire to the front locker actuator if that matters, it broke while out on a solid adventure. No other electrical work has been done, just mechanical stuff.

Steps taken so far: cleaned the throttle body well, as well as the IAC valve (the 05-06 valve is different, so did the best I could). Got it to start once with some throttle encouragement. Ran it hot on freeway speeds to try to free anything up. No stalls or trouble running then. After it was parked, tried to turn it on again with no luck. Has not started since then. Replaced the IAC valve with a new part (Mopar 4861552AC Fuel Injection... https://www.amazon.com/dp/B0049EJPKO?tag=wranglerorg-20), had to use a different bolt on one corner as the old bolt snapped, but that shouldn't cause an issue. Disconnected battery for ~30 minutes to clear codes/temp memory, no luck. Inspected what I could at a glance in my apartment garage (Intake hose, PCM connector that appears to lead to IAC, etc.), nothing abnormal I could see.

Not sure of next steps to take, any advice would be fantastic. Coincidentally, it didnt start the day I was headed to get new tires. Not sure if it could be a fuel pump/relay issue, PCM, or something else. I apologize if this is a double post, I've read a lot of somewhat similar posts, but would appreciate the expert take on this issue.

Happy to finally join!
-Spencer
 
Hey all,

First post. Have lurked quite a bit, thanks for all your insight over the years.

I have an 05 TJ Rubicon. A while back, I noticed I was low on gas, hesitated to start later in the day but figured it wasn't due to low gas (gauge read 1/8 tank, and I know there's a reserve). Got it started, filled up, washed him off. Noticed a CEL, so stopped by autozone on the way home. P0508, IAC system circuit low. Now the jeep will crank, but won't start, even with added throttle.

Relevant history (maybe): Had a PCM issue a while back (~4 years, low mileage). The shop I took it to fucked it up a few times. Finally found a new PCM, but they programmed it for an automatic FWD. They corrected this after taking it to a different shop to check their work. Has run fairly well since then, besides maybe some idle issues but never any stalls or difficulty starting. Also recently soldered on a new wire to the front locker actuator if that matters, it broke while out on a solid adventure. No other electrical work has been done, just mechanical stuff.

Steps taken so far: cleaned the throttle body well, as well as the IAC valve (the 05-06 valve is different, so did the best I could). Got it to start once with some throttle encouragement. Ran it hot on freeway speeds to try to free anything up. No stalls or trouble running then. After it was parked, tried to turn it on again with no luck. Has not started since then. Replaced the IAC valve with a new part (Mopar 4861552AC Fuel Injection... https://www.amazon.com/dp/B0049EJPKO?tag=wranglerorg-20), had to use a different bolt on one corner as the old bolt snapped, but that shouldn't cause an issue. Disconnected battery for ~30 minutes to clear codes/temp memory, no luck. Inspected what I could at a glance in my apartment garage (Intake hose, PCM connector that appears to lead to IAC, etc.), nothing abnormal I could see.

Not sure of next steps to take, any advice would be fantastic. Coincidentally, it didnt start the day I was headed to get new tires. Not sure if it could be a fuel pump/relay issue, PCM, or something else. I apologize if this is a double post, I've read a lot of somewhat similar posts, but would appreciate the expert take on this issue.

Happy to finally join!
-Spencer

Can you ring out the PCM cable to each pin on the IAC valve connector with an ohmmeter? I had a 2.4, but IIRC the 4.0 had issues with the harness near the firewall around the rear of the valve cover.
 
Check all the fuses.

Be sure the horn works, then swap the horn relay with ASD relay try to start, then fuel pump relay try to start. Can you hear the fuel pump run for a couple of seconds when you turn the key on?

05, 06 PCMs are known for failing. If they didn't put in a Wranglerfix PCM, there could be issues there. Wranglerfix rehosted it to a more reliable PCM.

The 05, 06 will start with the crank sensor or the cam sensor bad. If one is bad it uses the other. But it will be a long crank to start.

Turn the key ON, OFF, ON, OFF, ON quickly. Any codes will display in the odo, then "done." This will verify the PCM is alive as well.
 
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Check all the fuses.

Be sure the horn works, then swap the horn relay with ASD relay try to start, then fuel pump relay try to start. Can you hear the fuel pump run for a couple of seconds when you turn the key on?

05, 06 PCMs are known for failing. If they didn't put in a Wranglerfix PCM, there could be issues there. Wranglerfix rehosted it to a more reliable PCM.

The 05, 06 will start with the crank sensor or the cam sensor bad. If one is bad it uses the other. But it will be a long crank to start.

Turn the key ON, OFF, ON, OFF, ON quickly. Any codes will display in the odo, then "done." This will verify the PCM is alive as well.

You're a wizard as far as I'm concerned. Swapping the horn relay with ASD worked like a charm. Don't have an OBDII and autozone wouldn't take me 5 minutes before close to read any codes on it now. So is this just a bad ASD relay? Just find the OEM and replace?

Thank you for your help! This community is great.
 
Yup replace the...well, replace the horn relay. Better yet buy two.

I strip all the fuses and relays out of TJs I find in junkyards.

-Mac
 
You're a wizard as far as I'm concerned. Swapping the horn relay with ASD worked like a charm. Don't have an OBDII and autozone wouldn't take me 5 minutes before close to read any codes on it now. So is this just a bad ASD relay? Just find the OEM and replace?

Thank you for your help! This community is great.

Reread the last paragraph to read codes in the odo using the "key trick."
 
Disconnect the battery to clear the code.

How long does you usually disconnect? After I replaced the IAC valve, I disconnected for about 30 minutes. I thought that would be long enough. Though, that was before I swapped the relay fuses and got it started.
 
That should have done it.

Look into getting a bluetooth code reader to use with your phone.

Will do. Thank you for your help. What could cause that relay/fuse to go bad? Is this something I need to look into further, or is it maybe just because it's 20 years old?