Crank but won't start and fuel pump doesn't stop priming

Filthyoutage · Nov 17, 2023

Went out to start the Tj after work and it made a groaning noise which sounded like the fuel pump trying to go at first, not sure? Made another noise then the voltage and fuel gauge dropped out. Disconnected the battery then started it up again.

Fuel pump does not shut off and the jeep cranks but wont start. Has anyone experienced anything similar or have any idea what may be a cause.

Reading similar posts has me thing the pcm maybe dead, but I dont want to jump to that just yet.

CharlesHS · Nov 17, 2023

While the PCM may have died and you can contact Mark ( @Wranglerfix ) to assist you with that; there other problems that should be checked first prior to assuming your PCM is dead.
Disconnect the 32 pin harness connects from the PCM and inspect the harness connector clips and the PCM pins for oxidation (clean with anti oxidant) and reseat the harness connectors.
Follow the PCM communication harness along the firewall toward the drivers side behind the valve cover and around the right threaded head stud. Inspect the area of the split wire loom and wiring inside for signs of worn split wire loom and wiring insulation. This is a known problem where the threads from the stud can wear thru the split wire loom and wiring insulation causing the PCM communications to short to ground.

Filthyoutage · Nov 18, 2023

CharlesHS said:
While the PCM may have died and you can contact Mark ( @Wranglerfix ) to assist you with that; there other problems that should be checked first prior to assuming your PCM is dead.
Disconnect the 32 pin harness connects from the PCM and inspect the harness connector clips and the PCM pins for oxidation (clean with anti oxidant) and reseat the harness connectors.
Follow the PCM communication harness along the firewall toward the drivers side behind the valve cover and around the right threaded head stud. Inspect the area of the split wire loom and wiring inside for signs of worn split wire loom and wiring insulation. This is a known problem where the threads from the stud can wear thru the split wire loom and wiring insulation causing the PCM communications to short to ground.

Disconnected the pcm and everything looks to be in really good condition. Traced the wiring harness and there is nothing that looks damaged. Only wire that looks buggered a bit is the up stream o2 sensor wiring that the po has chopped and hard wired to the o2 sensor. The connection might have melted so they just soldered it. Before this problem started the engine was sputtering at idle. Probably should have mentioned that. Cleaned the iac and changed spark plugs prior to this and still no change.

Wranglerfix · Nov 18, 2023

@Filthyoutage G’day mate! What year is your jeep and were you having any issues prior to the no start?

Thanks,

Mark

P.S.

I would love to be on Biondi Beach at this moment or diving in Cairns!

Filthyoutage · Nov 18, 2023

Wranglerfix said:
@Filthyoutage G’day mate! What year is your jeep and were you having any issues prior to the no start?

Thanks,

Mark

P.S.

I would love to be on Biondi Beach at this moment or diving in Cairns!

G’day man,

Its a 97 and prior to the no start i was having a rough idling issue and the revs were occasionally jumping up and down. Didn't matter whether it was a cold start or up to temp. Cairns would be nice coming into summer now mate

Wranglerfix · Nov 18, 2023

I was there in March of 2008 and loved it!

unfortunately, your pcm has failed you. There are capacitors inside that leak over time and kill the board. Attached are a few photos that capture the carnage! I can get you a pcm on its way to you on Monday if you would like. Please send me an email to mark@wranglerfix.com with your vin, part number and shipping details and I will get you taken care of!

“She just smiled and gave me a Vegemite sandwich.” -Men at Work

Filthyoutage · Nov 18, 2023

Wranglerfix said:
I was there in March of 2008 and loved it!

unfortunately, your pcm has failed you. There are capacitors inside that leak over time and kill the board. Attached are a few photos that capture the carnage! I can get you a pcm on its way to you on Monday if you would like. Please send me an email to mark@wranglerfix.com with your vin, part number and shipping details and I will get you taken care of!

“She just smiled and gave me a Vegemite sandwich.” -Men at Work

View attachment 474995

View attachment 474996

View attachment 474998

View attachment 474999

fairdinkum mate, i was hoping it was going to be something so simple i would've felt stupid about it. Is there a way i can open the pcm without further destroying it to confirm it is toast? If it is i’ll definitely get a replacement from ya.
Cheers

Weasellee · Dec 16, 2023

Update? Having similar issues. Rough idle occasionally then today a no start but good crank. Fuel pump is priming. Went to get truck and trailer, came back, fired right up with a rough idle again. I’m thinking fuel pump is going but is there a way to confirm?

macleanflood · Dec 16, 2023

Weasellee said:
Update? Having similar issues. Rough idle occasionally then today a no start but good crank. Fuel pump is priming. Went to get truck and trailer, came back, fired right up with a rough idle again. I’m thinking fuel pump is going but is there a way to confirm?

Have you tested you fuel pressure? Should be around 43 psi.

-Mac

Weasellee · Dec 16, 2023

macleanflood said:
Have you tested you fuel pressure? Should be around 43 psi.

-Mac

I plan to in the morning. The rough idle them no start now a perfect idle pushes me towards the fuel pump. I’m really curious if there was ever an answer if one can open a pcm and “see” the condition.

macleanflood · Dec 16, 2023

I think they're glued shut and you need to bake them at a perfect temperature to get them to release...I would imagine it's like sealed headlights.

No first hand experience and I'll leave the baking to @Wranglerfix

-Mac

Wranglerfix · Dec 17, 2023

Weasellee said:
I plan to in the morning. The rough idle them no start now a perfect idle pushes me towards the fuel pump. I’m really curious if there was ever an answer if one can open a pcm and “see” the condition.

There is nothing to see inside unless you have the equipment and knowledge to test and repair. Curiosity killed a cat and many computers because a millimeter too far will kill the board.

Weasellee · Dec 17, 2023

Wranglerfix said:
There is nothing to see inside unless you have the equipment and knowledge to test and repair. Curiosity killed a cat and many computers because a millimeter too far will kill the board.

Well, I’ll hope it’s the fuel pump and not the PCM. Thank you sir.

Wranglerfix · Dec 17, 2023

Weasellee said:
Well, I’ll hope it’s the fuel pump and not the PCM. Thank you sir.

You can send your pcm into us and we will run it in our jeep as a courtesy for you.

Filthyoutage · Apr 16, 2024

Weasellee said:
Update? Having similar issues. Rough idle occasionally then today a no start but good crank. Fuel pump is priming. Went to get truck and trailer, came back, fired right up with a rough idle again. I’m thinking fuel pump is going but is there a way to confirm?

Update. Don’t want to leave this thread without finishing it off. After looking over wiring and having a mechanic run a scan and a few tests. I sent my pcm off to wrangler fix and it was toast.

Mark sent me out another one, I installed it back in the jeep and it fired up straight away. Slightly rough at the start which is expected after sitting for a while. I still have to piece a few things back together before i can drive it, but so far it seems to have solved my rough idling and definitely the no start issue.

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Crank but won't start and fuel pump doesn't stop priming

Filthyoutage

Member

CharlesHS

TJ Guru

Filthyoutage

Member

Wranglerfix

TJ Addict

Filthyoutage

Member

Wranglerfix

TJ Addict

Filthyoutage

Member

Weasellee

Jeep idiot

macleanflood

I break sh!t

Weasellee

Jeep idiot

macleanflood

I break sh!t

Wranglerfix

TJ Addict

Weasellee

Jeep idiot

Wranglerfix

TJ Addict

Filthyoutage

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