LJ died: fuel pump or something else?

[Nobody]

So I have had the LJ for 4 or 5 months now, always been a champ but I always had this aching feeling that the fuel pump was on its way out. Under heavy throttle it just seems to bog almost like the fuel pressure is dropping.

Last night I had some erands to run and I wanted to take the Jeep, go to jump in, turns over, starts, stalls. rinse lather repeat. pop the hood, check the fuses, 20a fuse for the fuel pump is not blown but looks like moisture got in, rusty, bubbly, etc. dont have a spare so I jump in my other car, run my errands, grab a new fuse, get home, pop it in, starts right up.

FF to today, went to go to the store this AM, jump in the jeep, made it 2 mi from the house, going up a slight hill, and it burbles, jerks, and then stalls, almost like it ran out of fuel. Gauge says 1/2 tank, but my cluster has the 000000 odo issue so I wouldn't be surprised if the fuel gauge had gone out. This is a secondary / snow time vehicle for me so I really havent driven it much this summer so I couldn't tell you if it had a half tank reading last week or last month. Try turning it over, fires briefly, then dies, just like last night. Check the fuse, its still good. Maybe its out of gas. call a local wrecker co, brings me some very expensive fuel, turns over, fires, runs for 3 seconds, dies. So i have them tow it back to my house.

Get home, plug in my scanner tool which I have used on this Jeep before; "could not read ecu". cycle the ignition, try again, reads ecu, 1 code found, go to pull code, no codes found, go back to main menu to try again, "could not read ecu". ????

So heres what I noticed after playing for a few minutes. When I turn the ignition on, if the fuel gauge goes to 1/2 tank, it reads the ecu, and engine will fire, albeit briefly. but, if you let it sit for a minute or so, or, cycle the ignition off / on too quick, the fuel gauge will read 0, the engine will turn over but not fire, and my OBD scanner will say could not read ecu.

It looks like the fuel pump unit is a pump and sender unit in one so if the pump is bad / shorting, then it would make sense that it would start when it reads a level but not start when it doesnt read a level, but.... why would that link to the obd reader? Am I looking down a potential ECU replacement? or am I overthinking this?

05 Unlimited 6mt 4.0 101k mi, did a full exhaust headers > tailpipe, fresh plugs back in April.

 

[rasband]

Sounds like the PCM is likely to me, but the fuel pump could be a factor too.

 

[CharlesHS]

Check the three 32 pin harness connectors and ECU pins for oxidation and IF the connectors are loose; snap the harness connectors into the ECU receptacles.
Inspect the split wire loom harness from the ECU to the vehicle sensors that is routed around the threaded head stud on the drivers rear corner of the head. The threaded head stud is known to rub thru the split wire loom and wiring insulation which will short ECU voltage and sensor communications to ground.
The engine and instruments will briefly start or read and stop as the wiring shorts.

 

[Nobody]

Check the three 32 pin harness connectors and ECU pins for oxidation and IF the connectors are loose; snap the harness connectors into the ECU receptacles.
Inspect the split wire loom harness from the ECU to the vehicle sensors that is routed around the threaded head stud on the drivers rear corner of the head. The threaded head stud is known to rub thru the split wire loom and wiring insulation which will short ECU voltage and sensor communications to ground.
The engine and instruments will briefly start or read and stop as the wiring shorts.

I checked the connectors at the ecu earlier and they all looked fine, that was one of my initial thoughts as well. I will check this section of the harness that you mentioned though as I did do a valve cover gasket not too long ago, hopefully I reseated that harness appropriately.

 

[AndyG]

You need @Wranglerfix, he is a PCM whiz- the @ sign notifies him- stalling when driving is indicative of a pcm failure- you can not lose dealing with him. Trust me.

 

[Wranglerfix]

@Nobody The main faults of an 05-06 manual pcm are stalling while driving and all O2 sensors showing bad when good. The pcm also controls the cluster and fuel guage.

Do you know if your Jeep has had the TSB for the o2 sensors performed on it? Double check that ad that could be one of your issues.

You can get the Jeep hot and tap on the pcm with a screwdriver handle and it will die if it is too far gone. The other way of knowing 100% is by sending it into me and I will run it in my Jeep.

You can call me at 866–888-7710 to discuss in further detail.

Thanks,

Mark Cantrell

 

[Nobody]

@Nobody The main faults of an 05-06 manual pcm are stalling while driving and all O2 sensors showing bad when good. The pcm also controls the cluster and fuel guage.

Do you know if your Jeep has had the TSB for the o2 sensors performed on it? Double check that ad that could be one of your issues.

You can get the Jeep hot and tap on the pcm with a screwdriver handle and it will die if it is too far gone. The other way of knowing 100% is by sending it into me and I will run it in my Jeep.

You can call me at 866–888-7710 to discuss in further detail.

Thanks,

Mark Cantrell

I dont know if it has had the TSB done, but I havent had any faults / CELs since I bought her. I did replace all 4 o2s when I did the exhaust back in April.

I am going to guess it is the PCM as one thing I did note after getting the jeep home today is that the PCM was very very hot; like cant touch it for more than 5 seconds hot, usually a sign of bad electronics, but it was also an extremely hot day here today and it had been sitting in the sun waiting for the tow and repeatedly attempting starts so.... Based on your info, likely culprit.
Ill call around to some CDR stores see if any can / will pull data off my VIN for the TSB, that said, do you referb PCMs?

 

[pagrey]

looks like moisture got in, rusty, bubbly, etc.

On just that one fuse, have you explored further because overall that's not good? It's extremely unlikely that just one fuse was corroded and messed up.

 

[Nobody]

On just that one fuse, have you explored further because overall that's not good? It's extremely unlikely that just one fuse was corroded and messed up.

All of the other fuses were ... different. IDK if the PO replaced that one at some point with a dime store fuse or what. Every fuse in that Jeep is the solid color fuses, this one was a translucent. Its a lifetime New England truck so lots of moisture, salt, and sand. If the fuse was as cheap as it looks it wouldnt be surprising for moisture to get in and eat it from the inside out.

 

[pagrey]

All of the other fuses were ... different.

If the corrosion was internal to the fuse that's good. I misread that as corrosion on the contacts in the fuse block and not in the fuse itself.

 

[Nobody]

If the corrosion was internal to the fuse that's good. I misread that as corrosion on the contacts in the fuse block and not in the fuse itself.

Just the fuse itself, block is quite clean.

 

[USParatrooper]

So I have had the LJ for 4 or 5 months now, always been a champ but I always had this aching feeling that the fuel pump was on its way out. Under heavy throttle it just seems to bog almost like the fuel pressure is dropping.

Last night I had some erands to run and I wanted to take the Jeep, go to jump in, turns over, starts, stalls. rinse lather repeat. pop the hood, check the fuses, 20a fuse for the fuel pump is not blown but looks like moisture got in, rusty, bubbly, etc. dont have a spare so I jump in my other car, run my errands, grab a new fuse, get home, pop it in, starts right up.

FF to today, went to go to the store this AM, jump in the jeep, made it 2 mi from the house, going up a slight hill, and it burbles, jerks, and then stalls, almost like it ran out of fuel. Gauge says 1/2 tank, but my cluster has the 000000 odo issue so I wouldn't be surprised if the fuel gauge had gone out. This is a secondary / snow time vehicle for me so I really havent driven it much this summer so I couldn't tell you if it had a half tank reading last week or last month. Try turning it over, fires briefly, then dies, just like last night. Check the fuse, its still good. Maybe its out of gas. call a local wrecker co, brings me some very expensive fuel, turns over, fires, runs for 3 seconds, dies. So i have them tow it back to my house.

Get home, plug in my scanner tool which I have used on this Jeep before; "could not read ecu". cycle the ignition, try again, reads ecu, 1 code found, go to pull code, no codes found, go back to main menu to try again, "could not read ecu". ????

So heres what I noticed after playing for a few minutes. When I turn the ignition on, if the fuel gauge goes to 1/2 tank, it reads the ecu, and engine will fire, albeit briefly. but, if you let it sit for a minute or so, or, cycle the ignition off / on too quick, the fuel gauge will read 0, the engine will turn over but not fire, and my OBD scanner will say could not read ecu.

It looks like the fuel pump unit is a pump and sender unit in one so if the pump is bad / shorting, then it would make sense that it would start when it reads a level but not start when it doesnt read a level, but.... why would that link to the obd reader? Am I looking down a potential ECU replacement? or am I overthinking this?

05 Unlimited 6mt 4.0 101k mi, did a full exhaust headers > tailpipe, fresh plugs back in April.

I have had my current 05 LJ for about two months and just the second week I had it, it died on me going down the hwy. No warning! It would turn over like it was going to start but never did. All electrical was working fine. Just to double check, I put jumper cables on it and no deal. I checked all the fuses and all were good. Had it towed to my mechanic and it was confirmed what I thought, the fuel pump died and it only has less than 120k miles, and $600 later, all is well in Jeepin land and Ol' Sarge is doing well. Good luck!!!

 

[txbemis69]

you should be able to hear the fuel pump by removing the gas cap and putting your ear to the filler neck while someone turns the key to the on position.