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Unread 12-12-2011, 05:26 PM   #1
ak_Z28
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Location: La Grande, OR
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My Jeep sputters and stalls like its running out of gas NEED ADVICE

1991 Jeep Wrangler
2.5L 5 spd

Heres what I've done to try and remedy the problem.

New fuel pressure regulator
New Fuel filter
New Cap rotor wires and plugs
Hollowed out the catalytic converter when I installed a new muffler (did this pre-existing the cat coming out)

What it does is usually after its about half way to normal operating temp on my way to work it stalls. I work the gas pedal and get some response and 2 seconds later it stalls again. All of my gauges remain constant and dont fluctuate. It only does this for a 2-3 min period then stops and runs normally. Sometimes longer periods of time, and sometimes it will go a week without doing it at all. It has done this since April of 2011 and I have replaced things that were kind of obvious that would cause a total power loss, but was never thinking it was the pump because its gone 7-8 months and has never done it consistently. The last couple of days I've seen a new problem. The fuel gauge either has no response or pegs completely out over full and stays there with only half a tank. Or it will randomly work, just takes 5 min to get up the right level. It always does it under load at any rpm above 1500 and at idle at around 2600-3000 but only when it acts up, other times its totally fine, no hesitation or stalling.

I was thinking of replacing the sending unit and pump but dropping $200 and still having the same problem would suck. I've heard the pumps can lose voltage through the original harness and cause these problems, and I've found the positive return from the pump (black and orange) it has two old splices in it but wires goin nowhere that have been cut. Ground to the pump is good (under the e-brake pedal). I just am at a total loss, Ive never had a pump do this, they usually just die all at once. If it is wireing related I'd like to know if anyone has ever had a fix to this to get the pump continual power.

Also I've come accross a thread where a guy has a ignition module failure, which I do get the occasional pop in the intake when it comes back to life, but I'm not leaning towards ignition, its just too random, but the 120-160 temp range has something to do with it.

Thanks for any intel, i usually run non-ethanol premium if that matters to any super jeep mechanics that might be able to help here.

Only codes are 21 (battery) and 51 (dont know)

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Unread 12-12-2011, 05:49 PM   #2
moonshinefuel
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The fuel gauge pegging and dropping like that seems to point to a connectivity problem, possibly a bad ground.
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Unread 12-12-2011, 05:53 PM   #3
oldtime_ironman
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1991 YJ Wrangler 
 
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Location: 14304 Niagara Falls, NY
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None of the above. I think very much that it's your O2 sensor, first of all (code 21). Because the ECU (computer) does not read the O2 sensor until the engine is up to a certain temp. And like you said it always happens at the same temp. So I would at least test the O2 sensor first - you should see about 1/2 volt between the sense wire and gnd.

So I would test and or replace that O2 sensor first - its probably whats causing a lot of the driveability probs.

There isn't any ign module in a 1991 - its all one computer.

As far as the gauges go, its a common problem. Basically dirty contacts behind the dash - I had this for the longest time. But, there's a quick and easy fix. Here's a write-up how to fix it, with pics:
http://www.jeepforum.com/forum/f12/r...ter-how-991307

Far as the fuel pump goes, I doubt it. You can measure the pressure at the injector rail, it should be about 31 PSI idling. Long as you have that, its good. It wouldn't hurt to put a bottle of Heet dry-gas or similar at this time of year tho. Hope that helps!
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Last edited by oldtime_ironman; 12-12-2011 at 05:55 PM.. Reason: details
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Unread 12-12-2011, 06:22 PM   #4
bigsquat
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i know you think its temp related but can you check the ground wire that attaches to the fuel pump plate. when i put mine in the spade lug that was there was loose. its not easy to get to tho. i made an access door for the future.you can see in pic one how rusty it can get there.
fuel-pump-001.jpg   fuel-pump-010.jpg   fuel-pump-011.jpg  
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Unread 12-13-2011, 04:58 PM   #5
ak_Z28
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Thanks for all the quick replies guys. I havent messed with the o2 sensor yet, but its a cheap easy to replace part so I'll try that out this weekend and post results (i'm sure its stock).

As for the rusted ground on top of the tank, very possible, I can't see up in there, just where the harness and breather tubes go, what does that ground run though? Is it a primary for the pump? I have one that is right above my e-brake lever under the dash that if unhooked the pump wont run at all. I think I also have the 15 gallon with the lock ring, not the 20 gallon tank with the bolt on ring, not 100% sure though. Let me know on that, and I'll run some gas out of the jeep and drop the tank this weekend too and check that out.

Oh and I have checked fuel pressure at idle and it is 31psi and 39 with the regulator vacuum line unhooked. So definitely no pressure problems at idle, just when it starts acting up.
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Unread 12-13-2011, 05:08 PM   #6
oldtime_ironman
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Quote:
Originally Posted by ak_Z28 View Post
Thanks for all the quick replies guys. I havent messed with the o2 sensor yet, but its a cheap easy to replace part so I'll try that out this weekend and post results (i'm sure its stock).

As for the rusted ground on top of the tank, very possible, I can't see up in there, just where the harness and breather tubes go, what does that ground run though? Is it a primary for the pump? I have one that is right above my e-brake lever under the dash that if unhooked the pump wont run at all. I think I also have the 15 gallon with the lock ring, not the 20 gallon tank with the bolt on ring, not 100% sure though. Let me know on that, and I'll run some gas out of the jeep and drop the tank this weekend too and check that out.

Oh and I have checked fuel pressure at idle and it is 31psi and 39 with the regulator vacuum line unhooked. So definitely no pressure problems at idle, just when it starts acting up.
Yeah that ground wire is in fact the primary for the pump and also the sender. Lots of guys just splice into that one and run an extra ground up to the tail light or something. Its the one that comes out by your brake pedal like you said. The gauges also have their own grounds as shown in the link I posted - the circuit board for the gauges eventually all runs into one ground wire on the engine block or by the brake pedal.

I'm betting on the O2 sensor for now.
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Unread 12-13-2011, 07:07 PM   #7
bigsquat
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it can be a pain figuring these things out. i did a bone head move on mine, i was driving down the road and it started stalling and acting like it was running out of gas. eventually it died and had to be towed home. my gas gauge said a little over a 1/4 tank. i put a new fuel pump in and found the tank was really empty. somehow the gauge was off. i do have a pretty good dent in the skid which is pushing up on the tank. maybe it through it off. at least now i have an easy access to get to it. good luck.
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Unread 12-16-2011, 07:25 PM   #8
ak_Z28
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Update

I havent had a chance to go down and pickup an O2 yet, was probably going to order one online here shortly. Anyway driving jeep around wed, thurs, fri no surges at all, about 20-25 miles. The gas gauge with some starts pegs completely over full, and other times reads normally. Its a crap shoot, but I'll check out the ground above the tank this weekend.

Just updating on how frustrating an inconsistent problem can be. Wish me luck on the O2 sensor.
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Unread 12-16-2011, 08:51 PM   #9
oldtime_ironman
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Quote:
Originally Posted by ak_Z28 View Post
I havent had a chance to go down and pickup an O2 yet, was probably going to order one online here shortly. Anyway driving jeep around wed, thurs, fri no surges at all, about 20-25 miles. The gas gauge with some starts pegs completely over full, and other times reads normally. Its a crap shoot, but I'll check out the ground above the tank this weekend.

Just updating on how frustrating an inconsistent problem can be. Wish me luck on the O2 sensor.
Did you try this for the gauges? I would do it before getting into the tank.
http://www.jeepforum.com/forum/f12/r...ter-how-991307

Reason why is that if the tank ground was bad, the fuel pump would cut out. But it starts and runs, so its gotta be the gauge ground.
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Unread 12-16-2011, 08:53 PM   #10
bigsquat
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1992 YJ Wrangler 
 
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if you dont want to drop the tank or put a big access hole ove the tank like i did. you could use a 2" hole saw with and put in a small hole to check it out. then use a knock out seal to cover it back up. the tank is pretty close without a body lift so you would have to be carefull. i hate dropping the tank. of coarse you would have to know exatly where to drill
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Unread 12-09-2014, 08:38 AM   #11
Sunshine1
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My jeep bogs down and occasional back fire when driving down the road

I have a 1993 Jeep wrangler 4.0L 6cyl , Automatic
I have put new plugs , plug wires, distributor cap and rotor, also new coil pack , new fuel filter (inline). I have plenty of fuel in my jeep i will be driving down the road fine and occasionally it will act like it is running out of gas. When i push the accelerator it will bog down even more and occasionally back fire. I can also hear the fuel pump making a constant whining noise, i was just going to go ahead and drop the tank to change the fuel pump , then with it back firing , I'm thinking i may need to change the 02 censor also. Can a computer be hooked up to a 93 ?
I appreciate any and all help,
Sunshine1
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Unread 12-09-2014, 09:01 AM   #12
fishadventure
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Backfire speaks several things but has to do with Unburned fuel igniting in the exhaust system. An intermittent ignition failure can cause it. Among other things. Random unpredictable issues are most often electronic or electrically caused but there are other possibilities.

Yes a 93 computer can be read. Start there.
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Unread 02-25-2015, 10:45 PM   #13
Shiny
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ak_Z28, did you get it figured out? My Yj is kinda doing the same thing...
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Unread 02-25-2015, 11:20 PM   #14
mike134
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Hi Shiny, welcome to the forum, I would suggest creating a new thread describing your problems. Most forums want you to continue old threads, but I think new very descriptive threads created on the /f12 forum really generate the best responses.

The problem is that you may or may not have done all of the debugging procedures described at the beginning of this forum thread. We want to start you at the beginning! In your post, please mention whther or not your YJ is your daily driver and what you have tried so far to get your jeep working.
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