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Unread 12-18-2006, 09:18 PM   #1
xwildman138x
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500 dollar 91 cherokee that wouldnt stay running now we know why it was 500 bucks

My mom and dad want to go wheelin with the pirates so they found a 500 dollar 91 cherokee limited 4.0 that they were interested in. I told my mom "we can fix anything 500 bucks and it runs but just won't stay running buy it we'll fix it". We've tried alot of things all of which needed to be changed anyway. This rig has 230,000 on it and now when it runs sounds great except it only runs for 5 seconds at a time. This is what we changed so far

1. plugs (no electrodes left on some of them I think they were original )
2. wires cap rotor all in horrible condition.
3. fuel pump (because it sounded like a dying animal)
4. fuel filter (so rusted I had a hard time telling it was a filter)

Now at this point it was running for 5 seconds and sounding good before it was running but hurtin. We figured TPS maybe thats the culprit. Bought a new TPS and threw it on. Seemed to run a little better after the TPS for the 5 seconds 10 if you feather the gas a little. At no point will it continue to run after 10 seconds. Now as you can see I'm new to the forum and I've never looked under a Cherokee hood before. My YJ was a whole different set of problems and the computer got chucked in the trash that fixed it. I searched every thread and found similar problems but not this exact problem.

Bought a fuel pressure tester and when the key is on I have 37 lbs when it starts it goes up to 40 then as soon as it starts running it drops in that 5 seconds to 0. Went back to the fuel pump unplugged the pump ran some cat 5 wire around each prong and plugged the plug back in. Ran the meter on the wires key on had 12 volts for 2 seconds while it pumped up, while it was running and I had between 3 to 7 volts while running then to 0, when it shut off 12 v for 2 seconds as it pumped back up. Replaced the fuel regulator no change. Changed the CPS and It wouldn't run on the new one, timing was off and hard start. Put the old one back in and it ran like it did before. Something is holding out the fuel pressure. Pulled off the Throttle body cleaned it and the IAC, both were gobbed up with stuff. Still same problem.

Unplugged the map sensor and it ran a little different. Left the map off and unplugged the IAC, started it and it ran like a top. I have a IAC on order for tomorrow hoping that this solves it. Our buddy skip that owns a parts store in town told us that after talking with a guy who works for a dealership that IAC's sometimes when they get gummed up they short out and can cause problems like this. Anybody ever run into this? Or hear of this happening? I can say one thing I learned alot about XJ's over the course of the last couple weeks and even though black beauty (my mom already named her rig) has been fighting us I would love to add a XJ to my vehicle family

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Unread 12-18-2006, 09:20 PM   #2
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for $500 more, get a rebuilt I6 out of a post 93, which means about 10 more hp.
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Unread 12-18-2006, 09:21 PM   #3
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It's a H.O.
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Unread 12-18-2006, 09:30 PM   #4
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hope its not the computer

the TPS on the HO engines arent adjustable are they?
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Unread 12-18-2006, 10:04 PM   #5
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Quote:
Originally Posted by sharpie1k
for $500 more, get a rebuilt I6 out of a post 93, which means about 10 more hp.
How do you figure the post '93s have 10HP more? According to the FAQ here are the specs for the 4.0L motors.

4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-95 and updated in 96-01 to 225 ft lb torque @ 3000 rpm (00-01 models use a distributorless ignition system)

Wildman have you confirmed that the Jeep will stay running if the pump continues to run? If not bypass the pump wiring and hardwire it straight to the battery and see what it does.
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Last edited by AznDrgn; 12-18-2006 at 10:24 PM..
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Unread 12-18-2006, 10:16 PM   #6
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Quote:
Originally Posted by sharpie1k
for $500 more, get a rebuilt I6 out of a post 93, which means about 10 more hp.
Nice idea, except his problem is with the electronics, not the engine itself. He could easily replace the engine and get nowhere with this problem.


I'd go with the IAC. If you disconnect the vacuum line to the MAP sensor, the engine will and should run like crap. If you can start it and keep it running with the gas pedal, yet it dies when you get off the pedal, it's definitely an IAC problem.
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Unread 12-18-2006, 10:33 PM   #7
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Quote:
Originally Posted by AznDrgn
How do you figure the post '93s have 10HP more? According to the FAQ here are the specs for the 4.0L motors.

4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-95 and updated in 96-01 to 225 ft lb torque @ 3000 rpm (00-01 models use a distributorless ignition system)

Wildman have you confirmed that the Jeep will stay running if the pump continues to run? If not bypass the pump wiring and hardwire it straight to the battery and see what it does.

excuse me, HO police. I am sorry I couldnt remember the EXACT year
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Unread 12-18-2006, 11:49 PM   #8
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change the battery.
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Unread 12-19-2006, 12:03 AM   #9
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Try putting a bypass wire across the two terminals of the ballast resistor on the driver side fenderwell. It's there to drop the voltage slightly on the fuel pump to make it run quietly.

The next thing to try is checking the fuel pump relay. It should be on the passenger side fenderwell just behind the battery.
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Unread 12-19-2006, 04:22 AM   #10
xwildman138x
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checked the battery 12.6 sitting, while cranking 11.6, running 14.2

changed out the pump relay and no difference, but never heard of the ballast resistor, saw a resistor on the diagram in the book but had no idea where it was. what does it look like similar to a relay?

The IAC will be in today so that will be another thing crossed off the list, I'll let you know what happens tonight.
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Unread 12-19-2006, 05:38 AM   #11
AznDrgn
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fuel pump resistor is that white block on the drivers side firewall.
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Unread 12-19-2006, 09:22 AM   #12
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Quote:
Originally Posted by xwildman138x
changed out the pump relay and no difference, but never heard of the ballast resistor, saw a resistor on the diagram in the book but had no idea where it was. what does it look like similar to a relay?
Found this thread, which may help you locate the resistor: http://www.jeepforum.com/forum/showt...llast+resistor

(There isn't one on my '96, so I couldn't say where it is or what it looks like, but I remembered the discussion coming up many times before.)
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Unread 12-19-2006, 09:35 AM   #13
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Quote:
Originally Posted by anony91xj
Nice idea, except his problem is with the electronics, not the engine itself. He could easily replace the engine and get nowhere with this problem.


I'd go with the IAC. If you disconnect the vacuum line to the MAP sensor, the engine will and should run like crap. If you can start it and keep it running with the gas pedal, yet it dies when you get off the pedal, it's definitely an IAC problem.
yes, try cleaning the iac. it is quick to do and it is usually the reason for stalling out with the 4.0
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Unread 12-19-2006, 09:44 AM   #14
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Here's a picture of the ballast resistor on a Renix XJ, for the HO's with the computer under the hood, it's just mounted back farther, closer to the windshield.
ballast_resistor_small.jpg  
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Unread 12-19-2006, 06:52 PM   #15
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Well found out a couple things today I changed the IAC, we cleaned the old one but it still seemed to be not working. So we put a new IAC on. Now I can keep it running, with the new IAC on there but it won't idle. I can keep it running if I give it some gas. Couldn't do that before for longer than 10 seconds. Read the voltages on the MAP, key on I had 4.9, the book said between 4.5 to 5.0 so thats good when I started it the voltages were all over the place. Pulled the vacuum line off and it idled. I'm thinking MAP is bad but I wouldn't be surprised if it didn't fix it. My parts guy has a MAP sitting on the shelf for me gonna pick it up tomorrow. The MAP is all rusted and the locking tab for the wiring harness is snapped off so the harness doesn't lock in properly even if it doesn't fix the problem can't hurt to have a new one as with all the other repairs. Also tomorrow want to look at the ballast resistor, like you said, I found it tonight thanks to you guys help, I really don't know much about resistors. Do I have to pull the wires off the ballast resistor and touch them together or do I just leave them on there and touch a wire across the two leads.
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