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Old 05-09-2014, 11:30 AM   #1
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93 YJ hesitation problem

I have a 93 yj with the 2.5l. I've been chasing this hesitation problem for the last 4 months. It runs fine, but when it gets between 2500 and 3000 rpms at a steady cruising speed, it hesitates like it has a misfire. When it happens, sometimes it backfires out the exhaust and sometimes it dies completely. If I push on the gas or let off it completely, it stops. Just does it between those rpms. It does it whether it's warm or cold. It doesn't matter what the weather is like, it still does it. It doesn't throw any codes either. It idles fine. Runs good until those rpms, but sometimes it feels a little underpowered, other times it runs like a raped ape.

So far I have replaced the cap, rotor, distributor, tps, crank sensor, plugs, wires, fpr, and fuel filter. I've checked all ground wires and vacuum lines. Everything was good there. I have a slight exhaust leak where the down pipe bolts to the manifold. Checked wires going to O2 sensor, they're in good shape. O2 sensor is less than 2 years old. Fuel pump is about 2 years old. Haven't been able to check fuel pressure yet because nobody rents them out around here. Please help! I'm starting to lose my mind.

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Old 05-09-2014, 12:24 PM   #2
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Sounds like a bad cat converter. Does the exhaust smell bad or rattle?

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Old 05-09-2014, 02:23 PM   #3
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No, exhaust smells fine. There's no cat on it. Michigan's pretty lenient on pre 1995 vehicles.
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Old 05-09-2014, 04:39 PM   #4
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It sounds like it could be an O2 sensor to me, but you stated yours is newer.

Have you pulled codes?
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Old 05-09-2014, 04:46 PM   #5
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No codes being thrown. The CEL hasn't lit up once while doing it, and I check every so often to make sure I didn't miss one. Nothing has been stored. All it shows is 12-battery has been unhooked, 33-typical ac code and mine doesn't have ac, and 55- end of codes. I wish the CEL would come on so I had a point of reference.
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Old 05-09-2014, 06:45 PM   #6
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If you said you haven't changed it already, I'd say TPS.
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Old 05-09-2014, 06:46 PM   #7
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Yep, already been changed.
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Old 05-11-2014, 01:20 AM   #8
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maybe you have low fuel pressure, and your pump cant keep up at high rpms. youre obviously losing something at that rpm range;least likely compression since you have no cat and this engines hardly ever jump time, so you could either be loosing spark, fuel pressure or injectors pulse, could you hook up an oscilloscope to the ckp?
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Old 05-14-2014, 12:00 PM   #9
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I don't have access to one. A friend of mine is going to bring me a fuel pressure gauge from his work. Hopefully that will help figure out this problem. I drove it around a little today after I cleaned the IAC valve and throttle body, but it didn't help. It actually felt a little worse, and now it does it when I step on the gas. Almost feels like it's running out of gas, but there's at least 5-6 gallons in it.
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Old 05-14-2014, 01:16 PM   #10
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Does it happen with a full tank?
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Old 05-14-2014, 02:44 PM   #11
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Yes. Doesn't matter how much gas is in it, it still does it. I'm pretty sure it's the fuel pump, but I'm waiting on the gauge so I can test the pressure before I drop the tank and change it.
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Old 05-16-2014, 10:20 AM   #12
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Now it's acting like it's running out of gas when I get on it. It'll spit and sputter until I let off the gas a little. There's at least a quarter tank in it.
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Old 05-16-2014, 11:43 AM   #13
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Might be an open in the fuel vapor recovery return line.
I had that happen on a car and without the proper vacuum/pressure it wouldn't draw gas correctly.
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Old 05-16-2014, 12:17 PM   #14
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What if my fuel lines were pinched in the back where the go through the frame. Would that cause these problems?
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Old 05-16-2014, 07:06 PM   #15
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I think you might consider checking the coil and crankshaft position sensor and associated wiring especially the grounds.
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Old 05-16-2014, 11:16 PM   #16
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Checked all of the wiring, cleaned up all of the grounds, new OEM crank sensor, and brand new coil. I'm getting good spark at all plugs and they are all a light tan color. I'm at my wits end. Took it out today, and it starts and idles great. Once you get on the skinny pedal a little, it falls on its face. Like it's almost out of gas. I think I'm just going to drop the tank and change the pump. It's the only thing I haven't done yet.
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Old 05-17-2014, 11:38 PM   #17
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Quote:
Originally Posted by yjester93 View Post
What if my fuel lines were pinched in the back where the go through the frame. Would that cause these problems?
What fuel pressure are you getting? Also make sure the pressure is constant, so leave the gauge on after shutting the jeep off, and double check it after 5-10 min
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Old 06-04-2014, 03:02 PM   #18
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Was getting 20 psi when it should have been 31 psi, so I changed the pump. Ran great for about 10 miles. When I turned around to go home, it died out on me and wouldn't start back up. Had to have it towed back home. I let it prime a few times to build up pressure, but there's not much pressure in the rail after doing this. Before it died though, there was no more sputtering. I thought my problems were solved.

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