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Unread 02-28-2013, 05:28 PM   #16
bbradUSMC
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I had this same problem in my '98 Sahara, turned out that it was my O2 sensor. I replaced it with a Bosch and had the same problem. Went around the engine replacing all kinds of junk to no success. Then I read up on here about Bosch O2's and a lot of guys are saying Jeeps hate them for some reason. I replaced it with whatever other brand the auto store had and presto, no more problem. If that doesn't work check for a short in your O2 harness.

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Unread 02-28-2013, 05:46 PM   #17
ducaticorse
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Had an 00 cherokee do the same thing. Was a bad valve :-(
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Unread 02-28-2013, 08:02 PM   #18
karik
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my guess it was the o2 sensor as well, but o/p said he changed his without improvement...

or a heat soaked cks, but he said that was changed too.that leaves cps.

wish i'd only changed one part at a time to see if that was it, but only have access to heated workspace once in a while.
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Unread 02-28-2013, 08:32 PM   #19
sethhawk1
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I found this same problem with a toyota and it actually turned out to be the engine temp sensor. It doesn't mean your overheating but the computer doesn't know what the temperature of the engine is to compensate. Yes there were two temp sensors one went to the temp sensor in the dash and the other to the computer. One way to test it would be to unplug when its missing real bad or not starting and see if conditions change.

I don't know if any of this pertains to the jeep, but its wort a shot.
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Unread 03-02-2013, 02:25 AM   #20
oakmckinley
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That's what I was suggesting too. The dash gage temp sensor is different than the one that feeds info to the computer.
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Unread 03-02-2013, 02:38 AM   #21
photontraveler
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When my TJ was doing that it wound up being the Crank Sensor. I hope this helps.
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Unread 03-02-2013, 04:03 AM   #22
Jonny Jeep
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TJs only have one temp sensor for the coolant temp, which is at the thermostat housing. The gauge displays what the PCM tells it to. If the gauge is operating normally the sensor should be ok. If the sensor needs testing it should be compared to the chart below. Could still be an overheating coil as I suggested earlier. Primary and secondary resistances should be 0.95-1.15 ohms and 11,300-15,300 ohms.

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Unread 03-02-2013, 04:40 AM   #23
oakmckinley
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What's that temp sensor in the intake for then?

Not doubting you Johnny jeep (because you're the man), just wondering.
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Unread 03-02-2013, 11:34 AM   #24
Jonny Jeep
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Intake air temperature sensor.
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Unread 03-02-2013, 07:12 PM   #25
oakmckinley
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And it adjusts the amount of fuel due to the reading? for colder/hotter air temps?
So if that sensor was not reading correctly?
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Unread 03-02-2013, 11:27 PM   #26
freeskier93
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Quote:
Originally Posted by oakmckinley View Post
And it adjusts the amount of fuel due to the reading? for colder/hotter air temps?
So if that sensor was not reading correctly?
It's possible. The intake temp sensor is used in conjunction with the MAP sensor to determine air density, which is pretty important to know for a/f ratio.
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Unread 03-03-2013, 08:04 AM   #27
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Both coolant temp and IAT sensors are used in conjunction with the MAP, CKP, CMP, O2 sensors for controlling the fuel mix and sync. Both temperature sensors will have an effect on the fuel injector pulse width. When resistive sensors fail they usually go open circuit and in the case of the coolant and IAT sensors they make the computer think the temp is -40 and this results in a rich fuel mix which can cause rough running but also causes a drop in MPG. Both sensors can be checked against the chart posted above.

The reason I suggested the coil earlier is that there's a thread in the XJ section where the guy swapped all sorts of stuff and the problem turned out to be a bad coil, which turned out to be cracked in his case. The trouble with heat soaking problems is the number of things that can be affected. It could even be a bad splice or connection that increases resistance as it gets hot.

It might be worth the OP checking the condition of his plugs since a sticking valve has also been suggested.
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Unread 03-04-2013, 01:19 PM   #28
JCarroll89
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Replaced the plugs, plug wires, cap, rotor, ignition coil, o2 sensors, crank sensor, IAC (found out pintle was broken when i was cleaning out the throttle body), cleaning all connections and battery terminals, and running seafoam through the engine and fuel system and she still couldn't hack it at highway speeds for more than 5-10 minutes. Fine during city driving.

Replaced the fuel pump assembly and I'm back in business, 300 miles and a weekend trip to Rausch Creek with no issues. I'm thinking the pump was on it's way out and could handle low demand while city driving but couldn't take the continuous high demand while highway driving. Guess and check isn't the most cost effective way to diagnose an issue but I did notice a pretty nice increase in MPG. I guess she was just being a typical woman, you know something is wrong but she won't tell you what (no CEL) so you just keep buying things for her until she's happy again. It's too bad I couldn't just put some roses in the tank but what can you do eh. Thanks for all the help & input
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Unread 03-04-2013, 01:42 PM   #29
bbradUSMC
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Quote:
Originally Posted by JCarroll89 View Post
I guess she was just being a typical woman, you know something is wrong but she won't tell you what (no CEL) so you just keep buying things for her until she's happy again.
That is my first Signature quote. Thank you sir!
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Unread 03-04-2013, 01:49 PM   #30
Jonny Jeep
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Glad you found the problem and got it fixed. Never really thought about the fuel pump getting heat soaked. I'd have expected it to be a more consistent problem.
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Rockauto 5% discount code can be found here... http://www.markviii.org/LOD2/products_services.htm

Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
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