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Discussion Starter · #1 ·
Hi Everyone, it's been a while. I've owned a couple of CJ7's and several TJ's and I am now driving a 99 Sahara 4.0 Stick w/ 132k miles that I love!

Of all the Jeeps I've owned I've never come across this issue so I figured I'd check to see what you all think... About 2 months ago I noticed when driving on the highway around 75mph once in a while it felt like the engine has a hiccup or stalls out. It being a manual would instantly jump start itself. As of late it seems like on certain trips it would do this several times others maybe once but now it is often, so often I am wondering where she is going to leave me stranded. It doesn't do this as often or much city driving. I have a 38 min commute most of which is highway driving.

I did have a fuel pump fail about a year ago which I had the garage replace. So I don't think it is the fuel pump or filter. I don't have any codes or lights coming on. It's been about 50k since I did a tune up so I'll be doing new plugs, wires, cap & rotor this weekend. Any other suggestions or am I way off?
 

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Mine did something similar, it ended up being upstream o2 sensor
 

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Discussion Starter · #3 ·
Mine did something similar, it ended up being upstream o2 sensor
Thanks Mudbug85603 but wouldn't the check engine light come on for an O2 Sensor. I did a long over due tune up (plugs, wires, cap & rotor) but that didn't resolve the problem. I think I'm actually getting worse gas mileage now. I'm thinking fuel pump but it's been a year. I wonder if they changed the filter (i think its all one unit).
 

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Thanks Mudbug85603 but wouldn't the check engine light come on for an O2 Sensor. I did a long over due tune up (plugs, wires, cap & rotor) but that didn't resolve the problem. I think I'm actually getting worse gas mileage now. I'm thinking fuel pump but it's been a year. I wonder if they changed the filter (i think its all one unit).
No it didn't set off the CEL on mine and no codes thrown either. Just a lazy response with a scan tool and too big of a difference between up and down stream readings with a scan tool is the only indication I had. .

The fuel filter is built into the pump and the filter should last the lifetime of the pump. Check your fuel pressure should be 49 +/- 2, if that's good then it's not a fuel pump.
 

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Discussion Starter · #6 ·
Same issue with my 02 TJ. Turned out to be loose crankshaft position sensor. Easy fix.
I took your advice and swapped out the CPS. Pretty easy DIY. I took the jeep on the highway and it seemed better. I pushed the jeep a little each gear (3k rpm) and got up to 85mph. I kept going up and down in speed from 70-80mph and it seemed to do great. After a few exits I turned around and went back. I got off the highway and continued to push the jeep at high rpm's. I'm sorry to report that it cut out again and stalled around 40mph. Good news is that it only did it once...

I might look into the 02 sensor now but I recall replacing my CAT about a year ago and replacing all the sensors.
 

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Mine did something similar, it ended up being upstream o2 sensor
Mudbug85603 looks like you hit it on the nose. Today I replaced the upstream o2 sensor drove a good 100 miles w/out issue. Thanks again!!
Just another example of why I love reading this forum.
Not having this issue, but knowledge is power.

Great work.
It's always nice to be back on the road and up to par.

Happy Jeepin'!!!
 

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The 02 sensors will eventually turn the CEL on, but it will be nearly undrivable before that happens.
 

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Could be, I'm only going on my own experience.
 
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