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 Post subject: Fuel ? issue
PostPosted: Sat Oct 28, 2017 8:23 am 
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Hard to explain what my Jeep is doing, but I'll try.

After not running for anywhere from a few minutes to a few hours. So, warm or cool engine. I'll start it and drive away. After just barely getting going, it will stumble and backfire thru the exhaust. I can pop it into neutral and "clear" it out a little and then it usually is fine. After that initial episode, it runs fine. Actually its running better now than it ever has once I get it up to speed. And as a bonus, it's getting better mileage. Go figure.

I'm leaning towards some kind of fuel issue like it flooding, but don't understand why it does it after taking off. It starts fine.

Fuel pump?
Injector(s)?
Some sensor?

99TJ with 4.0L Auto.


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 Post subject: Re: Fuel ? issue
PostPosted: Sat Oct 28, 2017 7:21 pm 
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Location: O'Fallon IL
Just to clarify, It'll start and run fine at idle (no load, in park), but once you put a load on it, that's when the issue occurs?

Does it start to stumble immediately once you drop it in gear, or do you have to start moving? Alternatively, if you were to start it and drop it in gear without moving for a bit, would it start stumbling then?

Does the ambient temp make a difference?

How long has it been doing this? Just started, or has it been getting worse over time?

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-Benno!
(Ben-No!)

’87 XJ – Scrapped
’94 Ranger – Parted out
Cookie Cutter ’99 TJ – Gone
'99 Mountaineer - Coming soon to a trail near you!
All our randomness and build threads can be found at http://www.MidwestNomads.com


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 Post subject: Re: Fuel ? issue
PostPosted: Sun Oct 29, 2017 5:21 am 
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Benno! wrote:
Just to clarify, It'll start and run fine at idle (no load, in park), but once you put a load on it, that's when the issue occurs?
It starts fine. Sometimes it will stumble and go into a rough idle for a few seconds. If it does, I usually clear it out with a couple rev ups.

Does it start to stumble immediately once you drop it in gear, or do you have to start moving? Alternatively, if you were to start it and drop it in gear without moving for a bit, would it start stumbling then?
I can usually take off without any issue. maybe 10-15 mph, then it stumbles and if I try to give it more to go faster, it will backfire thru exhaust. Again, I can pop into neutral and stomp it a time or two and it's fine.

Does the ambient temp make a difference? Doesn't seem to.


How long has it been doing this? Just started, or has it been getting worse over time?

Actually started it a little back in July. Before taking off on that 6000 mile ride I did. May have gotten a little worse. Around that time, I ran a couple bottles of some kind of injector cleaner thru it. Didn't seem to do anything.

The crazy part is its running great otherwise. I was running a tune on it, but set it back to stock with no difference. I have a lot of TPS issues. Related??
I haven't looked at throttle body lately, but took it off maybe a year ago and gave it a good cleaning. Idle air sensor??


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 Post subject: Re: Fuel ? issue
PostPosted: Sun Oct 29, 2017 5:23 am 
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See replies in red.


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 Post subject: Re: Fuel ? issue
PostPosted: Sun Oct 29, 2017 6:49 am 
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Location: O'Fallon IL
That was my first guess was TPS or Idle air control valve. Both are easy enough to check to see if they are bad.

TPS test : http://www.jeepforum.com/forum/f11/how- ... ost5747016 When doing the first test, if you run the TPS through its full range it should move smoothly (an analog voltmeter works best for this). If you see any weird movements, the the TPS is likely bad.

For the IAC, just pop it off and see if it is all gunked up.

That would be my first path to march down as it's pretty straightforward. The back firing out the intake points to timing, so the CPS would be the next spot I looked at after checked the IAC and TPS.

_________________
-Benno!
(Ben-No!)

’87 XJ – Scrapped
’94 Ranger – Parted out
Cookie Cutter ’99 TJ – Gone
'99 Mountaineer - Coming soon to a trail near you!
All our randomness and build threads can be found at http://www.MidwestNomads.com


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