Jeep is sputtering and backfiring

Astoud27

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Jul 1, 2018
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Location
Hilton Head Island, SC, USA
I have a 1997 2.5l Jeep TJ that has recently begun to give me problems. It started 2 months ago as an occasional sputter but later started backfiring as well. Initially, the backfiring sounded like popcorn popping and was muffled. At first, I could get it to stop while driving by throwing it into neutral and then back to drive but that worked for a short period of time. As the problem got worse I had to pull over and turn the key off and on a few times and the problem would go away for a while. So... it started getting worse and eventually it backfired extremely loud one time and died while going 60 mph. I could not get it to start and had to have it towed. I've read multiple threads by owners with a similar problem and I started fixing things based on recommendations I read but nothing has worked. So far, I have installed a new fuel pump, fuel filter, O2 sensors, ignition coil, crankshaft sensor, distributor, spark plugs & wire set. The most recent fix attempt was the distributor and that was done by my mechanic. When the installation was complete I picked it up and it drove perfect for about 15 miles and then it sputtered, backfired and died. After about 10 minutes it started and I was able to make it back to the mechanic without another incident. Two days later the mechanic called and said it was ready, again. He said he checked back over everything that was done to it and cleaned the injectors. It ran great for about a week and now it's doing the same thing except it's not dying, just sputtering and backfiring and then its fine. Honestly, I'd take it back to the mechanic but at this point, I feel I am just throwing away money because nothing has worked. I've done everything that I know to do so any new suggestions would really help!
 
I had a problem like this recently and it ended up being the ground on the engine block. It's near the distributor. Take it off,clean up the connections and make sure everything is tight.
 
Do you have a check engine light? If so, what was the code? I was thinking maybe a clogged cat, but you said it went away for a week. Did you use the NGK o2 sensors? If not, that could be part of the problem.


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Let me start by saying "welcome new members" to all of you. 4 in a row!

Jeeps can be particular about parts.

>what brand O2s were installed?
They like NGKs, there is a thread on here somewhere.

>what brand crank sensor?
They really like OE Mopar

>Bosch fuel pumps preferred by many.

Good luck!

Hey! Heads up, some may ask for Jeep pics. It's OK, they mean well.
 
Do you have a check engine light? If so, what was the code? I was thinking maybe a clogged cat, but you said it went away for a week. Did you use the NGK o2 sensors? If not, that could be part of the problem.


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The check engine light has never come on. I ran several diagnostics and no codes. Also, my mechanic didn't get any codes either. I did use NGK O2 sensors, Bosch fuel pump and OEM crankshaft sensor. However, I am unsure what distributor was used as my mechanic ordered and installed it.
 
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I had the same issue in like ..... 2007 lol. Drove me nuts. My Dad brought it to his mechanic and he put a new CAT on. Do you get the rotten egg smell?


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How.many.miles on the engine?
Did the mechanic do a compression test?
I'm just wondering if it's time for a valve job.
A backfire thru the exhaust means a plug is firing before an exhaust valve seats completely. I'm wondering if you have a burnt exhaust valve.
It could also be a timing issue.
No codes thrown?
 
I had the same issue in like ..... 2007 lol. Drove me nuts. My Dad brought it to his mechanic and he put a new CAT on. Do you get the rotten egg smell?


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Yeah, that’s what’s I said. Do you feel any power loss? Can you still pull a hill? Sounds like a cat to me other than the part where it was fixed for a week and no CEL.



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Yeah, that’s what’s I said. Do you feel any power loss? Can you still pull a hill? Sounds like a cat to me other than the part where it was fixed for a week and no CEL.



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No it was a friggin’ dog once it started sputtering. No power at all. Just enough to keep it running.


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I will definitely check for that tomorrow and update whether or not that was the issue.
I had a problem like this recently and it ended up being the ground on the engine block. It's near the distributor. Take it off,clean up the connections and make sure everything is tight.

I inspected the engine ground and didn't find anything wrong with it. I don't believe that this is the issue.
 
It sure sounds like a bad upstream O2 sensor even though I know you said you already changed both of them. Did you install the recommended NTK brand O2 sensor? Other brands are not known to work as well and Bosch O2 sensors generally have a bad reputation in our TJs.

One way to know if it's likely a bad O2 sensor or not is if the engine runs well when cold but starts sputtering/backfiring only after it has started to warm up, that' usually from a bad upstream O2 sensor. If it runs just as bad when it is first started and still cold, the problem is likely not caused by a bad O2 sensor.
 
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How.many.miles on the engine?
Did the mechanic do a compression test?
I'm just wondering if it's time for a valve job.
A backfire thru the exhaust means a plug is firing before an exhaust valve seats completely. I'm wondering if you have a burnt exhaust valve.
It could also be a timing issue.
No codes thrown?

No codes whatsoever. I called my mechanic and he stated that a compression test was performed. He stated he did so because he has seen a similar issue in another jeep that was caused by a slipped cam lobe, but stated all tests were normal.
 
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I had the same issue in like ..... 2007 lol. Drove me nuts. My Dad brought it to his mechanic and he put a new CAT on. Do you get the rotten egg smell?


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I had a completely new exhaust system installed including a new manifold and manifold gasket 2 years ago. I haven't noticed any weird smells. There hasn't been a change in exhaust color either.
 
It sure sounds like a bad upstream O2 sensor even though I know you said you already changed both of them. Did you install the recommended NTK brand O2 sensor? Other brands are not known to work as well and Bosch O2 sensors generally have a bad reputation in our TJs.

One way to know if it's likely a bad O2 sensor or not is if the engine runs well when cold but starts sputtering/backfiring only after it has started to warm up, that' usually from a bad upstream O2 sensor. If it runs just as bad when it is first started and still cold, the problem is likely not caused by a bad O2 sensor.
Hello hello, just making sure this microphone is working. :)
 
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