TJ running rough gas stinks bad, bogging down at times and back firing - JeepForum.com
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post #1 of 16 Old 04-17-2019, 03:39 PM Thread Starter
mgaither0
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TJ running rough gas stinks bad, bogging down at times and back firing

Hey everyone.


I have been away from the forum for sometime now. My TJ has been sitting on and off for 6 years now. Probably since 2012. I have driven it some in that time but it started running really bad about 2016 and kids and life has changed my free time and its not at my house but at my parents. I really want to get it all up and running again.



What is mainly going on is it either doesn't want to start real well because it sits a lot and its hardly run. The gas stinks really bad like on real old muscle cars and it has that back firing and popping you hear at times. Its also an automatic and when I shift from park to drive or reverse it will sort of bog down some like its harder on the engine to idle smooth. I have changed a lot of parts in trying to fix it. I changed the plugs, wires, cap and rotor. The throttle position sensor, MAP sensor, crank position sensor, oil pressure sensor because it wasn't reading the oil pressure. I did the idle air sensor. Also the gas while sitting I seafoamed and also used starbrite startron. For storage and also to help if the gas was going stale. Starbrite startron had helps with stale lawnmower gas before and restores stale gas. I also replaced the cat that was gutted and clamped up the exhaust. I thought maybe causing the backfiring and all because the exhaust was screwed. I still have a very small leak right at the muffler. I recently replaced the fuel pump thinking that was it with a not so expensive one. Don't remember what I bought but it was from one of the online parts sights about 2 years ago. After getting rid of the old gas and putting new gas and a new fuel pump in it ran better but still bad smelling gas and bogging down going park to drive or reverse to drive. Idles pretty smooth in park. Use to make almost a chopping sound like it had a clogged carb when going to reverse or drive. I replaced the rotor again thinking maybe it was a bad rotor.


Now I'm at a loss. Any suggestions here would be appreciated. Again it runs and runs somewhat better but still not great and it will back fire at times and cut off. It idles relatively smooth but does bog a little when going from park to drive or reverse.


list of parts replaced

1. plugs, wires, cap and rotor. Rotor a second time

2. Throttle position sensor
3. MAP sensor
4. Crank position sensor
5. Oil pressure sensor

6. Idle air sensor.

7. Catalytic convertor, clamps

8. Fuel pump


Any suggestions or ideas? Thank you

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post #2 of 16 Old 04-19-2019, 04:45 PM
mukluk
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Replace the old gas with fresh. Fuel treatments do help when a vehicle sits for some time but they can only do so much.
Make sure your battery is fully charged and your cable connections are good; our Jeeps are finicky about proper power supply.
Check for any stored or pending trouble codes, preferably with a scanner.
Make sure the air intake is clean, leak free, and you have a clean filter installed.
Check all engine vacuum lines and rubber fittings for possible leaks, check wiring for evidence of rodent damage.
Take the Jeep for a drive at least half an hour in duration, with at least ten minutes at highway speed to get things up to temp and help burn out any carbon fouling.

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2005 LJ Rubicon
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post #3 of 16 Old 04-21-2019, 03:25 PM
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"After getting rid of the old gas and putting new gas and a new fuel pump in it ran better but still bad smelling gas and bogging down going park to drive or reverse to drive. Idles pretty smooth in park. Use to make almost a chopping sound like it had a clogged carb when going to reverse or drive." Sounds like you have a fuel issue: likely a faulty fuel injector; you might be able to take them out and test em. They're not expensive to replace. Have you replaced the fuel filter?Checked the fuel pressure? Injectors don't like to sit a long time with bad gas and can cause a lot of havok. Good luck Sir.

Last edited by akhntr; 04-21-2019 at 03:37 PM.
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post #4 of 16 Old 04-21-2019, 03:32 PM
Jerry Bransford
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Does it run OK when cold and the problem starts once the engine starts to warm up? If so you have a bad upstream O2 sensor. If you replace it make sure to only go with an NTK or NGK. Avoid Bosch O2 sensors in Jeeps.

When you have a choice, buy American made.
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post #5 of 16 Old 04-23-2019, 11:30 AM
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Backfiring is timing. Miss firing is an air fuel issue. The difference is huge. Backfiring is when the cylinder is fired when the valve is open. That will cause a discharge fire through the intake.

Air, fuel issues are usually a sensor issue. Did you check codes?
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post #6 of 16 Old 05-01-2019, 04:36 PM Thread Starter
mgaither0
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Quote:
Originally Posted by akhntr View Post
"After getting rid of the old gas and putting new gas and a new fuel pump in it ran better but still bad smelling gas and bogging down going park to drive or reverse to drive. Idles pretty smooth in park. Use to make almost a chopping sound like it had a clogged carb when going to reverse or drive." Sounds like you have a fuel issue: likely a faulty fuel injector; you might be able to take them out and test em. They're not expensive to replace. Have you replaced the fuel filter?Checked the fuel pressure? Injectors don't like to sit a long time with bad gas and can cause a lot of havok. Good luck Sir.

i did replace the fuel pump and on this years TJ the fuel filter is on top of the fuel pump. Injectors I haven't checked. But its worth checking,
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post #7 of 16 Old 05-01-2019, 04:38 PM Thread Starter
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Quote:
Originally Posted by Jerry Bransford View Post
Does it run OK when cold and the problem starts once the engine starts to warm up? If so you have a bad upstream O2 sensor. If you replace it make sure to only go with an NTK or NGK. Avoid Bosch O2 sensors in Jeeps.
I know I replaced the downstream by the cat. Up stream I think I did a couple years ago. It seems to run consistently not well. Now I haven't had it out for a drive yet to see whats going on. Kind of worried it will cut off on me. Need to get new tags also but will shortly and after that will take it for a drive.
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post #8 of 16 Old 05-01-2019, 05:02 PM
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Up stream I think I did a couple years ago. It seems to run consistently not well.
If that upstream O2 sensor was a Bosch they will give problems. The only brand that works well in our Jeeps is NTK. Replacing the downstream O2 sensor won't affect the air-fuel mixture, only the upstream O2 sensor affects that.

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post #9 of 16 Old 05-01-2019, 05:36 PM
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The upstream is the only one that will effect fuel trim. Before throwing parts at it have you checked codes? Also replacing the iac isn't enough. Did you clean tg he throttle body especially where the iac goes in. There's an orifice inside to allow air bypass and the plunger can get stuck on crud buildup. Last would be the temp sensor. Check codes first

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post #10 of 16 Old 05-07-2019, 10:18 PM
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I had a very similar experience with my 97 2.5cyl this winter. Bogging, backfiring and overall running bad. I gave her a good time up (plugs,wires etc.) As well as I replaced the throttle positioning sensor and the upstream 02 sensor (only had 1). My jeep has honestly never run better.
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post #11 of 16 Old 05-29-2019, 05:41 PM Thread Starter
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Quote:
Originally Posted by Que89YJ View Post
The upstream is the only one that will effect fuel trim. Before throwing parts at it have you checked codes? Also replacing the iac isn't enough. Did you clean tg he throttle body especially where the iac goes in. There's an orifice inside to allow air bypass and the plunger can get stuck on crud buildup. Last would be the temp sensor. Check codes first

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i did and i sprayed it all with throttle bottle cleaner real good. I have also used the MAF cleaner. I have run some seafoam also.
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post #12 of 16 Old 05-29-2019, 06:12 PM Thread Starter
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Originally Posted by Deltacottonboy View Post
I had a very similar experience with my 97 2.5cyl this winter. Bogging, backfiring and overall running bad. I gave her a good time up (plugs,wires etc.) As well as I replaced the throttle positioning sensor and the upstream 02 sensor (only had 1). My jeep has honestly never run better.

would i be getting codes for the O2 though?
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post #13 of 16 Old 05-29-2019, 06:31 PM
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would i be getting codes for the O2 though?
Not always and not necessarily. The computer can't always tell when the O2 sensor data is accurate or not.

When you have a choice, buy American made.
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post #14 of 16 Old 05-29-2019, 06:49 PM
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Did you remove the iac and clean inside the throttle body?

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post #15 of 16 Old 06-23-2019, 05:35 AM
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I have a 99 TJ with very similar issue except mine only does it under load and when cold. it bucks and sputters for first half mile. It doesn't throw any codes. I have changed fuel pump and filter, cleaned tank and all new fuel, new plugs wires rotor and cap.
If I push clutch in I can peg tach and no missing. But dump clutch and under load it bucks and sputters, I am going to try that upstream NGK O2 sensor for sure. Any other ideas would be greatly appreciated.
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