Jeep bog while driving

[Moutaineerjeep13]

Hey yall, I have a 98 wrangler sport 5 inch lift and 33s, 4.0 6cyl,i had just bought it, I had to put a new exhaust on it cuz the exhaust was rotted, only savable part was muffler, so when I drive, it will go fine then out of no where it will bog, rpms up and down, and then boom it will take off, usally I'll be able to throttle out any ideas? New air filter tried, getting new radiator on Tuesday, I was thinking tune up? Fuel filter and pump?

 

[JPNinPA]

Start with checking things before changing things. This way if there is only one part that is an issue you don't add another bad part while trying to fix. I say this because many aftermarket sensors fail right out of the box. Only buy OEM sensors for jeep.


Now start with checking for stored codes.

This can be a bad TPS. Does it only happen at certain pedal positions? If so it is likely the TPS. Only by OEM.
Does it only happen when the engine is cold . If started warm it doesn't happen?
Does it happen when started warm but never when started cold?


If not:
Then your fuel pressure.
I read in another post you have you removed, replaced or tested the O2 sensors?? Confused on what you did. I read it as there are now no O2 sensors but idk. Please clarify.

After fuel then spark. All plugs and blue spark.

Air. Too much is as bad if not worse than none. Be sure changing the exhaust you didn't create an intake leak.

If all of this checks out then check the temp sending unit. On some years there are two one for the gage and one for the PCM. If the PCM is getting a too hot reading limp mode or misfiring. Will happen.

 

[Moutaineerjeep13]

Start with checking things before changing things. This way if there is only one part that is an issue you don't add another bad part while trying to fix. I say this because many aftermarket sensors fail right out of the box. Only buy OEM sensors for jeep.


Now start with checking for stored codes.

This can be a bad TPS. Does it only happen at certain pedal positions? If so it is likely the TPS. Only by OEM.
Does it only happen when the engine is cold . If started warm it doesn't happen?
Does it happen when started warm but never when started cold?


If not:
Then your fuel pressure.
I read in another post you have you removed, replaced or tested the O2 sensors?? Confused on what you did. I read it as there are now no O2 sensors but idk. Please clarify.

After fuel then spark. All plugs and blue spark.

Air. Too much is as bad if not worse than none. Be sure changing the exhaust you didn't create an intake leak.

If all of this checks out then check the temp sending unit. On some years there are two one for the gage and one for the PCM. If the PCM is getting a too hot reading limp mode or misfiring. Will happen.

Happens when its like 2 minutes down the road, the old exhaust was rotted out, so I had to replace it, it needs a radiator, but other then the bog it's perfect

 

[JPNinPA]

Happens when its like 2 minutes down the road, the old exhaust was rotted out, so I had to replace it, it needs a radiator, but other then the bog it's perfect

Answers to the many questions help direct where the problem is.

So does it happen at the same pedal position every time you hit that pedal position?[Y/N]
Does it only happen after a cold engine start?[Y/N]
So is the engine to temp when it occurs? [Y/N]
Was the engine warm before start?[Y/N]
Does your new exhaust have O2 sensors?[Y/N]
Are your O2 sensors new?[Y/N]




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[Moutaineerjeep13]

Only when it's cold, let it run for about 10 minutes and didn't do it, left work yesterday about 2 minutes after and it did it

 

[JPNinPA]

Ok that sounds like the temp sending unit. Note what temp the engine is at when it does it. Another possibility is an O2 sensor but first post up what temp the engine is at when it happens.


Was this an issue before the new exhaust?


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[JPNinPA]

There are tests to verify before you go and spend $$$ on new sensors.


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[Moutaineerjeep13]

Did it before new exhaust, temp goes to just under 210 about 190 195 ,but like I said only when it's cold

 

[JPNinPA]

Did it before new exhaust, temp goes to just under 210 about 190 195 ,but like I said only when it's cold

So the issue happens when the temp reaches 195 from cold.

With the engine cold, remove the plug from the back of the temp sending unit. Using a multimeter set to measure resistance, measure resistance of between the temp sending unit connectors. The resistance should read according to the chart below.

 

[Moutaineerjeep13]

Thank you guys, one more quick question for now, is it better to change both axle u joints or just 1 side at a time, guy at a work said one at a time but I would rather do both

 

[mmello13]

I usually fix thing in pairs unless it's expensive like wheel bearings haha. But the saying goes, don't fix something that's not broke. Haha

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[JPNinPA]

One at a time. Unlike brakes, balljoints, wheel bearings and a few others that seem to fail in pairs. U-Joints don't usually.
Plus there is not an advantage to doing both like having to open the axel anyway.


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[Moutaineerjeep13]

Yes, thank you, I've always done everything In pairs, but wasn't sure, thank you