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low power/bucking/backfiring on heavy acceleration

1998xj1985

1998xj1985

NAXJA Forum User
Location
Torrance, California
as title says. 98 4.0 aw4. yesterday in traffic i hammered down to get on the offramp, jeep just bucked and backfired then started working fine once it got some speed. did this at every stoplight on the way home under heavy throttle, everything works as normal under light throttle. doesn't do this every trip, seems very intermittent. i have a scanner and can read sensor outputs, but need to know what "good" values might be. i have a suspicion it may be MAP related because it has thrown MAP sensor codes in the past, never bothered to replace it because after cleaing they went away and never affected driving. looking for info on possible causes and test procedures for MAP and O2 sensors. thanks in advance
 
When my 97 did that it was the Coolant Temperature Sensor on the Thermostat housing. When the O2 sensor threw a code the engine ran fine.
 
My 2000 was doing that and it ended up being a sticking valve, wore a flat spot on the cam. Mine threw a code for a misfire on cylinder 6 when this was happening. Hope you have better luck, mine also head a crack in the 0331 head to help out.
 
Tim_MN said:
When my 97 did that it was the Coolant Temperature Sensor on the Thermostat housing.
Click to expand...

Coolant Temperature Sensor, not thermostat. It starts to read wrong, bad enough to cause issues, but not so far out of spec that it triggers a code.
 
Last edited:
Verify that your plugs for all of your sensors are making good contact. Just because they plug in does not mean that they're making good contact. I had what I thought was a TPS issue. I swapped it out and nothing changed. Symptoms very similar to what the OP is having. It ended up that the "barrels" inside the plug had became enlarged. I guess just from time and vibration. I took the plug apart and squeezed them down a bit. It's been running like a dream ever since.
 
HaleYes said:
Verify that your plugs for all of your sensors are making good contact. Just because they plug in does not mean that they're making good contact. I had what I thought was a TPS issue. I swapped it out and nothing changed. Symptoms very similar to what the OP is having. It ended up that the "barrels" inside the plug had became enlarged. I guess just from time and vibration. I took the plug apart and squeezed them down a bit. It's been running like a dream ever since.
Click to expand...


yeah, have been trying to monkey with that. TPS doesn't really click into place, others appear good. bent the little retainer clip on the tps and it clicks in now. didn't do it's little trick this morning on the way to school. will keep the thread updated with new news.
 
Im not a mechanic, but i had a car that did that. And it was my ecu reading to much air, because i had a bad hose from my air intake box to the engine. so check and see if you have any cracked hoses from your air intake to your engine if your jeep has a ecu im not sure if it does or dosnt.
 
just got a P0700 - transmission control module malfunction code.

Jeep was shifting at 3000 for every gear and didn't seem to want to downshift into 2 from 3rd or 4th. I am wondering if the stumbling issue might be transmission related? anyone out there have any info on pulling codes from the TCU?
 
1998xj1985 said:
just got a P0700 - transmission control module malfunction code.

Jeep was shifting at 3000 for every gear and didn't seem to want to downshift into 2 from 3rd or 4th. I am wondering if the stumbling issue might be transmission related? anyone out there have any info on pulling codes from the TCU?
Click to expand...

When my TPS sensor connection was on the fritz, I had shifting issues as well(didn't want to downshift)........I'm tell'n ya.....check out the connections.:D Especially the TPS.

Check the continuity between the plug and the plug on the ECM. I found that I had continuity. So, I ohmed the TPS. It showed good. That's when I noticed the connector issue.
 
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