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3rd/4th Gear Issue

537 views 10 replies 4 participants last post by  DeadLeg 
#1 · (Edited)
On my 95 ZJ, when I'm going up a hill with just enough throttle to keep my speed up, my Jeep will jerk and buck hard. The engine rpms never seem to change and there is no issues with lower gears.

If I hit the gas a little it will jerk worse.
If I hit the gas hard, it will down shift and accelerate fine.
If I let off and allow the car to slow down it will stop.

Ive noticed that it is worse when the transmission is cold.
Edit- This leads me to believe that something is clogged since the hot fluid is thinner.

I have tried changing the transmission filter and the fluid but it did not help. I did not see any pieces of metal on the trans pan magnet.

Any ideas on what I can test/check next?
 
#7 ·
ECM Codes 12 and 51

12 - PCM disconnected with 50 key cycles - I have never disconnected the PCM nor have i disconnected the battery recently.

51 - O2 sensor indicates lean air/fuel ratio. - Perhaps a weak fuel pump or clogged fuel filter?

No TCM codes present
 
#8 ·
51 - O2 sensor indicates lean air/fuel ratio. - Perhaps a weak fuel pump or clogged fuel filter?
Jerking or bucking at part throttle under load can be lean misfires. I would doubt that the fuel pump or fuel supply is the issue since you say it runs fine if you give it a lot of throttle. More throttle = more fuel demand so it should run worse if fuel was an issue. I would suspect a bad sensor but I'd also expect it to throw a code.

On the other hand a misfire will make the engine look like it's running lean (no spark = unburned fuel and lots of oxygen in the exhaust). That could be a secondary ignition problem like StPaul59 said. Check your cap, rotor, wires, plugs.

It's sort of a catch 22: lean can cause misfires and misfires can look lean.

It's also probably a good idea to look for vacuum leaks and maybe the various engine sensors especially any non-Mopar since the general consensus is that they can cause issues without setting codes. I've never experienced this even though I at one point had zero Mopar sensors but YMMV.
 
#11 ·
SOLVED!

Im a bit embarrassed but my #6 plug was completely shot. I ended up replacing plugs, wires, distributor cap, rotor, and ignition coil while I was at it.

Thanks for the help. I would have never thought the symptom would have led back to misfire.
 
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