schadelh

I haven't been driving the Cherokee much lately, just a few miles in town each week. Today I took it out on the freeway and as soon as I hit 45 or 50 it started bucking.

That being said, sometimes the torque converter lockup acts funky. It usually does this after an intermittent electrical gremlin stalls the jeep (its been a while since it has happened). I have been meaning to ask for the last few months, but its intermittent, and I dont go over 45 mph too often anymore. If I'm in OD, and below about 20% throttle it is unlocked, as soon as I hit 20% it locks up, and then it wont downshift until until I push the peddle down a lot further than normal (say around 80%, when normally it does it around 50%-60%). When I let the throttle up, once I go below 20% it unlocks the converter again.

Back to the bucking tonight. The bucking was worse when I gave it more gas, and seemed to only happen when the torque converter clutch was engaged (20% throttle or more). When the clutch wasn't engaged I noticed the RPMs fluctuating a bit (about 100 rpm wobble on the tach), but I couldn't really feel it.

Then the jeep did the electrical gremlin stall, I pulled over, started it back up, and everything was fine.

I am completely puzzled. Does the TCU retain any codes, or are there any transmission diagnostics that I can run? Would a bad TPS confuse the transmission? Could a bad TCU cause the jeep to stall?

I'm baffled....

tjwalker

Always post the year/engine for the most accurate replies.

To answer your question, the throttle position sensor is directly involved with the transmission shifting characteristics on the AW4. It should be ruled in or out early in troubleshooting ANY transmission issue.

The TPS can be tested. Let me know what year you have and I'll post the appropriate procedure.

schadelh

1995. 4.0HO. AW4

VTJeep

Bucking could be a few things. Either a sensor, or possibly a bad/failed mechanical unit or, there may be crud blocking fuel flow. Once fuel is really low, drop the tank and open 'er up. I think your pump/filter assembly is in tank (my 99 is.. I dunno when they switched from inline to in-tank). Either way, at start up, if it idles for a while (or at any point during operation) does it start sucking air hard at intake? This is usually when it is running dead lean, meaning a serious lack of fuel delivery. Outside of that, things like the TPS, IAC valve and o2 sensors should be checked over. But start cheap and easy!

schadelh

I'm pretty sure its not a fuel issue, it mobs around town just fine (under 40 mph), and never shows any sign of fuel starvation.

It sort of feels like a really hard misfire.

VTJeep

Is it popping (sorta like a backfire) at manifold when under throttle?

cruiser54

How long since a complete tune-up including plugs, wires, cap, and rotor?

schadelh

no popping (i do hear a pop in the exhaust when I rev it up passed 3k in neutral and let off the gas, but I figure thats normal)

Plugs, wires, cap and rotor were replaced in September. crank position sensor replaced in August.

cruiser54

Fuel starvation can cause a pop/misfire.

Have you ever checked the tightness of your intake manifold bolts? Pretty common for them to loosen up.

schadelh

wouldn't issues like this show themselves at all speeds, not just above 45-50 mph?

It gets around just fine (i.e. I wouldn't know anything is wrong) when I drive around town. I can stomp on it without issues, it shifts up and down fine, everything is good until I am in OD.

cruiser54

OD puts a heavier load on the engine than the other gears, especially when the torque converter is locked up. That load can cause a secondary ignition breakdown if anything is weak in that system. Take a look inside the distributor cap and note the condition of the terminals.

schadelh

Cap and rotor look like the day I put them on. no play in the distributor shaft or anything...

schadelh

I just drove it around all day today, and there wasn't a single issue.

This is really starting to confuse me...

cruiser54

I'm not sure on your 95, but take a look and see if there is a small group of wires grounded at the engine dipstick tube stud.

IIRC, 95s had a coil issue. can you see the name brand on your coil?

Remember that sensors and electrical connections can be intermittent and you may have to just try some stuff to eliminate possibilities.

If this Jeep were mine, I would be unplugging every connector I could see i the engine bay, visually inspecting it, spraying out both sides with contact cleaner and plugging it back together.