tortex53

Hello Everyone,

I just picked up a '92 Cherokee. I have a couple of engine/transmission problems that may be related.

The first problem is that it won't downshift when in "D." It feels like it is in 3 or 4 all of the time. However, if I manually shift the transmission with the gear selector, it doesn't have a problem.

It also has a problem revving up. The engine idles really smoothly and revs smoothly throughout the RPM's, as long as you're gentle with the throttle. However, if you try to accelerate quickly (both in Park or in gear), the engine bogs down around 2000 RPMs (even drops RPMs briefly) and begins to make popping sounds, almost as if it's backfiring through a carburetor.

Any help would be greatly appreciated!

Turbo X_J

Check all ground connections for continuity then test the TPS with preferably an analog VOM:
https://www.autozone.com/repairinfo/...&subtitle=test

cruiser54

What happens if you shift it manually?

Jeepwalker

Well, the first thing they say in the Chrysler troubleshooting tree before diving into electronic troubleshooting is to do a THOROUGH inspection of some of the things below. Reason for that is often that's the problem:
1) Check plug wires/cap/rotor. Especially for corrosion deposits on the dist cap pins (underside). Are the ignition wires good?? Spark seem to be solid ..to ALL plugs?? Plugs good? Firing order correct?
2) Inspect for (and clean if necessary) deposits on the throttle body butterfly (underside too) and throttle body bore.
3) Inspect vacuum hoses. Put a vacuum gauge on it. Mine pulls ~15" at idle but raises off idle and reaches 19" at around 1100 rpms. Could be an intake or other hidden vacuum leak. Your engine needs good vacuum to vaporize fuel. A vac gauge is your friend!
4) Fuel pressure, etc
5) Fuel good? I once had a lot of water in the tank of a vehicle from a gas fill-up. But I didn't recognize the relationship right away. Vehicle would idle great, but not run worth a crap at speed. It mimicked ignition problems. Took forever to uncover (which I only discovered by accident). Fuels with alcohol are more prone to moisture.
6) Then start looking into the electronics and wiring. Codes?? Does this have a manifold temp sensor that gets plugged up? Ohm out the sensor. On my chev truck once, a bad temp sensor would spoof the ECM into thinking it was the incorrect temp and throw off the fuel delivery and timing. Wasn't throwing appropriate codes. Use a multimeter when engine is cold and compare readings to ambient temp. Cruiser has superb troubleshooting tips. Don't forget to check the basics too....

Good luck.

cruiser54

The fact that it's not starting out in the proper gear needs to be addressed first.

tortex53

Sorry for the long delay in responding. I finally got a hold of a multimeter and some tools (hard to do in Costa Rica), so I'm going to start with the troubleshooting process.

The smooth idle but rough acceleration along with not downshifting in Drive does make me think the TPS. I'll start there and then move into JeepWalker's suggestions.

@Cruiser54, it does shift manually in 1-2 and 3.

Morat

Obviously go with the diagnostics first but if you do need to load the parts cannon, this is the best price I found for the solenoids a few weeks back:

https://www.ebay.com/itm/32175038030...m=321750380309

tortex53

I just checked the TPS. Assuming that I'm testing it correctly, I got 1.12 volts at idle and a max of 3.8 at WOT. I take it the TPS needs to be replaced. Unfortunately, I need to get the parts from the States and will be waiting until family visits in a couple of weeks. While I'm waiting, I'll check the cap and rotors, etc.

Should I also check the transmission solenoids? Are those something that would allow manual shifting but not automatic shifting?

Morat

Yes but don't go there until you've completed Cruiser's tests or I'll be in trouble :P

tortex53

Alright, so I finally replaced the TPS which didn't make any difference. I also sprayed throttle body cleaner into the IAC hole and the throttle body butterfly. That seemed to help a little. Spraying the throttle body cleaner definitely helps it start right away (otherwise you have to crank it a bunch in short bursts before it will start). Once it starts, it idles almost perfectly.

The Jeep has sat for quite a while, so the gas could be bad or have some water in it (it is Costa Rica after all). I put some fuel cleaner in the tank, and that has seemed to help a little. The tank is almost empty, and then I'll add fresh fuel to see if the fuel has been contributing to the problem.

The fuel pump is noisy which makes me think it should be replaced, but it seems to work fine.

Again, the problem is pretty much just between 2000-3000 rpms. After 3000 rpms, it has lots of power and accelerates quickly, but around 2000 it's a dog, which makes me think that what seems to be a transmission problem is actually just an engine problem. Could it be a timing issue? Is there a way to check/adjust the timing without a timing light?

Thanks!

cruiser54

THOROUGHLY clean the throttle body.

THROTTLE BODY AND IAC CLEANING

OCTOBER 30, 2015 SALAD 19 COMMENTS EDIT
Originally by TJWalker of CherokeeForum & JeepForum



The Idle Air Control (IAC) is mounted on the back of the throttle body (front for ’87-’90).

The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed.

Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

1. Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On ’91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
2. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
3. Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
4. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner.
5. It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled.

Revised 1-31-2016



Timing is done by the computer.

Make sure your intake manifold bolts are snug.
Closely inspect the tube from the throttle body to the MAP sensor.

tortex53

Will definitely do that as soon as I can get a throttle body gasket. Would this affect the 2k-3k rpm range? The engine idles well.

cruiser54

I guess we'll find out, huh?

This is maintenance stuff......

tortex53

Good point!

awg

I would try good fuel, and replace the fuel filter, if it doesnt want to rev.

In the case of fuel pumps I have replaced, they have a fine sock filter, which was covered in scum & slime

I replaced the whole assembly, (pump, sender, internal filter), not sure what arrangement the '92 has