First of all, I have a 1998 Cherokee Classic 4.0 4x4 Auto. 152,000 miles. I have had it for about a year and it has been trouble free aside from my heater core developing a leak.

Over Memorial day weekend, we went out of town and decided to take the Cherokee. We went about 300 miles in the trip and it was fine on Friday night for the trip over and on short trips while we were gone. On Monday afternoon, when we left to come home, the problem started.

At highway speeds (55+ MPH), when I would hit a bump, it would seem like the engine was cutting off for just a second or so ... maybe not even that long. The speedometer would drop about 10 or so miles an hour instantly and then go right back up. Overall, the truck would just lose about 2-3 MPH and would go right to being fine again. Also, if Cruise Control is being used when this occurs, it turns full off (truck loses speed until you push the accelerator and the green cruise indicator goes off). It did this a number of times on the trip. In some cases, the Check Engine light would blink for a split second (when an ODBII scanner is connected, no codes show up). On some occurrences, the fuel guage would drop to the position it is in when the truck is off (below E) and stay there (It comes right back to where it should be when the truck is turned off and restarted). When this happens, it sure seems like it is an electrical problem, but the radio never misses a beat and my radio takes about 10 seconds to give sound when powered on, so it would be noticeable if it was affected.

After some initial searching, I saw some similar sounding issues where people indicated that the Crankshaft position sensor could be the culprit. That has now been changed with a mopar replacement from the dealer. The truck seems to idle more smoothly as a result, but the original issue is still present.

In the beginning, it sure seemed like it always happened when we hit a bump, but now it seems like it can happen at any time, even on smooth road.

I guess my next course of action will be to get some electrical connection cleaner and find all plug type connectors and disconnect/clean/reconnect them and see if there may be a loose connection somewhere. I am not really sure where the important ones of those are located aside from the ones that are visible under the hood.

Has anyone had a similar experience or have any advice or recommendations for me?

Thanks,

Paul

 

I have not had this issue, but I agree that it sounds like a loose connection somewhere. Start with the battery cables and grounds, and move on from there. Also, are there any codes stored?

 

No codes that show up on the scanner that I have easy access to. I will take it to an o'reilly with a potentially better scanner and see if theirs shows something that mine may not. Not really sure if that will be the case.

 

If there were codes stored, I would expect any scanner to read them.

 

Well, after a good while of the problem not really showing itself, it has come back with a vengeance.

Since then, I have disconnected all connections that I could see under the hood and cleaned them with contact cleaner, then reconnected. This seems to have done nothing, but I figure it can't hurt.

Also, the issue now is starting to occur at lower speeds, even when accelerating from a stop. Sometimes, it will stutter and stumble and have a really hard time getting going.

Sometimes, it continues to have the issue and sometimes, I can go up to 10 miles and it will no longer have the issue. Very strange.

Again, when the issue happens, the check engine light comes on for a split second and then goes right back off ... no codes are stored. Also, in many cases, the fuel gauge will stop being accurate after this behavior. Immediately after the loss of power to engine, the speedo will drop (it will drop much more than my speed actually foes down, then comes back up). At no point do I lose blower motor power, radio power, etc., it is only engine power.

I have changed crankshaft position sensor. Would you think that Throttle position and camshaft position (pick up coil in distributor) could be culprits? I would also assume (possibly incorrectly) that if I had a bad spark plug wire, that I would just be getting a miss, more so than a complete power loss at engine for about a half second. A half second at 3000 RPM would require all plug wires to not have a spark for that amount of time. Also, I would think that if I had an electrical problem that was further upstream, that I would see more electrical issues, such as radio or blower motor while the issue was occurring.

 

mine 99 cherokee is doing the same thing, have you found a fix yet. i'm thinking about going through all the grounds first to see.

 

Same problem on my 92 did anyone ever find a cure?

 

Try looking in the direction of the MAP sensor, vac line or the sensor itself.

 

Recently I have been having this exact same problem with my 1999 XJ. the engine will buck and the speedo would drop momentarily on the freeway. I even had the exact same thoughts...at first I thought it seemed to coinside with hitting a bump (still seems like it) but if I go for pot holes or bumps I can't "make" it happen. It also seems to happen more often when I'm turning even slightly left, but that might be coincidence.

So far I have only changed the TPS and that made no difference. The things I'm gathering from the internet are:

- Crank Position Sensor
- ground cables
- Spark Plug wires and Coil
- O2 sensors

The fact that the speedo drops is the thing that makes me think it doesn't have to do with ignition, but I could be wrong.

Has anyone has any luck diagnosing and fixing this type of problem?

 

I know when my cps was first starting to go out my 98 would do the exact same thing.

 

My apologies ... I thought that I had posted a reply last Saturday from my phone, but I guess that didn't work.





First, see the attached pictures. I used my unmatched photo editing ability to show you where my issue was and you can see how I fixed it.

On the back end of the fuel rail, closest to the firewall, it is not a smooth back end. It is open, like a pipe. On mine, the bundle of wires in flex-loom were rubbing on the back of the fuel rail. This had rubbed a hole in the flex-loom and had also rubbed through the insulation of some of the wires inside. This is where my problem was. I think this is also why my problem started off intermittent and became worse and worse as time passed, since it was continually wearing.

What I did was open the flex-loom and pull the wires from inside. I had two wires that had been rubbed through. I taped those up and replaced the flex-loom and then used some cable ties to hold the flex-loom up, so that it wouldn't rub anymore. You can see those bright orange ties that I used.

I haven't had any issues since this fix.

 

I just bought a bunch of parts that will hopefully fix this issue, plus I'm going to look for any physical wire issues such as that or bad grounds. It occurred to me that there might be some stressed engine wires from the transfer case drop I did last year. Here's a list of what I just bought... even if they don't fix this particular issue, at least I have a bunch of new parts on the XJ:

- Crank Position Sensor
- Upstream & Downstream 02 sensors
- Coil
- Spark Plugs & Wires
- Dist. Cap & Rotor

I think the most likely culprits would be bad wires or the CPS...

 

I hope you got a OEM CPS. the after market one are garbage and most of the time they are bad right out of the box. If it does work they have a very short life span.

 

So far I have replaced both 02 sensors, and cleaned the IAC valve but none of that made any difference. I also spent some time looking over and jiggling sections of the wire loom while the engine was running, but didn't find any bad sections.

I also found out that this issue get pretty bad if I really floor it.

I bought the $42 Standard Motor Products CPS from Rock Auto. I hope it works...