Please help me of you can. I have a 1987 Jeep Cherokee with 4.0 and fuel injected that has what I’ll say is a bad misfire at higher speeds. It starts and runs fine if I’m running in town and off road at slow speed/RPMs it's fine. If it’s in 3rd gear and I’m running at 50 mph it will start missing, meaning it has a bad jerk. If it’s in overdrive it won’t start until 60 to 65 mph and the faster you go the worse it gets. In both cases it will only miss/jerk if I’m maintain my speed, if I’m accelerating or if I let off the gas it runs fine, smooth with no missing or jerking.
I have read as lot of postings but most don’t seem to relate to my problem. I have replaces the distributer cap and rotor, plugs and plug wires. My crank shaft poison sensor went out and I replace it. Even wander if I got a bad one I replaced it a second time. No luck
I took it to local transmission shop thinking it could be in the tranny, the guy took it on a 15 mile drive at low speeds and highway speeds and said he thinks the tranny is fine. He suggested that I replace the distributer. Thinking if the bearing or lower gear was ware it could have play or slop when it was NOT under acceleration. Just though I would check to see if other have had this problem before taking this as my next step.
If you have heard of this, what was your cure?

 

I would go through testing all sensors on the motor before I put money into anything. Sometimes it just needs some TLC and adjustment and you're up and running again.

Use this link to run through all sensor testing:
http://www.lunghd.com/Tech_Articles/...iagnostics.htm

Mine ran like a three legged dog when I got it and without any money I was able to get her running strong.

 

Start with new plugs, wires, cap and rotor.

 

Yeah, this first^^^^^^. Couldn't believe how much of a difference these simple and cheap things made on my renix.

 

Thank you for the info, I will start doing these tomorrow and I’ll let you know what I find out.
Most of all I like doing it without spending any money.

 

A nearly complete set of write-ups I've done on Renix Jeeps can be found at the attached link under Help and Resources. Most all of them require only time and effort and no money. I do think, however, you should spring for tune-up parts first.

www.jeepseekers.com

 

I wanted to thank you for the information, I know I’m slow at letting you know what I found but I’m trying to make sure I do my test correctly. I have found two things that didn’t test correct. The Manifold Absolute Pressure Sensor (MAP), I get the 5 volts on the supply terminal C but I can’t get anything from terminal B. Not sure if I should replace it or test for something else? I’m going to do some more reading on this.
I also found that the Throttle Position Sensor (TPS) was not working, I adjusted It and it helped take away the missing when running in overdrive but it still happen when I’m in 3 gear, seems to start around 40 mph.

I think I’m going to repeat all the test to make sure I have not overlooked something.

Let me know if anything else comes to mind

Thank you for your help

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I guess the link above that I posted is not good. Here is an outline of write-ups I've done regarding the renix Jeeps. Let me know what you want or if you want a prioritized list, I will do that.
　
Revised 04-18-2012
* means instructions have been written.
　
1-Ground refreshing, adding engine bay grounds, link to Kelleys WIP*
1a-Improving the instrument panel ground*
2- Checking sensor grounds*
2a- Repairing sensor grounds*

3-C101 Connector Refreshing*
4-Connector and relay /receptacle refreshing*
5-Coil/ICM contacts*

6- Snugging up intake manifold bolts
7-Throttle body and IAC cleaning
8-TPS testing and adjusting*
9-CPS testing and adjusting*
10-CPS wiring bypass
11-ECU connector refreshing
12-Distributor indexing
13-O2 sensor diagnostics
14-Setting base idle
15-Valve cover mod*
16-Sensor ground upgrade*
17-CPS Timing Advance Mod*
18-Headlight Harness Installation*
19-Trans Plug Connector Refreshing*
20- Rear Main Seal Diagnosis*
21-Vacuum Test For Exhaust Restriction*
22-Restoring Throttle Butterfly Adjustment