Another mystery problem with the Jeep. Need help

[cjomanche]

Hi everyone, I posted a thread a few months back regarding a "hiccup" I was experiencing at around 3,000 RPMs.  Well, it's still there, but after installing a new clutch master cylinder, it is appearing all over the place.  My wife has been driving the truck this week and she  barely made it to work yesterday, had to have it towed home. 

 

The truck drives completely fine until a little while after it gets up to operating temperature, then it starts hiccupping.  The tach needle flutters up and down, and the gas pedal becomes unresponsive.  It gets progressively worse as time goes on.  My friend thought it might be the throttle position sensor, but I swapped that out last night with a new one and it did not resolve the problem. 

Where do I go from here?  I've read some information about crank position sensors sometimes causing this problem.  Maybe some electrical short somewhere in the system?  What could be doing just fine until a certain temperature kicks in, and then starts having trouble?  I'm really stumped on this one.

 

Thanks

[mjeff87]

Disconnect the O2 sensor, drive it and see if it makes a difference.

[HOrnbrod]

You have a 91? Check for fault codes.

 

https://comancheclub.com/forums/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

 

 

[cjomanche]

3 minutes ago, mjeff87 said:

Disconnect the O2 sensor, drive it and see if it makes a difference.

 

Funny you mentioned that, I found a damaged wire leading from the O2 sensor the other day when I was under the Jeep.  I know I need to replace it, but I didn't think it would be causing the kind of issue I was experiencing.  Wouldn't it be fluttering and doing weird stuff immediately after starting the truck if it was an O2 sensor? 

[cjomanche]

3 minutes ago, HOrnbrod said:

You have a 91? Check for fault codes.

 

https://comancheclub.com/forums/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

 

 

I wish I could.  My check engine light bulb in the dash appears to be busted.  Another thing on my long list of repairs to make.

Does the manche have a place for a reader?  Sorry, this thing is still new to me. 

[HOrnbrod]

91's only have one O2 sensor. And yes, a damaged harness could be causing your what sounds like a misfire.

[Dzimm]

Look into the O2 sensor wire as well as your CPS.  Temperature can affect both of these sensors. 

 

I'd just replace the CPS to rule that one out.  Those have been known to test fine but still be the problem.  

[cjomanche]

2 minutes ago, HOrnbrod said:

91's only have one O2 sensor. And yes, a damaged harness could be causing your what sounds like a misfire.

Definitely a good place to start.   Thanks

[cjomanche]

2 minutes ago, Dzimm said:

Look into the O2 sensor wire as well as your CPS.  Temperature can affect both of these sensors. 

 

I'd just replace the CPS to rule that one out.  Those have been known to test fine but still be the problem.  

 

I will try to fix the damaged harness to the O2 sensor and if it doesn't work I'll do the CPS.  Never did a CPS swap but I hear it's kind of a pain. 

[HOrnbrod]

10 minutes ago, Dzimm said:

Look into the O2 sensor wire as well as your CPS.  Temperature can affect both of these sensors. 

 

I'd just replace the CPS to rule that one out.  Those have been known to test fine but still be the problem.  

 

Fix the O2 harness, then get the bulb for the CEL replaced. It's a simple matter of pulling the dash bezel, then the left dash side cover for the indicator light housing and swapping in a new bulb. Does the CEL light come on when you turn the ignition ON before starting during the bulb test? I'll bet you will find the bulb missing.

 

There's no test for the HO CPS, only a continuity test. And if if were open, it would never start. It's basically a useless test. Do get your fault code light working and this fix should be cake.

[Green Mesa XJ]

On the 91 There is a plug in the engine bay to connect a reader to, problem is it’s proprietary Chrysler requiring a special adapter. Getting a reader with the correct adapters now will probably be a pain to locate and expensive once you do. I would try to get the dash light working so you can read the codes that way.

O2 sensor could be a culprit. I’ve had bad injectors cause a brief hiccup feeling but never with the jeeps.



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[HOrnbrod]

2 minutes ago, Green Mesa XJ said:

On the 91 There is a plug in the engine bay to connect a reader to, problem is it’s proprietary Chrysler requiring a special adapter. Getting a reader with the correct adapters now will probably be a pain to locate and expensive once you do.

 

https://comancheclub.com/forums/topic/46667-actron-obd1-scanner/?hl=actron

[DesertRat1991]

34 minutes ago, cjomanche said:

Hi everyone,

...

I'm really stumped on this one.

 

Thanks

 

No reason to be stumped.  Stop buying random parts.  Fix the gauge cluster.  Have the truck tell you what's wrong. 

 

In the first 4.5mins of this vid he goes over how to remove the cluster and where the bulbs are:

 

https://www.youtube.com/watch?v=tGoSKgT2cJQ

[Green Mesa XJ]

 
https://comancheclub.com/forums/topic/46667-actron-obd1-scanner/?hl=actron

Nice. I got a Innova 3140 many years ago to read my Toyota’s computer. It came with a bunch of adapters for various OBD1 terminals, including Jeep. I was telling a friend about the kit a few years ago and discovered how much the price jumped.
From the looks of it Innova may be the same as a lot of other companies readers.


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[omega_rugal]

6 hours ago, cjomanche said:

Wouldn't it be fluttering and doing weird stuff immediately after starting the truck if it was an O2 sensor? 

 

 The ECU ignores the O2 sensor until it reaches operating temp and goes into closed loop... you may have a broken O2 and still be able to start and drive the truck..

[cjomanche]

 

23 hours ago, omega_rugal said:

 

 The ECU ignores the O2 sensor until it reaches operating temp and goes into closed loop... you may have a broken O2 and still be able to start and drive the truck..

 

That would explain why the truck drives normally until a while after it comes up to operating temp.  Good info.

 

I'm going to take an earlier suggestion and repair the gauge cluster bulbs first so I can see the information that the check engine light is giving off.