1988 cherokee idle issues
06-08-2012 | 05:22 PM
#31
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by cruiser54
Classic symptoms of poor crimps in the ground circuit that includes not only the TPS, but the CTS, IAT, and MAP. Seen it many times before. Whaddya think your ECU thinks of those signals? This can be fixed quite easily.
You used this test, right?
Cruiser's Renix Sensor Ground Test
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 05/03/2012
You used this test, right?
Cruiser's Renix Sensor Ground Test
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 05/03/2012
I also decided to look inside the c101 and holy hell there is so much gummed up black stuff in there its crazy. I'm currently scraping as much of it out as I can. I will not be able to completely do it right now because I don't have Carb cleaner or a small pick. I'm just useing my smallest screw driver. My wife is at work with my other xj so no parts sstore run for the fluids till later.
06-08-2012 | 05:24 PM
#32
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Yes, in my thread I posted a picture of my meelter in the setting that I used. It was set at 200. Please look at that just to verify that it was correct.
I also decided to look inside the c101 and holy hell there is so much gummed up black stuff in there its crazy. I'm currently scraping as much of it out as I can. I will not be able to completely do it right now because I don't have Carb cleaner or a small pick. I'm just useing my smallest screw driver. My wife is at work with my other xj so no parts sstore run for the fluids till later.
I also decided to look inside the c101 and holy hell there is so much gummed up black stuff in there its crazy. I'm currently scraping as much of it out as I can. I will not be able to completely do it right now because I don't have Carb cleaner or a small pick. I'm just useing my smallest screw driver. My wife is at work with my other xj so no parts sstore run for the fluids till later.
If what you're working on has a C101, I would keep cleaning with whatever you've got. Neat stuff in those things, huh?
06-08-2012 | 05:28 PM
#33
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by cruiser54
What year are you working on? It says 1990 in your avatar.
If what you're working on has a C101, I would keep cleaning with whatever you've got. Neat stuff in those things, huh?
06-08-2012 | 05:30 PM
#34
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I suspect you'll end up doing the procedure I outlined to fix it right. The C101 cleaning is never a bad idea. The sensor ground circuit isn't the only one that can be compromised. Your test results mimic exactly the ones on my wife's 88. That's where the sensor ground upgrade came from......
06-08-2012 | 05:36 PM
#35
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by cruiser54
I suspect you'll end up doing the procedure I outlined to fix it right. The C101 cleaning is never a bad idea. The sensor ground circuit isn't the only one that can be compromised. Your test results mimic exactly the ones on my wife's 88. That's where the sensor ground upgrade came from......
06-08-2012 | 05:40 PM
#36
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Plan on doing the wiring repair BTW.
06-08-2012 | 05:44 PM
#37
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by cruiser54
Jeep is responsible for the road tar in the C101. It's nice living in Prescott. Been here 33 years.
Plan on doing the wiring repair BTW.
06-08-2012 | 05:48 PM
#39
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
[QUOTE=DESERTXJ206;1825117]What wireing repair are you talking? Where the c101 gets cut out completely? IV heard of people doing that, in just worried my soldering skills wont due for that big of a project.
The one I PMed you.
The one I PMed you.
06-08-2012 | 05:50 PM
#41
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Normal. Those things gave us fits when the Jeeps were new. They didn't get better with age, did they?
Just getting the sensor ground circuit repaired and bypassing teh C101 with it is simple. Here's the same instructions I PMed you.
Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.
Where it's connector plugs into the harness you will see that one of the wires on the harness side is brown with a white stripe. Follow the brown with white stripe wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires with duct tape over them. They're from the TPS and the CTS. The 3 wires will be spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.
Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires with duct tape over them. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.
You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.
Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.
Zip-tie up your new sensor loom to allow for engine movement. I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.
Revised 03-09-12
Just getting the sensor ground circuit repaired and bypassing teh C101 with it is simple. Here's the same instructions I PMed you.
Find your Intake Air Temp sensor. It's the sensor just to the rear of the throttle body, has 2 wires, and screws into the intake manifold.
Where it's connector plugs into the harness you will see that one of the wires on the harness side is brown with a white stripe. Follow the brown with white stripe wire back into the harness. You'll have to open up the split-loom plastic sheathing to follow it. It will come to a splice with 2 other brown with white wires with duct tape over them. They're from the TPS and the CTS. The 3 wires will be spliced to a single wire headed toward the C101 connector if you have an 87 or 88. If you have an 89 or 90, you do not have the C101 bulkhead connector.
Now go to the MAP sensor. Follow the brown with white wire into the harness from there. You will find a splice with 2 more brown with white wires with duct tape over them. At the splice you will find the 3 wires connected to a single brown with white wire going toward the C101, or just along the firewall towards the engine if you have an 89 or 90. Along with the MAP sensor that you traced, they are the ECU sensor ground port and the diagnostic connector on the passenger inner fender.
You now have 2 sets of 3 brown with white wires, one near the firewall and one near the engine.
Cut the splices out of each set of wires eliminating not only the crappy factory splices, but also the single wire between them. Bring both sets of 3 wires together. Solder the 2 sets of wires together and insulate them properly with tape or shrink tubing.
Zip-tie up your new sensor loom to allow for engine movement. I prefer to cover it with some new split-loom or wrap it neatly with electrical tape when done.
Revised 03-09-12
06-08-2012 | 05:52 PM
#42
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
06-08-2012 | 05:58 PM
#43
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Yeah I could swear I have seen somewhere where people have conpletly cut out the c101 and soldered all the wires together if I am not mistaken. I could be wrong.
06-08-2012 | 06:00 PM
#44
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Oh, it can be done and I think it's a great idea. But, as far as the sensor ground circuit goes, it has multiple bad crimps in it before it goes to the C101 and some more on the other side of the C101.
06-08-2012 | 06:07 PM
#45
Thread Starter
CF Veteran
Joined: May 2011
Posts: 1,458
Likes: 2
From: Glendale,Az
Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by cruiser54
Oh, it can be done and I think it's a great idea. But, as far as the sensor ground circuit goes, it has multiple bad crimps in it before it goes to the C101 and some more on the other side of the C101.