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Shuts Off when warmed up.


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Hey everybody I’ve got a 1989 Jeep Comanche with a 7 inch BDS lifT kit. Recently this year it decides to shut off when it warms up which is about 10 minutes.The truck will turn back over after it sits for a good 5 minutes  Over the years of owning it I’ve replaced the CPS sensor, O2 sensor, refreshed grounds, cables, EGR valve, and replaced fuel pump.. list goes out. Reaching out to you guys in hopes to get my Wheelin Machine going again! Thnx 

46C8E08C-0541-4044-BBD7-0EBD9E5624E8.jpeg

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12 minutes ago, BcBrunner said:

Ok I was thinking he same too, I’ve got a fuel pressure gauge hooked up reading 35 at idle. While it’s running it will start to stumble but if I step on the gas it’ll power through it and not stall. Maybe weak fuel pump

https://comancheclub.com/topic/56190-grounds-and-general-wiring/

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My guess is that the CPS is getting heat soaked. Run two tests after the vehicle has been sitting overnight. Before starting it, test the CPS resistance (ohms). Then crank it over with the CPS disconnected and check the voltage it produces. Write down what you get.

 

Now ... start it up and let it run until it quits. Repeat the tests. Write down the results.

 

Compare. If the results go out-of-spec when hot, you found the problem.

 

How to test: 

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

 

Scroll to end for CPS

 

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Quick and dirty. Move the relays down one spot for testing purposes. Have you ever done the connector refreshing in the engine bay? 

 

Jump the ballast resistor on the left inner fender. 

 

Clean your C101 connector.

The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of more than 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.

That said, the cleaning described below is a real MUST DO right off the bat for any new-to-you Jeep. But, I strongly advocate eliminating the C101 at some point by following the procedure with photos and video in Tip 27. Soldering skills are required and it takes about an hour and a half.

The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the ¼” bolt and pull the halves apart. You will find the connector is packed with a black tar-like substance which has hardened over time.

C101 connectorTake a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.C101 connector

If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.

If you wish to eliminate this connector entirely (highly recommended), see Tip #27 – C101 Elimination

 

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together.

There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.Ballast Resistor

 

renix relay center.jpg

Ballast Resistor.JPG

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Hey back working on the MJ, tested my CPS cold and it read 208-218 , tested the COS after it stalls and it read 209-222. When I plug and unplug theCPS  sensor it seems to start back up for a few moments and die again.. Thanks for the help guys 

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8 minutes ago, BcBrunner said:

Hey back working on the MJ, tested my CPS cold and it read 208-218 , tested the COS after it stalls and it read 209-222. When I plug and unplug theCPS  sensor it seems to start back up for a few moments and die again.. Thanks for the help guys 

 

Check the output voltage on it while cracking.  The resistance check doesn't seem to have much validity.

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4 minutes ago, BcBrunner said:

When i tested the CPS those numbers are from when I was cranking on it

 

 

What is the meter set to?  Ohms?  Because that's in the correct range for the resistance test, which as I said, does not have much validity.

 

You need to set the meter to A/C volts and check it while it is being cranked.

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1 hour ago, DirtyComanche said:

 

What is the meter set to?  Ohms?  Because that's in the correct range for the resistance test, which as I said, does not have much validity.

 

You need to set the meter to A/C volts and check it while it is being cranked.

 

Agreed. The factory manual calls for the resistance (ohms) test, but the voltage test is what tells the tale. The fact that unplugging and reconnecting got a start, even momentary, strongly suggests that the CPS is your problem.

 

Has your vehicle had the TSB modification to bypass the main harness and connect the CPS directly to the ECU? That eliminates a lot of wire and reduces voltage drop -- which a tiny voltage like that can ill afford.

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54 minutes ago, BcBrunner said:

I’m located in Kamloops BC. I’m getting a .1 ACV reading while cranking on the CPS

 

That's too low.  Try your other one.  Most of the aftermarket sensors are junk and don't last long, which is really annoying.

 

I'm a handful of hours north in Prince George (well, I live there, I'm not there right now).  Good to see there's another BC member on here. :waving:

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35 minutes ago, DirtyComanche said:

 

That's too low.  Try your other one.  Most of the aftermarket sensors are junk and don't last long, which is really annoying.

 

I'm a handful of hours north in Prince George (well, I live there, I'm not there right now).  Good to see there's another BC member on here. :waving:

Oh hey right on!  Buddy of mine was just down visiting from Prince George! The smoke down here is worse than last year. So installed the newer looking cps and it’s reading .1-.2. Got steady fuel pressure when it stalls, it’s really got me stumped and it’s been like this a while.

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You could try Cruiser's tip of slightly enlarging the mounting holes on the CPS and pushing it closer to the flywheel.  http://cruiser54.com/?p=50

 

If it's .1-.2V it's really unlikely to actually start.  Of course I'm not sure how decent your multimeter is.  But it would appear to me that your spare CPS is just as bad as the other one was.

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43 minutes ago, BcBrunner said:

So installed the newer looking cps and it’s reading .1-.2. Got steady fuel pressure when it stalls, it’s really got me stumped and it’s been like this a while.

 

Too low. You need .5 to .8 volts.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm  (Scroll to the bottom)

 

Note that the section on the TPS gives you the TSB for upgrading the CPS harness. That's a good idea in any case, but if you're that bad right off the CPS plug, improving the harness can't make .1 volts into .5 volts.

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22 hours ago, Eagle said:

 

Too low. You need .5 to .8 volts.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm  (Scroll to the bottom)

 

Note that the section on the TPS gives you the TSB for upgrading the CPS harness. That's a good idea in any case, but if you're that bad right off the CPS plug, improving the harness can't make .1 volts into .5 volts.

Alright I’ll start with a new sensor and see what that does, thanks for the help.

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