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Unread 04-03-2013, 10:07 AM   #1
Bentone
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jeep comanche running issue!

Hey all! Have a 91 Comanche with the i6 4.0. Initially the problem was a freeze plug rusted out and I was leaking antifreeze, after installing new freeze plugs and intake manifold gasket, since it was already off and easy to do, I can't get the Jeep to run again. I have spark (new plugs) , fuel and the pressure seems good, and air! It did sit for about a month before being fixed completely. Initial start up, I got it running and took a test drive, at about 1/4 throttle it started to fall on its face, got it back in the drive way and added sea foam to the tank and also replaced fuel filter thinking there was a clog. I can once in a blue moon get it started, but then it wants to fall on it's face again. Starter fluid will kick it over but it won't stay running, anyone else have any issue like this? Next thing to try would be the fuel pump to see if that's clogged. I have done some research in other threads and haven't found any real possible answers, help me!!
Thank you in advance!

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Unread 04-04-2013, 06:09 AM   #2
cruiser54
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CHANGE the fuel filter. It's a maintenance item anyway. And, it could give you a clue to what the inside of your gas tank is like.

Any chance you bumped the fuel pump ballast resistor on the driver's inner fender during your repair and unplugged it or broke it?
ballast-resistor.jpg  
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If you own a Renix Jeep, you'll want to check this out. >

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Unread 04-04-2013, 07:03 AM   #3
Bentone
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Good idea cruiser, I didn't even think about the ballast! Ill check that when I get home, and if its not that then out with the fuel pump I shall go. Also do you know if too much seafoam in a tank can foul the fuel?
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Unread 04-04-2013, 07:09 AM   #4
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I don't use seafoam so I can't answer that question for ya.

Pick up a fuel filter on the way home.
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 04-06-2013, 09:15 AM   #5
Bentone
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So the ballast is good, the fuel filter has been replaced and I still can't seem to figure out my issue! I guess I'm diving into the fuel tank now.
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Unread 04-06-2013, 09:39 AM   #6
cruiser54
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Good plan.
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 04-06-2013, 02:55 PM   #7
Bentone
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so good news! i got the jeep running today and managed to take it out and about for a test drive, it seems to be running alright. it did however backfire a little and spit and putter in second gear at about 1/4 throttle again, i did not change the fuel pump. i added some new fresh fuel to the tank thinking that the old fuel in there has probably lost all of its octane since it was sitting for about a month and a half - two months. someone did tell me that the crank position sensor could be my issue for the back fire and slight sputtering i have, also takes about 8 cranks until it turns over and starts. any inputs if the CPS could be the culprit for the sputtering and delayed start?? Much thanks in advance!!
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Unread 04-06-2013, 06:47 PM   #8
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CPS low voltage could cause the long crank times. Why don't you check it?

Renix CPS Testing and Adjusting



Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.

Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.

The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.

Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.

You should get a reading of .5 AC volts.

If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.

Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.

A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.




Revised 01-26-2013
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 04-07-2013, 10:37 AM   #9
Bentone
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Alright, so I'm testing the cps tonight and honestly most likely just going to replace it, but I did notice this morning that when the Jeep decides to cut out and backfire it always does it right after my fuel gauge goes hay wire (jumps from full to empty and throws on gas light) then the guage will level out and go back to normal which then I have no back fire. Happens everytime that gauge starts jumping, that a definite failing fuel pump? Or am I looking into something else? This is my last thing to tackle then she'll be running good!
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Unread 04-07-2013, 12:08 PM   #10
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Quote:
Originally Posted by Bentone View Post
Alright, so I'm testing the cps tonight and honestly most likely just going to replace it, but I did notice this morning that when the Jeep decides to cut out and backfire it always does it right after my fuel gauge goes hay wire (jumps from full to empty and throws on gas light) then the guage will level out and go back to normal which then I have no back fire. Happens everytime that gauge starts jumping, that a definite failing fuel pump? Or am I looking into something else? This is my last thing to tackle then she'll be running good!
Ooooh. Bad ground at the fuel pump/sending unit?

That system grounds behind the driver's side taillight.

Got a multimeter and know how to use it?
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 04-07-2013, 01:45 PM   #11
Bentone
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I do have a multimeter, but I have not used it to test if a ground is working properly before. Pretty simple?
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Unread 04-07-2013, 01:50 PM   #12
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Quote:
Originally Posted by Bentone View Post
I do have a multimeter, but I have not used it to test if a ground is working properly before. Pretty simple?
Extremely simple.



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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 04-08-2013, 08:25 PM   #13
Bentone
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So, ground was bad so replaced the entire ground wire. Cps is good, just had to clean it off (its averaging 5v) its running decent but still stalled tonight on about a 5 minute drive. Last thing I can think of is could bad gas haunt me for a while? I did not drain the tank, just added new fresh fuel. And at this point I'm starting to think that I'm just getting spurts of the bad fuel still which is causing it to stall at random. I do love my Jeeps, but they also want to make me pull my hair out!!

This is the beast I'm working with though since I haven't kept up with my profile:

forumrunner_20130408_222430.jpg
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Unread 04-08-2013, 09:03 PM   #14
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Nice.
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Unread 04-08-2013, 09:11 PM   #15
cruiser54
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Very nice. Ever snugged up your intake manifold bolts and cleaned your throttle body/IAC?

Courtesy of TJWalker:
--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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