Cherokee Dies at idle

bremery88 · #1 (**permalink**) 07-20-2003, 07:00 PM

Hello,

This is my situation.... My '88 cherokee died in my driveway. It ran perfect before with no signs of failure. I tracked the problem down to the CPS sensor and replaced it. That allowed me to start the engine, and after 10 minutes of idling it dies. This did not happen before. In the process of doing the CPS I replaced the distributor cap, rotor, spark plugs and wires. Everything checks out fine will all the new stuff. I also tested the ICM and coil and they checked out ok. All of the vaccum lines seem to be in order, and hooked up correctly.

Does anybody have any clue why my cherokee dies at idle (1000 rpm)????

Thanks,

Brandon [img]modules/phpBB_14/images/smiles/icon_confused.gif[/img] [addsig]

MudderChuck · #2 (**permalink**) 07-20-2003, 07:00 PM

A stuck open EGR valve will do it (so will a stuck open PVC valve if you have one). Did you unhook the battery (for awhile) and reset your computer (might still be operating in trouble mode)? A fuel pressure test might also be helpful. Check the vacumn lines at the air box, if I remember correctly there is a low flow sensor (switch) in there, to richen the mixture a touch. And there is a multi vacumn line holder on the top front of the valve cover where the vacumn lines often rub through.

I´ve got a Haynes around someplace, I´ll take a look and get back to you.[addsig]

bremery88 · #3 (**permalink**) 07-20-2003, 07:00 PM

I have both the haynes and Chilton's manuals, and they really have been no help to this situation. I did a compression test and a fuel pressure test and everything checks out fine.. All the vacuum lines look good (no leaks as far as I can see) I checked the CCV valve and it was perfect. I started to check the PCV valve, and it seems ok, but the manual said to shake the unit and listen for a rattle.

The thing that is drving me crazy is that it drove perfect before it died... no sings of any problems. I know things can fail (like how the cps failed with no warning) Also if anything the engine is running lean, not rich. At least that what the old spark plugs suggest.

I'll disconnect the battery and let it sit for a while....

Thanks,

I'll report any findings as they come...[addsig]

MudderChuck · #4 (**permalink**) 07-20-2003, 07:00 PM

A lot of people have mentioned a plugged cat. I´ve always managed to change them out when they start to smell or the undercoating starts to cook.

A manifold vacumn test might tell you something. If I remember correctly (check the book) between 9 and 14 inches of vacumn. Low manifold vacumn is supossed to be an indicator of plugged exhaust.

A faulty 02 sensor is always suspect. But I´ve nenver had one go bad in the Jeep. I changed them at around 60-80 miles wether it was bad or not.

I´ve found many plugged vacumn lines in the wifes 87 over the years.

Good luck. Bye the way, check the plug under the distributor for chaffing.[addsig]

bremery88 · #5 (**permalink**) 07-20-2003, 07:00 PM

Update: The Jeep will run fine untill the water temperature reaches its normal operating temperature, then it will start to sputter and then die. I have not been able to work on it due to the fact that we got 12" of snow last night and this morning.

I do not think the cat is plugged... Its fairly new, and I've had the exhaust off a few time and everything seemed ok in there...

I am still looking into a manifold vacuum test....[addsig]

MudderChuck · #6 (**permalink**) 07-20-2003, 07:00 PM

Manifold vacumn gauge is a nice addition to the old tool box and doesn´t really cost much.

A leaky head gasket will usually cause sputtering as soon as the motor temp. goes up enough to build some pressure. Usual indications are rust colored plugs. Coolant colored or greasing feeling moisture coming out of the exhaust (some moisture is normal usually clear and oderless). Bubbles or foam in the coolant system, excessive coolant system pressure (hoses get really hard and swell).

Most of the sensor and regulatory systems kick in around 140 F. Before that most engine functions are pre-programmed. Disconnecting the 02 sensor or the temp. switch and/or the temp. sensor and checking for a change in driveability can be helpful in narrowing down the problem.

After test, disconnect battery to remove trouble codes.[addsig]

bremery88 · #7 (**permalink**) 07-20-2003, 07:00 PM

This is what I found out today. If I disconnect the vacuum connector where many of the line go, the jeep idles like it it supposed too. (Seems to run great when it has a vacuum leak). I bought a pressure tester and tested the EGR systems and it seems to be ok, but I am going to replace the EGR anyways because the results did not prove that it was 100% good. If that does not solve the problem I will go from there...

I also blew out all the vacuum lines...[addsig]

bremery88 · #8 (**permalink**) 07-20-2003, 07:00 PM

This is what I found out today. If I disconnect the vacuum connector where many of the line go, the jeep idles like it it supposed too. (Seems to run great when it has a vacuum leak). I bought a pressure tester and tested the EGR systems and it seems to be ok, but I am going to replace the EGR anyways because the results did not prove that it was 100% good. If that does not solve the problem I will go from there...

I also blew out all the vacuum lines...[addsig]

MudderChuck · #9 (**permalink**) 07-20-2003, 07:00 PM

By creating a vacumn leak, you probably fooled the 02 sensor into providing more fuel. Is it possible your air filter, is oil soaked or there is another blockage in the intake system?

By removing the vacumn connector, it´s also possible (in some vehicles) to make the computer switch from closed loop (sensor controlled functions) to open loop (pre-programmed functions) like I was thinking by disconnecting the 02 sensor or the temp. switch. Could be a faulty sensor, most commonly mentioned are mass air flow or 02.

I remember reading once that a rip or tear in the rubber intake from the air box to the intake manifold will cause erratic idle. In some models, at the opening for the intake manifold there is a spring loaded lid, that has been know to stick.

You can get your fingers in the back of the EGR and test for sticking (be careful not to tear the diaphram). Push the diaphram with your little finger in, it´s spring loaded to return. Should be a good 1/4 to 3/8´s inch movement.[addsig]