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1990 Jeep Cherokee woes

Old 06-28-2010, 10:00 AM
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Angry 1990 Jeep Cherokee woes

Hello,

I have a 1990 jeep cherokee that wont stay running. It will only stay running if you hold the key in the start position. It started doing this after big rain storms and would get progressively better as things dried out. A friend of mine said the culprit was one of two computer components, the main on-board computer, and another he refereed to as "The Brain" which apparently is located under the dash.


Can anyone confirm this is the case.

Also, can anyone help me find a pigtail for my rear lights on my Jeep?
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Old 06-28-2010, 10:03 AM
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You can get the wireing you need from a junk yard.
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Old 06-28-2010, 10:12 AM
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Originally Posted by scarmullet View Post
Hello,

I have a 1990 jeep cherokee that wont stay running. It will only stay running if you hold the key in the start position. It started doing this after big rain storms and would get progressively better as things dried out. A friend of mine said the culprit was one of two computer components, the main on-board computer, and another he refereed to as "The Brain" which apparently is located under the dash.


Can anyone confirm this is the case.

Also, can anyone help me find a pigtail for my rear lights on my Jeep?
If the connections got wet they might be corroded. The stuff I use for connectors and connections is called deoxit. http://www.caig.com/ WD-40 works okay but not nearly as well.

Start by disconnecting and cleaning the battery terminals. With the battery still disconnected clean all the connectors under the hood you possibly can including the ECU connectors.



Are you getting a check engine light or any codes? It also may be a faulty sensor.
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Old 06-28-2010, 10:21 AM
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No Check Engine lights were observed
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Old 06-28-2010, 02:10 PM
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if it dies after you release the key and only runs in the start postion it should be your ignition switch itself.
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Old 06-28-2010, 02:47 PM
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this happened on my friends xj i believe he has a 90 or 91. what happened was that module that the fuel pump hooks into on the fender by the air box was bad. how he fixed it was he actually wired his fuel pump to a switch. it works great for him and it makes for a good anti theft device
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Old 06-28-2010, 06:42 PM
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Your 1990 is pre-OBD - there's no functioning CEL/MIL. There is a window for one, but there should not be a bulb behind it (and putting one in there won't make it work, either. There's no circuit for it...)

The main engine control computer is under the IP, near you right knee. But, I doubt that's the problem.

Lift your hood, and check at the driver's side in/near the front corner. You should see a smallish (1/2"x1/2"x4") ceramic dingus held down with a single screw, and two wires connected to it. This is your fuel pump ballast resistor. Here's what I want you to do:

- Disconnect the two wires.
- Connect the two wires to each other. You may use a short jumper lead (use male 1/4" spade lugs, preferably shrouded, and 12-14AWG wire) or just clip them together (make sure they - and the clip - won't touch the chassis!) You can also remove the wire from one end of the ceramic piece and clip it to the other wire while it's still connected - this will help locate the thing.
- Start the engine. It's rather likely it will now start and stay running.

If this works, you have two options. 1) Replace the ceramic part. Take the old one in with you, and ask for a "Ballast Resistor" with the same nominal resistance (it's stamped on one of the spade terminals, up near the ceramic body.) They can either look it up by application or by nominal resistance (take your ohmmeter, pull the new resistor out of the box, and test it. They're rarely defective, but it's incredibly frustrating when they are.)

2) Make the bypass permanent. Use 12-14AWG wire, 1/4" male spade lugs, and either use shrouded terminals or cover the connexions with heavy-duty heat shrink tubing. Remove the resistor, don't remove the resistor - doesn't matter.

The ballast resistor was added to keep fuel pump motor noise down. This was a voluntary recall for 1987 and early 1988, and it was a factory part after mid-1988 (probably after ChryCo took over production in August.) My 1987 never had one, and it worked fine. My 1988 didn't have one - works fine. My wife's 1990 had one, it failed, and I bypassed it - she never noticed the noise. Problem solved, either way. I think it was added because people were buying Jeeps that shouldn't be driving them (if you want something nice and quiet, buy a Caddy. This is a truck...) but what do I know?
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Old 06-28-2010, 07:17 PM
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I'll be sure to try that, the Jeep is parked at my sisters house where it broke down and I haven't been able to pull it home.
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Old 06-29-2010, 11:09 PM
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My Brother in law replaced the ballast resistor and it still wont stay running.
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Old 07-05-2010, 05:16 PM
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Hey, Just wanted to let you know, I put the jeep on a trailer and took it down to a mechanic. He figured it out right away, the relays were rusted through.
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