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Engine Starts, then Dies When I Let Go Of The Key

AMCXJ88

NAXJA Forum User
Hey guys. I have an 88 XJ 4.0 Automatic with 201,000 miles. It will start and run until I let go of the key. As long as I hold the key in the start position, the engine will stay running, can be revved, etc. Once the key is let go, it dies instantly.

I have replaced the following in the past 2 days:

The fuel pump with an OEM pump that tested good.
The Ignition switch at the base of the steering column.
Bypassed the Ballast Resistor on the drivers side engine bay.
Swapped around the 4 relays next to the battery.


After all that I have listed above, Still have the same problem. No broken fusible links noticeable, and the starter relay under the relay panel cover looks in good shape with no burned wires going to it. Crank Sensor, TPS, and IAC are all about a year old.

I am at a complete loss. This all happened out of the blue. Any help would be great. Thanks.
 
First, reconnect the ballast resistor or you will burn out the ignition coil...

Do you have a FSM or at least some source for a schematic? You need to verify, with a meter, that you have the "run" voltages present at all of the locations it is required to be. Sound like a no volt condition on the "run" lines.
 
Pin 5 at the diagnostic connector is power to the fuel pump relay, should have power all the time. It comes from a fusible link.
Pin 6 is power out of the fuel pump pump relay when it is energized.

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Sounds like you have have bad fusible link or maybe a broken or open wire. I'd do some testing before I swapped any more parts.

You can also test at the 30 pin at the fuel pump relay socket, same wire as the number 5 pin at the diagnostic tester.

The ballast resistor in the *Renix* is for the fuel pump, not the coil or ignition module.
 
So should I take a multimeter to pin 5 & ground and make sure theres power? Same thing with pin 6? Then check for broken wires?

Thanks for the help so far!
 
First, reconnect the ballast resistor or you will burn out the ignition coil...

Do you have a FSM or at least some source for a schematic? You need to verify, with a meter, that you have the "run" voltages present at all of the locations it is required to be. Sound like a no volt condition on the "run" lines.
Ballast resistor for XJ is for the fuel pump, not the ignition, only to quiet the buzz, and taking it out poses no danger at all. Many years do without it.
 
So should I take a multimeter to pin 5 & ground and make sure theres power? Same thing with pin 6? Then check for broken wires?

Thanks for the help so far!
Pin 5 should have constant power, pin 6 should have power while the engine is running. I'm not exactly sure when the fuel pump relay closes, never had occasion to test that..
 
My take on it is, all vehicles have weak points, off roading tends to break stuff even quicker. Best to learn in the driveway than when your up to your buttcheeks in mud.
Another alternative is to find a girlfriend who is a mechanic and let her fix it.:helpme:
What did you ever find out about whether the fuel pump relay is closing or not?
This is a learning curve for me too, a little feed back can be helpful.
 
Even better if the girl friend likes mud!!!! :kissyou:

But

"In other words this Jeep is screwed. I will be either selling it or junking it ASAP"


With that kind of attitude, you have no business owning a 200,000 mile, 88 jeep!!!!

Sell it to some one with patience, and a little know how, so they can fix it with $1 worth of wire and a little careful troubleshooting.

I would run a jumper wire from the battery to the ballast resistor connector that runs directly to the fuel pump, and start it. If it keeps running, your problem is the power feed to the ballast resistor. In start mode the battery connects directly to the fuel pump, bypassing the ballast resistor, then after starting, power to the fuel pump switches to the wires and the ballast resistor path. I would start there.
 
This should be easy to find, but you need a meter. Rat Shack has them for $20.00... You are missing a run signal. Either fuel or ignition... Bypassing is an acceptable practice but, using a meter can tell you if it is a no volt or a low volt condition.

Using the meter, verify your battery voltage. The meter needs to be set to read DC voltage.

With the ignition switch in the run position, put the negative lead of the meter on the nearest ground point and then touch both sides of the ballast (one at a time) and look for voltage. It will battery on one side and slightly less on the other.

Again with the ignition switch in the run position, verify that the ignition coil has battery voltage to it.

The ignition switch in the start position has the run signals hot, the accessory signals cold (that is why your radio drops out) and, of course, fires the starter.

In the run position, both the run and accessory signals are hot.

In accessory, the ignition and fuel are shut down.

Buy the meter...
 
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