Starts then immediately dies

1990 XJ 4.0l I6 automatic. My jeep starts just fine then cuts out and dies almost right away. XIf I keep the key turned it stays running. XI replaced the ignition switch and the cps. XI dont think its the anti-theft feature(i have tried everything since i dont have the key) I have voltage to the ignition switch in the 'on' position. XMy fuel pump ballast resistor was smoking so it is bypassed(just ran the wires together). When the key was turned to the 'on' position the wires for the ballast resistor tested at .01. When it was turned to the 'start' position it topped out at about 8. XAll my relays appear to be just fine. XI tried swapping the fuel pump relay for a new one and nothing. I now have my fuel pump attached to a battery outside the jeep. I'm not that good with wiring and I'm kind of just stuck at this point. The next thing I'm going to do is take off the throttle body and thoroughly clean it. Please somebody know what's wrong with it

Key tumbler mechanism may be bad.

Gotta look at the fact that it stays running when you keep the key turned to the full START position.

If you keep it running till it warms up will it stay running? If so it would probably be your Idle Air Control Valve. Its not an uncommon failure.

yardape said:

If you keep it running till it warms up will it stay running? If so it would probably be your Idle Air Control Valve. Its not an uncommon failure.

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Wouldn't it be bad for my starter to try that? I'd rather not burn up a new starter

Maybe I didn't understand. If you start it can you keep it running by revving the engine?

yardape said:

Maybe I didn't understand. If you start it can you keep it running by revving the engine?

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No. The engine dies right after releasing the key no matter what

birchlakeXJ said:

Key tumbler mechanism may be bad.

Gotta look at the fact that it stays running when you keep the key turned to the full START position.

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Is the key tumbler the ignition cylinder?

The key tumbler is the part of the ignition switch that the
key fits in. It's separate from the actual switch, which is
on the left side of the steering column under the dash.
There's a rod/linkage running to it from the key tumbler.

This sounds like a bad electrical ignition switch; the one
under the dash. Is that the one you replaced?

So it is the ignition cylinder. I'm Gonna try hot wiring it tomorrow to bypass the ignition cylinder..maybe that is the problem. And i know it sounds like classic symptoms of an ignition switch or ballast resistor failure but its not. I replaced the ignition switch and bypassed the ballast resistor.