Another xj that fires up but shuts right off

Hello everyone. Glad I found this forum. Got a problem and need some help PLEASE. Have a 90 xj, manual transmission. Bought it from a guy who couldn't get it running....figured I was smarter than him...LOL. Nope. This is what it does......turns over and fires up. then quits. Every once in awhile it may run for about 4 seconds then just like someone turns the key it shuts right down. Heres what I did/checked.

Has 39psi at rail
Has spark
replaced crank pos sensor
jumped ballast res.
cap and rotor
coil
cleaned contacts on icm
checked voltage on MAP
think i checked TPS too.
pulled fuel rail back with injectors attached and cranked motor to verify gas squirting out of injectors.

When I pull plugs after cranking, they are carboned up and dry....??

Any ideas???

Could be the ignition switch

Can't remember when they quit using the fuel pump ballast resistor but that would be a classic description of the failure mode.

He jumped the ballast...

Ignition switch, cam sensor inside of distributor (also known as stator or synch generator) and computer itself are still on the suspect list.

Alaskan89XJ said:

He jumped the ballast...

Click to expand...

I understand that but the real question is whether or not the fuel pump continues to get power. It could be a broken wire.

I recommend that the power to the fuel pump be monitored to make sure it is there after you quit cranking.

Here's something worth trying as I suspect you may have a bad relay or a poor connection at teh relays. Those 4 relays on the passenger inner fender near the ICM? Remove them all, clean the contacts with a wire brush, spray out their receptacles and reinstall them.

Check the fuel pressure regulator for gas in the vacuum line, that floods the engine if the diaphragm leaks.

Pressure should be 31-39 (mine is 29-39), PSI, low pressure with the vacuum line attached, high with it disconnected. Try starting it with the vacuum hose to the FPR disconnected.

And verify fuel pressure with a gauge is still there when it dies (Another way to do what Old_man suggested).

if u havent got it running yet it might have an alarm...jus put the key in the door and unlock relock and unlock again then try to start it