Chrustoph Randall Ash

is the cause for my jeep starting and then dying when the key is relased from the start position to the "run" position. Any help with what each wire does and which colors correspond to them would be a huge help. Also any other sugestions to what may be the reason for why the jeep starts and then dies right away would be greatly appriciated. Thank you. Im getting fuel and spark vacuum lines are good

xjgerry

I recently read about a starting circuit resistor that in the old dodges did the same thing. Not sure of the proper name and it should be on the firewall, if applicable. best of luck.
Maybe when the new cps arrives the sun will shine agaain in my jeepdream.

dave1123

Obviously your 90 doesn't have chip-key security, so that was my first thought. Other than what was already posted, I haven't a clue.

fb97xj1

Fuel ballast resistor acting up, perhaps? I read of that causing issues similar to this somewhere before. PM Cruiser54, he knows more about that little thing than i.

lawsoncl

It's the white ceramic thing on the front drivers fender area. Bypass it and see of the problem goes away, then just leave it bypassed.

papablista

Ditto had an old cuda same problem, just jump it with a wire and you will know.

dave1123

That ballast resistor is there for a purpose. The coil is supplied with a full 12v when cranking, then is reduced to 9v when running so the coil doesn't overheat. Old style metal can coils will leak oil and plastic ones will crack if overheated. The switching is done in the ignition switch.

lawsoncl

No, you're thinking about old school points ignition systems. It's not an issue on cars with electronic ignition where the computer controls the dwell time on the coil. The fuel pump ballast resistor was added to the Cherokees to reduce the voltage to the fuel pump once it started to address noise complaints. It's not used on later models and lots of people have eliminated it with no ill effect aside from a little bit more noise -- typically after the resistor crumbled due to age.

papablista

Yes , It does have a purpose, I by no means meant to imply leaving a jump wire on it ( I should have clarified that ) just long enough to see if it was the problem, Those ballast are cheap.

dave1123

Sorry, you're talking to a dinosaur. I'm old enough to have worked on 6v systems! Yes, any resistor can go bad with age, especially wire ones. After all, a resistor is a heat sink and bound to fail. I wasn't aware the was one on the fuel pump.

lawsoncl

Making me feel young, and I started on TRS-80 computers.

A nice video for the OP.

Only2Doors

I have a 95 but when i had this happen to me i searched through all my grounds and looked into all kinds of stuff, but it beyond doubt was my ignition switch. Are you still having this issue ? I don't know what your wiring looks like but it would be easy to figure out by hotwiring your engine control, in mine it's the dark blue wire going into the 7 pin connector, to the red 12v supply, then take a small piece of wire and bridge supply to the starter momentarily, (yellow wire on mine) if it doesn't die without removing the jumper to engine control then its your ignition switch, if it fails to run still connected to the engine control circuit then i would start looking elsewhere reasonably. Dont know if this is still going on for you but if it is I hope this helps.