Question about 1990 Jeep Comanche

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Truck will start but when you release the key switch it stops

I first thought this was a fuel system problem, but after changing out the pump, fuel filter and the pressure regulator, I still had the same issue. I stumbled on to this only because I held the key switch in the start position a little to long. The truck will run if The switch is held into the start position, but as soon as you let the key switch return to the run position it stops. I have since changed the Ignition Switch (tilt wheel), key lock cylinder and the Ignition control module. After doing each one I had the same result. I also had a spare control unit and swapped them out and had the same result.
any help??

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  • ketch13 Nov 04, 2008

    I guess it would help if I told you it was a 1990 Jeep Comanche 4wd 4.0 inline 6


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One of the relays (black plug in boxes) beside the starter coil are defective or loose

Posted on Feb 02, 2009

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This could be several things. Before you changed the fuel pump, you should have checked to see if the problem is electrical, or mechanical first.

One of the first things you needed to do, was to check the fuel rail to see if you had the proper fuel pressure. This would have saved you a bunch if you had the proper pressure at the rail. You can purchase an inexpensive fuel pressure testor at Harbor Freight Tools.

The next thing you need to do is to find out if you have power at the spark plugs. If not, then you need to check out the distributor cap, rotor, plugs and plug wires. If these all are ok, then you need to check the ignition coil.

From there, if all seems ok, then you could have any one of several sensors bad, or a bad computer.

If you changed out the fuel pump yourself, then you must have some mehanical ability,

Posted on Nov 04, 2008

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You need a new ballast resistor

Posted on Nov 04, 2008

  • paul erickson
    paul erickson Nov 04, 2008

    sorry such a quick post

    just wanted to get to the point of what is wrong

    to put you in the mindset of what is going on in your engine compartment and why.

    as you probily know that a resistor cuts back the positive voltage and this is how th jeep runs when the key is in the run position.

    but when you need to start the engine it need more voltage and this is why the engine will run in the start position

    i hope this helps

    just call your local parts store and get a ballast resistor for your truck and install and you should be back on the road .

    good luck



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