97XJ 406

i have spent the last three days reading a bunch of forums trying to figure this out. i have a 1990 comanche 4.0 5 speed. i went to the store the other day and when i came out the jeep wouldn't start. got it home and the first thing i did was replaced the cps with a new one. when that didn't work i changed the coil with a known good one, still no luck. then i cleaned every ground on the motor, still nothing. finally i decided to swap in a different ecu and finally the jeep decided to run, i drove it around for a hour or so and came home. when i went to leave the same thing happened no spark. i'm getting pretty frustrated and would really like to get this jeep back on the road. any advice is appreciated. thanks

88whitecomanche

So it's crankIng and no spark?
Might be fuel...double check the ground behind the left tail light and switch around the relays to see if you have an malfunctioning one...

cruiser54

Testing things would be good.

+1000 on the taillight ground.

Ever been to www.cruiser54.com?

do Tips 1,3,4, and 5 for sure.

zebvance

Just cause you replaced the CPS it doesn't mean its good. Alot of the Cps from the local parts store are poor quality and have a large failure rate right out of the box. I would do cruisers tip on testing it to make sure its putting out the right parameters before you spend any more money on parts. for sensors you should always go OEM.....

97XJ 406

i've done tips 1,3,4, and 5 also tested the cps and got a reading of .3 ac volts.

cruiser54

.3 is low.

Look around the area where the CPS plugs in. See an identical plug with same colored wires but not plugged in?

97XJ 406

i am not seeing any other plugs that look similar? and that cps was purchased through oriellys

97XJ 406

i just swapped in a third ecu and now have spark again.

cruiser54

Well, that's good.

The factory had a service bulletin to replace the harness between the CPS and eCU. Part of the instructions stated that the old connector should be removed. some techs didn't do that...

Hence, some poor sap like you or me plugs a new cPS into dead harness.

97XJ 406

took apart two of the ecu's and this is what i found on both. something is shorting it out. not sure what but i definitely do not want to burn up another one.

cruiser54

Can you trace that to a pin on the ECU?

I have a pin-out for it.

97XJ 406

from what i can tell it looks like its going to D8

cruiser54

Here:

cruiser54

Take a look where the injector harness transitions from the front of the intake manifold down to the CTS, knock sensor and 02 sensor.

97XJ 406

i disconnected everything down there and pulled the harness up. took back the sheathing around the wiring and inspected them up to where they meet the injectors and did not see anything wrong. other then the knock sensor wiring has three wires and one of them was completely bare the whole way.