4.0 Starting Problems.

Air = OK

Fuel = OK

Spark = NOT OK

Heres the deal.

The jeep ran fine after I bought it. Occasionally, It would just choose not to start. If i let it sit for 24-48 hours It would usually crank right up. Ive waited 48 and still no crank.

It cranks fine, just will not turn over.

I tested the coil and found it was not giving off any spark. Replaced and still no spark.

Got out the trusty test light, and tested the connectors first. Power and Ground on the bigger plug are fine. The smaller plug with one yellow wire coming out of it gives a really weak signal on power and ground. In case this sounds confusing, I ground the test light and put the tip to the prong and a dull red light shows. I power the test light and a dull green light shows.

Bottom line, the coil is not firing. All the wires seem to be working fine except the fishy yellow one, (unless its accesory and it supposed to do that?)

Could this be caused by a bad sensor? Cam/Crank etc?

What do you guys think the problem is?

-Wade

check the obvious things first- cap and rotor, battery voltage then i would think the cps sensor is to blame. search for it, its notorious for causing no starts.

pete

Well it couldnt be the cap and rotor, the loss of spark is at/before the coil.

I did some searching, took all the relays off, dusted them off, jiggled the ground wire (braided) on the firewall, and it cranked right up.

I started working on other things, went back to start it with another failure. Tried the same thing again, jiggle ground, clean relays, still nothing...

so tired, frustrated and confused. I have 2 damn cars and they are both down!

THe cps sensor wire is in that general vicinity (wear the ground strap is) ? It goes down below the engine on the driver side to the tranny. I would check its wiring and disconnect it and try again- i really think that might be the prob.

pete

Yes, that is textbook CPS failure. Search here for methods on how to troubleshoot it..

I took all the relays off, brushed them off, put them back on and it fired right up. I killed it, let it sit until I was ready to go home and it wouldnt start again. I cleaned the relays again, wouldnt start.

Ill try the CPS. CPS being crank position sensor? I tried First Call/Oriellys and they said they do not carry it at all. Is this a "chrysler house" part only?

DC will have the part, but any parts store should have access to a CPS. Some prefer the dealer parts. Very important part. Go to your favorite auto store online (napa.com, autozone.com, etc) and compare the online prices.

Sounds like CPS, can be intermittent.

Fixed the bitch.

Starts great. Rusty's 4.5/Bilstiens/33's/Custom Subframes/Plasma Cutter next weekend.

thanks for all the help guys.

wadewells said:

Fixed the bitch.

Starts great. Rusty's 4.5/Bilstiens/33's/Custom Subframes/Plasma Cutter next weekend.

thanks for all the help guys.

Click to expand...

Hey you can't do that. what did you find?

langer1 said:

Hey you can't do that. what did you find?

Click to expand...

CPS Sensor. 30 bucks.

Had to drop the tranny crossmember and take the shifter linkage off to get my hands/tools up there.

THe Rustys is in and going on very very soon.