619SDjeep

I was a mechanic for 20 years. I changed careers in 2000 so I know my stuff pretty well. My 87 year old neighbor was on his back under his 2002 Jeep Grand Cherokee 4.0. Frustrated with the quick disconnects on the fuel filter so I stepped in to help. BTW, he is a purple heart veteran and an amazing guy. I changed the fuel filter, started the truck, and heard whining/squealing sound coming from what I thought was the fuel pump. Turns out it was a defective fuel filter making the noise. Who knew a fuel filter could make noise! Fuel pump from the dealer, napa fuel filter, and $250 later, I am back at square one. The problem is that the Jeep shuts off while driving. I got on the internet, did a bunch of research, saw all of the stuff about the PCM problems, figured it had to be the PCM. Changed the PCM, still have the problem. Embarrassing... Doing more research, wriggle test, checking grounds, new ASD relay. The PCM has never stored any codes. I know the crank sensor is a possibility. I am not sure what the sensor ohm range should be. I figured I could check the range against a new one if I go pick one up. It seems like the coil pack is all one unit instead of 3 separate coils. I assumed they would not fail as one. Now I am lost and out of money. Any expertise would be much appreciated by me and the owner. Thanks ahead of time.

Bustedback

Cam and crank sensors are the most likely causes, you need to figure out if you're losing fuel or spark. A can of starting fluid can help verify which one is the culprit.

619SDjeep

It runs. so not able to test like that.
I just picked one up from Napa.
I'll install it tomorrow morning and drive and post reply when I'm done. thanks

dave1123

Welcome to CF!

The CPS is a magnetic switch, actually a Hall-effect switch, that's either on or off. If you buy one, don't waste your money on anything but Mopar because of the quality of construction. You can tell by the magnetic pull that it's better than any other aftermarket one. It operates on 5 volts so connections are critical.

The way this works is when cranking the engine, the signal from the CPS tells the PCM that the crankshaft is turning. The PCM then energizes the ASD relay and the fuel pump relay. The ASD relay turns on the ignition and injector circuits. Any loss of CPS signal shuts everything down.

The flywheel has 3 spots on it that tell the PCM when a cylinder it at TDC, the cam sensor tells the PCM which cylinder to fire (there are only 3 coils in the coil pack and 2 cylinders fire at once, one of them on exhaust) and the rest of the sensors tell the PCM how much spark advance and fuel to give it.

I hope this helps and you don't feel like I'm telling you that you don't know what you're doing. This is purely instructional. A CPS will sometimes fail intermittently before it goes completely.