ralphb

The problem started with 99 Cherokee cranking but not starting. I have replaced the crankshaft position sensor and coil pack....still no spark. The fuel pump is running when turmed on. I have been told if it was a computer issue, the fuel pump wouldn't engage when turning the ignition. Should I replace the distributor pickup or is this a computer issue?

Thanks!!

Lowrange2

Where did you purchase the CPS? Have you test the CPS and Coil?

CCKen

Check a bunch of fuses.

Here's the Power Distribution Center (PDC). Check the following fuses to see if they are blown.

Fuel Injectors/Coil

ASD

Swap the ASD relay with the Radiator Fan relay.



Here's a guide to the Junction Block and the JB layout.

Check fuse 11.








.

ralphb

Checked all fuses. CPS and coil were brand new from NAPA and tested both after installation. Could it be computer with fuel pump still working?

autosurgeon

You have tested for power at the coil?

ralphb

Best reading I got going into the coil was 108...not sure if I'm testing right.

CCKen

Did you swap the ASD relay with the radiator electric fan relay and then try starting it?

CCKen

Do you have a Sentry Key Immobilizer System (SKIS)?

If you don't know for sure, look at your ignition key. The SKIS will have a Transponder Key that has a Gray molded cap on the end, as opposed to the standard ignition key with a Black (non-molded) end on it.

A defective SKIS will prevent the engine from starting after several attempts are made.

The fuel pump will initialize for 1-2 seconds when the ignition switch is first turned to RUN (before cranking the engine) to prime the fuel rail, but requires the ASD relay to be engaged, and sending a signal to the PCM for the fuel pump to run continuously. Same goes for the ignition system, the ASD relay must be engaged.

Read this:

ralphb

Yes, I swapped the relays and tried to start. No luck there. It has never had keyless entry/security.

CCKen

Okay.

How did you check for spark?

When you checked the coil, what does "108" mean?

Here's a few diagrams of the ASD and Ignition Coil Circuits:





Note in the Ignition Coil circuit that the Dark Green/Orange tracer wite at the connector is power from fuse 21 in the PDC. F21 receives power when the PCM activates the ASD relay. When the ASD relay is activated there is a steady 12 volts at the Dark Green/Orange tracer wire from the battery bus.

The Gray wire at the coil connector is the ground driver from the PCM. The PCM will provide a ground circuit to the coil primary windings, and will break the ground when it is time to fire a spark plug, collapsing the primary field around the secondary windings, inducing a high voltage in the plug circuit.

If, while starting, the PCM doesn't see a flex plate rotation signal from the CPS for a couple of seconds it will deactivate the ASD relay.

Possible defects:

Wrong CPS
Defecive CPS
Defective CPS wiring between the CPS and the PCM
No 5 volt reference to the CPS from the PCM

Defective ignition coil driver in the PCM
Defective wiring between the ASD relay and fuse F21 in the PDC
Blown F21 in PDC
Defective wiring between F21 and the ignition coil

A simple test can determine to see if the CPS is working and the PCM sees it working is to use an analog voltmeter. Touch the pin cavity in the ignition coil connector with the Dark Green/Orange tracer wire with the (+) probe of the meter and the (-) probe to ground. Have someone crank the engine over while you watch the voltmeter. You should see battery voltage. If you see voltage for a second or two and then it goes away, the PCM didn't see a signal from the CPS and dropped the ASD relay. If you don't see any voltage at all, fuse F21 may be blown or the ASD relay is defective. If you see battery voltage throughout the cranking cycle, the CPS/PCM/ASD relay/fuse F21/and wiring circuits are intact.

Do this test and tell us what you see.

ralphb

And she lives!! Thanks for the help...it was the distributor pickup. Quick and easy.