Crank - No Start

[tanno]

Try the plug to it first. Unplug it and plug it back in. If it starts then, the sensor is good. Mine was replaced only to have the same problem about a week later.

[kshelby99]

Okay - quick update. My crank sensor and wires from the harness to the sensor were in pretty bad shape. Replaced it - looks like it needed it anyway - but still no spark. Grrr!

Pulling the ECU and going to see if the local Jeep dealer will test it for me.

[tanno]

They should be able to if Napa, Autozone, Checker, Advanced Auto, PepBoys, etc. can.

Try these before spending the funds on a diagnostics test.


To do a complete test of the CKP circuit, you'll need a scan tool. But you can do a quick test of the CKP with an ohmmeter.

Near the rear of the right cylinder head, disconnect CPS wiring harness connector from main wiring harness.

/---^--\
| A B C |
\-------/

Place an ohmmeter across terminals B and C of the CPS connector. The meter reading should be open (infinite resistance). Replace sensor if resistance is indicated.



*** NOTE: For this test, an analog (non-digital) voltmeter is needed. Do not remove the distributor connector from the distributor. To perform a complete test of the Camshaft Position Sensor and its circuitry, refer to the DRB II diagnostic tester. Also see the appropriate Diagnostic Charts.

To test the sensor only, refer to the following:

Using small paper clips, insert them into the backside of the distributor wire harness connector to make contact with the terminals. Be sure that the connector is not damaged when inserting the paper clips. Attach voltmeter leads to these paper clips.

1. Connect the positive (+) voltmeter lead into the sensor output wire. This is done at the distributor wire harness connector.
2. Connect the negative (-) voltmeter lead into the ground wire.
3. Set the voltmeter to the 15 Volt DC scale.
4. Remove distributor cap from distributor (two screws). Rotate (crank) the engine until the distributor rotor is pointed towards the rear of vehicle. The movable pulse ring should now be within the sensor pickup.
5. Turn ignition key to ON position. Voltmeter should read approximately 5.0 volts.
6. If voltage is not present, check the voltmeter leads for a good connection.
7. If voltage is still not present, check for voltage at the supply wire.
8. If voltage is not present at supply wire, check for voltage at pin 7 of Powertrain Control Module (PCM) 60 pin connector. Leave the PCM connector connected for this test.
9. If voltage is still not present, perform vehicle test using the DRB II diagnostic scan tool.
10. If voltage is present at pin 7, but not at the supply wire:

a. Check continuity between the supply wire. This is checked between the distributor connector and pin 7 at the PCM. If continuity is not present, repair the harness as necessary.
b. Check for continuity between the Camshaft Position Sensor output wire and pin 44 at the PCM. If continuity is not present, repair the harness as necessary.
c. Check for continuity between the ground circuit wire at the distributor connector and ground. If continuity is not present, repair the harness as necessary.

11. While observing the voltmeter, crank the engine with ignition switch. The voltmeter needle should fluctuate between 0 and 5 volts while the engine is cranking. This verifies that the camshaft position sensor in the distributor is operating properly and a sync pulse signal is being generated.

If sync pulse signal is not present, replacement of the Camshaft Position Sensor is necessary.

I hope this clears it up for ya. Let me know.

[Dale Aeppli]

Originally Posted by kshelby99

About a week ago I got in my 90 Cherokee 4.0L in the morning and started her up. Slow start and all lights were VERY dim. Kind of odd. About two blocks down the road all the dash and headlights brightened to normal. Stopped at a convenience store for a soft drink. When I went back out and tried to start the Jeep to leave it would crank, but not start. Normal crank now. I did not hear the fuel pump hum when I turned the ignition on, so assumed it was the pump. Replaced it this weekend and same problem. No hum from the pump, normal crank, but no start.

I checked for fuel pressure at the rail with the new pump and when cranking I get 39 psi while cranking. Checked voltage at the wiring harness going to the pump and I show about 7 volts with ignition on and drops to between 5.5 and 6 volts while cranking (assuming I check it correctly). Pulled a plug wire (cylinder 3 I think) and held it to the head while my wife cranked the engine and I did not feel any spark.

Any ideas? I'm a shadetree mechanic, not hardcore.

Thanks.

Try checking voltage back at fuel pump where wiring goes into tank and pump. Where did you check for voltage and got t volts and 6 when cranking? dale jeepman600@aol.com

[kshelby99]

Dale,

My pump has a wiring harness at the rear of the vehicle by the tire. I check voltage at the harness, not the pump. The 7 volts was what was at the harness connector (so I assume 7 volts feeding the pump).

[Dale Aeppli]

Originally Posted by kshelby99

Dale,

My pump has a wiring harness at the rear of the vehicle by the tire. I check voltage at the harness, not the pump. The 7 volts was what was at the harness connector (so I assume 7 volts feeding the pump).

SOUNDS FUNNY THAT THERE ISN'T 12 VOLTS THERE THATS WHY THERE A RELAY SO IT GETS FULL VOLTAGE, DID YOU CHECK THE WIRING TO SEE IF THERE WAS A CHANCE IT MAYBE CUT OR FRAYED. HAD ONE FOUND SCREW HAD CUT INTO HARNESS HOLDIN IT IN PLACE.
DALE jeepman600@aol.com
Did you try unplugging and plugging the crankshaft sensor,still sounds like crank sensor

[kshelby99]

Crank sensor replaced - still no spark. I'll recheck the harness on the pump for voltage. I swapped relays on my fender (4 of them with 3 the same - I assummed one was fuel pump relay) but no help.

tanno - thanks for the info. I'll try checking the sensors again with VOM.

Part of the problem is that I am not reading voltage on ANY of my sensors. I am thinking ECU is shorted out. If so, would it prevent voltage to all sensors for a check with VOM? I can still check resistance but not voltage.

[Dale Aeppli]

Originally Posted by kshelby99

Crank sensor replaced - still no spark. I'll recheck the harness on the pump for voltage. I swapped relays on my fender (4 of them with 3 the same - I assummed one was fuel pump relay) but no help.

tanno - thanks for the info. I'll try checking the sensors again with VOM.

Part of the problem is that I am not reading voltage on ANY of my sensors. I am thinking ECU is shorted out. If so, would it prevent voltage to all sensors for a check with VOM? I can still check resistance but not voltage.

Check the 4 th. relay its the b+ latch relay it should have 12 volts. also check the fusuable links under relays. pull on each fuseable link if it stretchs its blown. When you turn the key on can you hear the fuel pump relay click dale

[tanno]

If the ECM / PCM is bad anything can or won't happen. It's a computer and you really can't tell what went bad in it if anything. All you can do is eliminate everything else being the issue. It is not unheardof to have the ECM / PCM to go bad even because of age. Electronics are not infalable just like everything else on the vehicle.

Try spraying some starting fluid in the throttle body and see if it starts...if it does, it's fuel related. Then you can ignore ignition and sensor troubleshooting. If it does not even try to start with starter fluid, then it's determined that it's an electrical issue.

[tanno]

I think they only original Electronic stuff still in my Jeep is the ECM and the Knock sensor. Everything else I have replace at one time or another.