douglas.highlander

Please help. I have a 93 cherokee 6cl 4lt. Stopped dead in it tracks. Not getting any spark. I've replaced the cam position sensor, the coil, and the distributor. I'm out of ideas. All three were going bad so I'm keeping them on the vehicle, but it still isn't getting spark. Plenty of gas(can smell it) but no spark. Even had a brave soul hold the #1 wire to check! spark plugss and wires are only 4 months old. Also, it is not the timing chain. The distributor spins when starting. All fuses and relays under the hood are good too. Ideas?

HudsonN

CPS.

Does the jeep just crank and crank but no start?

The CPS will not let the jeep spark as a safety precaution.



Troubleshoot and test, before you buy new parts.

The CPS is the most common failure, but not the only one that can cause a no-start.

The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.

Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.

Diagnostic steps to confirm the CPS is the cause of your no-start

You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start. Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.

CPS Testing

Crankshaft Position Sensor Connector (CPS/CKP)






TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 – 275 Ohms. . If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

douglas.highlander

yes. After the coil pack, got a small ignition, but then nothing. Turns like a champ, but no fire. Cam position sensor was changed. (Small curved, black box, two bolts on back of bell housing. )

HudsonN

Did you change the camshaft position sensor or the crankshaft position sensor?

The camshaft sensor is inside the distributor. The Crankshaft is on the transmission bellhousing.

douglas.highlander

cps has been changed. it was pretty worn out. Hot, warped. weak leads. But still wont start.

HudsonN

You buy an aftermarket or dealer CPS? A lot of aftermarket sensors are hit and miss with a lot being miss straight out of the box.

I'd consider testing the CPS again just to be sure.

If that tests out, i'd begin checking all your electrical connections and grounds. Those can also cause weird problems.

douglas.highlander

entire new distributor

douglas.highlander

I think I'm going to have to work on the grounds next unless there are other ideas.

HudsonN

OP, i think you're confusing the camshaft sensor and the crankshaft sensor.

Did you replace both sensors, or did you replace just one?

If you replaced the entire distributor, then you replaced the camshaft position sensor, not the crankshaft position sensor.

The crankshaft position sensor is up on the transmission bellhousing.

Pelican

Did you swap the ASD relay as suggested in the great info from HudsonN? I assume so since you say all relays are good.

What do you mean by "got a small ignition" after changing coil pack?

douglas.highlander

Small ignition was the timing. Never had to do that before. Pulling the distributor got it off one tooth. Took a bit but it's running again. Thanks to all who helped. At least I don't have to worry about ignition parts for awhile. They are all new. I'm assuming it was the coil pack all along. 200 bucks later and it was a 30 dollar part! Two bolts and a plug would have taken me 20 minutes.