94 GC No Fire Low Voltage to Pump

[docsplace]

Hi All! I have a 94 Jeep Grand Cherokee Loredo, Have a bit of a electrical problem, Since its been cold hear in ohio it does not want to start unless it gets above 40 degree. Iv'e been trying to test a few things and heres what I've did so far, Cahnge fuel pump because pump would work after a minute of turning key on if it is above 40* no results after changing pump, Voltage going to pump is only 5.1 volt. Changed computer with no results. checked all fuses. But I did notice a strange noise coming from distributer after I get it running. Might be a coil pack but would that cause a low voltage in pump. I'm going to try a coil pack hope that works but I keep reading about a lot of people changing Crank Sensors or Cam Sensors.

Any Help would be appreciated.

Thanks, Tom

[dksob81]

Sounds like the CPS to me. Does you CHECK ENGINE light come on as soon as you turn the key to the ON position?

If the CHECK ENGINE light does not come on then the CPS is bad.

[docscomputers]

No the check engine light does not come on, and is that the Crank Position Sensor or cam, Do you know where it is located? Thanks, Tom

[docscomputers]

Originally Posted by docscomputers

No the check engine light does not come on, and is that the Crank Position Sensor or cam, Do you know where it is located? Thanks, Tom

Never Mind I found It and How to Test It.

Thanks
Tom

[dksob81]

CPS - Crankshaft Position Sensor.
On the 4.0L engine it is located on the driverside bellhousing.
on the 5.2L engine it is lcated on the passengerside engine block, right behind the right cylinder head.

both of these are pretty hard to get to, but I think the 5.2L is deffinately the easiest of the 2.

[docsplace]

Well that checked out, There is no ohm reading across any of the connectors. I checked my pickup coil in the distrubutor and it is open which there should be some ohm reading of around 600. That would explain why there is no voltage or spark, 1 person told me that would also cause low or no voltage to pump. Anybody know for sure if that is the case?

Thanks
Tom

[dksob81]

The Crank Sensor would cause the low/no voltage at the fuel pump, but not the Cam Sensor (Pick-up coil). Replace the Crank Sensor!

[xj31]

You said the check engine light does not come on,right?It should come on for a few seconds when you turn the key on.If it does come on when the jeep starts and it doesn't come on and the jeep won't start,you might have a bad pcm.

[dksob81]

I thought about that one too, but he mentioned replacing it and it didn't help.

[xj31]

You're right,I missed that...

[docsplace]

Well I get no ohm reading to the pickup coil, Is the cps ahead of the pickup coil in sequence when intiating a start sequence. If the Pickup coil has no ohm reading which is just a coil that would mean it is bad right, and needs to be replaced????? Anybody have a schamatic to see which one is intiates first? The cps does not ohm which should mean it is good, otherwise no shorts.

Thanks
Tom

[dksob81]

The reason your not getting a reading from the Cam Sensor (Pick-up Coil) is because the PCM is not getting a reading from the CPS. If the PCM doesn't get a signal from the CPS it will not allow the engine to start (no spark, no fuel).

TRY this turn the key to the ON position and leave it in the ON position until the CHECK ENGINE light comes on, may take a few minutes, then when it does the jeep should start and you will have your reading from the Cam Sensor (pick-up coil). If it does not come on after 5 minutes then the CPS is SHOT totally. While you are waiting make sure you watch the dash for the Check Engine light, it will only appear for a few seconds.

[docscomputers]

Are we talking about the same thing, Pickup coil is inside the distributor and it is a coil NC it does not require power to get a ohm reading, If there is no ohms it is open or shorted. Right?

Tom

[docscomputers]

Well I changed out the cps with no results. Still the same problem. Going to change the pickup coil tomorrow, it is open and testing bad thats gotta be it I hope.

Tom

[dksob81]

Yes we are talking about the same things the PICK-UP COILD (in the distributor) is also known as the CamShaft Position Sensor.

To test the operation of the camshaft position sensor,

(1) Connect the positive (+) voltmeter lead into the
sensor output wire. This is at done the distributor
wire harness connector. For wire identification, refer
to Group 8W, Wiring Diagrams.
(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the volt meter to 15 VDC (or the closes to 12VDC, but no less then 12 VDC) While observing the Voltmeter crank the engine, the voltage should fluctuate between 0 volts and 5 volts.

Signal/output Wire - GREY/BLACK
Sensor Ground - BLACK/LIGHT BLUE


Did you try leaving the key in the ON position to see if the CHECK ENGINE light eventually comes on and start the jeep?