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94 GC No Fire Low Voltage to Pump


docsplace
02-11-2006, 03:35 AM
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
02-11-2006, 06:47 AM
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
02-11-2006, 08:47 AM
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
02-11-2006, 12:16 PM
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
02-11-2006, 05:11 PM
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
02-12-2006, 02:14 AM
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
02-12-2006, 07:23 AM
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
02-12-2006, 03:37 PM
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
02-12-2006, 07:15 PM
I thought about that one too, but he mentioned replacing it and it didn't help.

xj31
02-12-2006, 07:53 PM
You're right,I missed that...

docsplace
02-13-2006, 06:42 AM
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
02-13-2006, 07:07 AM
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
02-13-2006, 11:38 AM
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
02-13-2006, 05:46 PM
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
02-13-2006, 05:46 PM
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?

docscomputers
02-13-2006, 05:56 PM
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?


I was going to try that but didn't see much scence if the coill was open, I picked up a new coil tody and test the leads and it had a 786 ohm reading. But I will try the crank test tomorrow to see if it is pulsing power to the pickup coil just to make sure it is getting power to it. That would be a wise thing to do I guess. I Tried leaving the key on and like I said if it is cold out it will not do anything, If it warms up a little than it works.

dksob81
02-13-2006, 07:38 PM
well that wouldn't explain the CHECK ENGINE light not coming on, unless the CHECK ENGINE light bulb is blown.

docscomputers
02-15-2006, 09:40 AM
Well I Managed to get the pickup coil on yesterday and the jeep would at least start, But it still is not 100% It was warm outside so not sure if the temp had anything to do with it or not. But heres what a got. The fuel pump is running constantly for about 5 minutes and you can here the relay ticking constanly the hole time, When the check engine lite comes on it will start. Yesterday after running it for a couple hours it just shut off and would not start back up, Any Ideas? What else could cause that? I did put a used pump on it and I took the new cps back for refund. Both the old and the new cps tested ohm at around 800+ and the old pickup coil will now get a intermitent ohm reading, willl not read when it is cold but soon as you warm it up it reads 700+ ohm.

Confused
Tom

docscomputers
02-15-2006, 04:10 PM
Funny thing, I tested the voltage coming from the CPS to Pickup Coil and I have a constant 4.96v with key off and out of ignition. No fluxuation in voltage after cranking engine.

Tom

dksob81
02-15-2006, 04:37 PM
You shouldn't even have any voltage to either with the key in the OFF position.

docscomputers
02-15-2006, 05:11 PM
That's what I was thinking. Must me a dead short in some wiring harness somewhere. Something pulling voltage in the ignition maybe like the key is stuck on or maybe a bad switch. I gues I'm got to get in to wire test mode and see what I can figure out. This jeep also has a DEI Valet 471T Remote Start in it. May be something there. Have any suggestions?

Tom

dksob81
02-15-2006, 07:20 PM
The remote starter could be the problem.
Check for broken wires at the PCM connection, I have had a few wires break here.

xj31
02-15-2006, 09:34 PM
I still think it sounds like a bad pcm,especially since you said"The fuel pump is running constantly for about 5 minutes and you can here the relay ticking constanly the hole time, When the check engine lite comes on it will start."
I have seen this quite a few times.I know you said you replaced the computer but where did you get it from?

docscomputers
02-16-2006, 11:12 AM
The PCM is a junkyard model. Trying to keep from spending a lot of money on it. How do you do a self diagnostic on the jeep or do you have to have a PC Diagnostic Code Reader? Think I should try another?

Tom

dksob81
02-16-2006, 05:46 PM
Whats the part # on the PCM? I have a KNOWN GOOD PCM for a 94 Laredo 5.2L engine.

docscomputers
02-17-2006, 09:53 AM
I'll Check the part number a little later today but I do not think they will be the same, Mine is a 4.0L

Tom

docsplace
02-21-2006, 10:53 PM
The Numbers off the PCM are 56026993 10.0941-0902.4 3X1 910

I haven't had a chance to work on that for a few days so I have nothing new to report other than i'm going to try to hook up the old pump temperarely outside the tank to see if it will initiate and just try to see if I can find some broken wires, Still don't understand the constant 5v to the Pickup Coil.:banghead:

docsplace
02-27-2006, 06:07 AM
Whats the part # on the PCM? I have a KNOWN GOOD PCM for a 94 Laredo 5.2L engine. dksob81 What are the numbers off your PCM and What is your price?

Thanks
Tom

dksob81
02-27-2006, 06:47 AM
the part # is 56026113, but I doubt if it will work because it is for the 5.2L engine.

bringselpup
02-27-2006, 07:53 AM
56026993 doesn't seem to match what I'm seeing you need. Is that the Junkyard computer or the original one before you swapped?

Look here http://www.autopart.com/ecc/ECC1994JEEPGRANDCHEROKEE.htm

They will rebuild the original one for $149.00 also

http://www.autopart.com/ecm/chrysler.htm

docscomputers
02-27-2006, 09:22 AM
I see what you mean. Maybe they just do not have any with those numbers available. I looked at the 93,s, 94's and 95's no matching part numbers.

I'll call a chrystler dealer and see what I can find out

Tom

bringselpup
02-27-2006, 04:39 PM
I'll be interested to hear what they say about this. I can't make that number come up anywhere. Where did you find the number? Mine was on a sticker on the top of the module. Had to wipe 13 yrs of crud off to read it too. It was printed like this 56029-009.

The differences in that list for 94 as I see it are 7 or 8 different computers. Some of it is Calif emissions or not and some is factory theft or not but beyond that I assume it is minor differences in whatever parts were used building the vehicle.

docscomputers
02-27-2006, 05:02 PM
Are we talking about the PCM on the Drivers Side Inside Fender of the 4.0l GC

Tom

docscomputers
02-27-2006, 05:13 PM
I'll be interested to hear what they say about this. I can't make that number come up anywhere. Where did you find the number? Mine was on a sticker on the top of the module. Had to wipe 13 yrs of crud off to read it too. It was printed like this 56029-009.

The differences in that list for 94 as I see it are 7 or 8 different computers. Some of it is Calif emissions or not and some is factory theft or not but beyond that I assume it is minor differences in whatever parts were used building the vehicle.

You know what, I think someone may have screwed up, I read this after cleaning it up and what they, and I am calling a PCM that they sold me as a PCM has a Label below that says Electronic Brake System. I also notice a *5L* Under a Bar Code at the bottom right side. I wonder even if this is for a 4L engine. Is this the Right Part?

bringselpup
02-27-2006, 05:20 PM
Nope that sounds like the ABS computer. My PCM is on the firewall in the engine compartment passenger side kind of hidden by my radiator overflow tank. Do a search on Ebay for "jeep ecm" You'll see what it looks like.

docsplace
03-04-2006, 06:42 AM
The jeep is fixed. The problem was the PCM, Had got another from the yard that had antitheft and it would start and shut the jeep down instantly, Exchanged it for 1 without A/T and it fires and runs fine.

Thanks to Dksob81 and Bringselpup they had this diagnosed right off the bat.

To Close and let everyone know that reads this thread the Symptems I had was the jeep would crank and not start, If I waited a few minutes the check engine light would come on and I could hear the pump initiate and it would start and run fine. If it was cold outside you might wait 15 minutes. IT got to the point where it would not start at all. Changed the PCM with a JY model and works fine.

I now have a spare Good Pump and A Extra PCM if anyone needs 1. Pump is tested and will work the PCM is suppose to be a working pull, I can not test it because my jeep will not use it. If interseted e-mail me from the thread.

Thanks
Tom

xj31
03-05-2006, 04:35 PM
Thanks to Dksob81 and Bringselpup they had this diagnosed right off the bat.




Hey,I think I called it first,(post # 8 on the first page ,to be exact)LOL
Just kidding,glad you finally got it

docscomputers
03-06-2006, 08:49 AM
Yes I guess you did, Never stuck with me thru the hole mess is the reason I never remembered your reply. Well a lot of thanks goes out to you also.

Thanks
Tom
Docsplace

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