1994 jeep grand cherokee laredo will not start

mikemedic · 11-28-2004, 10:21 PM

hello everyone:
I just bought my daughter the 6.0 grand 4.0 with 161,000 miles on it. I bought it off a friend. The problem is intermittent will not start . It cranks but will not fire over. He seemed to think it was in the harness that connect the fuel pump, he has replaced the pump before along with filter, dist cap etc. I think its a crap shoot cause it does this so intermittent. like tonight, i cranked it and it would not start. tried several times to no luck. I check things and 10 mins later it fires up and i have restarted it about 10 times all fired on first crank. The last thing i want is my kid out some night late and it wouldnt start. any input will do
I am not a mechanic so be gentle and tell me what to check.I also notice that when i turn the key over it makes the humming noise like the fuel pump kicks on everytime so i am assuming its not the harness?

Help please

Meerkat · 11-28-2004, 11:04 PM

Welcome!
The first thing you need to do is pull any fault codes that might exist. To do this, turn the ignition key from off to on, to off, to on, to off, to on, to off, to on (not start). Numerical codes will display in the digital odometer. If you don't have a digital odometer, the check engine light will flash the number codes. The last number code will be 55 (finished). You can then let us know what codes you get and we'll break them. Hopefully, you'll have something that points out a defective part, such as the crankshaft position sensor (most likely problem).

Otherwise, we are going to have to line you up with some checks you can make the next time it doesn't start.

HTH

mikemedic · 11-29-2004, 05:00 AM

Ok so when it doesnt start..do the on/off sequence, it will flash codes....like the count the amount of times it flashes? I read somewhere about the crankshaft position sensor. If we don't get a code how can I test this sensor? Where is it's home? Thanks again in advance...I am also from West Virginia

Any advice will do
Mike

mr_user · 11-29-2004, 03:42 PM

Actually these codes are stored in your jeeps PCM (brain) and this method was brought up by the guys at Chrysler so that the average guy didn't need a DRBII scan tool to diagnose a problem. In other words, you can diagnose the problem anytime you'd like.

Also, I am willing to bet money that your problem lies within the CPS (Crankshaft Position Sensor). Many times, it is the culprit of an intermittent start. I will save the write up on a CPS check for when we know this is indeed the problem.

I suggest that you invest in a Haynes manual, especially with such a high mileage Jeep. It is the best $20 you will ever spend. If you do have access to one, the write up is in section 5-5 I believe.

HTH, Let us know,

Meerkat · 11-29-2004, 04:10 PM

Quote:

Originally Posted by mikemedic

Ok so when it doesnt start..do the on/off sequence, it will flash codes....like the count the amount of times it flashes? I read somewhere about the crankshaft position sensor. If we don't get a code how can I test this sensor? Where is it's home? Thanks again in advance...I am also from West Virginia

Any advice will do
Mike

If you're still in West Virginia, MOVE OUT NOW!! BEFORE IT'S TOO LATE!
How's that for advice?

Sorry, I couldn't resist that...

The crankshaft position sensor is located on the back of the engine, near the bell housing. There is a series of resistance checks than can be performed on it to verify it's condition. This are listed in the Haynes manual, I think.
Do you have a Haynes? It's so much easier to work on this stuff if you have a reference in hand.

BTW, what part of WV are you in?

mikemedic · 11-29-2004, 08:45 PM

thanks, actually my buddy gave me a chiltons for the jeep. I went out and started it like 10 times today and it was fine. How much are those crankshaft position sensor? The Chiltons kinda shows how to check it. so i disconnect the sensor at the connection and it says test the middle terminal to one of the outer terminals ? It looks like i could replace this myself hopefully. OK so if the CKP has three wires...middle right and left middle to one side should go to 5 volts or greater with ignition in on , then middle to the other terminal opposite the 5 volt one should fluctuate between 0 and 5 volts turning over the engine, and if using and average voltmeter the readind

should be 2.5 volts right?

Is the CKP the most problematic sensor in the 4.0 1994 grand cherokee

I will be amazed if I fix this..........

**Texas ZJ1** · 11-29-2004, 08:48 PM

Don't be amazed. Just know that you fixed something that half the guys here couldn't.

Hunter

mikemedic · 11-29-2004, 08:49 PM

I am assuming the CPK sensor and the CPS are the same right?
The chiltons call it the CPK sensor and Is this a dealer part?

mr_user · 11-29-2004, 08:52 PM

Yeah, Haynes refers to it as the Camshaft position sensor, I guess they all have their own lingo. The resistance check seems identical to the one I recall from the Haynes.

Good luck with that, let us know if you have any questions.

Nothing beats the feeling of saving the money/pure accomplishment of doing your own disgnostics and repairs.

Oh and yes, you can get this part from the dealer. Call around and see if any of the local dealers have these in stock, they should as it's very common. I forget the part number.

mikemedic · 11-29-2004, 09:41 PM

OK all you grand cherokee experts:

I do believe there is the CRANKSHAFT POSITION SENSOR and the CAMSHAFT POSITION SENSOR

THe crankshaft position sensor is the one by the tranny bell housing right
The camshaft position sensor is in the distributor right....

so I am led to believe we think it's the crankshaft position sensor right...according to some other sites this is the more sommon defective part?

Big Dumb White Guy · 11-30-2004, 02:51 PM

check your coil. i had a similar problem - that's what it was. have fun with that bad boy. they are a pain to get to.

greasefingers · 11-30-2004, 05:22 PM

I can tell that that if the PCM does NOT receive a signal from the Crankshaft Position Sensor, the enigine will not fire up. I forgot to connect mine once. The engine would turn over but no spark. Once connected it, it fired up right away.

goodolboy71 · 11-30-2004, 05:38 PM

Quote:

Originally Posted by mikemedic

OK all you grand cherokee experts:

I do believe there is the CRANKSHAFT POSITION SENSOR and the CAMSHAFT POSITION SENSOR

THe crankshaft position sensor is the one by the tranny bell housing right
The camshaft position sensor is in the distributor right....

so I am led to believe we think it's the crankshaft position sensor right...according to some other sites this is the more sommon defective part?

right.but i doubt its the camshaft ps...... my money is on the crankshaft postion sensor....i had simiular probs with my old 87 XJ...heck when it started to go out it would stumble and if the rpm got below 1000 it would die, 2 bolts on a metal strap is what help mine on

**Texas ZJ1** · 11-30-2004, 07:02 PM

I had a problem with my ignition coil. I ran through seven of them in about four years.

Hunter

garyontheriver · 12-01-2004, 01:38 AM

My 87 Cherokee had a 4.0L inline six. On cold mornings it wouldn't start at 530am but about 9am when it warmed up outside it started ok. when it wouldn't start ther was no spark to the plugs leading me to believe the coil was at fault. Since coils fail 100% I decided to replace the crankshaft position sensor after reading forums like this where people had a similar problem and the majority of fixes was the CPSensor.. I paid an auto shop $110.00 to replace it and it always started without a problem and had over 220k miles on it and ran gre

at when I sold it. Definitely replace the CPSensor.