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Amedee
Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 21868
Experience:  ASE Master Technician advanced level specialist. Wisconsin certified emissions state inspector
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1998 Jeep Grand Cherokee Laredo: coil, map sensor..rotor..wont start

Resolved Question:

I have a 1998 Jeep Grand Cherokee Laredo. It recently had a new crank shaft sensor, coil, map sensor, ignition wires, plugs, plug wires,rotor, and battery installed. Well it won't start. When I turn the key it cranks and cranks but won't start. I do smell a lot of gas as I'm trying to start it. I'm not flooding it so I don't know what is going on. I could use any help I can get on this.
Submitted: 3 years ago.
Category: Jeep
Expert:  Amedee replied 3 years ago.
Hello and Welcome to Just Answer. My name is XXXXX XXXXX I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with.

The first thing to do is to be sure the computer is awake. Turn the key on and check reference voltage to the tps, cam and crank sensors. If there is full reference voltage, check to be sure the ASD relay is engaging when trying to start the engine and that there is power to the injectors and coil/coils when cranking. IF there is no power to the injectors or coil when cranking and the ASD relay is not engaging, then we might have a bad cam or crank sensor (or a valve timing issue).

If there is no reference voltage to these sensors with the key on, then the computer might not be waking up. We will need to check all powers and grounds going into the computer with the key on. This includes, all powers through the computer fuses, fusible links and even the ignition switch.

Hint: Sometimes the cam and crank sensors can short out and pull the computer down temporarily. If all powers and grounds check out and we still do not have any reference voltage to the cam, crank or the tps, then disconnect them one by one with the key on to see if the reference voltage comes back. If so, then one of the sensors is bad and will need to be replaced.
Customer: replied 3 years ago.
I just went out and tried what you suggested. When I turn the key to the on position, all of the gauges show fine. I turned the key and now it just makes a clicking sound. The battery is showing power (plus I just bought this battery two days ago) and all the lights are bright and strong.
Expert:  Amedee replied 3 years ago.
SO the engine is not even cranking over...correct?
Customer: replied 3 years ago.
Right. It was yesterday but now it's not. It's just making "rrrr" sound and clicking
Expert:  Amedee replied 3 years ago.
Do you have 5 volts to the tps and map sensor with the key on?
Customer: replied 3 years ago.
Well I'm an idiot and you will have to tell me how to see that when I go out to the Jeep. It's sitting outside and will only take me a second to go look if you just tell me where to look.
Expert:  Amedee replied 3 years ago.
No problem!

Disconnect the map sensor connector. Turn the key on and measure voltage on all three wires going to the map sensor.

Let me know!
Customer: replied 3 years ago.
I don't know how to disconnect the map sensor connector. I don't know a lot about vehicles and I just bought this Jeep two days ago from an individual who said "it runs great!" I think I might just have to have it towed and have a mechanic actually work on it. I could work on the older model cars, like changing alternators and stuff myself but this new computerized stuff I'm clueless on.
Expert:  Amedee replied 3 years ago.
IT is really easy! It just un clips.

Do you want a picture of the location of the map sensor?
Customer: replied 3 years ago.
That would be awesome!
Expert:  Amedee replied 3 years ago.
Here you go! It is right next to the throttle body. (right below it in the picture)

graphic
Customer: replied 3 years ago.
Thanks for the picture. Do I need a voltage regulator to check the wires?
Expert:  Amedee replied 3 years ago.
No.. you just need a voltmeter.
Customer: replied 3 years ago.
Okay. I don't have one of those so I guess I will go buy one and check that out. Before I finish this up, could there be any possibility that it might be the alternator?
Expert:  Amedee replied 3 years ago.
NO.. the alternators do not cause the engine not to crank over..unless of course is it locked up. If you suspect it it locked up, just remove the belt and see if the engine cranks over.

Edited by AMEDEE on 2/23/2011 at 4:21 PM EST
Customer: replied 3 years ago.
Okie Dokie. I will see what I can do. I want to thank you so much for your help. I'm going to get off here now and try the things you suggested. I do appreciate your help.
Expert:  Amedee replied 3 years ago.
You bet!

I hope this helps. You can always accept my answer now, and repost back again later on if you have any more questions. If you want to discuss it some more just hit "reply", it's free to do so otherwise don't forget to hit "accept" and leave positive feedback if you found my answer helpful.

Regards

AMEDEE

Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 21868
Experience: ASE Master Technician advanced level specialist. Wisconsin certified emissions state inspector
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