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Amedee
Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 24412
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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I have a 1999 Jeep Cherokee. Will crank but not start. No

Customer Question

I have a 1999 Jeep Cherokee. Will crank but not start. No fault codes. I replaced the crankshaft sensor. A mobile mechanic friend who has looked at it says he cannot find the 12 volt signal. Can you give me some suggestions as how to go about troubleshooting on my own. I have a voltmeter for test equipment.
JA: Thanks. Can you give me any more details about your issue?
Customer: What do you need to know?
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Submitted: 9 months ago.
Category: Jeep
Expert:  Amedee replied 9 months ago.

Hello and welcome! My name is ***** ***** I can assist you with your question. First thing to do is check to see if the engine has spark. If so, check to see if the engine runs on starting fluid. If it runs on starting fluid, then you just have a lack of fuel. If it does not have spark, you need to check the ignition system and computer system to ensure it is in good working order.

Customer: replied 9 months ago.
It has fuel. How do I need to proceed to check the ignition system and computer system?
Expert:  Amedee replied 9 months ago.

I would start by checking to ensure that the computer is awake with the key on. Check to see if the check engine light comes on with the key on and that the TPS has 5 volts with the key on.

Customer: replied 9 months ago.
What is the TPS? and if this checks out, what do I need to do next? The mobile mechanic who has worked on it says he can not find the 12 volts.
Expert:  Amedee replied 9 months ago.

If this checks out, the cam and crank signals need to be checked using a lab scope

Customer: replied 9 months ago.
I have installed a new crank sensor. Do you mean an oscilloscope and if I had access to one, how would I go about checking those signals and what would I be looking for?
Expert:  Amedee replied 9 months ago.

YES, that is correct. You would be looking for a signal from both the cam and crank sensors while the engine is turning over

Customer: replied 9 months ago.
Where would I test those signals and what should I expect to see?
Customer: replied 9 months ago.
Is there a technical reference on the internet that I can access?
Expert:  Amedee replied 9 months ago.

You can test these right at the sensors or directly at the PCM. You are going to want to see an on off signal as the engine is cranking over.

Expert:  Amedee replied 9 months ago.

Did you have any further questions?