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rpmdiag, Tech and Instructor
Category: Ford
Satisfied Customers: 8048
Experience:  Since 1975
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OK...So i have a 1999 Mustang GT and everything worked fine

Customer Question

OK...So i have a 1999 Mustang GT and everything worked fine until my engine went out. Then i bought the 03 Mach 1 engine from Ford Racing and had a mechanic install it. After the installation he said the engine was not running right and he had to get a new computer for the engine. He installed the new computer but told me he had to modify the wiring harness so it would fit. Now my A/C system is screwed up. The A/C compressor stays constantly on (no cycling) in the "OFF" and "VENT" positions and will not run the compressor in the "NORM AC" and "MAX AC". I've since dropped the car off at the Ford dealer to see if they can fix it but the have had the car for 2 1/2 months with no answer.
Submitted: 1 year ago.
Category: Ford
Expert:  rpmdiag replied 1 year ago.

Hi, I’m Ron and I can help you.
I have been in this business since 1975 and also teach automotive repair. I am confident we can resolve your problem together. Please understand that I don't know your skill level. I can't see, smell, hear, or touch the vehicle either, so it may take a few replies to get to satisfactory results. Please be patient!
I also try to give all of the information you may need, expecting a “positive rating” in return. I will also continue assisting you after you have rated me, if necessary. If there is any reason I cannot get a positive rating, please let me know why “in advance”, so I can go another direction for you. I am sorry you’re having this problem; I’ll help you through it.

This should never have gone this far, now no one has a clue of what to do next. Is there any way you can go backwards and get your old motor back and repaired etc?

Thanks, Ron

Customer: replied 1 year ago.
No that is not possible. The old motor was junked and the computer to that engine was sent in as a core for the new computer.
Expert:  rpmdiag replied 1 year ago.

I'm really sorry to hear that. The problem here, is that no one is going to want to work on this due to all the previous issues and parts that were changed. There are no good procedures for anyone to follow because it's not the same stock car as it once was. Computers and wiring harnesses should never be change to meet a different motor, now all the senor reading will be wrong too. I think the best person that could help you is an electrical specialist to check all the wiring right now. I'm really sorry this happened to you.

Thanks, Ron