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John Crouch
John Crouch, Ford Mechanic
Category: Ford
Satisfied Customers: 1835
Experience:  22 years of Ford service, and Ford senior master certified in diesel, gasoline and hybrid vehicles
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I have a 2007 Mustang GT supercharged. The spark plugs that

Resolved Question:

I have a 2007 Mustang GT supercharged. The spark plugs that came with the supercharger were put in at the time. I was told that it would be a good idea to change the spark plugs. I pulled the original ones out and replaced them with similar heat range/gap spark plugs. After swapping them, the car idled a little rough and drove very inconsistant. I decided to put the original plugs back in. After doing so, the car still has a rough idle to the point of stalling. Any ideas?
Submitted: 7 years ago.
Category: Ford
Expert:  John Crouch replied 7 years ago.
My name is XXXXX XXXXX I will try to answer your question. First what supercharger kit did you install? was this a new kit or a used one? It should have came with detailed instructions for install and also a programmer to recalibrate the processor. The plugs that came with the power adder really should be used since they are the correct heat range (when running a supercharger usually colder plugs are required). There could be a number of things that could be causing your issues. it could be fuel related, spark related, a vacuum leak or even a issue with the mass air flow sensor. At this point I would recomend that you research in your area for someone who specializes in dyno tuning of modified vehicles. I live on the Mid-Atlantic area of the east coast and when I instaled the blower on my 98 saleen I took my car to a place called evolution performance in PA. I thought that my car was running well after doing the mods and installing a mail order tune with a SCT programmer. Well after leaving the car with them for a day or so when I got it back it was like night and day. Car idles very nice, has more power and torque than I could ever imagine. they said that they did a couple of pulls when it first got there and it was making about 360Hp at the rear wheels, after they got done with it the last pulls were at 428 Hp at the rear wheels. It was not a cheap thing to do but even with me being a senior master tech I simply do not have the equipment or the experince to modify the perameters of the pcm and was very glad that I spend the money to get this done.
Customer: replied 7 years ago.
I have had this set-up for 8 months and havent had a problem til now. I was told to replace the spark plugs every 10,000 miles to keep my car at optimal performance. I have the Edelbrock E Force Street Kit and it came with Autolite HT0 spark plugs. I replace them with Ford Racing plugs. First, would it be alright to drive the car? Second, could it be a gapping issue? I figure it might not because I put the old spark plugs back in and the problem continued.
Expert:  John Crouch replied 7 years ago.

If the plugs are the same style as the factory 3 valve head spark plugs there is no adjustable gap on the plugs.

You said that it was running well. Was it running well until you replaced the plugs or was this just a try to get rid of the problem. When the issue started were you just driving normally or was it a racing type senario? Sorry for asking so many questions but without being able to actually look at the car I need to ask as for as much info as possible. Did the kit include something that changes the pcm programing? Have you contacted Edlebrock to see if they have any ideas?


If the problem did not start until you changed the plugs i would recomend getting a set of the autolite plugs and put back in the same ones that came with the kit.

Customer: replied 7 years ago.
The car didn't have the problem before I changed the plugs. I just did a change of the spark plugs. Before I did this, it ran fine. After I did this, it ran very funny. I have been told that there is a specialty tool that can gap these colder range spark plugs. The gap is 0.045" and it needs to be between 0.032"-0.035". I bought the tool and bought new spark plugs. I put the oem coils back on per the tuner and it still was running rough. My plan is to gap them smaller and see if that helps. Hopefully, it does. Also, is it normal to see and smell gas on the spark plug itself?
Expert:  John Crouch replied 7 years ago.
I would put the original plugs back in for now. there may be a tool for bending the end to adjust the gap, its is a aftermarket tool and not one that is used at the ford dealerships. Normally you would not see or smell gas on a plug when it is removed.
Customer: replied 7 years ago.
The original plug aren't working either. I am at a lost for words. I just bought all new everything and will put the new plugs in with the new coils. Hopefully, it works!
Expert:  John Crouch replied 7 years ago.
Did you check to see if there were any codes stored? I am wondering if there were any missfire codes in the pcm. Hopefully new plugs and COP's will get you right. Please let me know what you do find.
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Customer: replied 7 years ago.
No codes stored.......