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Discussion Starter #1
Ok, I'll admit up front I didn't do a search. But not real sure what to search for! I'll explain the problem and maybe someone can help out.

A friend and coworker of mine just traded his 9x Camaro SS for an 02 Mustang GT (a step up in my opinion). The car runs good, and sounds good and has the usual "bolt on mods" that street racers love today. BBK intake, MAF, TB, and Plenum. A louder exhaust, and lowering springs. The car came with a Diablo tuner as well.

The problem is the transmission (guess I'd better say its an automatic LOL). When in normal Drive (with the OD switch in normal position) the car shifts WAY too soon, and even more so under hard acceleration, then it has a hard time making its mind up between 3rd and OD. If you accelerate from highway speeds (as if to pass a car) it again bounces between 3rd and OD. If you turn OD off the car shifts normally, letting the car go up to redline before shifting up to the next gear during hard acceleration. Under relaxed acceleration (day to day use) it shifts normally.

The previous owner is a self professed street racing junkie, so I have to wonder if he did something to the tune or the transmission to make it do that (though I have no idea why he would). Or if there is something wrong/broken with the transmission. Any thoughts?

I offered to help the guy do a J-Mod but figured it'd be best to have a properly functioning transmission first.
 

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The first thing I would do would be to remove the diablo chip and see what happens. If the trans starts shifting normally with the chip out, then I would say it is probably something in the tune. If removing the chip makes no difference in how the trans shifts, then you might have something messed up internally in the trans. As far as I know though, the OD button is just an electronic lockout, and should have no effect on the lower gears.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I agree - get rid of the chip and see what that does for him. The O/D off button is that and only that - prevents overdrive. Nothing more, nothing less.
 

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Discussion Starter #5
Well, as stated earlier, I got the impression that the previous owner was one of those guys who does no research, and just bolts on what others have said would work. I don't know if it has a Diablo "chip" or not, I think he used a Diablo tuner to modify the tune. I also think that the same genius installed some kind of "shift kit" in the transmission. That would be my biggest fear for him... How do you "uninstall" a shift kit?
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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If he drilled the separator plate then he'd have to find a new, unmolested plate to swap in. That and replace the EPC solenoid - I recall from reading Jerry's articles that some shift kits have you adjust the set screw on the back to change the pressure. Without knowing how to set it properly (or to find out if it was changed) the easiest thing to do to be sure the pressure is correct is to replace it all together.

Without knowing what was done to the trans, it's hard to suggest what to do to undo it.
 

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Discussion Starter #11
Without knowing what was done to the trans, it's hard to suggest what to do to undo it.
Thats pretty much what I told him. And thanks for all the help. I realize its hard to know what to do with such limited information.

He's now got some kind of cylinder "leak" around one of his spark plugs. I think he should be more careful of buying cars from self proclaimed "street racers". LOL
 

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I have a mustang gt around the same year. I also have the same tuner. Have he remove the diablo tune and see if it fixes the issue.

Report back.
 
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