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Hey guys got a quick question that some of you may have the answer to. I have a 2005 mustang GT with the 5 spd manual. My only mod so far is the diablo tuner and a k and N drop in. I have been running the 93 tune for the past 6k miles and that may be my problem. I have put 93 gas in it from BP every time but that may have not been good enough. On long trips sometimes I will go from 5 to 3rd gear on the highway and it seems to miss bad. It seems to buck untill I lift and get below 65 mph. At that point i can go WOT again to red line in 3rd with no issues. This is NEVER an issue when just doing short ( less than 50 miles at a time) drives. I have only noticed this when traveling from WV to Bristol TN and from WV to Daytona ( where I am at now). I never get the trac light when this happens nor do I get an SES light. It has happened once when I had the trac control off. This issue does not happen every time even on long trips, just when I really need 3rd gear not when I just want it for fun. I brought my tuner down with me and I have flashed it back to stock to see if this resolves the issue. Has anyone else had this issue? Is it safe to drive around all the time on the 93 tune? There is no place in WV that I know of that I can take it to for a custom tune so the best I have for now is the 93 tune. On a side note whats the performance difference between the 91 and 93 tune? Would driving around on the 91 tune be safer. I was just wondering if anyone else has this issue and if they figured out a solution. Thanks in advance for any help.
 

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I really don't have an answer for you. I guessing the Diablo tune you have might be a problem. If you put the car back to stock, then you should run 91 gas.
Call Adam at ST Motorsports (stmotorsports.com) in California. This guy is great, he was here at my house to complete the tune he did. I have a 05 GT Saleen S/C, automatic and he used the Diablo tuner (he made a tune for my car) and now the car runs great. 354hp/350trq

Good luck.

Ed
 

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MSgt46270 said:
If you put the car back to stock, then you should run 91 gas.
Ed
Shouldn't he run 87 octane since that is what the stock car is tuned for? I have heard people saying it is "throwing your money away to use anything higher than 87"

Everything else being equal, has anyone noticed a difference when running a 91 tune, over an 87 tune? Wondering how much difference it makes. Dyno- or seat-of-the-pants-wise.
 

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I have been running the predator with the C&L 93 octane tune on 94 octane fuel since my car was new without issue. The only thing that I've experienced is the TCS engaging on a 5-3 downshift if I hit a bump in the road simultaneously.
 

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I have experienced the same problem and I have a completely stock 5sp GT running 89 octane. My personal opinion is that there is some sort of fault with the fuel injection system, intake or most likely electronic throttle control.

As far as the fuel rating goes, higher octane fuel burns slower and is less susceptible to premature ignition. So, unless you increase your compression ratio you are wasting your money and possibly causing minor damage to your engine.
:sterb:
One engineers opinon. A ford engineer is likely to blame for the bucking problem so take it for what it is worth.
:handball:
 

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JetBlack said:
Shouldn't he run 87 octane since that is what the stock car is tuned for? I have heard people saying it is "throwing your money away to use anything higher than 87"

Everything else being equal, has anyone noticed a difference when running a 91 tune, over an 87 tune? Wondering how much difference it makes. Dyno- or seat-of-the-pants-wise.
It can make a big difference with a good tune. Running the factory tune on premium is as you said, pretty much pointless, but with a proper custom tune, more HP can be unlocked by tweaking ignition timing, etc.

The results of that are verifiable by either a real dyno or the "butt dyno" method
 

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And by 89 I mean 87... (edit)
MSUslacker said:
I have experienced the same problem and I have a completely stock 5sp GT running 89 octane. My personal opinion is that there is some sort of fault with the fuel injection system, intake or most likely electronic throttle control.

As far as the fuel rating goes, higher octane fuel burns slower and is less susceptible to premature ignition. So, unless you increase your compression ratio you are wasting your money and possibly causing minor damage to your engine.
:sterb:
One engineers opinon. A ford engineer is likely to blame for the bucking problem so take it for what it is worth.
:handball:
 

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There have been a couple threads on this, a while back. It seems to do this with or without a tune, but not on a consistant basis, at least with the GT. I had it happen stock, once coming down off cruise control to 4th at aout 70, and then once downshifting about the same way from a steady state, non-cruise control drive. I have also had it happen once since I put in the JLT intake and SCT tune. I haven't heard of any real answers, but speculation points to a flaw in the elec throttle control or something. My solution has been to push in the clutch and pop the accelerator a couple times real quick before downshifting. Seems to wake it up, kind of
 
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