99 GT wont go faster than 110 MPH
 

I own a 99 GT 5-speed. With the nice weather, I've been driving it a lot more. There's a nice patch of highway where you can open 'em up on. I am kind of surprised that my car wont go over 110mph. There is pedal left and the RPM's arent way high.....just wondering what could cause this????

The car has 76,000 miles on it. Has 3.90 gears and some minor mods: BBK cold air intake, accufab 70mm throttle body and plenum, MAC catback exhaust, Diablo Predator tune. The car runs great, no computer codes, and gets up to 105 fine....then it starts to lose its balls. Feels like its being held back. Its nowhere near the rev limiter, and I took out the top speed governor with my tuner.

Can my factory catted H-pipe be that restrictive? or does this sound like a lack of spark, fuel, ???

I'd appreciate any help.

That is strange...wish i could help ya...my 01 GT with 3.73's will do 135+ and was still pulling before I slowed down. hope someone can chime in and help ya.

pull off the diablo performance tune. maintain the deleted speed limiter and the altered gear ratio setting but that's it. let us know how it does. I'll bet the tune is really shitty.

I'll remove the Diablo tune and see what happens. I'll let you guys know.

With 3.90's I saw 160+ (needle went past where the stop peg used to be)

were you treading uphill, or fighting a headwind ?

You should see around 120-125 in 4th, and then in 5th it will loose a ****load of power, but you can still power through it with the 3.90's. Can be slow sometimes.

+1 on the tuner.

Its happened a few diff times on diff roads. The roads have been flat(not going uphill) and clear/calm days, so its not due to strong crosswinds or anything.

Just re-read my Diablo owner's manual. I decided to check for any codes, even though the check engine light never came on. Sure enough, there was one code stored. Said something like: "rev/Speed Limiter reached". I know I took this out of the tune too! There are actually two speed limiter parameters to turn off.....so, maybe I just turned one off....or maybe it just didn't take when I downloaded???? who knows. Anyways, I cleared the code and set both parameters off again and re-entered the tune. Hopefully this works. I'll find out tomorrow and let you guys know.

So, if this is it, the factory speed limiter is about 110 MPH on a 99 GT. I feel so violated! :)

What if Andys previous post is his last post and visit to this forum?
:poke:
Its not smart to be traveling on public streets at those speeds.

Heyyyyyy.............

I knew I'd catch some flak for this. I just want to see what this car can do. Just a short burst and back down.

yea i tested the top speed out on my 6er out on a 4 lane rd by my house at midnight a few times, nooobody on the road...i was disappointed that it only went to 115mph before it hit the limiter :-( i got a chip and don't want to risk the possible jailtime to find out the top speed

I had actually heard that some 00 GTs came with 16" rims, and because of that they were limited to 110, but I don't know if the same is true for the 99s. Do what everyone is saying, and start with the tuner, and then go from there!

This is stupid and doesnt belong in Mod Tech.

I will say though, Diablo "Performance Tunes" SUCK ASS!

That's the results I've seen. I had really bad problems with repeatable results from the diablo revolutions software. One time you'd load a tune and it'd do one thing then the next time it'd do something totally wacky. Almost like the tunes were corrupting themselves...

In any case the factory speed limiter shouldn't even approach on until well after 110. Mine made it to 140 before any tuning (and before I shut it down).

Public streets are not a good place for this sort of thing but the reality of the situation is they're sometimes the only place that actually exists. Choose your location with care, be picky about time and weather and be willing to lose your license if you get tagged. No running from the cops... they'll beat you like you owe em' money.

Called the DiabloSport tech guys. They said that there are so many Ford computers that some have problems with the Predator removing the speed limiter. They said to turn both on....that didn't work either. So, I just ordered an SCT2. Atleast these are vehicle computer specific(you have to give them your computer code). We'll see if this works. If it does, I'll have a Predator to sell for cheap!

i will tell you...i pegged out the speedo on my 04 six...dont ever do

the diablo tech guys are clearly idiots... You have to give them your code so they can make sure to give you a tune with the correct feature pack and dashpot setup. There's absolutely zero difference in how Diablo and SCT update the program... they determine a value and a variable and flash the ECU with it. They just suck, that's all.

The xcal2 is a really nice tuner and SCT's tunes are decent right out of the box. I'd still have the AF hand curved.

yea i got it up to 115 one night for a brief minute, at the track of course lol, but nvr pegged it. what is the top speed of our cars? or fastest anyones ever gone in a 6er in here?

maybe it is the ecu cutting the fuel off at 110, i don't know that much about the stangs but i do know our goat are set at 158 to 162 from factory, with plenty of pedal and rpm left. we can tune ours out so maybe you can to for that year. jjust my 2 cents.

IN a 6er, one of my friends brought his to 120, and it hit the limiter

yea i've seen/heard of them goin' to 120, but i'm curious about the absolute top speed of one w/no limiters...

i'm guessing the absolute top speed will be somewhere between 120-engine blowing up. jk jk

haha, jackass.

i havent had any problems in the diablo, i've tuned quiet well actually. my freinds dad works as a state trooper and he has one of those hand hell radar guns and i got him to clock me at 142mph topped. main thing about the diablo is dont tune everything at once, take baby steps...you'll be much happier.

Man, this thread is all over the place.

First, we don't condone speading, buit this guy is really trying to address a technical issue, so I am fine with it.

Secondly, we keep getting these types of threads in the Drag Racing Forum which is supposed to be used for Track Discussions. This needs to be addressed with the Mods.

Third, I will never use a Diablow product on my car. They suck! They dicked-up my tune beyond belief and then I had to wait 5 months for them to fix it and I finally gave up. SCT products and the tuners are superior. I know Diablow has won races...blah, blah, blah, but I have a blown motor over a year ago that I partially blame on those guys. First tune they sent me was for another car and I drove on the tune for weeks before I figured it out.

Fourth, mail order tunes are risky no matter who you use.