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Recently (500 mi ago?) I had 4.10 gears/bearings/tune installed into my 04 GT. I'm still getting used to the changes and how it drives, which makes me vague to whether or not I actually have a problem. I drive ~40 miles one way to school. 35 of those miles are straight highway and interstate. As far as mustangs go, before the installs my average per tank was pretty good(maybe flirting with high 300's close to 400). I would fill it up closest gas station once the light came on. After the install my car is at like 20mpg even running 93 economy tune. Its not the mileage that bothers me, its a freakin mustang. I was just worried something might be off as I couldn't shake the feeling while I was driving that something wasn't right. I did have a pass or two of fun, but the car never exactly seemed the same after.
So i went searching. Pulled off the filter from my american muscle CAI (not the greatest but it works) and it was still perfectly clean. No obvious spots where a hose had come loose. Idle is pretty steady, its def different, but not like dropping, the needle shakes around 800. No codes. HOWEVER... I did find something on the Intake manifold. at first I thought it was a scratch from a wrench replacing plugs or attaching the CAI. then I ran my finger across it and it went all the way down to the block. Turning the car on doesn't make it feel any different, but under the hood there is a smell of gas that I dont recall before. (almost like starting a car with the throttle pushed) Anyway, I've read that these are prone to cracking, and was wondering if any of this sounds fishy or if Its just me worrying about my baby and its all related to my new gears and tune? maybe i just need to get over it :)

All Ford wisdom is appreciated :worship
 

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That doesn't look like a crack, it's a seam from the mold. I doubt your intake is cracked; most cars that experience this problem run like complete dogcrap, if at all, or are puking coolant. Yours does neither. As far as gas mileage, the 20 you get is right on par with me (I have 4.10's too). I get about the same, maybe like 21.5 if it's highway miles and I keep my foot out of it. As far as the gas scent, if you think you smell gas then it's definitely worth a look. It could also be exhaust fumes that you are mistaking for fuel or you could just be paranoid (don't feel bad, we all go through it once in a while), but since it's a potential safety issue I would slide under the car and inspect the lines and fittings starting at the tank, working toward the front of the car.
 

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Reverse your tune back to stock, see if there is any difference in mileage. Could be a problem with the tune.
Also inspect plugs, could be running rich, hence the gas smell. A dark plug will indicate a rich condition.
 

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Discussion Starter #4
At first I thought it was just a seam too, but it felt like it got progressively deeper as it went toward the block on the back side. It certainly not running like complete crap so maybe it is just the tune. If it ain't broke don't fix it.. When I put my tune back to stock my speedo will be uncalibrated correct? I'm not worried about it, I just haven't tried it. And thanks for the replies socal and raptor!
 

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Assuming you're using a Diablo or SCT handheld, you should be able to calibrate the speedo even if not using a performance tune, refer to the user manual for how to do this. You can reflash it back to stock for a minute if you like, but aside from a little less power than what the 93 tune offers I don't expect you'll notice any difference. As far as the manifold goes, if you really suspect there's an issue then get a can of carb cleaner and with the engine running, spray just a little bit over where you think the crack is. If idle speed and/or quality changes, then this would likely confirm the crack.
 

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Discussion Starter #6
I'm using an sct tuner so I'll search around the options. I never had a reason to change settings on the stock tune but Im going to be able to find it. I'll search around the work station for some carb cleaner and if I have some I'll spray it on while I put on the tower brace check the plugs and seafoam it. it can't hurt anyway.
 

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Absolutely go back to the stock tune, unless you have the car run on a dyno and tuned right. Your handheld should enable you to change the speedo for your 4.10's within the stock tune also.

I have some off the shelf tunes that just run like garbage, reek of unburned fuel and get horrible mpgs. I had a 93 tune that I couldn't even get 200 miles out of a tank, on a car that would always get right around 250 miles.

The 2004 intakes have updated coolant crossovers and are not prone to cracking as much as the earlier ones. If you car isn't consuming coolant, I wouldn't even think twice about it.
 

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Discussion Starter #8
I'll call up bama if the stock tune makes everything better. I'll find out soon after school
 
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