I will paypal $10 to the person who solves this problem

[Green94GTvert]

I am working on a friends 93 Mustang GT and we have a problem after installing a newly built engine. I'm ASE certified and experienced when it comes to fords. The problem we are having is a hesitation when accelerating heavily, it's feels like an ignition miss but I'm not sure that it is. The only thing that sticks out on the car is a whistle from the IAC motor, it whistles from the top of it (closest to the hood). The problem is only when you get in the gas hard, if you baby it you are alright. If you go wide open, it's alright. I thought at first it was a vacuum leak, and we've checked and rechecked everything. Here's a little bit of info about the build:
306 DSS long rod kit
GT40P heads ported and flow bench tested
AFM n41 cam
edelbrock performer upper and lower intake
BBK 70mm TB and EGR plate
24lb injectors and PRO-m MAF claibrated for 24's
smog pump eliminated
off road x pipe and 1 chamber flow masters
aeromotive fuel rails with #8 feed from stock lines and #6 return to stock line up front. FPR is set at 40psi with line off and ignition timing is at 12 degrees

I really have no clue where to go from here besides to try to backprobe the o2 sensors and see what their reading. I backprobed the TPS and it's right at 1.0v. What else should I check, as I said before, whoever tells me where to look and solves the problesm will get $10 paypaled to them. I'm tired of dealing with this and I want this thing to run so we can dyno it and get some numbers at the track.
Adam

 

[jerryD]

pull the codes and see what you get.

i don't see what fuel pump your running. do you have a guage mounted so you can see what the pressure is doing while getting on it? the whistle is prob from your BBK throtle body.

 

[Roland69]

Maby the stock ignition is too weak for that build. Just a thought

 

[Aliate X]

Sounds like a problem with your MAF.

If it had something to do you with your MAF, it would accelerate fine if you slowly lay into it, but if you stomp it, it would fall flat on its face.


Did you check for vac leaks?

 

[Roland69]

I thought at first it was a vacuum leak, and we've checked and rechecked everything

 

[HISSIN50]

The problem is only when you get in the gas hard................. If you go wide open, it's alright.

I consider these loose phrases to be almost interchangable. Please clarify if you can.

 

[Euphoric306]

hissin i believe he means if it's slowly laid into WOT then it does fine, but the sudden stomping on the gas into WOT is what causes the hesitation. i've heard of whistling from the IAC motor being a sign of it going out, but that wouldn't be cause for the problems you're describing

 

[jrichker]

Does the problem occur when the engine is warm or cold or both? What codes did you get if any? What are the vacuum readngs at idle & at cruse? Is the vacuum reading steady or does the needle sweep back & forth?

 

[1988WHTGT]

Check the seal for the cover that comes off on the upper intake. I had that problem and had a whistle and it was coming from the removable side plate on the upper. Also check lower intake gaskets. Had the same problems againa and had a lower intake gasket that slid down a little causing a leak.

 

[Green94GTvert]

I will pull the codes as soon as I can guys. To clarify the problem, it is fine as long as you go wide open right away, if you go from say 1/4 throttle to 1/2 throttle quickly, it bucks and jerks like an ignition miss. If you're cruising at 1/2 throttle and go WOT, it is just fine. I will get a vac gauge on it too and drive it to see what happens. Thanks for your help so far.
Adam

 

[shallowreef]

I doubt this but, could he be flooding the engine with too big of injectors? I don't really know but it seems like he has too much fuel and not enough air?

Then again i really went out on limb for this one.

 

[trents99]

Whistling is from the TB as mentioned above. Go here to check on fixing it

http://www.allfordmustangs.com/forums/showthread.php?p=440596

 

[RaceDvr50]

Questions

Did you set your TPS when you installed the new throttle body? Also what is your fuel pressure set at? The 24lb injectors will not properly atomize fuel below 40psi so I would set them at no less than 42psi. I have seen some problems with people swapping in 24's and setting them to 38psi, one person reported a 0.5 second off his 1/4 mile after he took my advice. Good luck, also if you aren't already running one a Accel 300+ or a MSD 6AL can really perk things up.

 

[Strype]

My friend had the same problem... ended up being a bad MSD dizzy cap and a wire change

 

[silverhemi]

Not trying to be a smartass, but.....You do realize the N41 needs a minimum of 30# er's and and 80mm MAF according to AFM?

 

[Bad92GT]

bump your timing to 16* degrees and call me in the morning.. lol

 

[bsedwebt70-5.0]

MAF - mentioned earlier - clean the heated wires with electric parts cleaner - free fix....

 

[Green94GTvert]

The problem could very well be MAF, we're going to mess with it here in a bit. It is a granatelli 75mm, not a PRO-M like I at first thought. I've heard these MAF's are almost a joke after talking to AFM. One of the guys at AFM told my friend that the 24#ers will work but probably not make as much power as say the 30's with a 80mm good maf. We're going to clock the maf differently as the AFM tech told my friend to and I'll post later if it worked or not.
Adam

 

[87'GTstang]

I experienced a problem like this awhile ago. Vacuum was low but reading okay at idle, but it had a large amount of hesitation. Turned out to be the lower intake gaskets slid a bit and caused a small internal vacuum leak.

 

[Raginstang]

here is a serious thing to check, I noticed you are running aftermarket heads, make sure you are using the right length spark plugs, if the head is taller and you use a stock plug it will arch into the spark plug holes at low throttle and light throttle, but at full throttle the ignition spark will be enough to jump into the cylinder and work fine. I know this cuz I had the same problem you are having when I got my Twisted Wedge Heads used, nobody told me I needed a longer spark plug cuz the head was taller and I was using stock length plugs, had bucking at low speeds and part throttle, but ran like a bat out of hell on full throttle, checked EVERYTHING, finally I called Trick Flow and they asked me what plugs I was using right off the bad, replaced em and boom, perfect. look into it, just a thought