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Discussion Starter · #1 ·

My father met with Dan from pro-dyno in Winston-Salem last year to tune my S197 mustang. Dan may remember the case, but we were having problems with the car surging in 5th gear around 1500-1700 RPMs. After taking a ride with my father to witness the problem, he mentioned that he thought it could be the throttle body causing the problem. He also said that it is nothing that will cause the car to functionally fail when driving.

We did get the car tuned that day and I must say that the tune is amazing. After that, we replaced the throttle body, cleaned the MAF sensor, replaced the fuel filter, replaced the battery, had the alternator checked but not replaced, had the vacuum lines checked and to no avail, we are still experiencing a the surging. I drive the car to work daily, so I have been trying to pinpoint the exact circumstances when the car will surge. The only time I experience this is when I am cruising in 5th gear around 55-60 mph and I slowly increase the throttle (RPMs increase from around 1200 to about 1500-1800). I experience the problem right before I give the car enough throttle to shift down from 5th gear to 4th gear. Usually, I can duplicate it when coming off of a decline and going into an incline. That transition when I start to press the gas is when I experience the surging most of the time. (Again, before giving the car enough throttle to downshift).

I have noticed the problem occurs a significantly higher amount of times when I am starting to ease into the throttle when going up a hill. So, every day coming home from work, there is one specific hill that I have noticed the problem more times than not. I have tried absolutely everything (AC on/off, Headlights on/off, radio on/off), and it is always hit or miss whether I can get the car to do it. There are no specific user-controlled circumstances that I have been able to relate to the problem. So, instead of throwing money at the car trying to replace every single thing, I decided to come to you guys to see if there is any specific order to where I should begin. As of right now, I think my first move will be to replace the alternator with a high-performance alternator.

Car Specifications:
2005 Ford Mustang GT
FRPP Axle Backs
Magnaflow X-Pype
Shaker Cold Air Intake
XCal Tuner

Roush Underdrive Pulleys (The kit only came with two pulleys instead of the three that we saw in most kits. We thought maybe this could be a problem since the alternator pulley remained stock. We thought maybe when putting the car in a bind at low rpm in 5th gear would be under torquing the alternator, causing the surging sensation we are seeing).


Sorry guys, I completely left out a huge part of the equation.

In April last year, I snapped the main shaft in the transmission. (Hard to believe, but I will post a picture on my profile). So, my father and I took the transmission out and had one of his friends, someone who works for our local ford deanship rebuild the transmission. He rebuilt it and we got it back in the car and the speedometer was jumping all over the place and we couldn't get the car to move. So we thought the transmission was built wrong yada yada yada and we took it to the ford dealership. They tested the car with their computer and said it was the PCM. The ordered the PCM, took two and a half months to get the thing and put it in the car only to have the speedometer do the same thing. Another guy took the transmission out and checked it, only to realize the speed sensor was put it backwards. We pulled the transmission, had the original guy fix his work (got our money back for the tranny work because his negligence caused us to pay for a whole new PCM). So, after about 7 months, we get the car back on the road and I noticed that the car is pulling this surging nonsense. We took the car back to our ford dealership who told us there is nothing wrong with the car according to our computer. So we took them out on the road and showed them our problem. They told us the only thing they could do was to start throwing money at the car to try to troubleshoot the problem. (At this point we were fed up with paying them for their crappy work because they made us replace the PCM for something that was not even related). So, that is when we went and met with Dyno Dan to see if it was possibly the tune that was the problem. And that is where my original thread begins.
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