1999 mustang losing power at the end of road race - MustangForums.com



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Old 10-19-2017, 12:58 AM   #1
roadcourse 99
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Angry 1999 mustang losing power at the end of road race

I have a 1999 mustang GT that I only take to the track and road race. It is usually about 10 to 12 laps and 20 to 25 minutes on the track at a time. The first run the car runs perfect every lap. Usually the second race is also good. Like clock work in the 3rd run (below a half tank of fuel) I start to lose power. I always get 121 mph in the long straightaway. The power loss starts gradually with the next lap at about 110 then 75 is my top speed when I have to get off the track. If I let off the gas it takes off a little but dies back down. If I let it cool down for a couple of hours it will run normal again for may 20 minutes then I lose power again. I have changed the fuel filter, changed to MSD COILS, ngk iridium plugs, steeda underdrive pulleys, cold air intake, poweraid throttle body spacer, 160 high output alternator. Pacesetter 3 inch long tube headers. I have just ordered a Walbro 255 fuel pump but I am just guessing at this point. Nothing has fixed the problem. I pay 300 per day for 5 races and I never get past the 3rd. Can someone please help?
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Old 10-19-2017, 02:56 AM   #2
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Damn. Are you able to add more fuel after the second race so you aren't below half a tank? I am not sure why though letting off on the gas would have the car still take off (accelerate a bit) and then slow down unless there's an issue with the line leading to the throttle body that opens the blade, or a computer issue.

Is your car tuned, either by a dyno or email/data logged tune?
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Old 10-19-2017, 10:48 AM   #3
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Your situation could probably benefit from some data logging of these runs, have it all looked over by your tuner. And probably has nothing to do with your power loss issue but I would still lose those iridium plugs in favor of copper. Same with the aftermarket coils, in favor of oem.

I think you may be onto something with the fuel pump replacement, it is possible that the stock pump is underperforming but you would need to datalog to confirm. Would also be nice to know if the PCM is retarding timing for some reason, like maybe due to engine temperature.
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Old 10-19-2017, 12:46 PM   #4
roadcourse 99
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No the car is not tuned. I don’t really know anything about tuning or data logging. Is it something I can buy or should I take it to someone? I can add gas after second race and I planned on it this last run. It started raining and I never added fuel. I missed the 3rd run due to the rain. The car sat for 3 hours between runs and the 4th race it ran perfect. I parked for 1 hour and added 5 gallons before the 5th race and I still lost power with 2 laps left. The temp gauge always shows perfect. Is there a chance that the fuel pump is getting too hot? It is working extremely hard. I get about 70 miles to the entire tank of gas. Something is definitely getting hot and malfunctioning. Can it be the fuel pressure regulator?
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Old 10-19-2017, 03:44 PM   #5
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Could be any of the above, honestly. As far as tuning and use of handheld devices they are pretty easy, once you plug into the OBD port almost self explanatory. Your best option would be to find somebody local who can strap the car to a dyno, but will also be the most expensive option. Next is buy a handheld device and do remote tuning - they will send you a device preloaded with "custom" tune files specifically for your car; you upload the new tune and datalog using the device and then can send the datalog file back to them for review and adjustments as necessary. There are several established and reputable people you can deal with on this, Brenspeed and Steeda just to name a couple. I have nothing against Bama (American Muscle) but I have a feeling you would be better served by others; Bama has been known to take several tries before getting a tune revision right (and occasionally they never do) whereas companies like the other two I mentioned will usually have you dialed in after one or two runs, assuming it wasnt perfect right outta the box. There are others as well, so be sure to do your homework on that. Personally I have only dealt with Bama.

You mentioned having LT's.... Because these relocate the upstream O2 sensors further back from the cylinder head, they can and usually do require some adjustments made via tuning in order to get the sensors reading correctly again. The fact that you have LT's and are still running a factory calibration could definitely be at the very least contributing to your power loss issue.
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Old 10-21-2017, 12:54 PM   #6
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We ran into two problems with our Lemons car that acted similarly. Our fuel pressure regulator failed and was replaced. That fixed things for a while but we started hving problems later. We pulled the fuel pump and found the welds that attach the pump to the bracket had broken. This caused the main fuel line to chafe and caused loss in pressure. It really effected the car when the fuel level went below the break as the pump was then sucking air. It was a weird failure but a new pump fixed it.
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