I have a 2007 Shelby GT, 4.6L with the following mods: CAI, 62mm throttle body, charge motion delete plates, Ford racing cams, American Racing long tube headers, x-pipe, and Magnaflow exhaust. Recently it has started to stumble and backfire on acceleration and pops and backfires on deceleration. It also will not acceleration beyond about 4000rpm. It just goes flat if I punch it. I have checked for air/vacuum leaks,fuel leaks, disconnected hoses or electrical connector and all looks good. It is not throwing any codes and the check engine light has not come on. The fuel pressure at idle is 39-40psi which is on the low side but within spec. I put new spark plugs in, checked them after a few miles and all looks good. I have tried two different sets of coils with no change. I am thinking the the fuel pump or fuel pump driver module might be bad. Anyone have any ideas/thoughts?

 

fuel starvation issue perhaps. How old is the fuel filter?

 

Fuel filter is new. Less than 50 miles on it. Fresh gas in tank.

 

Fuel injectors maybe?

 

I was thinking injectors, too, but thought that would show up as a fouled plug or two. All eight plugs look normal and have less than 500 miles on them. I find it hard to believe all 8 injectors are bad.

I pulled the computer harness connectors, cleaned them, and reconnected. Did not see any corrosion or bad contacts. Decided to load the default stock tune. The engine now runs as it should and revs to redline with ease. Somehow my custom tunes got screwed up.

 

Is that 62mm throttle body a Ford part or BBK? Aftermarket throttle bodies for these year cars are known to fail. It doesn't explain the recovery after you went to a stock tune but its something else to consider.

 

It is a Ford Racing 62mm throttle body. Going back to the stock factory tune in the ECU allowed the engine to run up to redline, or close to it, without cutting out. I did not have time to reload one of the custom tunes to see if they worked or not. I will try that this weekend. If the same thing happens the tune file or files have been corrupted somehow.

 

The stock tune is pretty good on learning. Maybe the custom tune wasn't opening up the throttle body all the way, starving it of air, or maybe too much fuel was being dumped and your were getting spark blowout (which if it is, could be fixed by gapping down the plugs), but it sounds like it is all tune related at this point.

 

Today I took the Mustang for a longer test ride with the stock configuration and all seemed good. The check engine light came on as expected and the code was related to the charge motion hardware which no longer exists on this engine. Stopped and downloaded one of the custom tunes along the way. Figured if I had problems I would know immediately and could go back to the stock configuration easily. But the engine now ran great with the custom tune installed. Something must have gotten corrupted in the ecu and the tuner could not correct it by reloading the tune. It could clear the problem by reverting to the stock configuration and then reloading the custom tune.

 

Glad it seems you got it figured out. I'm always nervous when I change tunes in my car. I had it get stuck once after it completed 100%. Went to start it up afterwards and I got a DTE Error message on the dash and no crank. After trying to reload the stock tune twice, it finally went back to stock then uploaded the tune fine.