This problem has me stumped. I have a 91 Mustang GT vert with 70k and 5.0 Auto.
The car suddenly has a slight hesitation. When I open the throttle wide open, the car starts to break loose, then you can feel the engine hold steady (speed is about 25mph) for about a half second- then she rips loose with no problems.
I do not have any backfires or predetonation.
I have done the following mods that may affect this problem:
Removed smog system completely and rerouted belt.
Installed 3.73 gears- VERY NICE!
9mm Ford Racing wires
K&N filter in factory box with silencer removed
factory plugs set at .60
2.5" MAC from CAT back.
Problems started when I added the following:
76mm MAF with 76mm inlet pipe w/ 19lb calibration tube and I reused the original sensor. I put back the original MAF and the problem went away- but could definitely notice the change in HP.
Since this mod- but after the problem- I have installed 24lb Ford racing injectors, 24lb calibration tube, Kirban fuel regulator and new vacuum hoses. No change in the problem. I now can't reuse the orginal MAF to make the problem go away due to the injector change.
I have tried 10-17 degrees of timing- no change.
TPS is at .98
Fuel pressure is 40lbs with vacuum off- and about 28 or so with it on.
I have a list of upgrades, but want to correct this problem before I jump ahead.
Anyone have any ideas?