Engine hesitates badly when transmission shifts

My 1991 Aerostar (4.0 w/automatic overdrive) has developed a bad hesitation when shifting from 2nd to 3rd gear (right at 60MPH) but only under full, pedal-to-the-floor, acceleration. It's not just a sputter or a lag, but it feels more like somebody flips off the ignition (or maybe like some sort of govenor).

I have to back off the accelerator slightly for it to recover quickly and complete the shift, otherwise it will hesitate and sputter for several seconds before finally shifting and going back to normal engine speeds.

I did find that if I back off on the pedal just slightly when it's about to shift, then I don't experience the hesitation.

As an experiment I continued to "floor it" and found that when it goes from 3rd to overdrive at around 85MPH, I will sometimes get the same lag. However I don't have the problem going from 1st to 2nd gear.

Note that I don't have the problem all the time. Maybe 75% of the time. It definitely will happen if the engine is not up to normal operating temperature. However it's inconsistant once it does does reach normal temps.

I love the 4 liter engine in my Aerostar. It's great for all the highway driving I do. But this hesitation thing gets a little frustrating in passing situations.

Any insight as to what my be the problem will be greatly appreciated.

Thanks!
-Mark

[QUOTE=makippert]My 1991 Aerostar (4.0 w/automatic overdrive) has developed a bad hesitation when shifting from 2nd to 3rd gear (right at 60MPH) but only under full, pedal-to-the-floor, acceleration. It's not just a sputter or a lag, but it feels more like somebody flips off the ignition (or maybe like some sort of govenor).

I have to back off the accelerator slightly for it to recover quickly and complete the shift, otherwise it will hesitate and sputter for several seconds before finally shifting and going back to normal engine speeds.

I did find that if I back off on the pedal just slightly when it's about to shift, then I don't experience the hesitation.
Mark,check the obvious. The wires, plugs and vacuum lines if possible. Throw some techron or Lucas gas treatment in the tank. It may be something simple like a bad wire. If the plugs or injectors are a little dirty the gas treatment should help.
As an experiment I continued to "floor it" and found that when it goes from 3rd to overdrive at around 85MPH, I will sometimes get the same lag. However I don't have the problem going

My 1991 Aerostar (4.0 w/automatic overdrive) has developed a bad hesitation when shifting from 2nd to 3rd gear (right at 60MPH) but only under full, pedal-to-the-floor, acceleration. It's not just a sputter or a lag, but it feels more like somebody flips off the ignition (or maybe like some sort of govenor).

I have to back off the accelerator slightly for it to recover quickly and complete the shift, otherwise it will hesitate and sputter for several seconds before finally shifting and going back to normal engine speeds.

I did find that if I back off on the pedal just slightly when it's about to shift, then I don't experience the hesitation.
Mark,check the obvious. The wires, plugs and vacuum lines if possible. Throw some techron or Lucas gas treatment in the tank. It may be something simple like a bad wire. If the plugs or injectors are a little dirty the gas treatment should help.
As an experiment I continued to "floor it" and found that when it goes from 3rd to overdrive at around 85MPH, I will sometimes get the same lag. However I don't have the problem going from 1st to 2nd gear.

Note that I don't have the problem all the time. Maybe 75% of the time. It definitely will happen if the engine is not up to normal operating temperature. However it's inconsistant once it does does reach normal temps.

I love the 4 liter engine in my Aerostar. It's great for all the highway driving I do. But this hesitation thing gets a little frustrating in passing situations.

Any insight as to what my be the problem will be greatly appreciated.

Thanks!
-MarkMark, check the obvious first. Sometimes under load or rpms a bad wire or dirty plug or injector will cause the car to bog. Try some techron or Lucas gas treatment in the tank. If possible check the vacuum lines near the intake manifold for cracks. Start with the simple stuff.