my 90 gxl idles fine and starts great. but at constant throttle (5th gear 3200rpm) on the highway the car gerks and backfire. I have replaced the fuel filter cleaned the plugs. The gass is ok (i think).

The voltage does drop to ~12 volts.

the car idles fine with the negative lead of the battery. the car also idles withthe lights and rear defrost on as well asthe fan on full

if anyone has any ideas please share

thansk mike

 

Sticking ACV or mis-adjusted TPS and a bad alt

 

Not to gang up on you, but you've got something wrong with your charging system. Either the alternator or the wiring from the alternator to the battery.