Stumble/Back-fire at 75 mph

[Rod Rodriguez]

After dealership fixed the Alt they had no Alt so had it rebuilt but to 96 Caprice spec's at my request. Know they have to try and deal with a stumble/back-fire at 75 mph. Any suggestions as I'm having to call from Las Vegas Nv. to Enid Ok to tell the Tech(?) how to fix the T. It is stock w/TPS inhanser & hi-out put fuel pump

 

[blackbuick87]

Since you are not driving the car it is almost impossible to fix the problem over the phone. If it is backfiring at 75 it is certainly backfiring at other times. Without scantool info it is also almost impossible. The car is probably lean, so you have a fueling problem. check the MAF, O2 sensor etc, but if the damn dealer cant figure that out you need a new mechanic

And what the hell is the dealer doing driving your car at 75mph?

 

[Rod Rodriguez]

Thanks Bob D. Enid is aprox 80 miles from Oklahoma City. The T is maybe as old as the tech(?) but I'll call to see that they check the MAF,O2,and readjust the fuel pressure regulator to get more fuel flow, when I first took the T in one of the kids didn't why the fuel pressure wouldn't drop below 35psi when he removed the vacuum line from the regulator. I have a power plate could that help? Hope that the check engine lite came on so that it might leave a code. Would the Cam or Cranke sensor or the EGR need adjusting?

 

[blackbuick87]

This place is scary. Before they blow it up "test driving it" I would take it out of there until you get home.
The power plate would not cause this problem unless you knocked something off during the installation. If the vacuum line is not on FP will not rise with boost and it will go lean.