When the system is active for heat or air, we have had the ac system completely rebuilt including a new compressor, dryer, and a new POA low pressure valve, and a new blower motor. Above 3300 rpm the motor starts to miss and backfire. I have also replaced the distributor cap, rotor button, coil, condensor, wire from the coil to the distributor, wire from the starter to the coil. Our mechanic doesn't have a clue as to what the problem may be. All he wants to do is replace more parts. If there is anyone who might have a clue as to what the problem can be  I would realy appreciate the help with this.

 

Thank

 

Rod Socha 

 

Thank you for your fast response.

 

Yes all the problems with the heating and air started after the mechanic played around the the ac system.

 

I never have checked the alt. to see if the output was low with the blower on. But I will in the next couple of days.

 

Thanks

 

Rod Socha

 

This is Rod, in the past week I tried your suggestion about the alt. I was really hopeful that this would solve our problem, the alt is charging the battery at 14.7 volts with the blower on. Since this has something to do with the asto-air feature on this car I unpluged the air condictioning compressor and no longer have the missing and backfiring with the selector in the heating position. The guy at NAPA thought that maybe the battery was to small for the size motor and car, so I bought a new battery. Guess what I still have the problem. And I have four months to come up with what the problem is. 

 

Rod Socha

AND the drag, even if normal, many creating some pulse at the crankshaft.  If you have a sloppy timing chain that could cause the cam and points to bounce creating poor operation.