This has to be the strangest thing I`ve ever ran into here. Have a 91 s10 blazer, 4.3 , 4 wheel drive. If I turn off the heat/defrost controls it will start bogging out like timing off. Turn heater, defrost, ac, or vent on and runs ok. Now the fan also has to be in one of the center spots. On low fan or high fan will miss but not as bad.This has got me wondering if I need to take blazer to a priest or a mechanic! Actually my mechanic said not him. Advised I replace blazer rather than repair. Any ideas where to start? Timing good, knock sensor new, most sensors are new. What would heat and air have to do with spark? Am lost here.

 

Wire grounding out somewhere maybe? How does the voltage hold while it is cutting out?

 

Maybe something stupid like an alternator or a battery, funny things happen when batteries go bad.

 

volts seem to go up slightly,around 14, normally just under 14. Have noticed a slight noise from alt but was suspecting belt. Not really worn though. GFuess its not a big deal, just very strange. was going to pull control for heat and air but it`s not coming out. Or at least not very easily. Both Haynes and Chiltons say unscrew, pull out and unhook. Yeah, right, can`t pull out far enough to get anything unhooked.

 

If the altenator squeeks at all the bearing are probably going, you should test it at orilleys or autozone for free. Autozone does it when it's on you car I think, not sure.
And if you have the oldschool heater controls on right side of the steering wheel don't mess with them, they are a bitch and you will probably break something getting them out.

 

Thats what I thought about heater controls, they are on right side of dash. Can I pull the dash(digital) and get to wiring harness from there? Pulled stereo , lighter and back window switch today and can`t access from there. Alternator not really sounding like bearing gone but will have it tested just to be sure. Cheked out wiring harness in engine and not seeing anything bad there.

 

I pulled out my heater/AC controls several times. The only electrical parts on there is the switch for the fan speed and the panel lights... not much there. The rest is cable and vacuum. I had a short with the fan switch plug. The wires got hot and melted the plug internally and shorted out the fan intermittently. It took me months and several parts until I figured it out.

 

Just a guess as the previous people have stated is, what if its something to do with a ground wire?

I have a tercel as my work car and she has alot of problems. Her favorite is when i run the radio, and the heater fan inside, I get a buzz on the radio like a chopper flying overhead. Being totally noob about electrical, thats what Im guessing is happening to her.

You said it drives bad when some things are on or off? Try checking all your wiring. Something might be crossed. Maybe a corroded electrical wire, or perhaps something rubbed off the insulation on one as a result, it may be coming in contact with something external and filtering off your charge. There are wires all throughout the body of your vehicle. It might be a good idea to test any you can find, or do a visual inspection.

Just a guess though.

I had bearings go out on my S-10 before. It bogged the engine briefly, but then everything ran fine until I stopped. then it wouldnt crank over, the bearings siezed. After that it stripped the starter because I tried to get the truck to start. I had pieces of bearing all over the engine, little silver metallic flakes.