Chevy S10 Difficult To Start

[nmiller90]

I have a 1991 Chevy S10, 4.3L that has been having some trouble starting lately. It's very sporadic when it does it, but when it happens, if I hit the gas it will start, but it will shake horribly until I let off the gas, when it will then stall out. Then, if I let it sit there for about five minutes or so and then I try again, it starts just fine. When it stalls out, the check engine light will come on. So I checked the codes, but all I'm getting is Code 12 over and over again. I thought it might have been a spark problem, so I changed all the spark plugs as well as one of the plug wires that was bad, but that didn't help. I also changed the air filter, cap, and rotor as well, but that hasn't made any difference.

 

So my next thought is that it could be a sensor problem, but I'm kind of short on cash and I want to avoid throwing unnecessary parts at it. Anybody have any thoughts on which direction I should take this?

 

UPDATE: So I messed with it some more and finally got a code reading. I got Code 33, map sensor voltage too high. I talked to a mechanic and explained the symptoms, and their guess was the fuel pump, or something similar that is causing low fuel pressure. That seems plausible, but my next question is can a bad fuel pump cause the map sensor code to go off?