Hello there! I just joined this Chevy forum, so I'm looking forward to chatting with other Chevy fans!
I recently purchased a used 2003 Express 2500 standard body, with a 4.8 liter. It has 220k kms on it, and is in good shape and runs well. However I am getting terrible fuel milage, so I've started to try to diagnose that. First off, the exhaust smells quite rich, which points to it being a fuel/air mix problem. I hooked up an obd2 scanner, and I've started playing around with it looking for anomalies. The first thing I've found is the atmospheric pressure data and voltage information provided by the MAP senser is quite wrong. The pressure is displayed at -10psi at idle, and stays pretty much steady or drops slightly when throttle is applied. The voltage also does not change with throttle input. I checked the manifold pressure with a vacuum gauge, and it checks out within spec at -17.5 psi. The other strange thing is when I checked the voltage at the MAP plug, with the engine off but key on, I'm getting two different readings from two of the three wires, those readings being 7 and 10 volts respectively. What makes that more confusing is the obd2 code that I am receiving is p01070, or low voltage from map senser at pcm.
Going from all this, I first tried replacing the MAP senser with a different one, but it does not change anything. The data readouts for pressure and voltage do not change, and the code remains the same. I know this is very confusing, so my apologies, this is the best way I can explain it. I really don't know what to start checking from here... I guess I should follow the map wires for shorts and worn sections? I'm 17 so I don't have much experience with this sort of thing. But I'm realitively mechanically inclined, so hopefully I'll be able to figure something out.
Thanks so much for any feedback I get!
Cheers, Ian.