Pontiac Repair: 96 fuel consumption, mass air flow sensor, fuel consumtion

Question
i have a '96 Pontiac transport, 3.4L van. it has always been a little heavy on the fuel but this last year it has been exceptional. i have brought it in for the standard tune up(plugs, wires) and wheel pressure is always kept up, if not a little over inflated. the exhaust is not black but it smells bad when we come to a stop. almost enough to make your eyes water. in the last few weeks it has been sucking the gas like its free! this weekend we went approx 200-300km and it used almost 3/4 of a tank! i realize its old and it does have almost 250000km on it but that doesn't account for the tremendous amount its using. i have a 6.6L diesel and it gets better mileage than this van. im not ready to get rid of it yet, i have to wait a year to pay off the loan for the truck before getting into another for an car but i cant afford to keep putting gas in at this rate! what id like to know is, can i do anything more to it to get it back to the way it was? i do regular oil changes but haven't changed the coolant, does that matter? i cant afford a new payment but im putting in almost half in gas.
any help is greatly appreciated!
darren

Answer
Hey Darren:

well this is a bit odd. No service engine soon lamp has come on? if so have the van scanned for codes and see what me be stored. if the fuel consumtion is that far off it should turn on the service engine soon lamp. anything more or less then 15% off the optimal fuel mixture should trip a codes and the light on. with out the aid if a truse scan tool there is nothing you your self can do with this. You need to see what the engine senosrs are showing the engine computer and you need to see what the fuel trim is "rate of delivery" with out that you just guessing as to what the issue is. something you can try and it doesn't cost a lot is buy a can of mass air flow sensor cleaner its a product made by a company CRC and it is sold in a spray can take the sensor out and clean it follow the direction on the can can see if that helps make sure you put the senor back in the right way it can be put in backwards and that will cause even more issues. good luck :-)