.29 is actually within range (while driving). I'm assuming we're talking volts. 5 volts go into the sensor, if the tank is under pressure it can go as low as .1, if it's under high vacuum it can go over 4 volts. Mine reads 1.39-1.41 volts with an open cap (for your reference). Your mechanic could very well be right about needing to replace it. PO440 is a bear of a code to chase down because it's rather general. There's other more specific codes, but if it's an intermittent problem the computer can't pin it down to a specific sensor or solenoid. Your fuel gauge could also have bearing on the problem. If the truck doesn't have a consistent idea of how much fuel is in the tank it doesn't know what it should see for expansion or contraction of the fuel due to temperature changes (or fuel tank pressure as it were).

 

Can this FTP be changed with out dropping the tank?

 

Will having this code on cause gas mileage to go down because its the EVAP system for fuel vapors? I am trying to find out why my truck is running fine, but only getting around 220 miles(350kms) to a tank.

 

Well thats was one of the many main reason i got reid of the truck i would spend at times over 90$ in gas weekly just going from home to work. Now i have a 08 Sonata and spend only 30 weekly. Iv changed almost evey part that had to do with evap system to no avail even two different shops with no luck on finding to cause. O also keep in mind that these truck came with two types of tanks a small one and a bigger one. Small tank= less miles more fill stops.

 

I think its a 16 gallon tank or just a bit larger. I know on most vehicles when the EVAP system is removed(going to a return fuel system on high hp cars) and people delete the EVAP system their mileage goes into the toilet. So I was curious if this could be the case on these vehicles. For what I get for mileage I am tempted to toss in a newer 5.3L or even a 4.8L V8. It will probably do better on gas, but I dread having to deal with the oil pan and wiring it up. Plus I paid $2000 for the blazer

 

Yea that it well be a great amount of work for a V8 swap if your looking just to get good gas mpg maybe check into if its passiable for the straight 5 liter engine that comes in the GMC Canyon truck its acually a BMW Block.