[V8] poor fuel economy....please add this to the wiki

[allanvega at comcast.net]

Below is a cut and paste I wrote up in reply to Sams poor fuel economy on another forum. I thought most of you could use it since the advise usually given here leaves members grasping at straws. I don't have wiki posting privileges, so if someone want to do it for the benefit of the list, that would be great. Al 





Having just done this swap, a few months ago myself, I can tell you that you do not need an adjustable fpr to run the ford 19lb injectors. They are rated 19lbs @something like 40psi, and the v8 fuel pressure is 4bar, roughly 60psi. basically, the 19lb injectors flow the same as the stock 4.2 injectors at any given fuel pressure. 

As for your fuel consumption problem,there are a few key sensors that will cause poor fuel economy. These sensors can be bad, and not throw a code, so you don't want to rely on codes alone (there's is a lot of truth when the techs at audi tell you "codes are just a guide") let me explain. if you have a dirty maf or iat sensor, the ecu will still receive a signal from them, it wont be an accurate signal, but the ecu will assume it to be valid, because it only recognizes short to ground or open circuit. Given the motronic relies on these two sensor to calculate and adjust a/f ratio, its important to ensure the ecu is receiving a valid signal. CRC makes a great product I like to use as a maintenance tool, its called MAF cleaner, and leaves no residue behind, unlike some tb/carb cleaners out there. So, pull codes(as a giude) if those two sensor check out ( no short, and no open circuit) then move on to cleaning them. 

Next sensors to check and replace are the lamnda/coolant sensor on the right rear head, and o2 sensor. I The lamnda/coolant sensor tells the ecu if the motor is hot or cold, and adjust fuel enrichment accordingly. A false reading from this sensor can(and does) cause the car to run rich all the time, and eventually kills that nice new o2 sensor you just replaced. Let me say right now that the o2 sensor is the last sensor you want to replace. The reason why you don't want to replace it first is this: if you have a dirty iat,maf, or lamda/coolant sensor...it will eventually cause the o2 sensor to fail. I like to replace the coolant/lamda sensor and 02 sensor together. If you follow these steps in this order, and you actual motor is mechanically sound, You to can enjoy 20-24mpg highway.