Here's something you injected truck owners might want to read.. Had a 1990 GMC 1-ton rack body truck come in my friends shop--it was running rough,stalling,and had bad hesitation.,low power too.we figured the fuel pump was failing--pressure test showed pressure a few lbs lower than specs called for..the gas gauge didn't work either,so pulling the pump was a nesessity anyways..they opted to cut an acsess hole in the planks of the wood bed,rather than yank the tank out.. (but they later found it impossible to replace the new unit,since it had several inches of tubing made to it,unlike the stock one!--had to pull the tank anyway! ) After all the BS of installing the new pump,the gas gauge worked fine again--but it still ran exactly the same! ..the new pump was over 200 bucks! --and they were scratching their heads trying to figure out the problem..truck had no "codes" showing,and everything else looked good..no crushed exhaust pipes,or bad plug wires,etc.. Then ,as it was running,it just quit!..we swapped the fuel pump relay with the A/C relay,and it fired up again,but ran no better--then it quit again,and would not start!..then ,a stroke of luck--a guy with a nearly identical truck pulled in,and wanted to get an oil change..we tested the wires going into the fuel pump relay on both trucks--our "dead" one had no power in a green wire,that the other truck DID have power in (with key "ON")..AH-HA! We cut the insulation back on that green wire--it had about 2 strands of copper left,and a bunch of green powder for nearly a whole foot back!..we chopped out the bad section (yes,there WAS power there a foot back!),and we spliced a new wire and connector on it..the truck instantly fired,and ran perfectly...good thing they had to change the sending unit (part of the pump assembly) or all that work and $$$$ would be wasted!.. You guys with EFI trucks that run crappy might want to check the wires to the pump relay!!..this truck ran crappy for nearly a year,and other mechanics tried a lot of "fixes" that didn't help at all!..