1991 fullsize 2wd dr 5.7 As the title says. tried a new map sensor same results checked for vacuum leaks found none. Ran codes got a 13 and a 44 disconnecting the o2 sensor doesn't change a thing. Runs perfect with map disconnected either electrically or without vacuum. if you apply over 10 inchs of vacuum it will either die or surge badly between almost zero and 1500 rpm's. Any ideas or anyone seen this before. Cap, rotor, wires, plugs are new. it carries 19 inches of vacuum at idle.

 

did you check the coolant temp. sensor? often times when they go bad they show it to be -40 all the time, and will run like crap (if it starts at all) and won't set a code

 

Ok I fixed it. I tested the fuel pressure and only had 3 lbs totally dead headed and the fuel pump relay jumped to run all the time. Bought a new pump and pull the tank down. When I pulled the module out I found the hose from the pump to the steel line was split. This hose is only about 1 3/4 inches long. Since the truck had 175,000 miles I went ahead and replaced the pump it came with a new hose in the kit. Put it all back together, it fired up and idled perfectly and drove out good for that many miles.