milesg

I have a 68 chevy k 20 pickup that i recently had a lq4 engine swap done on a few months back. since i got the truck from the shop i have been experiencing a bad surge when i drive more than a few miles. The engine is completely stock and the fuel pump is a new walbro 255 inline pump. the first pump u had was a msd and it did the same thing. i am getting a steady 12.5 volts at the pump even when it surges and 53 psi at the rail when cold. Once the truck gets warm the psi drops to around 20 psi and then goes back up to 53. If i try and give it more than part throttle it will drop and almost cut out. i have been fighting this for a month now and could really use some help from someone who knows more than me about the fuel system.

S10xGN

iTrader: (11)

Electric pumps don't surge. It can only be the regulator or the wiring to the pump is so trashed it's causing the swings (which you say is constant). Check the pump ground (make sure there's no paint under the lead) and run a hot wire straight off the battery to eliminate wiring...

N20zuki

What fuel tank are you running and how much fuel is in it? It may be cavatating and causing the pressure drop.

nuntheweiser

Maybe a dump question but does it have a return line? If not that pump probably just burned itself up.

realsquash

iTrader: (1)

What is the battery voltage when the truck is running? 12.5 at the pump seems pretty low, and makes me suspect something is wrong with the wiring.

imma_stocker

iTrader: (19)

Assuming EFI with correct rails and return system....

As others said, triple check wiring and ground. External pump needs to have air pass over it to keep temps under control. If you have it in a tight spot, I've heard of computer or bilge fans moving enough air to keep them from overheating.