roccoboost

Recently when sitting at idle the truck seems to have a slight "lope" to it. Was idling smooth as glass before. Also seems slightly down on power, but no boost gauge hooked up to verify if there is a drop off. Im not seeing any extra smoke when I am idling or at full throttle. The truck is stock, besides a 4" exhaust and automatic. Any ideas what it might be.

93flatbed

A weak lift pump, or air getting into the supply side of the fuel system. A fuel pressure reading would be very helpful for diagnosis.
Justin

roccoboost

I have a new piston lift pump to be installed. The current lift pump appears to be the original, and probably is a little on the tired side. I was planning on hooking up a fuel gauge when I switched LP's. I will have to double check the hose connections back at the tank to make sure they are ok as well.

93flatbed

Well since your doing some supply work, you may want to just upgrade the pickup side to 3/8". But thats just a suggestion.
Make sure the lift pump is low pressure, or plan on doing a regulator.
Good luck

dodgetrucker75

strange, my 75 did this the other day, started it and it sounded like a cammed big block gasser, did this for a minuete or so and then everything was normal, never happened before, and i have 3/8 gravity fed lines,so no chance of bleed off, and good pressure on the gauge...

wannadiesel

It's air. You have a leak somewhere.

roccoboost

Is it possible that the air leak could be caused by the lift pump some how? Are there any places in particular to check for air sneaking in? I replaced the old rotten leaking fuel lines a few months back with rubber lines from tank to pump. One long piece for supply and one for the return with no breaks in between.

93 12v

How do you find an air leak anyway? Because I have a similar problem. Lopes a little in gear, slight ping/knock in park. It's between this and a weak injector, I think.

93flatbed

The way I go about finding an air leak is to apply air pressure to the tank and look around the fuel system for fuel to start coming out. Wrap a shop rag around an air blower and put it in the fill neck of your tank.
Good luck they can be a chore to find.

93 12v

Thought so. Do I need to limit the air pressure so as not to damage the LP or IP? My air is set at 120. Thanks.

wannadiesel

Less than 5 psi. You don't want to split the fuel tank!

93 12v

That would be a disaster! Thanks Dave!