fuel pump, or gas cap?

[sleeper_dave]

'91 Suburban, 350 TBI, 4x4, 1500.

I've been having a problem with some hesitation on the highway, only at 70+, despite a new cap, rotor, plugs, wires, fuel and air filter. I'm also having a problem with my truck dying like it's out of gas, when there's still a significant amount in the tank, primarily when it's really cold out. Yesterday it died repeatedly with 1/8 tank before it warmed up enough to get me to the gas station.

This all leads me to suspect a fuel problem. But I also noticed that my fuel cap says "vacuum only" on it, and when i opened it yesterday, there was a lot of vacuum (0 out, 51 a few days earlier). Is this normal?

So, my question, is my fuel pump dying, or do i have the wrong gas cap on my truck?

 

[R72K5]

yeah vacuum is not a good thing, try running truck with no cap for a few days first

then go from there

if not then its high rpm fuel delivery problem, new filter, pump, etc

plus you shouldnt be running around with less than 1/4 tank in an EFI vehicle

not good for the pump,

try not to do it often

fuel is all that lubes the internals of the pump, the pump isnt at bottom of tank, and it doesnt lay on its side, it stands vertically

 

[dyeager535]

Sounds almost like your EVAP system is messed up.

I'm not sure that having a lot of vacuum in the tank will cause it to stall, but maybe it will? Someone can chime in on that.

I'd probably try running it a bit with the cap loose, but only long enough so that you know the problem should have been repeated, to see if the problem disappears.

Does it start ok? If its having a hard time starting too, I'd be checking to see what the ECM thinks the temperature is.

 

[R72K5]

yes vaccum in a tank will cause lack of delivery, especially higher revs, have had and seen ti happen a few times, TBI only pumps 9-13PSI, not hard ot overcome that with vacuum in tank

 

[scrappyk5]

whenever i take my cap of my s15 to fill up it seem to blow out alot of air.
does this mean there is something wrong?.
it runs fine.

 

[sled_dog]

likely you just need a new gas cap if there is vaccum like that. I had that happen when I removed my evap canister. Made the mistake of plugging the line instead of puting a breather on there.