Engine is hard to start and idles poorly at 1/4 tank reading

[68ls1]

Hope someone may have a reason on this. When fuel gauge is showing 1/4 tank or less, Blazer become stubborn to start and idles poorly. I currently don't have truck to look at.
Mechanic who did brake, suspension and some mechanical repair commented on this, and put more fuel in.
When I first brought it home, there was around 1/2 tanks and started easily etc. As we ran fuel down while testing things including temperature gauge replacement, once fuel gauge got to around 1/4 it again became hard to start.
I think put around 10 gallons in to Blazer for my trip to body shop, and it again started easily on all occasions.
After the drive it was down to showing 1/4 tank, but driving normally. As soon as I pulled up, put trans in park it stalled, like out of fuel.

Fuel gauge could be out, but seemed to operate perfectly on trip, original mechanic had put some fuel in it and was still acting poorly. Put new fuel pump on but situation remained, put more fuel in, problem gone.

The truck does have the remnants of an auxiliary tank, so fuel lines are a bit of a mess. This is planned to be fixed.

Any other thoughts on this, why fuel feed would diminish when tank gets low?

[72gmguy]

Maybe the sending unit is off a bit and when it reads a quarter it’s really empty.

[68ls1]

Originally Posted by 72gmguy

Maybe the sending unit is off a bit and when it reads a quarter it’s really empty.

Definitely a possibility, but mechanic had put around 5 gallons in to truck, and gauge was showing 1/4, but still playing up. Thought it was fuel pump, so changed that, still not playing nice, put more fuel in and was much better.

We could get it to start at low level, just took multiple attempts.

I'm wondering if the venting canister maybe an issue?

[jaros44sr]

I had a Japanese beetle floating in my tank, it would shut off fuel when it was low, took me forever to find the problem. I would start by looking for the problem by checking flow at fuel pump inlet and then go backwards to the tank, maybe blow out lines with about 5 psi of air

[68ls1]

Originally Posted by jaros44sr

I had a Japanese beetle floating in my tank, it would shut off fuel when it was low, took me forever to find the problem. I would start by looking for the problem by checking flow at fuel pump inlet and then go backwards to the tank, maybe blow out lines with about 5 psi of air

Thanks, yes as soon as I get truck back from body shop I'll put a fuel pressure gauge on line.

I'll check tank for any insects too

[ochre 72]

Sounds basic but maybe fill the tank, let it run down till the symptom happens. Fill it back up and see how many gallons that takes as compared to factory capacity. See if it’s really a 1/4?
Seems the sending unit arm could be bent.
You could have some sludge in the bottom that more fuel dilutes and it only becomes an issue with less fuel? Just random thoughts.
Good luck with it

[68ls1]

Originally Posted by ochre 72

Sounds basic but maybe fill the tank, let it run down till the symptom happens. Fill it back up and see how many gallons that takes as compared to factory capacity. See if it’s really a 1/4?
Seems the sending unit arm could be bent.
You could have some sludge in the bottom that more fuel dilutes and it only becomes an issue with less fuel? Just random thoughts.
Good luck with it

Thanks, yes random thoughts help.

[BigBird05]

When I had a truck with dual tanks the selector valve was messed up.my truck would run out of fuel. It seams that it would send the return fuel to the 2nd tank. Water in fuel? Methanol fuel loves to attract water. Fuel gauge off? Maybe a rust hole in the pickup tube?

[68ls1]

Originally Posted by BigBird05

When I had a truck with dual tanks the selector valve was messed up.my truck would run out of fuel. It seams that it would send the return fuel to the 2nd tank. Water in fuel? Methanol fuel loves to attract water. Fuel gauge off? Maybe a rust hole in the pickup tube?

Thanks, my gut feel is it has something to do with old dual tank set up, even though old tank no longer there, the fuel lines are.

Thinking maybe I should have blocked the old feed line, getting air?

[BigBird05]

Originally Posted by 68ls1

Thanks, my gut feel is it has something to do with old dual tank set up, even though old tank no longer there, the fuel lines are.

Thinking maybe I should have blocked the old feed line, getting air?

When I had that problem, I was on the side of the road and just bypast the valve completely. It stayed that way for the rest of the time that I owed it.