Mechanical fuel pump woes

[MagicRat]

My '84 Jeep (with a Chevy 2.8 V6, and a carburetor) has a mechanical fuel pump on the side of the engine.
This pump has one inlet, one outlet (to the carb) and one fuel return line (going back to the gas tank)

Would blocking off the return line cause the pump to fail?

I was stranded in a remote area (in heavy snow yesterday) when the steel return line rusted off. I blocked off the return line to fix the leak. The engine ran fine for about another hour then the fuel pump stopped pumping.

The pump was 18 years old so I am wondering if it failed simply because it was old or if I caused the failure by blocking the line.

FWIW plenty of mechanical pumps have no return line at all. I believe the only use for the return line is to keep the fuel circulating to prevent vapor lock. Is this correct?

[curtis73]

Most pumps with return lines are higher volume pumps. They have a long pump stroke which (if left unchecked) can result in higher pressure. Blocking the return line can increase pressure at the carb inlet.

For instance, GM did that return line thing a lot on cars in the 70s/80s on HD cars or vehicles with AC. They were totally un-necessary, but blocking the return line isn't really an option. Most GM pumps put out 3-4 psi. Blocking the return can cause 6-8 psi.

As for whether or not it caused the pump failure, I would say a definitive "maybe." But, when you replace it, there is a good chance you can find a pump for the 2.8 that doesn't have the return and you can skip the problem in the future. Try looking at pumps for non-AC trucks. Compare pumps from everything that got a carbed 2.8; S10s, blazers, celebrity, fiero, camaro/firebird... see if you can find one without the return. Just borrow the Carter book from the parts store and compare part numbers with photos in the back of the book.

[MagicRat]

Thank you for the input.

This vehicle is pretty heavily modded, with a Holley 390 4bbl carb. it did occur to me that the fuel pressure would increase but the carb showed no sign of float bowl overflow (but Holleys are pretty tolerant of higher pressure).
I can see that an old, marginal pump would fail under the extra strain.

I'll look for the non-return type of pump. If that does not work, then I'll go for a plunger-type electric pump.

[MagicRat]

Quick update.

Before buying a new pump, I checked the fuel line. In the past, sometimes rust or a porcupine has damaged a line, usually affecting vehicles in storage.

I found about 100 lbs of snow jammed in between the gas tank and the rear axle, accumulated from my snowy highway drive. The weight of the snow had snapped the fuel line itself.