88 245 - Which fuel pump is the problem?

[rgk]

I have hesitation under load and have narrowed it down to one of the fuel pumps. I used to have an open circuit due to corrosion at the in-tank pump leads. I fixed that problem, but still the hesitation persisted.

The problem went away for the most part when I filled up the tank about 3/4 full. Now that the tank is at about 1/2, the problem is slowly rearing its ugly head. So which is it? Here are my perceived arguments for either possibility:

Main pump: open circuit caused in-tank pump not to work, overworking the main pump. Rear pump is doing all the work. A full(er) tank allows the rear pump to work harder by cooling it with fuel.

In-tank pump: pump is the cheap brand and has simply worn out. Hesitation goes away when tank is filled up because capillary action (siphon) helps to feed main pump. When fuel gets low, capillary action does not have effect, and car stumbles.

Take note that I can hear both pumps working. Anyone want to take a vote and pose an argument?

[lummert]

I vote for in-tank pump. I say this because if the main pump quits the car won't run. Ask me about my fuel pump experiences.

[jimmy57]

I also vote for in-tank.
If you have a properly functioning in-tank pump you will have fuel flow out of the line at injector fuel rail if you jumper the in-tank pump to run by itself.
As I recall your in-tank pump has been changed. I take that to mean the connector hose between pump and the metal fuel pipe of tank unit is good.
One other thing: is there a possibility the leads got revered to in-tank pump?
A car will will have your symptoms if that pump runs backwards...........
I know this the hard way. You'd think the pump would keep it from running but apparently the in-tank pump is ineffective going reverse rotation but it creates drag for the main pump that goes way up when the fuel level gets below gravity feed level to main pump.

[rgk]

Thank you both.

Jimmy, yes connector hose is OK. Also, I have checked, re-checked, and triple-checked that the pump is running the correct way. There is a little direction indicator stamped on the bottom of the pump. I have briefly attached it to a 9V battery while out of the tank just to make sure the leads were properly connected and that the pump was running the right way. I have read about cheap aftermarket sender units arriving wired backwards...

[rgk]

Jimmy, it was the connector hose between the pump and the metal fuel pipe. My first two inspections of the sending unit proved fruitless. I never removed the hose and inspected it in detail, an oversight that cost me weeks of stress.

Oh well, I've got it fixed now!!

I also vote for in-tank.
If you have a properly functioning in-tank pump you will have fuel flow out of the line at injector fuel rail if you jumper the in-tank pump to run by itself.
As I recall your in-tank pump has been changed. I take that to mean the connector hose between pump and the metal fuel pipe of tank unit is good.
One other thing: is there a possibility the leads got revered to in-tank pump?
A car will will have your symptoms if that pump runs backwards...........
I know this the hard way. You'd think the pump would keep it from running but apparently the in-tank pump is ineffective going reverse rotation but it creates drag for the main pump that goes way up when the fuel level gets below gravity feed level to main pump.