fltechpilot

I've come across a few threads on here that have discussed listening for the external fuel pump to run during engine cranking to determine if it is working. This leads me to believe that the proper operating sequence for the pump is to run during cranking, then stop running and have the in tank pump take over after the car starts.

This makes me question the operation of my fuel pump. My external fuel pump always runs while the car is running (I can hear it whenever the car is stopped and at idle). The car runs fine, but I'm wondering if the in tank pump isn't operating properly. Is this normal for a U.S. 1984 car, or do I seem to have a problem?

SeanR

In-tank pump always runs with the external. One does not run with out the other unless there is a failure. Can you show us the links that lead you to think this so they can be edited for future reference?

fltechpilot

Sean, thanks for your input.
In regards to the posts that I mentioned, I had read it awhile ago and had been thinking it over for some time. In all honesty, I probably misinterpreted the posts. On a related note, I changed my fuel filter over the summer and it looks like the fuel pump is original. The car is 28 years old and has 89,000 miles. What are your thoughts on replacing a fuel pump as a preventative measure? Is their reliability a function of age or mileage (or both)?

jayc67

Seems the in tank pumps are the one causing real grief. If my car had dual pumps I'd take out the one in the tank as a preventative measure and go with a single pump.

My opinion on fuel pumps, from other cars over the years anyway, is that they fail when they fail. Sometimes that's when practically new and sometimes it's never. You might put in a brand new one that dies 3 months later, so why bother.

fltechpilot

That's interesting. I hadn't considered that option. Would the external pump be capable of shouldering the entire load on its own?

SeanR

I'd leave up to your ears. Yes, a new pump will be in your future but is your current one making a high pitched noise? Screaming for help? Yelling at you to change it?

If not, just drive the car. Most pumps, when they go, will get noticeably louder. I'm of the opinion that he intake pump is more hassle than it is worth and advise going with the in-tank strainer instead, but it's 50/50 on if people do it. Go with what you feel better with.

jayc67

Some cars do just that. I'm not sure of the timeline on which cars had dual pumps and which didn't though.

James Bailey

Nick you have no intank pump that was later years. Your fuel pump runs al the time if the engine is running and when cranking on the starter motor all excess fuel just returns to the fuel tank via the return line that goes on top of the tank to the fuel level sender

jayc67

Huh, always thought it was the other way around, that the dual pump was an older design.

When did it change, and do you know what led to the change?

SeanR

James would know, but the dual pumps were from 78 to mid 80 and 89 plus.

depami

This is correct.

Pumps only run when crank shaft rotation is sensed by “speed and reference mark sensor” (CPS).

With the exception of maybe a short burst at ignition on, not sure though.

SeanR

That is true on the later cars only.

James Bailey

The very earlyCIS cars had an under tank pump and one in the right rear wheel well. The "extra" in tank pump was added as an option for high temp areas to reduce fuel boiling under vacume as the external pump sucked fuel....then was added to all 928 for a while around 89-90. The internal pump is very prone to failure of the hose inside the tank rendering it useless.

jayc67

Thanks for clearing that up. Makes more sense now. Must have been a REALLY hot place, Middle East maybe? I have a single fuel pump and it gets surface of the sun hot here in August and never had problems.

fltechpilot

Ok this clears things up a lot for me. Makes much more sense .