Fuel Pump Issue
Sandy
Fleet Mechanic
Joined: Mar 2014
Posts: 1,926
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From: Saskatchewan Canada
I think what is happening here is that the rear pump has become noisy. Possibly a sign of imminent failure?
Pumps are supposed to run continuously with the engine running. They share the same ECM, fuel pump relay, inertia switch, etc. So any difference noted between tanks is also isolated to that tank.
Pumps are supposed to run continuously with the engine running. They share the same ECM, fuel pump relay, inertia switch, etc. So any difference noted between tanks is also isolated to that tank.
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Joined: Aug 2003
Posts: 1,859
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Fuel pumps have been known to act strange for years and still perform reliably.
Sandy, any chance you could post the link to the PIP stuff you read?
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
My history was cleared but I think this is what I read. In my post I was referring to the relay continually running but I was calling it the pump. Even I know the pump has to run to supply fuel.
I'm not sure about an '88, but on the later models ('94-'96) the "thing" that tells the ECC to continue running the fuel pump are the PIP pulses coming from the distributor, indicating that the engine is running.
The way it works: Turn the ignition to "on" and not to "start", and the ECC will run the pump(s) for about 1 second. Then the ECC waits to see the PIP pulses indicating that the engine is turning over. Keep getting PIPs and the fuel pump keeps running (the ECC tells the fuel pump relay to stay picked).
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Listening to both tanks with a screwdriver, when selected, the front does not make the buzzing sound like the rear tank. You don't need a screwdriver to hear the rear buzzing. I made a recording of the sound but I have not been able to load it here. I would imagine all is well but I don't remember hearing the buzzing before. As I said, until yesterday, I haven't used the rear tank in a couple of months. Sandy
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Eventually I will replace pumps and sending units in both tanks on both vehicles. Maybe high volume to support some power increases. Both of my old Fords have faltered on switching tanks in the past, years ago. One ran bad on one tank for a whole trip cross country, years ago. The original pumps must be tough. They healed themselves over the long haul.
I have a feeling that a lot of these old trucks are getting so bad that pump noise is way beyond what the users call a problem. Feel lucky that your hearing is good enough to hear it and your truck is quiet enough so you can hear it.
I have a feeling that a lot of these old trucks are getting so bad that pump noise is way beyond what the users call a problem. Feel lucky that your hearing is good enough to hear it and your truck is quiet enough so you can hear it.
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