Quickee- F.I. Spider - What Turns the fuel Pump on?

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jgoodfellow
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Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by jgoodfellow » Wed Oct 10, 2018 3:17 pm

A friend's spider sometimes takes a few tries at cranking before it fires.
While discussing possible issues, like dirt in the fuel filter, or the fuel rail
losing pressure shortly after shutdown, we talked about the pump.

He tells me that as soon as he puts the key in, he hears the fuel pump running.
(By which I think he means, when he turns the key to ACC, before the cranking the engine)

This doesn't sound right to me. I thought what enabled the fuel pump to run, was
the air metering flap moving off closed, which tells the ECU to fire up the pump
(and the injectors).

Do I have this wrong?

Thanks,

John
'84 Pinin Spider Azzurra
'72 124 Sport Spider
Long Island, NY
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by jgoodfellow » Wed Oct 10, 2018 3:21 pm

Also - someone mentioned that the fuel rail should maintain pressure for an hour or more after
the ignition is killed. Is that a function of a one way valve or similar component in the pump itself?
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by bartigue » Wed Oct 10, 2018 4:24 pm

You have it right, the fuel pump should not come on without air passing through the AFM. The AFM has a micro relay that turns on the fuel pump. What you describe is a dual relay that has been jumped to force the pump to run, or the AFM was modified so the pump is on all the time.

I've never heard of a specific time for pressure to be held in the rail. Under normal conditions it pressurizes as soon as the pump is engaged if not already at pressure. It takes a Bosch pump about .000002 seconds to pressurize the rail. Unless the regulator has failed this is not your issue. However, a bypassed pump leads me to suspect something was wrong and it may be that your regulator is shot and someone thought forcing the pump to run would help.

If you turn on the key and count to ten, then try to start it, does it start right up? If so then I would suspect the regulator has failed and you are having to build up pressure. Could also be a weak pump. Could be several things, like the cold start not working.
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by jgoodfellow » Wed Oct 10, 2018 5:05 pm

Thanks Brad, I will pass that along.
I think you meant micro-switch in the AFM though, not micro-relay?

John
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by spider2081 » Wed Oct 10, 2018 6:54 pm

A friend's spider sometimes takes a few tries at cranking before it fires.
This issue is often times a failing ignition switch. Is the car starting the instant the key is released from the "start" position? The ignition switch contains 3 set of contacts. usually the "start" set become intermittent first but sometimes the set of contacts that power the coil when the car is cranking become intermittent and the car starts as the key is returning to the "run" position of the ignition switch.

The AFM contains an open contact (can visibly inspected) with the black cover removed from the AFM. Sometimes the arm that moves the contact to open the contacts bends and needs to be repositioned. Sometimes people bypass the switch. It is neither a micro switch or a micro relay.

I have opened a few Bosch FI pumps and they contained a check valve internally located just before the output port. Not sure if less expensive aftermarket pumps would have a check valve.
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by jgoodfellow » Thu Oct 11, 2018 10:04 am

Very interesting David, thank you. If I ever knew about the 3 contacts I had forgotten about them.
I do recall that someone many years ago did a a FAQ on the old Mira site with color photo's
showing how to rebuild an ignition switch, maybe that is still available.

Actually, I just checked; - it was Chris Coulter and it is available here: https://mirafiori.com/faq/content/switch/index.html

Thanks also for the clarification on the AFM switch innards and the check valve on the pump.
I would not be surprised if aftermarket cheapo pumps left that valve out.

John
'84 Pinin Spider Azzurra
'72 124 Sport Spider
Long Island, NY
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by spider2081 » Thu Oct 11, 2018 11:26 am

John
I might be able to further assist you directly, my email is flyme194@gmail.com
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by atruscott » Fri Oct 12, 2018 10:49 am

Yep - the switch inside the AFM is activated by a small arm that hangs off the wiper that tracks with the door. "People" have a habit of bending that arm outwards slightly so that the switch is permanently closed and thus the fuel pump turns on when the ignition is turned on. The way it's supposed to work is that the engine pumping air pulls the AFM door, which moves the arm off of the switch - which means when you have a crash and the engine stops, the fuel pump stops too.
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Re: Quickee- F.I. Spider - What Turns the fuel Pump on?

Post by whitehause » Sun Oct 14, 2018 8:32 pm

What Turns the fuel Pump on?
For some it's a candlelight dinner, for others it might be a walk on the beach, all fuel pumps are different :mrgreen:

Sorry, just had to.
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