fuel pump with the key on

[fimrite]

Hello all. Tried doing some searching here and I've been unable to find an answer. My 75 fuel pump used to come on with the key turned to run, I'd wait 10 seconds and then with a couple peddle pumps it would fire right up. My problem this year is the pump doesn't come on until it's cranking and takes 10-15 seconds to fire up. Any thoughts on why the pump doesn't come on with the key in the "run" position now? I hate cranking the engine for those 10-15 seconds.
Thank you very much for any responses.

[18Fiatsandcounting]

Do you have an electric or mechanical fuel pump? I thought the electric fuel pump didn't come until later model years, so if you have a mechanical fuel pump, it will take some pumping to get the fuel to the engine. That being said, if the fuel is draining back to the tank after a day or two, that would indicate other problems.

-Bryan

[fimrite]

It is an electric pump in the trunk.

[18Fiatsandcounting]

OK, thanks. Well, the pump does work when you're driving, otherwise you wouldn't get very far before the carb ran out of gas. So, it sounds like an electrical issue in that the pump doesn't run before you start the car, but it does eventually run. Could be sticking, bad electrical connection that "works" with some vibration, etc.

I'd start by measuring the voltage you see at the pump when you first turn the key to "run" but before starting. If the voltage is low or fluctuates or slowly rises, then it's likely an electrical issue. Try jiggling the wires going into the back of the ignition switch, as one very common issue in these cars is that the contacts inside the ignition switch slowly fail, leading to all sorts of electrical gremlins.

If the electric pump is original, it may be time for a new one. But I wouldn't assume that's the issue at this point.

-Bryan

[SteinOnkel]

I bet your ignition switch is on its way out.

Or the home depot crimp job in the trunk is starting to fail. Wouldn't be the first time. Ignition on, not enough voltage to overcome massive amount of resistance in corroded crimp joints. Engine on, alternator charging, it's just enough to get the pump going.

[spider2081]

I think mid 70's Spiders had a fuel pump relay and an ignition control relay that were energised by the oil pressure switch that lights the lo oil pressure light in the dash.I think the fuel pump relay is one of the relays installed under the hood on the driverside fender well.
I suspect the relay or the relay's socket contacts are your issue. The relay appears to switch an unfused power to the pump when the engine is not running and a fused power (inline fuse behind fuse panel) to the pump when the engine is running.

If the relays are in their original positions it would be the outboard relay closest to the firewall.

hope this is some help

[SteinOnkel]

Mid 70's spiders had mechanical fuel pumps?

[spider2081]

I think mid 70's Spiders had a fuel pump relay and an ignition control relay that were energized by the oil pressure switch

Does your Low oil pressure warning light light up when the key is on and engine not running? Does you car still have dual ignition points or has that circuit been modified??

[spider2081]

I think mid 70's Spiders had a fuel pump relay and an ignition control relay that were energized by the oil pressure switch that lights the lo oil pressure light in the dash.I think the fuel pump relay is one of the relays installed under the hood on the driverside fender well.
I suspect the relay or the relay's socket contacts are your issue. The relay appears to switch an unfused power to the pump when the engine is not running and a fused power (inline fuse behind fuse panel) to the pump when the engine is running.

If the relays are in their original positions it would be the outboard relay closest to the firewall.

hope this is some help

[fimrite]

I think mid 70's Spiders had a fuel pump relay and an ignition control relay that were energized by the oil pressure switch

Does your Low oil pressure warning light light up when the key is on and engine not running? Does you car still have dual ignition points or has that circuit been modified??

No oil light and yes it still has the dual ignition points.

[fimrite]

Thank You all on the responses and good feedback, I'll definitely let everyone know what I find.

[spider2081]

No oil light and yes it still has the dual ignition points.

If the low oil pressure light is not lighting I would first make sure the wire is still on the switch. If it is the remove the wire and ground it while its grounded with the ignition switch in the "run" position the low oil pressure light should light and the fuel pump run.

[SteinOnkel]

No oil light and yes it still has the dual ignition points.

If the low oil pressure light is not lighting I would first make sure the wire is still on the switch. If it is the remove the wire and ground it while its grounded with the ignition switch in the "run" position the low oil pressure light should light and the fuel pump run.

On the risk of being completely ignored once again: Carburetor Fiats had mechanical fuel pumps, afaik. My 1978 certainly does and there is no relay panel inside the engine bay. I could be wrong in saying they are all like that, but I doubt that. It would be the first oem I've heard of that installed an electrical fuel pump to a carburetor vehicle, especially with a relay.

I think you are leading OP on a wild goose chase. I think it much more likely that a dpo added an electrical fuel pump and slapped it near the tank somewhere with shoddy wiring that has now failed.

We shall see.

[spider2081]

My suggestions are my opinion based on the wire diagrams I have looked at in the Clymer repair manual for 67-80 Fiat Spiders. The wire diagrams show the relay and an electric fuel pump. I looked at 74,75, 76 wire diagrams the 1976 was easiest to view. It also shows a drawing of the relay locations. If they also have a mechanical pump that would not be shown on the wire diagram.
My opinions are based on these wire diagrams. My Spiders are 1980-1982 so I have no hands on knowledge of a 1975. I simply researched available reference material.

[SteinOnkel]

Well, I've got a 1978 and it has a mechanical fuel pump w/o relays. And I was just looking at a 1974 engine the other day with you guessed it, the mechanical pump on the side of it. Also, none of the vendors carry an oem electric fuel pump for 1966-1980.

It seems op could take the mystery out of this pretty easily, but as is often the case on forums he/she is being stingy with the information.