Fuel Pump Cycle Module - Needed ???

[Byron454]

Thanks all for the input. Ive delt with these fuel systems for over 20 years have seen them on the wiring diagrams always wonder about there operating strategy,
but never remembered to pursue the information when I wasn't actually making the repair to the vehicle. sounded like a good time and place to ask the question.


Byron

[blue68deville]

Since I had the connector in my harness already, I installed the hot fuel module in the caddy last summer, just to see what it does.
It provides a 20ish second extended prime in the key on eng off position, and does not run the fp after shut down. It's back in my spare parts box, didn't see the point in keeping it installed.

[1project2many]

Interesting. FSM wording strikes again. I've got some stories about diagnostic tests that forget key steps and lead to wrong, expensive diagnosis, too.

[lionelhutz]

Since I had the connector in my harness already, I installed the hot fuel module in the caddy last summer, just to see what it does.
It provides a 20ish second extended prime in the key on eng off position, and does not run the fp after shut down. It's back in my spare parts box, didn't see the point in keeping it installed.

That would make more sense. The module just has power, ground and the wire connecting to the fuel pump. So, when it sees power first applied to the fuel pump some internal circuit connects the module power to the pump wire for 20 seconds.

It never made any sense to me that the module could start timing when the fuel pump relay turned off. It would be rather difficult to detect the relay going off using the pump wire if the module itself has connected the pump wire to power. And the module would have to be "on" when the PCM turned-off the relay or the pump would blip off for a second.

[1project2many]

It also makes more sense that it would only be needed to push vapor out of the lines at key on. A neat point is that I was never involved in diagnosing a vapor related issue on the TBI trucks, even during the 106 degree days we'd get in MT. But I have been on several road calls for Ford trucks that died due to fuel vaporizing in the lines. Ever hear someone recommend adding diesel fuel to a gas engine to cure a hot stall? It worked.