CALL ME DENSE UMM, BUT WHEN SWAPING FROM TPI TO CARB WHY DO PEOPLE USE AN INLINE FP BETWEEN THE STOCK IN TANK PUMP AND THE CARBS REGULATOR? WON'T THE REGULATOR JUST BLEED OFF THE UN-NEEDED GAS FROM THE HIGH OUTPUT STOCK PUMP AND SETTLE AT 7-9 LBS?

 

I don't recall anyone saying to use an in-line fuel pump between the in-tank pump and return-style regulator. Some people have asked about using an in-line pump because the in-tank pump is dead.

There has also been talk about using an engine-mounted return-style mechanical pump with an in-tank electric with no regulator.

That's all I ever recall hearing.

 

o.k. then, so a correct set up for this swap is:

stock in tank efi pump to a 3 port regulator, bleed off excess and return to tank, send 7-9 lbs. to the carb.

for my 89' then do you know if my fp wiring is bundled into the wiring going into the ecm? or is it apart of the driver side bulk head wiring?

 

Well, the return port to the factory return line. It really isn't a "bleed off".

That part is over my head (at least, beyond my personal exposure).

 

Thanks for your input.

I did find out the fp does run wiring to ecm for 89'

 

FP gets power through 2 parallel sources:

1. A FP relay that is activated by the ECM.

2. Through the oil pressure sending unit when oil pressure is above 4 PSI.

The FP relay controlled by the ECM is the primary source of power, the OPSU switch is the backup.

 

Haven't delved into this for quite awhile, but I believe people install an inline pump when the ECM has literally been removed, while the other's that rely solely on the intank pump will keep the ECM in tact, but ground the FP relay for a constant feed to the intank pump....

 

Sorry if this is stupid. Why does one need a regulator between the pump and the carb. Isn't that, in part, what the floats are for? Or is it that the TPI pump can deliver sufficient pressure to overcome the needle and seat thereby keeping the float bowls overly full?

Jon

 

The floats are only designed to work with single digit fuel pressures - like 5 to 8psi... a typical EFI electric pump makes around 45-55psi, which would be way too much for a carburetor float to handle.

EFI and carburetion systems work on totally different principles... EFI is hugely dependent on fuel pressure being exactly right for it to work properly, which is why the fuel pressure is so high. A carburetor does not need any fuel pressure to work properly - as long as there is enough fuel moving to the carb to keep it 'topped up' then the carb will work just fine, regardless of the actual fuel pressure.

 

You can remove the ecm and wiring all you have to due to get your fuel pump to work is to look at the wiring harness that the ecm plugs into and find the white wire wich I think is like the fourth one over on the plug and run power to it. this will eliminate your problems and another thing is that the intake pump will get hot and break down over time without the bypass regulator that is why you need the bypass regulator and it will also decrease you fuel supply for the carb.