I shimmed the spring in my FPR .117". I got a gauge hooked up before I started it to get an idea of where the pressure would be.

I ran the fuel pump with the engine off and the gauge reads 12.5 psi.

This doesn't make any sense to me. I thought stock fuel pressure was 13 psi. If so, how could shimming the spring not crank the pressure up thru the roof? I would think that the pressure would be HIGHER with the engine off.

Anyone have some input?

I wish I knew the rate of the FPR spring...because I'd like to get a stiffer spring without buying so goofy contraption from JET or Turbo City.

 

if the pump can only generate 12.5 psi of pressure, no ammount of additional load on the spring will get the pressure up. You could try it with the engine on. The increase in voltage with the alt. turning may help the stock pump make more pressure. if i recall correctly, the stock one maxes out at 14 psi when new.

 

Sucks. I guess that's what I get for not taking a base reading first.

My fuel pump has 130k miles on it. Oh well...looks like it's coming out when the weather gets warm.

Any pump recommendations? I know Summit carries a TPI pump rated at some rediculous LPH. The pumps are almost identical. IIRC the TPI is a little longer.

 

Where have you been? Just about everybody on this website deals with Walbro pumps only. For under $100 for the whole kit you can't beat it.

 

I've been in the garage building the most beast M-Body in town

I'll check out Walbro...I need to do something so I can get back to driving the Stro. The Mustang sucks for all this winter crap we've been getting. Not having a washer fluid pump or defrost really bites.

 

Stock OEM spec for TBI fuel pressure is 9 to 13 psi. Stock OEM TBI pump is rated deadhead at 20 psi. May want to check this thread before getting the pump:

https://www.thirdgen.org/techbb2/sho...hreadid=161570

There is another thread a little further down called "problem with new motor" or such. It is the predecessor to the above thread.

RBob.

 

I found out that the pressure is higher with the engine running. To cycle the fuel pump I was jumping the outer 2 pins in the oil pressure cut off harness.

I put a real thick spring in the FPR today. I checked the pressure by jumping the pins...the gauge read 14.5 psi. I drove it around the block once and the BLM's went right to 108. So I took the engine cover off and had a look and the gauge was at 20 psi! When I would stab the throttle the gauge would drop to ~15. I guess that's too much for the old pump to handle.

I shimmed everything up using the stock spring again and I got the pressure at 15.5 psi.