1bad91Z

iTrader: (1)

A while back, I noticed that fuel pressure started dropping from 39.5 to the high 20's. I originally adjusted my holley billet TPI regulator down to SVO specs 39.5 PSI at idle with vac line off. So, I bought a replacement pump (Holley 255 lph intank pump). I removed the tank and installed the new pump properly, I even made sure that the float was floating before reinstalling the locking ring. Then I put it all back together (rear end, exhaust, suspension, everything.....) and turned the key on. I'm still reading mid-high 20's PSI on the FP guage and now my gas guage is pegged at full. The gas guage worked fine before removal of the tank.

My questions are:

Should I just try to add a ground wire to the top of the sending unit to see if guage moves and is this auxillary ground necessary?
How is the sending unit grounded from the factory, (the 3 wire harness)?
Should I just buy a freakin' new sending unit?
Could the wiring in the factory sending unit (inside tank), cause low voltage to pump intern causing low FP?
Does anyone know if the stock regulator's diaphram and the holley's diaphram are interchangable?

I called holley, they don't sell a replacement spring and diaphram for their regulator, they want you to buy a whole new regulator...

Thoughts, suggestions, comments?

THanks!

1bad91Z

iTrader: (1)

Well, I bought a new sending unit ($199.00) from O'rielley's. I'll return it if I can find the problem with the orginal unit.

But, does anyone know if I can use a GM diaphram in a Holley AFPR?

Viprklr

iTrader: (5)

Apparently Widarsson did it.

https://www.thirdgen.org/forums/afte...fpr-pos-2.html

Beau27

Well here is something that might help you. My fuel pump dropped to 20 psi so i decided to replace it. I ordered a new one and put it in. I still only had 20 psi. So i finally figured out that there are three different pumps for my car (1991 305 TPI). I think the problem for me was that i asked for a TPI (wich is 40-45) and they thought i said TBI (wich is around 20). So there is just a bit of info that might help ya.

1bad91Z

iTrader: (1)

The new pump that I used is a Holley 255 lph (Made by Walbro) pump. It's WAY beyond the capacity of a stock TPI 350 pump which is rated at 155 lph.

The only thing I can think of is that the spring in the Holley AFPR has become weak. I haven't tried adjusting it further yet though. I'm still in the process of finding time to drop the tank again to replace the sending unit.

Rob Wade

I would drill a hole in a flange of the tank (where there is no fuel.....usually a corner of the tank) and run a wire to ground. That will tell you if its a grounding issue.

1bad91Z

iTrader: (1)

Well, I dropped the tank and removed the factory sending unit. I plugged it's harness connector in, turned the key on, and manually moved the float up and down. The gas guage didn't move at all, it was still pegged at full. I then plugged in the new sending unit and manually moved the float up and down. The gas guage moved accordingly. Next, I assembled the new holley pump into the new sending unit, reinstalled the tank and hooked up all the lines. When I turned the key on, the gas guage read correctly and the fuel pressure hit 39 psi and held there without bleed off.

I believe the whole problem was bad wire(s) on the intank side of the factory sending unit. Maybe there was resistance in the sending unit's power wire to the pump causing low voltage and intern, low pressure. Upon visual inspection, there are no breaks or tears in the factory sending unit's wires or insulation, but the part of the wires that go into the connectors look slighty discolored like they may have been burnt a little.

I was going to just cut the floor pan above the tank and install a nice Summit aluminum trap door to make fuel pump changes easier, but when I realized that I would still have to cut through 4 metal gas lines with fuel and or fuel vapors inside, I decided to do it the hard way and not blow up my garage!

Oh well, I'll reinstall the rear end and rear suspension AGAIN tomorrow......

1bad91Z

iTrader: (1)

Update:

I finished putting the car back together and fired it up. Fuel pressure only got upto 25 psi at idle with vac line disconnected!

I turned the car off, and then turned the key to the on position (to prime the fuel pump again), and it hit 25 and held with no bleed off in fuel pressure. I checked for leaks and could not find any. I then turned the Holley AFPR dial all the way and could only get 35 PSI out of it with the vac line disconnected (29-30 PSI with vac line back on) at idle. The regulator doesn't leak out of the vaccum port. There are no leaks to be found in the fuel system anywhere. The 255lph Holley (Walbro) pump and sending unit are brand spankin' new. The Holley AFPR is about 5 years old though.

So, I'm stumped. The only thing I can think of is that the Holley AFPR's spring has become weak over time or that the fuel pump is getting low voltage (which I doubt). Or maybe my Autometer electric fuel pressure guage is reading incorrectly.

I'm going to pull the plenum next weeked and install a new factory non-adjustable regulator to see if I can get the 43psi that it's rated at. Also, I guess I need to check fuel pump voltage.



This sucks......

PneumaticTire

If you have to go back in the tank again, I would not be bolting up the suspension untill you test the pump first. Did you check for restrictions at the fuel lines? Maybe a kinked line, or something? Try a different fuel pressure gauge.

Viprklr

iTrader: (5)

You could also have a fuel pressure gauge hooked up to your rail. Set the pump to keep running with the fuel pump test port, start pinching the fuel return line. If the pressure on your gauge goes up then your pump is fine.

I've had 4 holley afpr's and not one of them works correctly. I ended up putting a quarter inside the housing so that I could raise the pressure to where I needed it.

watajob

iTrader: (29)

Did you change the fuel filter yet?

1bad91Z

iTrader: (1)

Update:

I installed a new fuel filter. Guage still read 35 PSI after I cranked the Holley AFPR all the way up. I then installed a brand new factory regulator which is non-adjustable at 42 PSI. After that, guage read 24-25 PSI. I then removed the Autometer FP guage electric sending unit and hooked up a mechanical FP guage. The mechanical guage read 42 PSI at idle with vac line off !!! I guess my Holley regulator, factory fuel pump and fuel filter were good after all.....

So, looks like ALL that work was for nothing!!

Well, at least I have NEW parts installed that I "shouldn't" have to worry about for awhile. I've been wanting that 255lph pump for some time anyways.

Now, I'll retune my PROM beings I can't adjust my fuel pressure anymore. When I port match my plenum even bigger to the TPIS big mouth gaskets, maybe I'll reinstall my Holley AFPR.

But anywho, car is running fine for now!

Viprklr

iTrader: (5)

Sucks but IS good to hear.
Sucks that you had to spend unnecessary money.

1bad91Z

iTrader: (1)

Just bought the replacement Autometer full sweep 0-100 psi electric sending unit. It was $110.00 shipped from Summit!! My **** hurts, I don't know if I should take a shower or smoke a cigarette after that raping I took! If it takes a crap again, I will ditch the electric guage in place of a mechanical one that just bolts to the rail and stays in the engine bay. A brand new Lunar series electric FP guage like the one on my A-pillar is now $250.00 ! I paid alot less than that when I got mine from Summit a couple years back. Also, my Lunar series tach that I paid $210.00 for brand new from Summit is now also $250.00. Maybe they've gone up in price due to all the problems and replacements they had with this line of guages?

firebirdjosh

iTrader: (1)

What's the deal with fuel pressure gauges being such poor quality? My jegs one is very inaccurate as well- should have figured $20 was too good to be true.

1bad91Z

iTrader: (1)

I have an Autometer electric guage that's inside the car on the A-pillar. The guage works great, it was the electric sending unit that feeds the guage that went bad.

Xlr8torZ28

iTrader: (19)

I always try to check the most simple things first, so I dont blow money chasing a problem.... glad its fixed