xdamagedx

Anyone have any suggestions or advice on this: I bought an 89 GTA without an engine and put my carbed 350 in it. I tried putting my mechanical fuel pump to the outlet side of the in-tank fuel pump, hoping it would draw through it, but there was no such luck. It's also looking like my gas gauge may be dying (probably from building up varnish from sitting in the same spot with the same nasty fuel for 10 years). Should I replace the in-tank unit and try to regulate that pressure down to something usable that isn't going to kill my carb? or should I do something like getting a sending unit out of an earlier 3rd gen that didn't have an in-tank pump so I can use a mechanical/ seperate electric pump?

vetteoz

iTrader: (13)

Depends what is cheapest option
You have to drop the tank either way.
Do you still have the stock return line in the car?
If not, your decision is already made

DRock89RS

well if you wanna keep the in tank pump get a 3 port fuel pressure regulator, and block off the mechanical pump. thats what im going to be doing when i put my 350 in early next week. or get a sending unit and pull the stock one. just my .02 cents

The Devastator

You have basically two options.

1 Drop tank. Replace fuel pump with pickup hose. Reinstall tank. Use mechanical pump. Plug return Line. -------CHEAP

2 Drop tank. Replace faulty fuel pump. Buy metric fuel line to an adaptors. Adapt factory fuel lines to 3/8 hose. Use a return style adjustable fuel pressure regulator. --------about 400 bucks

1ADan

iTrader: (4)

i personally followed devastator's #2 option; stock fuel pump will supply more than adequately for a carbed setup and it keeps the pump in the tank away from the motor. always worried a failed block-mounted pump could wipe out my lower end....

The Devastator

I have run both in my car and now that race pumps makes a mechanical pump that will feed my EFI setup I'm going back to mechanical for price and simplicity. The racepumps stuff is outta your price range for this project tho.

The pros to using the electric pump are you can run the pump with the engine off, and the stock electric pump will last a long time on a carb setup. Those pumps are made to run at 43.5 psi. You're gonna be running anywhere from 3 to 9 psi so the load on the pump is alot lower. It flows enough to feed a pretty huge dual carb setup too.

The cons are its more complex than a mechanical pump setup. You are gonna need some adaptors to convert the retarded oringed metric power steering pump fitting they used on the fuel lines to a common size like 6AN.

The pros to the mechanical setup is its extremely simple, very cheap, and lasts a long time.

The cons are it costs horsepower to drive a mechanical pump. This a very negligable amount of power, and I believe that the alternator load created by running the electric fuel pump is probably very close.

bottom line you need to decide what setup fits your personal needs. But this is about all there is to it.

camaronewbie

1) If replacing in-tank pump, get one for a TBI car - much less fuel pressure to regulate.

2) I can't see where this would be $400. MAYBE on a bad day $200. TBI pump $50, Mallory FPR $100, $50 misc (need 6ft of fuel inj hose at $3.49 per ft and a couple $4 brass fittings from hardware store and a $10 fuel pressure guage).

3) You HAVE to use a return style FPR if using an intank pump - like the Mallory 4309. Not any 3port reg will work!

4) You need 3ft of 5/16 FI hose, and 3ft of 3/8 FI hose - the feed line is 3/8, return line is 5/16. Also need a brass fitting (from any hardware store) with a 5/16 hose barb that will fit the return line connector, and same for the feed line with 3/8 hose barb. Everything I needed for this was at my local ACE Hardware in the plumbing section - just took me a few trips to get the right sized stuff.

5) Last thing is a $10 fuel pressure guage put in the rubber hose between regulator and carb so you can adjust fuel pressure from OEM down to 5psi for the carb.

The Devastator

I never bought a tbi pump. The last TPI pump I bought was a walbro and was almost 300 bucks. Plus I had to run braided stainless hose because this desert will destroy rubber hose in 6 months.

camaronewbie

O I C ... never been to the desert .... but I do love dessert!

xdamagedx

"You have basically two options.

1 Drop tank. Replace fuel pump with pickup hose. Reinstall tank. Use mechanical pump. Plug return Line. -------CHEAP

2 Drop tank. Replace faulty fuel pump. Buy metric fuel line to an adaptors. Adapt factory fuel lines to 3/8 hose. Use a return style adjustable fuel pressure regulator. --------about 400 bucks"

That's what I was kinda figuring would be the case... thanks for the info. I'll probably end up doing something along the lines of #2 because I've got a nitrous oxide setup, and even with my "upgraded" Holley fuel pump, it seems to starve for fuel when I spray... which can result in BAAAAAAD things if any of my safety measures decide to NOT work.
Thanks to everyone for the replies.

xdamagedx

Excuse my thread resurrecting....

I finally broke down and got to work on this whole issue. I replaced the fuel pump with a TBI rated one (i figured it would have less pressure than the normal TPI pump) and plumbed/wired it in. I took the adjustment screw all the way out (as per Mallory instructions) and powered up the pump. My gauge strangely read 15+ psi nearly instantly. I killed power hoping to have not popped anything in my carb
Instructions say it should have less than 3psi with screw out. I quickly tried again after pressure bled down, this time pinching the carbs feed line, to the same result.
Should I:
1. somehow replace the return line with something bigger (I believe it's 5/16" now and the feed is 3/8")
2. use a non-return regulator before the return reg.
3. T-off the return and use another line (theres a seperate free vapor line also going back to the tank) to also use as a return
4. use a resistor to lower the voltage going to the pump
Any worthwhile opinions and ideas are very welcome.