1964SS

iTrader: (1)

Hey gang, I completed my LS1 swap in my 64 Chevelle back in November and the car has been running great until this past weekend. First thing I noticed was that the car was not starting as quickly as it did before. I checked and replaced all the spark plugs and still had the same issue. I also noticed that I had lost a great deal or power so I picked up a fuel pressure gauge to test the sytem and found the problem, but not sure which to replace first.

With key on I have 0 psi. After several cycles of key on and off I can start to see the pressure raise just a bit.

With car at idle I have 30 psi which seems to hold under acceleration.

With key off the fuel pressure drops to 0 within a couple seconds.

I'm running an external walbro 255 pump with a corvette filter regulator.

I've heard that these pumps don't last long, but I didn't think it would fail in 5 months.

Do you think the pump is shot or the regulator? both parts where purchased new 5 months ago.

I'm running a fuel cell in the car so I can't really add an in tank fuel pump. What would you recommend I use?

Thanks for the help!

garys 68

iTrader: (1)

Block the return line from the regulator and check pressure.
If it's still low, it's the pump.

fox12303

iTrader: (7)

Do the return check as mentioned above but also do a voltage drop check to be sure you have a steady 12-13 volts at the pump. Low voltage would also give you low pressure. Check the pump ground too.

How's the pump wired? What gauge wire did you use? Should be at minimum 12-14 gauge wire. Anything smaller and you could have voltage issues, typically when it gets hot. So cold I would think your pressure would be normal with a steady drop but you say you have to cycle the key to get pressure. So I doubt it's the wiring but it's something to keep in mind.

bczee

iTrader: (12)

Where are you measuring the pressure, at the fuel rail ?. if so.. and your pressure drops after you turn it off. .You might have a bad / leaky injectors.. ? or yeah.. check out the FPR... possible it went bad.

BC

1964SS

iTrader: (1)

With return line crimped off the pressure went up a couple pounds. It's still well below where it should be. I guess I need to order a pump. Is there another external pump that would work better then the walbro?

Thanks for the help.

fox12303

iTrader: (7)

I believe most electric pumps have check valves though my experience is they are not very effective. So pressure bleed down is not all that uncommon. I would continue to look for the cause of the low pressure and not focus on the drop after the key is off.

I thought Walbro made a decent pump. I'd go Holley or Aeromotive. Airtex and Delphi are quality OEM's as well as ACDelco.

Lonnies Performance

iTrader: (16)

It is more likely the hose in the fuel tank failed instead of the check valve.

1964SS

iTrader: (1)

This is an external pump.

bczee

iTrader: (12)

Yeah.. possible the pick up has something sucked up onto or in it. Try using compressed air to blow back into feel hose leading to the pick up to see if it clears out.

BC

1964SS

iTrader: (1)

I pulled the fuel rail today and checked all the injectors. Nothing is leaking so the problem is pump for sure.

1964SS

iTrader: (1)

I replaced the fuel pump and had the same issue so I picked up a regulator and it fixed the problem. FYI blocking the return line must not be a valid way to determine which unit is bad. After removing the regulator I compared mine to the new unit. On the new unit I can blow through the output and it comes out the input, but if you block the input the unit holds pressure. On my old regulator when I blocked the input and blew on the output it leaked out the bypass return line. This immediately told me the unit was bad.

bczee

iTrader: (12)

Great to hear the problem has been resolved.