Fuel Pressure Problem

my1stgn

Active Member
Joined
Nov 20, 2005
Here is the problem. Under boost say over 15lbs, my fuel pressure strarts to drop down to around 40psi. Im going off my KB hood mount gauge. I have a 340 Walbro maybe like 1-2 years old (bought it new) with a hotwire kit. Also run 60lb injectors with a PTDBB 61 turbo. Have a Extreme Extender chip also if that matters. Heres what I have tested so far.

I checked the adjustable fuel pressure regulator. With the hose off is at 48psi and when I use a vacuum pump and run 15" of vac, the feul pressure drops. At idle when I increase pressure with a pump at the fuel press. reg to say 15-20psi, the fuel pressure increases that amount and it doesnt dropp off if I hold it there. Also checked for power. Found with the car running and under boost Im still seeing 13.5-14v @ the alternator and the same voltage at the wire right before the fuel pump near the tank. So I think I ve eliminated a "wire/power" problem and the regulator seems to work fine. Could it be the fuel pump that is bad? And which fuel pump should I go with? I plan eventaully to run in the low 10's. Also fule filter was changed less than a year ago. Thanks!
 
Sounds like the fuel pump can not keep up with the demands of the engine.


OR your fuel filter is clogged.
 
OR, you have a major leak in line to adj FPR that typically INCREASES FP w/ increasing manifold pressure (in place of vac @ idle)...
 
Sounds like the fuel pump can not keep up with the demands of the engine.


OR your fuel filter is clogged.

But I thought the Walbro 340 was good for 10 sec 1/4 mile? Im just running about 18psi when it starts to drop fuel pressure. At first when under boost the fuel pressure will rise to about 60psi then when I get over 15psi of boost it starts to drop down. I hit around 20-24psi boost and its way down to around 40-45psi fuel pressure and a/f goes from about 11.0:1 at WOT with good fuel pressure and when fuel pressure drops to around 40psi my a/f increases to about 13.5:1 so I get off it. No knock or anything. I might try to fuel filter first. What fuel pump do you guys recommend if I end up changing it? Thanks again!
 
I had exact same problem. Fuel Pump was garbage.

If you bought your Walbro 340 in the past 2 years...chances are you have the new design "169" pump that accepts a stock type strainer instead of the big one "GSS340M" pump.

I've been seeing a lot of these "169" pumps thrown in the trash can due to the same problem.

255L/hr is enough for mid 10s, any faster you should consider a double pumper, or an external aeromotive setup.

If you're only using a single in tank pump I would try to find a good used old style GSS340M pump or roll the dice and buy another "169" pump.
 
But I thought the Walbro 340 was good for 10 sec 1/4 mile?.....What fuel pump do you guys recommend if I end up changing it? Thanks again!

Yes, a GOOD one should be--but yours is likely now DEFECTIVE--for whatever reason. FPR vac/ pressure compensation diaphragm questionable? Try replc't 255 l/h kit (for turbo buick) from fullthrottlespeed... Good luck!
 
I got my Walbro from Poston's a little over a year ago. So they are common to fail huh? I have a buddy who has a Red's Armstrong fuel pump for sale for $100. Are those any better? What other fuel pumps are people running here successfully? Thanks again fellas!
 
Hi,
Walbros are prone to failure. I would say yours is on the way out. They are great pumps, but they don't last long.
 
Hi,
Walbros are prone to failure. I would say yours is on the way out. They are great pumps, but they don't last long.

So then Walbros only last 1-2 years before failing? Thats pretty crappy seeing as I have my stock fuel pump on my Grand Prix for 7 years and 180k miles and never had a problem. So which fuel pump do people go with for high performance and longevity?
 
So either the people who read this post don't use a fuel pump,or don't know what type of fuel pump they have. I doubt everyone here changes out their fuel pump out every 2-3 years right? What other brands are there that are good? The one ft has is the same one I got
 
So either the people who read this post don't use a fuel pump,or don't know what type of fuel pump they have. I doubt everyone here changes out their fuel pump out every 2-3 years right? What other brands are there that are good? The one ft has is the same one I got

I think it's just like anything else. When units are made in mass quantities there tends to be some defected ones.

I bet if you roll the dice and get another "169" Walbro it will work for ya.

Just like when I had to take 3 starters back to the parts store before I got one that worked...but that's autozone though.
 
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