Fuel pressure issue..
Thread Starter
TECH Apprentice
Joined: Apr 2011
Posts: 390
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Fuel pressure issue.. I have noticed that my car does run well under part throttle and full throttle typically. However under hard loads like a long steep hill, or when I mat the gas it will feel really weak and then pick up on the top end.
I ran my scanner on the car, and it will have normal timing curves under light throttle (40deg to 30 deg variable) but when I stand on the gas, it drops to 8-10 deg and the engine feels confused and doesn't pull whatsoever.. pulling ignition timing due to knock im assuming
I put a fuel pressure guage on the car (B&M brand, not some ebay junk) and it is idling at 47-48 psi. When I rev it, it goes up to about 50 then dips to about 40 psi. when I hold throttle at around 3000 rpm, it stays around 45 psi.
Think its time for a new pump? Currently it has a Buick GN oem replacement pump which I think is supposed to run at 43 psi rail pressure, but it always seemed to run fine.
After my tune, there was a good bit of timing changes.. so I guess now its really showing how lean the motor is going and pulling timing.
I ran my scanner on the car, and it will have normal timing curves under light throttle (40deg to 30 deg variable) but when I stand on the gas, it drops to 8-10 deg and the engine feels confused and doesn't pull whatsoever.. pulling ignition timing due to knock im assuming
I put a fuel pressure guage on the car (B&M brand, not some ebay junk) and it is idling at 47-48 psi. When I rev it, it goes up to about 50 then dips to about 40 psi. when I hold throttle at around 3000 rpm, it stays around 45 psi.
Think its time for a new pump? Currently it has a Buick GN oem replacement pump which I think is supposed to run at 43 psi rail pressure, but it always seemed to run fine.
After my tune, there was a good bit of timing changes.. so I guess now its really showing how lean the motor is going and pulling timing.
Fuel pressure is your proble... The Gen III/IV engine EFI requires a regulated 58psi of fuel to the injectors. You have the wrong pump.
Tell us more about your fuel system, what Fuel Pressure Regulator are you using and is it adjustable ?
Tell us more about your fuel system, what Fuel Pressure Regulator are you using and is it adjustable ?
Thread Starter
TECH Apprentice
Joined: Apr 2011
Posts: 390
Likes: 0
All fuel lines were custom bent for this application and are new - gas tank is new, sending unit is new. The car does not sit at all I drive it about every day so there isn't any rust or debris in the line - also verified by pulling fuel filter, blew it with an air hose and no debris at all.
I need a new pump I think.. Walbro 255?
So, there is nothing you suspect to be restricting the fuel pressure.. so.. if your at 47-48PSI (which is at the LT1 pressure range). You should get a properly spec'd pump .. yeah.. the Walbro 255's are the most common choice. I use them myself.
Becareful until you change it.. you don't want to run it Lean..
good luck
BC
Becareful until you change it.. you don't want to run it Lean..
good luck
BC
Last edited by bczee; Dec 10, 2012 at 02:24 PM.
