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Quick question....let's say you have a Camaro, Mustang, etc with a fuel injected V8...lets say it's a naturally aspirated fuel injected V8...ok now when you accelerate from a cruise, does the fuel psi change much, if any at all?
On most Port fuel injected (vs Throttle body injection), the PSI will increase on the avg between 5-10 psi. In early models, psi was controlled by a vacuum sensitve regulator. Opening the throttle lowered the vacuum, and psi would increase. Some engines, the psi regulator is on the fuel rail under the hood, some on or in the fuel tank. The regulators in or on the tank run at a constant pressure.
On some newer models with no fuel return line, the psi is controlled by pulsing the fuel pump on and off. The pump is off for a longer time at low speed/idle, and on longer at higher engine speed.
Remember that fuel pressure for fuel injection is much more than for carbureted engines. 10 pounds compared to 100 pounds.
10psi on a carbed engine i certainly hope that you are not running that much pressure as most carbs only want 4-6psi at most. and unless you are running alcohol or nitromethane, 60psi is more than enough fuel pressure in an injected engine.
as to the op, yes fuel pressure does go up when you accelerate. most efi engines run about 35psi at idle and normal cruise rpms. when you accelerate, the fuel pressure will go up as indicated about 5-10psi depending on the type of fuel system. for instance most return line systems push the fuel pressure up about 10psi since the pressure regulator is generally referenced from engine vacuum, and is generally an on/off deal. later systems that do not use a return line will ramp up the pressure as needed, up to 15psi, as the system determines how much fuel pressure is needed and changes the fuel pump rpm to get the needed pressure.
Remember that fuel pressure for fuel injection is much more than for carbureted engines. 10 pounds compared to 100 pounds.
I do understand this. Carbs run on 5-7 psi. My turbo V6 Buick runs at 38-40 psi at cruise and then when under boost conditions it gets up as much as 68 psi. But that's because it has to be pressurized for the added air. (1 lb of fuel per 1 lb of boost, running 25 lbs of boost)
I have a fuel pump that doesn't go much over 46 psi w/o bypassing pressure.....that had me wondering if it would work on something like a 5.0 Mustang or a 5.7 Camaro since I didn't think they'd reach that much psi, but wasn't sure.
I do understand this. Carbs run on 5-7 psi. My turbo V6 Buick runs at 38-40 psi at cruise and then when under boost conditions it gets up as much as 68 psi. But that's because it has to be pressurized for the added air. (1 lb of fuel per 1 lb of boost, running 25 lbs of boost)
I have a fuel pump that doesn't go much over 46 psi w/o bypassing pressure.....that had me wondering if it would work on something like a 5.0 Mustang or a 5.7 Camaro since I didn't think they'd reach that much psi, but wasn't sure.
if you want more fuel pressure, you can always get an adjustable regulator, most of those will allow up to 60psi line pressure if oyu feel you need to go that high. understand though that the more you raise the fuel pressure on an injected engine, the richer the fuel mixture will be. it is an efi racers trick to ad fuel without going to larger injectors.
Yeah I know, I don't need more fuel psi, just wondering if a pump that tops out at 46 psi is enough for a Mustang or Camaro with a V8.
its not the pump pressure that you have to worry about, pretty much all efi pumps will put out more pressure than the regulator will allow. what you need to deal with is the pump volume. if the pump volume is capable of handling the needs of a V8 engine, then it doesnt matter what V8 it is used with, unless it is a high performance build. as i recall stock V8 pumps put out about 190gph of fuel volume, which is plenty for a stock V8.
My 1996 mustang gt will not run. It will crank and fire up for a second and then die. I have checked the injectors they are all good. I cleaned the fuel rails and that didn't help. I can hear the fuel pump humm when I turn the key to the on position before I crank it so I figured that was good. I was getting fuel pressure so I didn't worry about it. But after a while of taking shots in the dark I tested the fuel pressure. It was 10 psi while I was cranking. Should it be a lot higher than that? I've never had the engine running so I don't know
Not sure on your Ford, but on a GM, if the book calls for 52 psi, it won't start on 50. That 10 psi sounds awfully weak. I will do some checking and be right back.
Book calls for 35-45 psi on the '96 Mustang GT. Looks like you need a fuel pump.
Last edited by Electron; 04-06-2016 at 07:46 AM..
Reason: Added info
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