Texas5.0

I have been doing searches all morning about fuel pressure and have not been able to find the answers I am needing.SoI have a few questions.

Stock fuel pump on an 89 is 88 lph or 110 lph?

Will a stock fuel pump run 24 lb injectors at the 40 psi if an adjustable fuel pressure regulator is used?

dillon1340

a stock fuel pump is 88. if you put on 24lb because you needed more fuel then you need a better pump too.

Texas5.0

That may be true... but I am needing to know if the stock will run the 40 psi.

luckythirteen13

if you need the 24's then no, it wont hold 40psi. if you have a stock motor and have 24's, the injectors wont be open very long which will along the pump to support 40psi.

i have a 255lph pump in my garage i dont need if you want one cheap.

Texas5.0

I don't understand that sentence...
My motor is not stock. I have the mods listed in my sig line and I am somewhat knew to the building a motor thing but wouldn't the injector not being open as long allow the pressure to build?

5.0rick

If you are making more than 330 HP@ the flywheel, then you will need to step up from 19# injectors to 24#s. If you move up on your injector size, you will also need a new Mass Air Flow sensor (MAF). Fuel pressure on your stock regulator should be ~47 psi with the vacuum disconnected (that is what my 89 is set to with the stock pressure regulator per my Autometer gauge).

Rick

luckythirteen13

oops, my brain is faster then my fingers. i was trying to say, if the motor doesnt need the big injectors, your pulse width will be very short which means you wont have a lot of fuel going into the motor so the pump will be able to keep up, but if you actually need those 24's, i wouldnt trust the stock pump. i know when i did heads, intake and bolt ons (still stock cam) my stock fuel pump couldnt support 24# injectors

Texas5.0

I am not making more than 330 at the flywheel and I have the correct mass air for 24#'s.
I guess the question I am asking is not as easily answered as I thought. My problem right now is that I am running around 22psi on my new 24 # injectors. I just bought an adjustable fuel pressure regulator and got to thinking about the entire fuel delivery system. I was wondering if the stock fuel pump would have enough pumping ability to get the system up to 42 pounds with the mods that I have and with 24 pound injectors and the new adjustable FPR.

5.0rick

Hi Texas 5.0,

1st and foremost, let me ask the following:
What MAF are you running?
What EEC-IV are you running?
Are your 24# injectors the FMS blue ones?

Let me start by saying that the stock fuel pressure should work fine if your injectors and MAF are designed to work with each other. You should not have to play with the fuel pressure at all.

If you are having problems, you may not have what you think you have. BTW just in case, the 93 Cobra MAF requires the Cobra computer (X3Z) to work correctly ( It has a different transfer).


On your question regarding the fuel pump size, let's look at the math ( this is a guestimate)

19#/hr injector flows 200cc/minute or 12000cc/hr. There are 1000cc in 1 liter, so you could say 12 liter/hr. That is for 1 injector at 100% duty cycle. Multiply by 8 injectors and you get 96 liters/hr at 100% duty cycle. Now, let take a more realistic duty cycle like 92%. 96 liter/hrX 92%=88.32 liter per hour. So basically, the stock fuel pump will roughly support19# injectors (8 of them) at 92% duty cycle. These numbers are not exact, but you get the idea.

Using the same calculation, the stock fuel pump will support the 24# injectors at 73% duty cycle (which is still an overall flow of 88 liters/hr). 24# injectors flows 252cc/minute.

BTW,with a Brake Specific Fuel Consumption of .5, the 19# injectors and 88 liter per hr fuel pumpsupport around 290HPinstead of the 330HP I mentioned earlier.(the fuel pump being the limiting factor, that is if you wish to push the injector duty cycle past 92%)

Where in Texas are you? I am in Round Rock, just north of Austin.

Regards,

Rick

Texas5.0

Hey rick, thanks for the info. I am sure that my MAF is calibrated for the injectors and yes they are the blue ones... as for as the EECV-IV uhhhhh, not sure. I thought that was the system that was used from 1983 to 1995. I was not aware of any sub-systems, but there isa ton that I do not know. I got the pressure set and have run the car for a few weeks and need to check the pressure again.

I am an hour south of Houston... right on the coast.