Fuel Pressure Readings
 

I have a stock 1999 502 Mag MPI. I have done a search and it appears I should have 41-46 PSI of fuel pressure. But, I couldn't find WHEN I should have this pressure? Is it measured with the key switch on and the pump running, at idle, at WOT, etc?

Also, should fuel pressure increase or decrease as rpms increase?

Thanks.

Re: Fuel Pressure Readings
 

Re: Fuel Pressure Readings
 

It should be done @ WOT. I run my 454mags @ 42psi but mine are not stock motors.

Re: Fuel Pressure Readings
 

Well, my research was done here and now I am getting conflicting numbers. Some are saying 41-46 and others are saying 28-32. BIG difference. I guess I will order a Merc shop manual for my motor.

And yes you are correct it should have the same fuel pressure all the time. Thanks.

Re: Fuel Pressure Readings
 

Scott,

I believe the lower numbers were for the older VST systems and the higher numbers are for the cool fuel system. That being said, I'd rather buy a manual now and know for sure rather than an engine and a manual later. :D

Re: Fuel Pressure Readings
 

Getting ready to order now! I spoke with a member last night that had a manual for 1995-1997 502 Mags and the VST motors were 32-36 lbs and the Cool Fuel were 28-32lbs. So, according to that the Cool Fuel had lower pressure. But, obviously some changes could have been made between 1997 and 1999.

Re: Fuel Pressure Readings
 

Mine are 2000's with cool fuel and I checked it static last summer and it was in the mid 40's.

Re: Fuel Pressure Readings
 

same here BG

Re: Fuel Pressure Readings
 

BGIII and 29Kilroy, do you guys have stock motors? Thanks.

Re: Fuel Pressure Readings
 

No they are not but I am sure that they started in the 40's. Are you putting an adjustable regulator on or just concerned that you may have an issue?

Re: Fuel Pressure Readings
 

My old motor (worked 502MAG) ran 45psi
I ran a red aeromotive pump and had to increase the stock pick-up to a 3/8th to hold 45@wot.

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Base motor was a '98 but like i said it was modified.

Re: Fuel Pressure Readings
 

I'm thinking I MAY be running too rich.

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Manual on the way! Should be here tomorrow. :D

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Manual states 34psi at idle for VST system.

Re: Fuel Pressure Readings
 

Mine is a 1999 with the cool fuel system.

Re: Fuel Pressure Readings
 

Just got my manual. It states 43lbs for MEFI3 with cool fuel.