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.

If you've done the research, and that's what it tells you for fuel pressure with a MPI (Multi Port Injection), I would think that's what you should have ALL the time.

Robert

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

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.

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.

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.

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

same here BG

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

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?