mats

Does anyone know what the fuelpressure should be on a 1998 502 MPI?

Dave_N

MEFI 1&2 - 34 to 38 PSI
MEFI 3 - 41 to 45 PSI

Dave

mats

Thanks Dave

Is there a way to know what SW version I have?

Dave_N

MEFI 1 and 2 controllers have the connectors coming out of the ends, MEFI 3 come out the top.

Dave

mats

Hi

the engine I have is actually a 502 MPI 1999, 0L611168, but with the old style ECM. Is there any chance that someone has crammed in the MEFI 3 Sw in the old ECM HW? Is there anyway to read out the SW version with a scan tool?

Dave_N

mats,
According to the Merc service manual, serial numbers 0L085433 and above are MEFI3. There is no way to program a MEFI1 or 2 ECM with a MEFI3 calibration. A scan tool will tell you the MEFI version and calibration checksum.

Dave

mats

Thanks Dave

My engine is a hybrid. The one who modified the engine (Mercruiser)seem to have done only half the job. ECM , fuelrail and wiring harness is the 1998 style but the fuel pressure regulator and the rest of the engine is 1999. That creates an interesting situation since the fuel pressure is different between the years.

Also the injectors differ between the years and I dont know what year injectors I have and I know even less if it matters.
Does the computer just send a signal and tell them to open for a certain time? For a given time and fuel pressure, do they deliver the same amount of fuel? Do you see what i am getting at. Is the fuel pressure regulator mated with the injectors or with the ECM SW?

Mats

Dave_N

Interesting. There were no MEFI2 502's (may use a MEFI1 in a MEFI2 case), so I guess it's a MEFI1. There were different injectors used on the MEFI1 and MEFI3 502's, and they may (not sure) deliver different amounts of fuel with the same fuel pressure and injector pulse width.

MEFI1 (1993-1998) used Keihin injectors, part # 805225A1

MEFI3 (1999-up) used GM injectors, part # 861260T

If you have a 1998 fuel rail you probably have the 1998 Keihin injectors. I would think that the MEFI1 pressure, 36PSI, would be correct.

Dave

mats

Hi

It is the 1998 injectors so most likely the whole fuelsystem is 1998. But according to Mercury Marine the corresponding fuel pressure regulator 860349A1, delivers 28-30 psi.

Dave_N

The Merc EFI Tech Guide that I have lists regulator 860349A1 as the correct regulator for a 1998 502Mag MPI and is designed to maintain 36 PSI system pressure. Don't know why the conflicting info.

Dave