Hello Guru's

A very newby question.

I have a Maxum 2900scr with a 7.4 vortec MPI with a mefi3.
I have had nothing but over fuel issues since i bought it. It was rebuilt not long before i bought it.

All my readings seam fine except for the vacuum

The vacuum on the map is reading10.26 psi which gives me 6.47 ms on the injector timing at idle.
I can manually pull the psi down to 7.86 psi which leans the motor out beautifully and gives me 5.06ms on the injector.
I believe this indicates a non standard cam. Other than pull the motor and find a new cam,,, is there a way to reflash the mefi 3 to accept a new vacuum curve ?

Thank you in advance for your thoughts.

Can reflash the ECM using MEFI Burn software. Can the fuel tables and about anything you want. The issue is if your MEFI 3 is password protected, most are. So if you can find the Bin file for your motor.

Is the 10.26 your getting at idle? If so need a compression test

I was getting 155 plus on all cylinders

Getting much over 150 I would expect a defective gauge unless motor is rebuilt and compression has been increased. Either way sounds good because they are all within the same number

Could be the prior owner messed with the ECM not knowing what they were doing.

Your talking psi and not vacuum (in Hg) so at 10 psi (right side scale) your over 65 MAP and 10 in Hg. At idle your motor should be at around 18 in Hg and 40 Map

The motor is fresh so good compression,
i cant send the stats from the test today of the map as im only new on here, but the map measures in psi on the mercruiser programme. Not sure why. I believe the cam is whats causing the issue. So im hoping a remap will stop the high fuel ms