7.4 gen 6 nightmare

[Bassmaan]

Hi there. Needing a little direction.
I have a mercruiser 7.4 gen 6 mpi with a mefi 3 in my Maxum 2900. Just finished a rebuild as the oil was filled with fuel.
Changed maf, iac, dizzy sensor , injectors plugs , cap and leads.
swapped out ecu.no difference
Still wants to run like a lumpy cam. lacked power to plane as well. compression is 145 to 150 on all cylinders .
ive checked the volts on the sensors and they read 6.2 v . is this an over voltage ?
fuel rail pressure at turn key is 40 psi and drops to 35 on start.
Would love to know your thoughts

 

[alldodge]

The 5V circuit should be 5V exactly. If your meter is accurate then this will cause all kinds of issues.

Fuel pressure should be 43 psi running. Dropping to 35 will not be enough to keep it running within spec.
Disconnect the vacuum line at the regulator or plenum to see if pressure increases

If pressure does increase then its either the pump or regulator. The regulator can be tested on the bench using air pressure and a air regulator

 

[Bassmaan]

The 5V circuit should be 5V exactly. If your meter is accurate then this will cause all kinds of issues.

Fuel pressure should be 43 psi running. Dropping to 35 will not be enough to keep it running within spec.
Disconnect the vacuum line at the regulator or plenum to see if pressure increases

If pressure does increase then its either the pump or regulator. The regulator can be tested on the bench using air pressure and a air regulator

Thanks for that. Its definitely got all kinds of problems haha. Been doing my head in.

 

[achris]

Be aware, the zero volt rail for the 5v reference voltage is NOT engine ground. It's an independent 'ground'. You need to measure the 5v between the 5v and ground pins on one of the sensors itself.