Low Fuel Pressure on 2000 Mercruiser 7.4 MPI

[CLi87]

I've been trying to tackle this low fuel pressure problem on my boat for quite some time, my original symptoms was fuel pressure would go to 40 psi then drop to 20 psi with key-on engine-off, running psi would be 28 psi then 32 psi with vacuum hose disconnected. I've since replaced the fuel pump and fuel pressure regulator with OEM quicksilver parts and now I'm getting 40 psi then drop to 38 psi with key-on engine-off and I'm getting 32 psi with engine running at idle and then 42 psi with the vacuum hose disconnected. I've also tried running the engine on a separate portable fuel supply with no change in pressures so I guess now I'm looking at either a collapsed hose which is probably unlikely as these are some big hoses, an issue with the fuel rail, or could the "fuel damper regulator" located next to the distributor cause these kinds of problems? or is there some other test I could do to narrow down the low pressure problem?

 

[alldodge]

This should probably be part of your existing thread, same subject

I'm thinking you have 1 or 2 injectors leaking, and doing the injector balance test will identify which one(s).

Reason: the pressure stays at 42 psi with vacuum line disconnected

The fuel gauge might also be slightly off and would explain the slight variation in high/low readings

Could test the fuel pump by blocking off the FP Reg with a valve, and note don't let pressure exceed 60 psi

 

[CLi87]

This should probably be part of your existing thread, same subject

I'm thinking you have 1 or 2 injectors leaking, and doing the injector balance test will identify which one(s).

Reason: the pressure stays at 42 psi with vacuum line disconnected

The fuel gauge might also be slightly off and would explain the slight variation in high/low readings

Could test the fuel pump by blocking off the FP Reg with a valve, and note don't let pressure exceed 60 psi

Sorry, I thought it would be better to start a new thread because my original thread was just asking to identify a particular part.

Is there any way to do an injector balance test without a scanner or will I need to buy one? I have the mefi 3/4

I had replaced the fuel pump first originally and the psi readings didn't change at all, then after replacing the regulator it helped some.

 

[alldodge]

I doubt it.
The balance test has the pressure built to max then a pulse is sent to one injector. Readings are recorded after each pulse . Pulsing them by hand will not provide exact pulse width to compare

 

[alldodge]

Could send injectors out for cleaning and flow testing