POWER LOSS OVER 3,000 rpm

[chrisambrico]

I am the very proud owner of a 99 Stamas 31 Express with twin 350 Mags. Developed a power loss that is fuel related. Normally, I would just change the fuel pump, but I have seen many posts of others with a similar problem and had replaced the pump, cooler and regulator with no success. With twin engines it offers an easy comparison. I was losing power in the port motor over 2800-3000 rpm. After some basic evaluation, felt it was a fuel concern. Check fuel pressure and found it to be 25 psi at idle, and 32 psi with vacuum line disconnected. Took it out and once under load it stayed pretty steady at 30 psi which appears to be the spec. Being a little confused, I compared to the "good" starboard engine. Fuel pressure was 40 psi at idle and over 50 psi with vacuum line disconnected. I would normally consider this a fuel pump issue, but again, based on some posts I have read, that seems to be the one thing that never works. Unfortunately, never seem to get to conclusion and many posts are 10 years old. Any help is appreciated. thanks in advance.

 

[alldodge]

After some basic evaluation, felt it was a fuel concern. Check fuel pressure and found it to be 25 psi at idle, and 32 psi with vacuum line disconnected. Took it out and once under load it stayed pretty steady at 30 psi which appears to be the spec.

Without a motor serial number I'm going to guess your pressure is low, and should be 43 psi at 1800 rpm. The starboard motor is correct

Its either the regulator or the pump. To test Reg remove it and use air pressure with a regulator and see if it opens around 43 psi

 

[chrisambrico]

SERIAL # OL303410 - mercruiser manual indicates proper fuel pressure to be 34-38lbs. However, symptom chart in Fuel injection general diagnostics is measuring against a value of 25 psi (above or below). Since it is measuring 25, I followed chart both ways (yes it is lower than 25 and no it is not lower than 25), both lead to a blockage in fuel system. Checked all lines, no kinks that I can see. Ran engine on opposite tank, no change.

 

[alldodge]

Your correct 30 psi and even though the starboard has no current issues it has to much pressure if its in the same serial range (not been replaced, Reg 807952A1)

Check plugs, cap and rotor, and compression test