Motor wont rev under load

[jceee]

I have seen quite a few posts related to this issue but let me tell you where I am at....1996 Four Winns Horizon..5.8L omc/volvo fuel injected i/o. First pull out this season I crossed the battery terminals...tripped a breaker, reset back to normal power. First drive of year...seemed to run ok...bout 20 minutes in no power when taking off and wont rev up to full rpms... checked plugs looked good...changed fuel water separator. There are two pressure valves one on the top of the engine and one right next to the high pressure fuel pump. The one on top read 32 psi. The valve next to hp pump read 0 psi. Does this indicate bad hp fuel pump or is there something wrong with the valve. Can these pumps be cleaned. Any help appreciated!

 

[Scott Danforth]

your fuel pressure is low

 

[jceee]

Any idea on steps to fix? Thank you

 

[alldodge]

The one on top read 32 psi.

From my findings I'm seeing your high pressure is good if you were at idle, and low if at higher rpms
(31 psi +/- 3 @ idle and 39 psi +/- 3 it either key ON and motor OFF, or WOT)

Your other fitting should be the low pressure pump not high and its low
(5 psi +/- 3)

Part numbers for pumps are
high 3857650
low 3858261

Check your fuel filter to see if its full and then dump contents into a clear container to see if you see anything else but clean gas.
If the fuel filter is not full check the antisiphon valve on the tank

 

[jceee]

Thanks, so you are saying the pressure valve near the high pressure pump actually measures the low pressure fuel pump pressure? Also I do have a full fuel filter..and the gas is free from obvious water..thanks gor the pressure info..
are you thinking I may need.to replace both the low and high pressure fuel pumps?

 

[alldodge]

are you thinking I may need.to replace both the low and high pressure fuel pumps?

Not yet

I'm saying that the port on the pump should be low pressure (LP) and since your not getting enough fuel. If the LP pump does not supply all the fuel the high pressure (HP) one needs, the the high falls off some.

The first thing is to find out is why the LP pump is low. Is it due to a restriction or weak pump?

 

[jceee]

Ok sounds good to me..could you please suggest how to diagnose that?

 

[alldodge]

If your saying the fuel filter was full (note I asked it was full) when removed and checked?

The remove the fuel line from the tank going to the fuel filter. Place the line into a gas can, and if need be add fuel line to the line so it will go into the can. Run for a little while on a hose then check fuel pressure

 

[jceee]

Excellent I will try that...is there a better time to check the filter when it would show empty, I pulled it after use about an hour after pulling it out of the water and it was full.

 

[alldodge]

It being full then your good, no need to recheck

 

[jceee]

And safe to run a line right to a normal 5 gallon fuel tank with the gas line through the opening?

 

[alldodge]

And safe to run a line right to a normal 5 gallon fuel tank with the gas line through the opening?

Yes, just make sure the can is secure so it doesn't move and is far enough away from anything that may spark

 

[jceee]

Ok havent checked the fuel tank side yet...but I rechecked pressure with a better guage... hp fuel is dead on...low pressure is also dead in at idle...but when given gas in the water the low drops off from 4-5 to almost 0. It will recover but is this normal to see a drop off of pressure on the lp side under load..or is this an indication of an issue...thanks

 

[alldodge]

low drops off from 4-5 to almost 0

Yes that is an issue. Use the remote tank to verify its not the tank

 

[jceee]

Ok great maybe getting closer...any idea what size the black main fuel line is to use as remote...I'm not near the boat now and want to purchase thanks

 

[alldodge]

Unable to say for sure but in most cases it will be 3/8

 

[jceee]

Thank you. Forgot I wanted to mention that I get no fuel pressure at either valve with just key on motor off. I hear both pumps activate when I turn the key but the gauge doesn't move until started. Interesting cause specs above say I should.

 

[alldodge]

Agree, that isn't good

 

[jceee]

Is this indicative of something?

 

[alldodge]

Is this indicative of something?

The fuel pressure regulator should be able to slow the pressure drop. It could be the reg or leaking injector(s)