Testing fuel pump pressure?

[LGnBama]

I have a 1981 Mercruiser 228 HP (305 ci) with a mechanical fuel pump. From what I have seen posted on here, the correct way to test the fuel pressure is to do so while running under load? My question is, Can an accurate pressure reading be taken using the starter to turn the engine over, but not actually running the engine? I hooked a guage to my fuel pump and got only 3 to 3.5 psi doing this. Just curious to know if this is an acceptable method of testing, or do I need to take the boat out on the lake and test under load?

 

[Reel Poor]

Re: Testing fuel pump pressure?

If your havin a problem that you suspect may be a fuel issue, the pressure should be check under the same conditions the the problem occures in. Pressure should be tested with engine running under a load to get an accurate reading of pump capability.

Pressure should be around 5/7 PSI and be capable of pulling about 15 inches of vaccum on the suction side.

 

[hullofalottatrouble]

Re: Testing fuel pump pressure?

i think you can get away with testing it on the trailer.. i would test it with the engine running thou.. if you find the pressure is low you will want to also do a vacuum test on the other side of the pump.. that may indicate a restriction in the fuel line vs a bad pump.. thats at least what i found when i did my test last year.. bad antisiphon valve

 

[hullofalottatrouble]

Re: Testing fuel pump pressure?

if you T in a vacuum gauge on the suction side you dont want to see any vacuum.. that would indicate a restriction.. i cant find my test specs but think you want something under 2hg on the vacuum side and for my AC mechanical pump its like 5.25-6 on the pressure side at 1000 rpm...

 

[LGnBama]

Re: Testing fuel pump pressure?

Thanks for the replies! I am still searching for the problem. I can just feel the boat starving for fuel at WOT as the RPM's go from 4300 to 4000.

 

[Reel Poor]

Re: Testing fuel pump pressure?

Did you do any of the test mentioned above?