marine 350 cu. in. TBI rebuild & fuel pressure

I have a 1997 31ft Mainship Sedan Bridge with twin 350 cu. in. 270hp engines. The port engine will not throttle up. I am seeking advice on where to check the fuel pressure and what the pressure should. I would also like to know where I can get TBI information and rebuild kits. Engine Model # is S350S-31SB Serial #20275

Welcome to ME.com

As you will soon learn, the mid-90's vintage TBI systems were orphaned very young and there is limited availability in all respects.

The Fuel pressure should be @ 30 PSI and will require an adapter to measure...some of the chain auto part stores will "lend" you a kit with the gauge and adapters. The adapter is nothing more than a $30 inverted flare T ...

Rebuilt kits can be found on the internet...if your location supports it, a local injector rebuilder / EFI shop is usually your best source of parts and knowledge

I have made a fuel pressure testing device with short pieces of brake line tubing, a tee with two 5/16 hose barbs which I have used to connect to the fuel supply line and the TBI fitting on the back of the carb. I conneected my gauge adapter to the smaller of the two lines coming out of the back of the carb and I didn't get any pressure reading at all. I believe that line is the return to the fuel tank now that I saw the larger diameter line on the other side of the back of the TBI. I also have since learned that this engine has (2) two fuel pumps. So I think I was hooked into the wrong one and I am going to Advanced Auto store to buy the larger inverted flare fitting with the short piece of brake line tubing of which I slide a piece of 5/16 gas line over the end that I don't have screwed into the system and connect the other end of the hose to the fuel gauge tee that I made. Then I am going to connect it to the larger inverted female fitting on the back of the carb and will try to get a reading at that point. For the record I also swapped the ECM from the Starboard (right) side engine with the module on the port (left) side engine since they are both Identical and it didn't change anything with my problem of lack of accelration and no ability to even idle the port side engine. I hope this info is helpful to someone that might have a problem similar to mine. I am determined to narrow this issue down to the real root of the problem before I replace or rebuild any parts that may not be bad. Thank you all for your help and advice, I will keep you posted. Steve (Chief1048)

Heard from the OP; he asked that I post this:

Originally sent by chief1048:
"....the issue was narrowed down by checking the fuel pressure and finding it well below spec. I replaced the low pressure.primary fuel pump on the 350 cu. in marine power engine and the engine ran fine. I hope this test helps other with similar problems of lack of acceleration. I also checked the pressure on the high pressure pump to be sure it was ok, which it was. Fuel is pulled from the tank with the low pressure pump first. This can also be verified by a ticking sound when the key is first turned on before you start the engine. Once the fuel system is pressurized the ticking stops and you are ready to go."

And now we have the rest of this story.....