kpetry
Member
- Jul 19, 2008
- 362
- Boat Info
- 2002 Sea Ray 340DA
- Engines
- Twin 8.1 Horizons, inboard
I have twin 4.3 carbeureted Mercruisers in my 99 290 DA, which have developed a starting problem. They have both developed the same problem, seemingly almost simultaneously.
When the engines are cold, after sitting all week, they take lots of cranking to start. They act like they are not getting enough fuel. Once running, they run fine, up to and including full throttle. Once we stop, let's say for a raft-up for a couple hours, they usually start fine, but then die after running (idling) for about a minute of so. It's like they are running the fuel out of the fuel bowls, and then can't get any fuel to replace it - almost like vapor lock. Dumping raw fuel down the carb throats will cause them to start and run fine after a couple tries.
Today when I had them run and then die after restart as described above. (after running them for 30 minutes under load), I tore into the fuel system on the starboard engine. I felt along the fuel lines. The hottest part was definitely the fuel bowls of the carb due to engine heat. Then lines themselves were relatively cool. I cracked open the fuel line at the carb - no fuel while cranking the engine. I cracked the line going into the fuel filter/ water separator - still no fuel. I checked the electric fuel pump voltage - good to the pump. I jumpered across the oil pressure sensing switch that controls the fuel pump, and the fuel pump ran fine, non stop with the ignition on, (but not cranking the engine) and EVENTUALLY started pumping fuel up to the carb. Reconnected the fuel lines at that point and all ran well thereafter.
My theory at this point is that there are one or more faulty check valves in the system that are letting the fuel siphon back into the tanks via gravity. Then, an air locked or possibly weak fuel pump is having difficulty getting fuel back up to the carb. The local dock "expert" says the electric fuel pumps have a built in check valve, and there might also possibly be one where the fuel lines enter the tank. He also says the factory pumps are 11 years old (400 hrs), and should be about worn out.
Due to the fact that the lines down to the tank are completely empty of fuel when this happens, I'm not ready to believe it's simple vapor lock - never had a problem with this before this summer.The fuel is new this spring, delivered from a commercial fuel truck which we use frequently for farm fuel. The fuel filters/water separators are new this spring. WHATS WEIRD IS IT'S SEEMED TO HAPPEN TO BOTH ENGINES SIMULTANEOUSLY OR IN QUICK SUCCESSION!!!??? They each have SEPARATE lines entering a common tank. Could my luck be that bad?
I'm tempted to replace at least one of the fuel pumps to see if that solves the problem. Does anyone know anything about this check valve/anti siphon issue, and where these might be located? What are your thoughts on a "weak" electric fuel pump that seemingly pumps enough fuel under full throttle load? Thanks in advance for your help!
When the engines are cold, after sitting all week, they take lots of cranking to start. They act like they are not getting enough fuel. Once running, they run fine, up to and including full throttle. Once we stop, let's say for a raft-up for a couple hours, they usually start fine, but then die after running (idling) for about a minute of so. It's like they are running the fuel out of the fuel bowls, and then can't get any fuel to replace it - almost like vapor lock. Dumping raw fuel down the carb throats will cause them to start and run fine after a couple tries.
Today when I had them run and then die after restart as described above. (after running them for 30 minutes under load), I tore into the fuel system on the starboard engine. I felt along the fuel lines. The hottest part was definitely the fuel bowls of the carb due to engine heat. Then lines themselves were relatively cool. I cracked open the fuel line at the carb - no fuel while cranking the engine. I cracked the line going into the fuel filter/ water separator - still no fuel. I checked the electric fuel pump voltage - good to the pump. I jumpered across the oil pressure sensing switch that controls the fuel pump, and the fuel pump ran fine, non stop with the ignition on, (but not cranking the engine) and EVENTUALLY started pumping fuel up to the carb. Reconnected the fuel lines at that point and all ran well thereafter.
My theory at this point is that there are one or more faulty check valves in the system that are letting the fuel siphon back into the tanks via gravity. Then, an air locked or possibly weak fuel pump is having difficulty getting fuel back up to the carb. The local dock "expert" says the electric fuel pumps have a built in check valve, and there might also possibly be one where the fuel lines enter the tank. He also says the factory pumps are 11 years old (400 hrs), and should be about worn out.
Due to the fact that the lines down to the tank are completely empty of fuel when this happens, I'm not ready to believe it's simple vapor lock - never had a problem with this before this summer.The fuel is new this spring, delivered from a commercial fuel truck which we use frequently for farm fuel. The fuel filters/water separators are new this spring. WHATS WEIRD IS IT'S SEEMED TO HAPPEN TO BOTH ENGINES SIMULTANEOUSLY OR IN QUICK SUCCESSION!!!??? They each have SEPARATE lines entering a common tank. Could my luck be that bad?
I'm tempted to replace at least one of the fuel pumps to see if that solves the problem. Does anyone know anything about this check valve/anti siphon issue, and where these might be located? What are your thoughts on a "weak" electric fuel pump that seemingly pumps enough fuel under full throttle load? Thanks in advance for your help!