modriscoll91
Recruit
- Joined
- Oct 9, 2017
- Messages
- 2
Hey guys,
This site has long provided me with information that has saved me thousands of dollars. I wasn't able to find any strings with this issue so wanted to a)hopefully get this resolved and b) provide the information so that when someone else has this issue (let's face it... volvo penta fuel issue.. it's gotta be out there).
Volvo Penta 5.7 GI PMDA. 1000 hours.
Story so far: No issues with performance from time boat leaves the dock until about 50 minutes into "running time". Right around 50 minutes (with the "run" consisting of 20 minutes of 3500 rpm cruise, then idle for 10 minutes, then 20 minute 3500 cruise, the engine begins to bog down in a surge like manner (only surging downward in RPM). The engine will bog down and eventually bring the boat down to 2000-2500 RPM range where it will maintain that without issue (but giving me no high end RPM performance). Now, if I throw the boat into idle and wait two minutes, I can get the boat back to WOT and great performance for 1-2 minutes before the bog down issue happens in the exact same way. I've taken the boat out multiple times thinking it was possibly bad fuel, issue happens at same time in same way. When the boat bogs down, if I open the engine hatch I can hear the high pressure pump whining considerably (with the whining going away after the 1-2 minute idle "break"). Once the whining goes away, I can throttle up and the engine will perform for the 1-2 minutes without whine, until it returns and the boat bogs down.
So, I started troubleshooting. I first checked "down stream" by pulling both fuel filters. I have one in line 10 micron fuel/water separator. I pulled this off (checking for any residue - it was clean). Then dumped the fuel in the filter into a mason jar. No separation, no gunk. Then I pulled the fine filter right before the low pressure pump, same deal, clean fuel, no gunk no residue on filter gasket (paint etc.). I then pulled all the fuel hoses off their fixtures and blew air through them, no kinks, no blockages. Seemingly all good there. Hmmm...
Next stop I pressure tested my fuel rails. (This is where I get mad at myself). My manual mentioned low pressure spec in the range of 5-8 psi in the fuel rail and VST reservoir (where the shrader valve is for access to test)pressure rail). I hook up the manifold to the shrader valve and test at idle at dock and under load. My reading at idle is 4-5 (I have a 50psi manifold and it was hard to tell exactly). I figure close enough. I then pressure test my high pressure side at the fuel rail access port (via shrader valve in line). My reading here is 15 psi. My manual calls for spec in the mid 30 to low 40 psi for the high pressure line. Immediately, I go aha! I've found it. I've got a high pressure pump whining, I'm seemingly starving for fuel as I'm bogging down, and I'm "out of spec" for my high side pressure. So, I go buy the high pressure pump and swap them out. I take it out for a spin, the issue appears at the exact same time. Well.. That sucks. So we pressure test at sea, right before my high pressure pump starts whining, the psi at the VST reservoir access point drops to ZERO. Thirty seconds after that, the engine bogs down in the same fashion mentioned above (high pressure starts whining and no high end performance).
So I do a little more reading, and I find out that high side spec for TBI is really 15psi (meaning I was in spec the whole time and never had to replace my high side pump - I'm not mad over it, as performance has actually increased a little (RPM "floor" when the pump starts to whine is now slightly higher) and well.. its the cost of doing business). Note to everyone: Consult multiple sources before you go swapping out parts In this case, my "foolproof" manual has a spec call out for a different "multi-port system" where evidently high side pressure is much higher.
Next I pull all the fuel rails and ensure no blockages. All good there (blew pressurized air through them). I also pulled the fuel rail fixtures into the VST (but not inside the VST), no gunk and fuel looked good. I also checked my injector "spray". It is conical and no drips. However, I have yet to check them when the boat bogs down at sea. It is safe to say the injectors are performing great for the first 50 minutes (WOT easily achieved with no hiccups).
However, I still have my problem and am a little hesitant to go swapping out that low pressure pump. I have read some literature that mentions there is a raw water jacket (used for cooling) around the bottom of the VST tank and that at times, the small housing for which the water comes in (via raw water pump circulation) can become blocked by salt deposits. After 50 minutes, perhaps the flow of raw water into the VST isn't sufficient enough to cool the fuel and hence turning the VST tank into pure vapor and causing the high pressure pump to "whine" as it is starving for fuel?
Or possibly, I am facing mechanical failure of the low pressure pump after 50 minutes of use? Therefore starving the VST of fuel supply and dropping PSI to zero which then causes the high pressure to starve for fuel and cause performance issue?
One other thing I haven't checked.... the anti-syphon valve on top of the gas tank pickup. But given the high end performance for the first 50 minutes, I'm not sure this comes into play. I have also heard that a non-functioning gas tank relief opening (the one that burps up gas when your tank is full when you are filling up gas) can create a vaccum in your gas tank and effect performance. I ran the boat with the gas tank fill open (no top) and still had this same issue.
Ok rant over, I believe I have everything in here. Has this ever happened to somebody before??? Any help much appreciated.
This site has long provided me with information that has saved me thousands of dollars. I wasn't able to find any strings with this issue so wanted to a)hopefully get this resolved and b) provide the information so that when someone else has this issue (let's face it... volvo penta fuel issue.. it's gotta be out there).
Volvo Penta 5.7 GI PMDA. 1000 hours.
Story so far: No issues with performance from time boat leaves the dock until about 50 minutes into "running time". Right around 50 minutes (with the "run" consisting of 20 minutes of 3500 rpm cruise, then idle for 10 minutes, then 20 minute 3500 cruise, the engine begins to bog down in a surge like manner (only surging downward in RPM). The engine will bog down and eventually bring the boat down to 2000-2500 RPM range where it will maintain that without issue (but giving me no high end RPM performance). Now, if I throw the boat into idle and wait two minutes, I can get the boat back to WOT and great performance for 1-2 minutes before the bog down issue happens in the exact same way. I've taken the boat out multiple times thinking it was possibly bad fuel, issue happens at same time in same way. When the boat bogs down, if I open the engine hatch I can hear the high pressure pump whining considerably (with the whining going away after the 1-2 minute idle "break"). Once the whining goes away, I can throttle up and the engine will perform for the 1-2 minutes without whine, until it returns and the boat bogs down.
So, I started troubleshooting. I first checked "down stream" by pulling both fuel filters. I have one in line 10 micron fuel/water separator. I pulled this off (checking for any residue - it was clean). Then dumped the fuel in the filter into a mason jar. No separation, no gunk. Then I pulled the fine filter right before the low pressure pump, same deal, clean fuel, no gunk no residue on filter gasket (paint etc.). I then pulled all the fuel hoses off their fixtures and blew air through them, no kinks, no blockages. Seemingly all good there. Hmmm...
Next stop I pressure tested my fuel rails. (This is where I get mad at myself). My manual mentioned low pressure spec in the range of 5-8 psi in the fuel rail and VST reservoir (where the shrader valve is for access to test)pressure rail). I hook up the manifold to the shrader valve and test at idle at dock and under load. My reading at idle is 4-5 (I have a 50psi manifold and it was hard to tell exactly). I figure close enough. I then pressure test my high pressure side at the fuel rail access port (via shrader valve in line). My reading here is 15 psi. My manual calls for spec in the mid 30 to low 40 psi for the high pressure line. Immediately, I go aha! I've found it. I've got a high pressure pump whining, I'm seemingly starving for fuel as I'm bogging down, and I'm "out of spec" for my high side pressure. So, I go buy the high pressure pump and swap them out. I take it out for a spin, the issue appears at the exact same time. Well.. That sucks. So we pressure test at sea, right before my high pressure pump starts whining, the psi at the VST reservoir access point drops to ZERO. Thirty seconds after that, the engine bogs down in the same fashion mentioned above (high pressure starts whining and no high end performance).
So I do a little more reading, and I find out that high side spec for TBI is really 15psi (meaning I was in spec the whole time and never had to replace my high side pump - I'm not mad over it, as performance has actually increased a little (RPM "floor" when the pump starts to whine is now slightly higher) and well.. its the cost of doing business). Note to everyone: Consult multiple sources before you go swapping out parts In this case, my "foolproof" manual has a spec call out for a different "multi-port system" where evidently high side pressure is much higher.
Next I pull all the fuel rails and ensure no blockages. All good there (blew pressurized air through them). I also pulled the fuel rail fixtures into the VST (but not inside the VST), no gunk and fuel looked good. I also checked my injector "spray". It is conical and no drips. However, I have yet to check them when the boat bogs down at sea. It is safe to say the injectors are performing great for the first 50 minutes (WOT easily achieved with no hiccups).
However, I still have my problem and am a little hesitant to go swapping out that low pressure pump. I have read some literature that mentions there is a raw water jacket (used for cooling) around the bottom of the VST tank and that at times, the small housing for which the water comes in (via raw water pump circulation) can become blocked by salt deposits. After 50 minutes, perhaps the flow of raw water into the VST isn't sufficient enough to cool the fuel and hence turning the VST tank into pure vapor and causing the high pressure pump to "whine" as it is starving for fuel?
Or possibly, I am facing mechanical failure of the low pressure pump after 50 minutes of use? Therefore starving the VST of fuel supply and dropping PSI to zero which then causes the high pressure to starve for fuel and cause performance issue?
One other thing I haven't checked.... the anti-syphon valve on top of the gas tank pickup. But given the high end performance for the first 50 minutes, I'm not sure this comes into play. I have also heard that a non-functioning gas tank relief opening (the one that burps up gas when your tank is full when you are filling up gas) can create a vaccum in your gas tank and effect performance. I ran the boat with the gas tank fill open (no top) and still had this same issue.
Ok rant over, I believe I have everything in here. Has this ever happened to somebody before??? Any help much appreciated.
