2004 Volvo Penta 8.1 GII-E Losing Power - Backfire and Howl at Flame Shield

GaReLAXing

Recruit
Joined
May 6, 2014
Messages
1
I have a 2004 Chaparral Sig 350. The engines are Volvo Pentas 8.1 GII - E. The port engine, which had a compression test on April 4 and a new impellar installed, was my "good" engine (starboard engine has low compression on cylinder 4 affecting RPM somewhat - scheduled headjob for this winter). On Saturday as I was coming back to the slip the RPM gauge started to swing wildly, but no "heard or felt" issues with the engines. Both gauges had been doing this since the boat test, just not so wildly and I was told I should get the RPM gauge serviced. Then on Sunday, as we came out of the hole, the boat had no power, and when I backed the throttles down I could hear the port engine start to backfire. Then it quit. On a restart it backfired but started, however, whenever throttle was giving it would choke out. Limped back into dock on one-engine, and when ran at the dock, the engine throttle body area (sound out of flame shield - where butterfly valve is located) would start to howl and it shut down.

Read on one site that the tach wire can cause this. Another site (here and others) also read it was probably starving for fuel - but symptoms didn't quiet point that way. Regardless, I went up last night and took the flame shield off and started the engine and it started fine. There is a sensor of some sort on the underside of the flame shield but can't find information on that or what it does (guess that's my first question - does anyone know what that is, reason, and where it is fed to or from?)

Turned the engine on and listened to the fuel pumps prime (low to high) which kind of validated it's not the fuel pumps. Engined fired up and idled great - about 1K on rpm (second question - what is the right idle RPM?) Cleaned the flame shield off, replaced, and the engine continued to run great. Gave a lot of throttle - up to 3 and 4K RPM with no problems. So took it for a cruise. Boat ran awesome. Half way in to the cruise the tach started spiking again - but the engine ran fine so we cruised for about 20 minutes. We shut her down..watched the sun go down...and about 30 minutes later started back up. When we hit the throttles to come out of the hole...same issue as Sunday. Shut the engine down and limped back in. Restarted at dock, no problem, so backed in and shut her down.

So questions:

3. What could cause this?

4. I'm going to disconnect tach wire at gauge and see what happens - they are rusted - so I'll clean them - but why would this cause the issue?

5. Could it be the sensor on the back of the flame shield?

6. Any other thoughts?


I'm also going to drop the fuel filter and check it out, but it seems as if the butterfly isn't opening, and thus starving the engine. My thought is that is why I get the high pitched tone.

Any help from the experts out there would be appreciated.

Gary
 
Top