Volvo Penta 5.0 trouble going above 2000 RPM

[smcroy]

Hi, first timer here. I have twin VP 5.0L, 2003, GXI-C (fuel injected gas). Owned it since 2006, mostly self-maintenance. After commissioning it this spring, taking it to my home marina, both engines ran great at 1200-1500RPM for several hours. Trying to open it up, one engine gets to around 2000RPM, then starts coughing and won't go above 2000. Continued on at 1500 for another 2 hours, flawless.

In the marina, unloaded, when I repeat the test, I throttle up to around where 3000RPM would be, and the engine starts oscillating between 1200 and 3000RPM, around 2 sec at low speed, then it throttles up to 3000 for 2 seconds, coughs, wheezes, then drops back down to 1200, over and over.

I changed the spin-on fuel filter, and saw no water. Connected a fuel pressure gauge to the high pressure line, and saw 45-55lbs all throughout the oscillation, no big changes, so it feels like fuel is ok.

I'm looking for suggestions on what to try next. I just borrowed a friend's OBD2 scanner to try out this week, though I've never used one before; hopefully it will point to a bad sensor (engine temp?) or give me something to investigate. I read on this forum to be sure the oil is not over-full, which I'll check also. Beyond that, any ideas? In what order would you attack this? Thanks for any help.

 

[dsiekman]

Re: Volvo Penta 5.0 trouble going above 2000 RPM

I'm not a mechanic by any means, but following logic you are looking for something affecting both engines. I would think the likeliness of the same sensor going bad on both engines is pretty slim. The only two systems I can think of that could effect both engines in that way would be raw water intake (temperature related safety mode), or main fuel supply. Assuming temperature is not your issue, I think I would try to isolate one engine at a time, either with a clean remote tank of new fuel or by only running one engine up to WOT to determine if you have a fuel starvation issue.

 

[smcroy]

Re: Volvo Penta 5.0 trouble going above 2000 RPM

The problem is in just one engine, not both.

Update - I checked the oil level, and in fact both engines had about a quart too much. However, this did not affect the problem. Reseated a bunch of cables, but no luck. The OBD2 scanner I borrowed did not fit my engine, which uses a MEFI-4 ECU with a different (marine, not automotive) connector. So I've ordered the Diacom software and cable from Rinda Technologies; at $600 it's a big investment but will probably get reused in the future.