2006 volvo penta gxi-f 5.0 sluggish, losing rpm when cruising

New member here, I spent the last few days searching the forums looking through other peoples issues with the 5.0gxi-f and seems as tho I am not alone. Also due to the weather i am stuck doing research instead of starting diagnosis of the issue(s) i am having. This is why i decided writing this thread might give me a good game plan as soon as its warm enough to flush out the antifreeze and get the boat ready for another tough season.

The issue:
Last season the boat had a very difficult time getting out of the water, sometimes even not getting up on a plane at all and i noticed the following.
Starboard engine has a very noticeable whining noise at all speeds almost sounding like a power steering pump whine/groan- maybe related, maybe not.
when the boat finally gets out of the water i usually cruise with both engines from 3000-3200 rpms depending on the wind/tide which usually gets me going abbout 19-22knots. almost all of last summer i noticed, when cruising, the starboard engine will lose RPMS and drop to about 2800 and you can really feel it and see it on the S.O.G/. Usually throttleing up will bring the speed back up and eventually the engine will hold its speed at the desired 3000-3200. Wide open throttle everythingt seems ok boat has no problem reaching 30knots. when slowing down to enter the harbor/channel usually the starbord engine will surge approx 200-400 rpms when around 1000rpms accompanied by a very loud "sucking" noise from that engine (its like it sucking lots of air thru the throttle plate or massive intake leak). Every once and a while the engine will stall when docking or slow speed maneuvers, in the beginning of the season it would usually restart no problem but as the season went on sometimes the engine will crank but not restart- once it cools off it will start back up but need to neutral throttle it. cold start engine fires right up but will have the loud "sucking" noise as i said before. When i winterized it this past fall i had a difficult time getting engine started (cold) and when it did finally start it ran very rough for about 5 minutes until missfires cleared out and then ran fine until i fogged it and put her to sleep.

These engines have always been maintained by the marina mechanics up until now. Besides regular maintanence the following repairs have been done leading up to this condition.
Coils/ignition modules replaced multiple times due to water leaking thru hatch onto coils.- water leak has been rectified
complete engine wiring harness- once again from the leaking hatch
electronic fuel pump assembly (2-3 seasons ago)
fuel injectors removed and cleaned professionally
new exhaust manifolds, risers, bellows ect for both engines this time last year.


port engine does not show any of these symptoms and seems to be running perfectly (for now)
also has alot of new parts similar to the starboard but the engine harness was not needed.
please note each engine has separate fuel tanks (aluminum) but i have ran the stbd engine on both tanks with no change

My plan, after reading some threads on this forum is to start off with new plugs, wires, cap/rotor- these are definitely due. Hopefully that is all thats going on but i feel there is other issues present- im thinking fuel system. My next steps will include
Fuel supply to the pump assembly
fuel pressures at pump and rail
check for vacuum leaks
compression test (only if necessary- tight squeeze between the 2 engines)

If any of you members have any experience dealing with any of the said symptoms and have any helpful tips/known problems with this setup i would greatly appreciate it.

In regards to checking DTC's from the engine control unit is there any scanner available that i could buy to check the DTC's and read live data? and information on this would be very helpful.

Thanks for adding me to your community and thank you for taking some time to read my thread and hopefully aid in getting this boat ready for another tough summmer.

First step in troubleshooting is a compression test, followed by an open air gap spark test which i would run before spending big $$. a tune up before spark test couldn't hurt.

2X on the compression test and then a leak down when you find a low cyl.

5.0 ltr engines are not very good. Sorry. The Flat Dist Cap you have on your engine will cause engine failure. I change those caps every season, Cheaper than a tuliped valve.

Iridium plugs must also be used.

If you do not find any weak cylinders, do a complete tune up with wires, cap, rotor and plugs then move on to checking the fuel pressures. The fuel Mod on your engine is subject to failure.

I had similar problem with my 5.o GXI. The noise you describe sounds like the high pressure fuel pump that is starving. Start by looking at the pump connector because it is right in front of the engine and it easy to damage by accident when working around the engine.

The fuel pumps go bad very often. the carter pumps were painted black on the inside and outside... the unlead gas with ethanol eats up the paint on the inside and plug up the system. had to replace my pump. sounds like the powere steering also the pump becomes hot to the touch.

bmzags said:

...................... and when it did finally start it ran very rough for about 5 minutes until missfires cleared out and then ran fine until i fogged it and put her to sleep.

Click to expand...

According to the Volvo Penta info, the 5.0 GXI-F is fitted with MPI.

For the MPI system, we do not "Fog" in the conventional fashion.
Instead, we introduce an oil-enriched fuel mixture into the fuel delivery system. This can be added to the main fuel filter cartridge, followed by operating the engine for XX minutes.
(some people call this "fogging", but technically speaking it is NOT!)

If the conventional fogging solution was to accidentally enter an MPI system air sensor passage, it may cause problems.


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I have a similar sluggish engine and I have a couple clarifications to your post:

(1) Are you saying that you should not do a typical "fogging" of the system by spraying fogging oil into the intake manifold during the winterization process? I currently do this now on my 5.0 GXI-G engine.

(2) I tested my fuel pressure a week ago and it showed 50-52 psi (using the connector with the schrader valve). Is this a good pressure? I looked through the specs and can't seem to find the correct psi that I should expect.

(3) also, while I'm asking, and it is related to the original post - what is the correct compression PSI for the 5.0 GXI? I did a compression test and my results were between 105psi and 115psi. I think this is low and could be why I am getting poor power from the engine, but I would really value your advice. Also, if it is on the weak side, would it be worth it to try one of the engine conditioner additives before tearing the engine apart for a rebuild?

Thanks,
Don C.

Try running a decarb."engine tuner" through her