VP 5.0GXi-B issue - low RPM/problem with a plane

[fourwin_ns]

Hi All,

I need your support with my issue with my 5.0GXi-B with SX. When I bought a boat it was equipped with 5.0Gi 250HP on which I had 53km/h speed (according Garmin). Then I decided to change engine and I bought 5.0GXi-B 270HP and started to having problems. Situation is like that:

1. Engine works really fine, regular 600RPM on idle, with no loading RPM's can easily increase when push the throttle up.
2. Problem starts when I want to get the plane with more than me on board. It seems engine is not able to get higher RPMs than 4000. It looks like no torque or sth.
3. I can add that 8th cylinder have some issue, as the spark plug is flooded (with oil or fuel) and also dark with a carbon (electrode).
4. Compression test: 12-12.5bar except 10.5bar on 3rd cylinder, but I suppose it's still in line with Volvo specs.

I replaced fuel pump, ECT temp sensor, camshaft sensor, distributor cap, rotor, ignition wires, map sensor, fuel pressure regulator. Also exhaust manifolds and raisers. Everything above is new, no chinnese stuff but Recmar/Sierra.

Is anybody can advise what is the issue that engine doesn't have enough power? Can it be caused by tthis one wet cylinder? Any advice for further diagnostics?

Thanks in advance for the support!

PS. Radio SX 1:60, was the same sterndrive on previous engine. Prop 3 blades 15 1/4 x 15

 

[alldodge]

Welcome

Tell us more about the engine swap?

Was the Gxi a new crate motor (as complete drop in with new ECM) or one out of another boat?

12 to 12.5 bar (174 to 181 psi) is way to high for that motor. Either the gauge is bad or there is liquid in the cylinders. The one cylinder at 10.5 bar (152 psi) is where a new motor would be.

Compression between cylinders should be no more then 10% which would be 10.5 bar + 10% = 11.55 bar (152 psi + 10% = 167.2 psi)

 

[fourwin_ns]

Welcome

Tell us more about the engine swap?

Was the Gxi a new crate motor (as complete drop in with new ECM) or one out of another boat?

12 to 12.5 bar (174 to 181 psi) is way to high for that motor. Either the gauge is bad or there is liquid in the cylinders. The one cylinder at 10.5 bar (152 psi) is where a new motor would be.

Compression between cylinders should be no more then 10% which would be 10.5 bar + 10% = 11.55 bar (152 psi + 10% = 167.2 psi)

Hi alldodge,

I replaced whole engine, with ECM. Gauge meter is new, just bought it for measurements. Maybe I cranked to long (9-10 times) during measure? But such measurements I had also during dry test in the mechanics garage when purchasing.

Volvo Penta sais the lowest compression shouldn't be less than 75% of the highest. So even if we take 75% of 12.5bar it's still 9.4 not 10.5...

Btw...amount of oil I provided was ca. 5 liters as per the Volvo specs, however when I check oil level on gauge (long metal stick) it's much more above the regular. Also when engine is cold...How it's possible??

 

[Lou C]

Those dipstick tubes can make it hard to get an accurate measure of the amount of oil in the engine. Due to the engine heating up & cooling the level in the tube will rise & fall. Pull out the dipstick and let the level in the tube stabilize for about 5 min & recheck. They often do read higher with a cold engine.

 

[alldodge]

So this is a used motor?

Cranking it more times would not increase the amount of pressure
Your motor uses a flat style cap. Check timing of the distributor.

Check the fuel pressure at the rail, should be 50-60 psi (3.4-4.0 bar)

 

[fourwin_ns]

Those dipstick tubes can make it hard to get an accurate measure of the amount of oil in the engine. Due to the engine heating up & cooling the level in the tube will rise & fall. Pull out the dipstick and let the level in the tube stabilize for about 5 min & recheck. They often do read higher with a cold engine.

Checked yestarday on cold engine, when came after one week. Oil level was much higher than allowed range...weird

 

[fourwin_ns]

So this is a used motor?

Cranking it more times would not increase the amount of pressure
Your motor uses a flat style cap. Check timing of the distributor.

Check the fuel pressure at the rail, should be 50-60 psi (3.4-4.0 bar)

Thanks for advice! I know how to check rotor position, but not sure how to refer it to particular cylinder...what thas it mean "enggine is at number 1 cylinder TDC"? Is it connected with cam retard degree? This is I would like to check but not have at this moment diagnostic tool

 

[alldodge]

When looking at the front of the motor, number 1 cylinder is the right front spark plug. To get motor at number 1 Top Dead Center (TDC) the crank shaft would be rotated until both valves are closed and the piston is at top of stroke.

To find stop of stroke the valve cover would be removed to watch the valves, then use a piston stop bolt or something else to find TDC.

Doing all the above can take some time. You could try to move the distributor about 1 degree from current position and try a run. The distributor would need to be scribe marked for current position, then moved. The mark will reference current location so if moving distributor made things worst

 

[ESGWheel]

Here is a video (link) in how to use a Piston Stop Tool and find TDC. As AllDodge says its involved and as the video highlights you can damage the piston if you use the starter motor (or do not have a good feel while turning over the motor by hand). You need to have ALL the spark plugs removed to do this.

Also, I am concerned about your ‘overfilled’ oil on your dipstick. In post 1, comment (3) you say: “I can add that 8th cylinder have some issue, as the spark plug is flooded (with oil or fuel) and also dark with a carbon (electrode).”

I think its possible you have fuel from cylinder 8 leaking into the crankcase. So, your overfilled oil may really be oil + fuel. Pull out your dipstick a few times and wipe the oil onto a clean rag. Idea is to get a couple of millimeters of oil onto the rag. Then smell the rag. Does it smell strong of gas? If yes, that is not good and suggest focusing on this as it may require an engine rebuild.