volvo 2002 losing power

[paulwitney]

I have a 1984 vintage volvo penta 2002 that starts well but often when put into gear drops revs to almost stopping. Eventually after 10-30 seconds picks up again. Then ocassionally slows again but not to same extent. Have replaced both fuel filters but noticed some diesel sludge on inlet of main fuel filter and cleaned it out. Any suggestions??? Also have noticed the alternator charge jumps to around 16V for short periods. Engine slows but not to same degree.

 

[michael_w]

Check out the pipework between the tank and the primary fuel filter. I've often found crap here. Usually enough for the engine to idle, but conk out when accelerated.

Have you looked at the strainer on the lift pump too?

 

[andy_wilson]

The clue..

..is with the alternator.

With a standard (50 Amp?) alternator you should reach maximum charging of about 14 volts at 1400 or 1500 rpm (can't remember exactly).

Your symptoms are typical of plenty of small yacht auxilliaries, and I have the same issue with my VP 2002. At 1500 rpm the engine is probably only producing 4 or 5 hp. With the usual losses, and a bit of rounding up, at full charge rate (low batteries) the alternator will absorb around 1hp (12v X 50A = 600W = 0.8 Hp plus friction and heat). This will not be a problem if you are using the 'start in neutral' control. The engine will reach 1500 rpm where the batteries get fastest charge rate.

The problem arises when the propellor is also absorbing power from the engine. If you were able to plot a graph of the engine output power at various rpm, the power aabsorbed by the alternator (steadily rising from almost zero at tickover to around 1hp at 1500rpm) and ADD to that curve the power absorbed by the propellor, you will find that the engine HP curve starts with power to spare. Even in gear it can just stay ahead - just. As it warms up it produces more engine power, and as a small amount of energy it put into the batteries, the alternator load reduces, but this is self defeating, because as revs. then try to rise, the alternator Voltage and hence current and load rises towards a maximum at 1500rpm.

The result, where the power output and combined loads meet, is the maximum revs. you are going to get until the batteries take some charge to relieve the alternator load.

If the charge voltage is jumping to 16 volts, not only is there a problem with the regulator that may damage the batteries, but the extra power soaked up by the alternator will further prevent the engine revving. Do you have an advanced charge regulator? These have a bulk charge mode but this should be around 14.5 V, and certainly under 15 V, even for short periods. This is clearly a fault - provided your meter is accurate.

Your main issue however is due to alternator load. Some smart chargers have a 'ramp up' feature to alleviate the problem. Some - wise owners - have them installed with an override switch.

Imagine a convivial night at anchor, chilly evening so the diesel heater has been on, interior lights, anchor light and CD player. Then the wind gets up and changes direction to make it a lee shore. You decide to clear out in a hurry, only to find that the engine just will not rev. to drive the yacht into the wind.

As I mentioned, I have the same problem, as do many others.

 

[BAtoo]

Not sure about the alternator - electrikery bit too complex for me - however for a diesel to run properley - once started - it just needs air thro the air-intake and CLEAN fuel without air or cr*p i it- they are not rocket sciene bits of kit. So as you are finding sludge somewhere in the line I would look carefully for the source; another filter somewhere you dont know about ( they do exist); sludge in the tank to engine line; poor seal after your spring srevice letting air in etc. - recheck all the joints you have touched; water separator; blow thro the feed line etc etc.
Just been thro the same rigermarol to correct a siimlar problem.
If you are sure it's not the fuel then it might be the alternator.

 

[paulwitney]

Thanks for advice, will check each item.

 

[KRG]

My 2002 behaves in the same way as andy_wilson has described, I have a sterling regulator and if the batteries need a lot of charge then i can't move until the load has reduced on the alternator, the revs just wont increase once propellor is engaged (fixed 3 blade 13x9).

You could test it by reducing the load on the alternator.

 

[DJE]

I Agree. Several Volvos in Sadlers and Starlights have had fuel problems which were eventually traced to a gauze filter on the bottom of the dip pipe inside the fuel tank. (Usually a plastic Vetus tank.)

 

[paulwitney]

My tank is a 60 litre stainless tank and I suspect there may be a layer of sludge in the bottom. Apart from other checks next step will probably be to drain and clean out the tank and lines to the primary fuel filter...... hope so anyway!!!!