Loss of Revs - Volvo KAD 42

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Mar 3, 2015
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I have a 30' Flybridge cruiser with a single KAD 42 that has 850 hours. I now have a sudden loss of revs on the engine. The engine runs great, starts easily and idles nice, with no black or white smoke, but when under load, I cant get more than 2500 rpm. Out of gear I can get 4000 rpm. I have had the boat out of the water and antifouled, outdrive removed and serviced, including checking the props. (DP 290). I have had all of the injectors removed, tested and serviced. I have had the injector pump removed and serviced, I have had the turbo removed and tested/serviced. I have had a new higher volume lift pump installed. I have had the aftercooler cleaned and serviced. All filters replaced and all hoses checked. I have had the fuel tanks checked for correct flow and have had pressure gauges on the fuel lines to check that correct fuel flow is ok. The Supercharger cuts in nicely at 1500 rpm and the boat takes off nicely but will on go to 2500rpm at WOT. The engine has very little electronics and the throttle is a cable and WOT checked ok. So far I have spent over $14,000.00 in repairs and maintenance and still have the same problem. I did however get a new starter motor and a new alternator just prior to the loss of revs happening. Does anyone have any ideas where I could go from here.
 

HorizonblueDK

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May 27, 2010
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I have a friend who had a 34' flybridge cruiser with twin KAD 42 inboards, who had exactly the same problem(on both engines), but he never found out what the problem was. He sold the boat with the problem. One thing that could be interesting to check, is the boost pressure. Find a mechanical pressure gauge and a long hose so you inspect what happens, when you hit the throttle.
 

alldodge

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I have a 30' Flybridge cruiser with a single KAD 42 that has 850 hours. I now have a sudden loss of revs on the engine. The engine runs great, starts easily and idles nice, with no black or white smoke, but when under load, I cant get more than 2500 rpm. Out of gear I can get 4000 rpm. I have had the boat out of the water and antifouled, outdrive removed and serviced, including checking the props. (DP 290). I have had all of the injectors removed, tested and serviced. I have had the injector pump removed and serviced, I have had the turbo removed and tested/serviced. I have had a new higher volume lift pump installed. I have had the aftercooler cleaned and serviced. All filters replaced and all hoses checked. I have had the fuel tanks checked for correct flow and have had pressure gauges on the fuel lines to check that correct fuel flow is ok. The Supercharger cuts in nicely at 1500 rpm and the boat takes off nicely but will on go to 2500rpm at WOT. The engine has very little electronics and the throttle is a cable and WOT checked ok. So far I have spent over $14,000.00 in repairs and maintenance and still have the same problem. I did however get a new starter motor and a new alternator just prior to the loss of revs happening. Does anyone have any ideas where I could go from here.

:welcome: to iboats

You have tried about everything to see what the issues is. Agree with Horizon that need to check the boost pressure, or the super charger (SC) is not disengaging. The SC works once the engine is warmed up from 1200 to 2400 rpm to help remove a flat spot and get heavy boats up on plane. After 2400 rpm the SC is disengaged and the turbo is the only boost source. The engines work very well but they are also complicated and should only be messed with by a trained Volvo Tech. The belt which runs the SC needs to be change every 200 hours and the oil is changed separately from the engine oil.
 
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Mar 3, 2015
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Thanks HorizonblueDK. I have had a boost pressure tested under load and the Volvo mechanic said it was down but only ever so slightly and shouldnt make much difference. Also AllDodge, I can disengage the SC manually once the boat is almost on the plane (12kts), i can then engage it again but there doesnt seem to be much difference. Also, the Volvo mechanic said the engine temp is high when i am at WOT, which is only 2500 rpm and he said it seems that the engine is working very hard. When i reduce the revs back to 2000 rpm the temp come back to normal. I would like it fixed as the compression is within specs and the engine seems to be in good condition. I just dont know where to go from here, (and neither does the Volvo mechanic) (scratches head)
 

alldodge

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Thanks HorizonblueDK. I have had a boost pressure tested under load and the Volvo mechanic said it was down but only ever so slightly and shouldnt make much difference. Also AllDodge, I can disengage the SC manually once the boat is almost on the plane (12kts), i can then engage it again but there doesnt seem to be much difference. Also, the Volvo mechanic said the engine temp is high when i am at WOT, which is only 2500 rpm and he said it seems that the engine is working very hard. When i reduce the revs back to 2000 rpm the temp come back to normal. I would like it fixed as the compression is within specs and the engine seems to be in good condition. I just dont know where to go from here, (and neither does the Volvo mechanic) (scratches head)

Just to talk out loud, a gas engine when you put more fuel in it then it can use, the gas has a cooling effect and heat is reduced and engine runs worst because of carbon build up. Put to much diesel in an engine then it can use the heat increases. I'm thinking the air intake side is OK, the air comes in as fast as the engine wants it. My thought is the exhaust, is there a restriction somewhere?

If the exhaust is clogged up, fresh air cannot be pulled in in sufficient amount to burn the fuel being pushed in. If boost pressure is down slightly this can also be caused by back pressure. What kind of muffler system is on the boat?
 
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Hi alldodge, re the exhaust, I'm not sure what type, there is a large pipe running from the turbo down to the transom and then through the leg of the motor. I have had the leg off and turbos off and I am sure the volvo mechanic looked at the exhaust for restrictions but I can't be sure. I will run it by him again.
 

alldodge

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I was thinking it may go through a muffler before it went through the leg, without a muffler were back to a puzzler.

As you say it doesn't make since. Tank, lines both supply and return have been cleaned, and filters replaced. Injectors and fuel pump tested and/or replaced. Throttle cable is being moved to WOT position. Intake and exhaust is open and coolers cleaned.

Diesel needs air and fuel, the more of both is feed the more power it will produce. Don't see it being the prop or timing because it use to do fine then all of a sudden it did not. You have done everything and nothing has helped. Only thing left is "maybe" a compression test. Don't really think it would be that because you wouldn't have a smooth running engine at idle.

I don't have any other ideas other then you need an expert. No offence to your mechanic but I would see what it would take to get a Volvo expert to take a look.
 

rbh

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Could there be any mechanical or electronic advance for the injector pump sticking or not working fully?
When they put the pump back in could it be a degree or two off, teeth not aligned or not timed right?

Yup, going with a timing issue
 
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Thanks alldodge, I have had a compression test done too, all 6 cylinders are within specs. RBH, I have had the injector pump of twice, bench tested and calibrated and the injector specialist who did the work and fitted the pump came onboard for a 2 hour sea trial and the fiddled and farted about and still couldn't find an issue with the pump. They just shrugged their shoulders and said lets go back, there is nothing more we can do, we don't know what is wrong. The Volvo mechanic was onboard too and couldn't offer any further assistance. This is doing my head in.
 

rbh

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^^^^
Ah crud!

You got to hate those days when even the tech is stumped. The reason I said timing was if you do not get a full advance the engine runs rough and bogs out?
If the injector pump is out a tooth it can still run but usually rough at the top end

When its drawing in fuel could a line be collapsed or collapsing? not enough fuel past a certain RPM? pick up in the tank is partially plugged? fuel cap is not allowing in enough air (making a vacuum in the tank) (fuel filter collapsed.

And not bird or beast built a nest in the intake? (thats always a good one)

 
Last edited:

Scott Danforth

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if your low on boost, the EGT's skyrocket, and you get tell-tale black smoke pouring out the exhaust while the motor falls on its face.

if your timing is off, she wont make revs or power. if the timing is too far advanced, it will run a bit hot.

if you have a fuel restriction, she wont make revs or power

if you have a fuel return restriction, she wont make revs or power
 

K-2

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Apr 3, 2011
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Can you reach and feel the exhaust boot? See if it is hooked up properly on both ends, & feels the correct shape ?
There was a guy a couple years ago and the boot came loose on one end and came off , the mechanic forgot to tighten that hose clamp.
The boot got squashed and bent over by the drive turning, pinched off. Long shot but it's a quick check.
 

alldodge

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How do you check / adjust timing ?

Don't know for this engine but most diesels use a two pin method. The engine is rotated until a pin (3/8 bolt) slides in through the bell housing and into the flywheel. The fuel injection pump has a side cover which is removed and the pump is rotated until a pin (3/8 drill bit) slides in. Now the engine and the pump are locked in position. The pump is then mounted on the engine.

The pump is not rotated like a distributer. So the timing is either dead on or 180 degrees out. You can check timing but it takes a special piece of equipment which goes inline with number 1 cylinder fuel line. The testing is usually done if an issues shows up. IMO I don't think this would be an issue because the pump was removed twice and there were no changes with each reinstall.
 
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Hi Reimatic, No I havent. I have another marine engineer looking at it. Do you have the same symptoms?
 

reimatic

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Apr 29, 2013
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Similar problem but mine is powerless already before sc kicks in
Works little better now after increased fuel ammount on injector pump 2 turns on adjustment

Done all the repairs you mention but still i think my injection pump not working correct i will get this removed once more later
 

mokicruz

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Jun 29, 2015
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Caterpillar Coal trucks ran fuel lines between the the cab and frame rails, as the cab mounts wore down it would smash the fuel line where top end fuel flow was limited enough trucks couldn't achieve full speed and ran fairly hot. Kinked fuel lines pre filter trash limiting fuel flow causes the same symptoms. Plugged exhaust as previously stated can cause similar problems but boost from turbos suffer.
 

Supercose

Cadet
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Jul 21, 2015
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I have same problem with Reefencounter.

I have 1995 Wellcraft Martinique 27 with single Volvo KAD 42.

Boat was cruising perfect but one day it suddenly crushed.

In neutral rpm goes up to max. 4000 but under load it stucks at 2300 rpm with 7 knots. (Max. speed was 35 knots)

There are no any smoke or unusual sound or else.

I changed compressor, turbo, injectors, fuel pump, indercooler, filters but nothing changed.

Hull is clean and propellars are new. Fuel tank is clean and fuel flow is good.

Does anyone have idea how i handle this problem ?
 

Supercose

Cadet
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Jul 21, 2015
Messages
7
Any news Reefencounter ? Did the problem solved ? Please update because I am having the same problem.
 
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