Yanmar Diesel acceleration problem.

[chorscroft]

I've been having this problem for ages now and thought I'd describe it here and see if anyone can help.

The boat is a Redbay Stormforce 8.4m wrap-around and the engine a Yanmar 6lp-stze 300hp with a Bravo 3 Leg.

The problem I'm having with it is the acceleration is painfully slow and the engine seems to get bogged down within the mid rev range.

What seems to happen is when you first push the throttle forward there's a rapid increase in speed up till about 1500 Revs. At this point the Revs increase very slowly as the boat comes onto the plane and up until about 2500 Revs and then again it accelerates rapidly from 2500 Revs up till about 3700 at WOT.

I'm fairly sure the problem isn't the boats weighting, and I assume the prop's are fine as it is within the recommended rev range at WOT.

I'm thinking the problem is something to do with the engine itself.
Does anyone have any ideas/suggestions etc of what to try or what to check?

Cheers

Conor

[The Beard]

On two occasions I've come across a similar problem, although not on a boat; sorry. One time it was the fuel pump that needed re-timing and the second was the turbo (ouch). I'm afraid that probably wasn't a lot of use but as most marine diesels either are versions of HGV engines or are based on them, they may be places to start.

Nearly forgot. The diesel pump fault was exacerbated by injectors that needed a damn good clean.

[codprawn]

Is it the same when you adjust the trim? It is a bit strange because you would expect it to bog down at lower revs. I know Goldfish RIBs inject air/exhaust into the prop to cause it to slip to keep the turbo on boost.

Could even be too much prop grip?

[chorscroft]

Originally Posted by The Beard

On two occasions I've come across a similar problem, although not on a boat; sorry. One time it was the fuel pump that needed re-timing and the second was the turbo (ouch). I'm afraid that probably wasn't a lot of use but as most marine diesels either are versions of HGV engines or are based on them, they may be places to start.

Nearly forgot. The diesel pump fault was exacerbated by injectors that needed a damn good clean.

I was also thinking it could be fuel related issues. Is there any way to isolate an issue in the fuel system or is it a matter of paying a mechanic to take a look?

[chorscroft]

Originally Posted by codprawn

Is it the same when you adjust the trim? It is a bit strange because you would expect it to bog down at lower revs. I know Goldfish RIBs inject air/exhaust into the prop to cause it to slip to keep the turbo on boost.

Could even be too much prop grip?

Almost exactly the same when trim is adjusted. Slight difference when the leg is trimmed right in but still painfully slow.

Too much prop grip? I've never heard of this before.

It's running 2 x 4 blade 26 pitch bravo 3 props, counter-rotating. I'd imagine that would be pretty grippy.

Again, anyway to isolate this as the problem?

[Paul Beaurain]

Hi there
Worth a discussion with Redbay as you are clearly on their doorstep.
I wonder if the initial set-up was too cose to ideal- in that a 5 % deteriation on any one aspect, drag, turbo loss of boost, engine efficency etc could all cause the symptoms.
I would think 24" props were more normal. Again ask Redbay.
Was the boat like this when you got it?

Paul

[m chappelow]

think i would have a look at air /fuel filters first ,,,even if its not smoking ect,,,also what type of diesel fuel are you using ,white ,red ,heating oil ,

[doggypaddle]

wastegate on turbo sticking open possibly?

[codprawn]

Originally Posted by chorscroft

Almost exactly the same when trim is adjusted. Slight difference when the leg is trimmed right in but still painfully slow.

Too much prop grip? I've never heard of this before.

It's running 2 x 4 blade 26 pitch bravo 3 props, counter-rotating. I'd imagine that would be pretty grippy.

Again, anyway to isolate this as the problem?

I may be barking up the wrong tree but basically too much grip causes the engine to bog down off boost - much the same as a quick 4wd turbo car - to get it off the line quickly you have to slip the clutch to keep the engine spinning at high enough revs for the turbo.

As I said Goldfish RIBs have done this mod to their diesels to make the prop slip at slow speeds to get the turbo to kick in earlier.

As your problem is after 1500 rpm it prob is not the problem but you never know - changing props could help if so.

[IBWET]

Originally Posted by chorscroft

Almost exactly the same when trim is adjusted. Slight difference when the leg is trimmed right in but still painfully slow.

Too much prop grip? I've never heard of this before.

It's running 2 x 4 blade 26 pitch bravo 3 props, counter-rotating. I'd imagine that would be pretty grippy.

Again, anyway to isolate this as the problem?

Some props have holes (PSV) it allows exhust gas to exit into the water flow at slow speed,as an idea it came from peaky race engines in the states.

I'd be looking at filters first,although your engine picking up towards the top end sort of discounts that,my thoughts lead me to your turbo.....sorry mate.

[chorscroft]

I've just realized I forgot to mention something.

Last season we would occasionally have an error light coming up on the dash, which said "boost", which I now after a little googling I think meant that the boost pressure was too high.

We asked Redbay about this, but as they mainly deal in yamaha's there couldn't really help us except to say it should be OK to run it, which we did and the light stopped appearing. Whether this was due to the problem fixing itself or the bulb in the error light going I'm not sure.

Does this perhaps point towards the turbo, possibly the wastegate if it's talking about pressures?

[chewy]

Boost, could be high or low boost pressure and does relate to your turbo. The higher the boost the faster you go... until you bend the rods!

[Leapy]

Originally Posted by chorscroft

I've been having this problem for ages now and thought I'd describe it here and see if anyone can help.

The boat is a Redbay Stormforce 8.4m wrap-around and the engine a Yanmar 6lp-stze 300hp with a Bravo 3 Leg.

The problem I'm having with it is the acceleration is painfully slow and the engine seems to get bogged down within the mid rev range.

What seems to happen is when you first push the throttle forward there's a rapid increase in speed up till about 1500 Revs. At this point the Revs increase very slowly as the boat comes onto the plane and up until about 2500 Revs and then again it accelerates rapidly from 2500 Revs up till about 3700 at WOT.

I'm fairly sure the problem isn't the boats weighting, and I assume the prop's are fine as it is within the recommended rev range at WOT.

I'm thinking the problem is something to do with the engine itself.
Does anyone have any ideas/suggestions etc of what to try or what to check?

Cheers

Conor

When you say the problem has been "for ages" it suggests that it wasn't like that earlier so my comments are based on it was right once, but now it's gone pear shaped.

If that's the case, it's difficult to think it's anything to do with the prop unless you've replaced it and the problem is coincidental with that.

If the engine produces the same-old maximum power it's difficult to think it's an engine mechanical problem.

If, after getting out of the hole, you've got the same max speed - and therefore maximum power - then the turbo is clearly working at least in part.

If you can achieve maximum power and maximum speed that suggests you're achieving maximum fuel flow so why would it be 'restricted' at mid-range? Blockages and restrictions generally restrict flow at all flow rates, not just at mid-range flows.

This brings me back to the turbo or its control mechanism...do you know at what rpm the turbo did or should start to deliver? Typically, this should be around 1200rpm(ish). If the onset of boost is delayed, for whatever reason, then this might explain the smart get-away (by sheer engine cubic inches), lethargy in the mid-range where boost is not forthcoming, followed by restored performance when the turbo belatedly kicks in.

I wonder if there a control system fault in the turbo mechanism? Is it electronic or mechanical control? If the latter, try and figure out what the mechanism is and does all appear connected and correct? If it's electronic control I fear it's a dealer visit.

[doggypaddle]

does sound like a sticky wastegate. remove the linkage from the actuator and see if the flap is free. if not plus gas and wiggle it until all the corrosion and carbon is washed out of the spindle bush and its free again.
I occasionally get the same problem on the landrover, exactly the same symptoms, no loss of ultimate power but all the lovely 1200 rpm grunt vanishes!
I think the overboost light may be a clue its been sticking shut, mine used to do this and when it eventually overboosted enough to open it would stay open!

[chorscroft]

When I say ages, what I really mean is as long as I can remember. It used to be my dad that would always have driven and sorted out maintenance (evidently not very well ).*

I also think that the engine isn't producing maximum power as I can remember a few years back the boat would easily do 40+ knots at WOT, whereas now it only manages 37-38 knots ish.*

How do I find out whether or not the turbo is mechanically or electronically controlled. Do yanmar keep archives of this info along with data about when the turbo should kick in? (*6lp-stze )

Also were abouts on the engine would I find the linkage and actuator to clean?

Cheers

Conor

[Cruiser]

We had a similar problem with a 12 Litre Volvo D12 turbo. Acceleration always slowed through a fixed rev range and was good below and above as you describe. After all sorts of tests on fuel filters, air filters, turbo etc turned out to be a faulty sensor on the turbo which was pulling back the fuel flow through that rev range. New sensor and shes been like new ever since

[doggypaddle]

Not wishing to be funny, but if you really dont know what or where the wastegate is, and the way it works I would get a good marine diesel engineer to have a look at it. starting with an oil and filters change, then checking fuel compensator and wastegate linkages, and fitting a boost gauge and checking boost pressure vs engine rpm.
Is a chicken and egg situation with this, if your fuelling is not correct then you wont generate the boost, and conversley if you aint got boost then it won't fuel up correctly.
I wouldnt fiddle with pump settings or anything else until everything else is ruled out. thats one advantage and disadvantage with a turbo diesel, one turn of the wrong screw on the pump and you may gain masses of extra power, over do it or get it wrong and you will have a sump full of pistons.
in short if you dont know about turbo diesels leave it to someone who does.....it may be much cheaper in the long run

[Leapy]

Originally Posted by doggypaddle

...in short if you dont know about turbo diesels leave it to someone who does...

[nik]

If there is lots of black smoke it could be a sign of blocked air filters.
I am pretty sure yanmars use mechanical fuel injection.

[doggypaddle]

which is why i said he should get it serviced, though to be honest its unlikely, theres not usually much dust in that enviroment.
could be a blocked exhaust though. I think it was Gmacs pac22 that was down on power, and suddenly regained it when the exhaust flexi exploded in a shower of water steam and soot