Diesel power surge

[Stour-boy]

I have Volvo penta AQD21A with a 280 leg , when I am running about 1800 rpm just occasionally the engine rpm increases and the bows lift revs go up to 2000 for a couple of seconds and the revs drop back to where they were originally, I have gone back through the deisel forums here but to no avail. The engine is not turbo charged and is the basic diesel lump no mods.
Am. I right in thinking that if it is filters or primary pump or air leak it would starve and slow up ?
Could there be an injection pump fault with the governor ?
There can't be much left so if anyone has had a similar problem would you reply please.
Thanks,
Stour-boy.

 

[alldodge]

Re: Diesel power surge

I have Volvo penta AQD21A with a 280 leg , when I am running about 1800 rpm just occasionally the engine rpm increases and the bows lift revs go up to 2000 for a couple of seconds and the revs drop back to where they were originally, I have gone back through the deisel forums here but to no avail. The engine is not turbo charged and is the basic diesel lump no mods.
Am. I right in thinking that if it is filters or primary pump or air leak it would starve and slow up ?
Could there be an injection pump fault with the governor ?
There can't be much left so if anyone has had a similar problem would you reply please.
Thanks,
Stour-boy.

Do you have any slop in the throttle linkage?

Is the a single helm setup or dual?

What kind of boat is this?

 

[Stour-boy]

Re: Diesel power surge

Hi Alldodge, in answer to your questions, there isn't any slop in the throttle linkage, It's a single helm and the boat is a seamaster 23. This has not suddenly happened but is getting more frequent, I thought it was clutch slip at first but then the bows wouldn't go up would they.
Stour-boy

PS.the hull is semi planing.

 

[Stour-boy]

Re: Diesel power surge

Hi Alldodge, in answer to your questions, there isn't any slop in the throttle linkage, It's a single helm and the boat is a seamaster 23. This has not suddenly happened but is getting more frequent, I thought it was clutch slip at first but then the bows wouldn't go up would they.
Stour-boy

 

[alldodge]

Re: Diesel power surge

Since the engine revs up and speed does increase I don't see anything slipping. Without anything attached to the engine which would cause the issue such as a waste gate, I'm leaning toward the governor. If the engine was slightly starving for fuel it could cause part of what your seeing but it would not do it for long before something else would show up, such as total power loss. Before I would have the injection pump checked out make sure your fuel pump is working up to pressure and your filters are clean (I'm sure they are, just mentioning it)

 

[HT32BSX115]

Re: Diesel power surge

Since the engine revs up and speed does increase I don't see anything slipping. Without anything attached to the engine which would cause the issue such as a waste gate, I'm leaning toward the governor. If the engine was slightly starving for fuel it could cause part of what your seeing but it would not do it for long before something else would show up, such as total power loss. Before I would have the injection pump checked out make sure your fuel pump is working up to pressure and your filters are clean (I'm sure they are, just mentioning it)

Are you using a bit more oil than usual? If the throttle is NOT moving and it's NOT governor related, have a look at your oil/air separator, breather tube etc if installed............... If there's liquid oil being sucked into the intake, it will cause a run-a-way if you're in neutral with possibly catastrophic results!

 

[Stour-boy]

Re: Diesel power surge

Thanks Alldodge, I reckon the lift pump is the easiest to check before changing filters,then change filters and recheck lift pump to see if there is any difference,reading through the forums on lift pump pressures I reckon 12 to 14 psi would be about right.
Thanks for your input.
Stour-boy.

 

[Stour-boy]

Re: Diesel power surge

Hi HT 32, I haven't thought of that although about 45years ago I was involved with a dumper engine that was running away on its sump oil that was quite hairy fortunately lifting the stop lever and disconnecting the injector (single cylinder petter engine) it still ran,that is when the penny dropped so cautiously I gradually used the decompression lever and was able to stop it without any damage. I shudder to think what damage a multi cylinder engine could do especially as most don't have decompression levers.
I will check the breathing system but the engine is using very little oil.
Thanks for the info and bringing back memories of a petter engine screaming its nuts off.
Stour-boy.

 

[HT32BSX115]

Re: Diesel power surge

Hi HT 32, I haven't thought of that although about 45years ago I was involved with a dumper engine that was running away on its sump oil that was quite hairy fortunately lifting the stop lever and disconnecting the injector (single cylinder petter engine) it still ran,that is when the penny dropped so cautiously I gradually used the decompression lever and was able to stop it without any damage. I shudder to think what damage a multi cylinder engine could do especially as most don't have decompression levers.
I will check the breathing system but the engine is using very little oil.
Thanks for the info and bringing back memories of a petter engine screaming its nuts off.
Stour-boy.

Yeah. It was a problem with VW (NA) diesels years ago.

Seems the cast aluminum intake/air filter "box" was plumbed from the valve cover (oil "separator") to the air cleaner box.

Problem was, the separator wasn't separating! The bottom of the air cleaner 'box' would slowly fill with oil until there was a couple of inches in the bottom of the box.

Then if you turned too abruptly (left or right .....can't remember) the oil would sort of 'slosh' into the intake causing an uncontrollable acceleration!

It didn't last long since there wasn't all that much oil in the air cleaner box but it could be a little scary!

VW ended up doing a safety recall to "fix" the problem. Some diesels have been known to "blow' a seal in the turbocharger (or blower in a 'jimmy") and consume the oil going to the turbo or blower!

They would run at a crazy high RPM if unloaded until they ran out of oil. It's not pretty!


Regards,


Rick

 

[rbh]

What kind of conditions are you running in?
If your drive is trimmed way out you may just be blowing the back out of the wave if your running in med/high chop.

(Yup the screaming jimmy, also fun to watch them run backwards- 2 forward gears 18 reverse).