Tamd 74/75 engine revs change whilst running

[Robert adam]

Hi
has anyone had a problem with unstable RPM on volvo penta tamd 75 engines ? The problem is the engines operate fine then after perhaps 5 minutes of running one ( usually the port but not always ) revs increase or decrease by a hundred rpm or so. Seems completely random in time and amount of increase or decrease some times changing by as much as 500 rpm. Volvo could not give answer and 2 separate op o dealers failed to fix and gave up.
I’ve tried removing condensate water from ecu As suggested in another post on this forum but that did not help.
Anyone got any ideas?
thanks Robert a

 

[gery w]

Sounds like the potentiometers in the throttle levers playing up, is it single or dual station?

 

[gordmac]

Something wrong in the governor? It holds the set rpm by varying the fuel with changing load, it seems to have stopped doing that properly.

 

[petem]

Could be one or a combination of the following:

1) RPM / Speed sensor issue
2) Potentiometer issue
3) Loose / corroded connection somewhere in the system (check all connections to the ECU)
4) Something wrong with the injection pump
5) A battery / charger / alternator issue
6) Some kind of fuel supply issue

You've just got to swop components between the engines until you find the culprit.

 

[Robert adam]

Thanks all who replied I greatly appreciate your time.
I did consider potentiometer fault but Volvo did not think it likely and the 2 dealers who tried to fix problem did not say it was fuel. I could well be wrong but I’d have thought they could have tested them? Also I tried switching off engine sync and both engines had fault so to me that would mean both throttles have same fault. Maybe they have?
fuel governor problem sounds also sounds possible would that affect both engines? I really don’t know how they work is it part of injector pump? Yep speed sensors a def pos — forgive my lack of knowledge but any idea where they would be and how to test them. I will check connectors to ECU . Don’t think injection pump as both engines and intermittent problem i would have thought continuously hunting if injector pump, changed all batteries a couple of times and had new battery charger volts read ok about 27/28 when engine running. Don’t know how to check fuel supply but have fuel filters changed every 2 years and make no dif. good Idea swopping components but as both engines have simi fault not sure if I would find answer. I will try all suggestions and post how I got on. Thanks again for all your help if any other suggestions I will be happy to try as well

 

[andy59]

I have a pair of 75s and when starting from cold they always run 1 or 2 hundred rpm high then settle back to idle after about a minute , so must be a cold start system that presumably has temp sensors to control it so maybe look there, does rpm change under load ?.

 

[volvopaul]

I have a pair of 75s and when starting from cold they always run 1 or 2 hundred rpm high then settle back to idle after about a minute , so must be a cold start system that presumably has temp sensors to control it so maybe look there, does rpm change under load ?.

Correct Andy , ecu has start up high idle speed 750 for approximately 30 seconds , after that programmed idle speed takes over .

To OP , possible fuel pressure maintaining valve fault giving unstable injection pump fuel pressure .

 

[Bandit]

It could be a partial fuel blockage or air being sucked into fuel lines, check prefilter elements, fuel bowls and seals for integrity and cleanliness / fuel bug first.
Another one is to blow fuel line with a dinghy pump back yo fuel tank and reprime to see if it dislodges debris.

 

[SEARANGER ANCASTER]

Cold start feature as prev mentioned , mine does it too

 

[Robert adam]

Yes both my engines run for about 1 minute at higher revs from cold start but I think this is by design. I think it’s keep engines from labouring when cold and improves cold oil pressure circulating also warms up engines faster. Had fuel filters changed many times since problem started. Don’t believe it’s fuel starvation as both engInes achieve max load rpm 2600 with boat doing 31-32 knots. Problem does not happen at full revs / speed. Could be air getting into fuel line I have not noticed any diesel leaks but I will check over all joints but as with a part blocked fuel line I don’t think it would affect both engines with syn Off but I’ll give any idea a go.
Just read back my first post for op o it should read Volvo ! er think it was auto corrected

 

[Elessar]

Hi
has anyone had a problem with unstable RPM on volvo penta tamd 75 engines ? The problem is the engines operate fine then after perhaps 5 minutes of running one ( usually the port but not always ) revs increase or decrease by a hundred rpm or so. Seems completely random in time and amount of increase or decrease some times changing by as much as 500 rpm. Volvo could not give answer and 2 separate op o dealers failed to fix and gave up.
I’ve tried removing condensate water from ecu As suggested in another post on this forum but that did not help.
Anyone got any ideas?
thanks Robert a

Are you sure the throttle levers aren’t moving?

If I drive mine hard in a head sea the levers can creep forward.

I keep meaning to tighten them up……

 

[Robert adam]

thanks for idea but unfortunately not the problem. Happens in smooth water as well.

 

[DavidJ]

Just looking for clues.
Have the engines ever run trouble free under your ownership?
If so did the problem with both engines start at the same time?

 

[Robert adam]

Engines were fine for about 2 years seem to remember fault started just after warranty ended. Can’t remember if both engines developed problem at same time but I guess so as sync system would alter revs on other engin. I have on numerous occasions switched off the syn and both engines still play up but the port changes revs over a greater range ie starboard does not change more than 200 rpm port will go up or down by max 500rpm.

 

[Portofino]

Have you had a Volvo scan tool the most recent version on it ? Vodia I think it’s called .
This needs to come from a guy who subscribe s to VP so an official dealer at the highest and most expensive level .

It should eliminate all this vague sensor and fuel pressure theory .
Save you in the long run by avoiding being walked down the parts throwing path .

It will or should look closely at injector health , spot intermittent injector opening times or turned around on the screen you should see synchronised times or what ever .Injector voltage etc etc . Check if one’s a bit low etc .

 

[volvopaul]

Have you had a Volvo scan tool the most recent version on it ? Vodia I think it’s called .
This needs to come from a guy who subscribe s to VP so an official dealer at the highest and most expensive level .

It should eliminate all this vague sensor and fuel pressure theory .
Save you in the long run by avoiding being walked down the parts throwing path .

It will or should look closely at injector health , spot intermittent injector opening times or turned around on the screen you should see synchronised times or what ever .Injector voltage etc etc . Check if one’s a bit low etc .

Doesn’t have to be the dealer , I’ve got the diagnostic key for the earlier edc engines .

 

[Andyroonot]

What are your engine serial numbers?
These engines may be subject to a campaign for the installation of a module between the throttles and engine to stabilise the throttle signal and cure a known issue that causes fluctuating engine rpm with gear engaged.
A serial number check would tell you if it’s required/been completed already

 

[volvopaul]

What are your engine serial numbers?
These engines may be subject to a campaign for the installation of a module between the throttles and engine to stabilise the throttle signal and cure a known issue that causes fluctuating engine rpm with gear engaged.
A serial number check would tell you if it’s required/been completed already

SPM unit

 

[Robert adam]

Thanks for that I will find engines serial numbers and try Volvo again. It would be great if there is a straight forward Volvo fix. I will also look into Vodia? Does anyone know when engine recall was made? I had my engines registered but was never told of a recall.

 

[petem]

Have you had a Volvo scan tool the most recent version on it ? Vodia I think it’s called .
This needs to come from a guy who subscribe s to VP so an official dealer at the highest and most expensive level .

It should eliminate all this vague sensor and fuel pressure theory .
Save you in the long run by avoiding being walked down the parts throwing path .

It will or should look closely at injector health , spot intermittent injector opening times or turned around on the screen you should see synchronised times or what ever .Injector voltage etc etc . Check if one’s a bit low etc .

The thing is Porto, there's limitations to what Vodia can measure. For example, the engine diagnostic system can measure the resistance across a sensor and compare it to some parameters to determine if it is faulty. But it can't detect an RPM sensor that has become contaminated with rust.

Also, if there are voltage issue with the feed to the ECU then the ECU can give incorrect fault codes.

Finally, I'm not sure how you think that injector issues can be detected when they are mechanical injectors (I suspect the same applies to your engine).