Power VIS issue

[SD1too]

Ok, just to warn you Cosmin that removing the plastic manifold chamber to access the RH cam cover is quite a job. The worst part is two hidden screws at the back. A Haynes manual will be helpful.

Simon

[Cosmin161]

This thread can be marked as SOLVED

Dave sent me a part to fix the power VIS. Many thanks to Dave for his help.
Now both VIS motors are working!

Now for my feedback regarding the vis motors:
With the tester connected to the car, I have noticed that the VIS motors go active, depending on how much the throttle pedal is pressed and not necessarily depending on the rpm of the engine. I could press the throttle jus a little and go up to about 5000 rpm and the tester would not indicate that the vis motors are "active" or I could fully press the throttle and the Vis motors will instantly go active and open the flap and butterflies , from 1000 rpm all the way to the end of the rev range. This makes sense because now I have better low end torque and the car pulls better at lower rpm.
It is not correct to say that the engine has more power with working VIS motors than it had without them but it is correct to say that the engine delivers the power that it had at 4000 rpm, without working VIS, sooner at around 3000 rpm, with working VIS and now there is plenty of torque at 2000 rpm. I don't have to downshift to overtake anymore.

Conclusion of this thread : WORKING VIS MOTORS ARE A MUST!
Best regards and many thanks for your help

[SD1too]

Originally Posted by Cosmin161

Now for my feedback regarding the vis motors:
With the tester connected to the car, I have noticed that the VIS motors go active, depending on how much the throttle pedal is pressed and not necessarily depending on the rpm of the engine.

Correct!

I can endorse this having made the same discovery some years ago (with the assistance of T4). It's the rate of change of throttle opening to which the VIS system reacts; in simpler language that's how quickly the accelerator pedal is pressed.

Thanks for posting this Cosmin.

Simon

[vitesse]

Sorry need a bit of help here as the description I have in Rover’s Technical Brochure doesn’t match that which is given here.

“about 5000 rpm and the tester would not indicate that the vis motors are active” - at 5000 rpm both VIS motors should be active according to Rover.

“I could fully press the throttle and the vis motors will instantly go active” - if I fully press my throttle I’d expect the same as the engine is now well over 6500 rpm.

When the helpful Rover 54 (Ed) connected his T4 in London to my car in Sweden he tried to test the VIS motors. I followed his instructions pressing the throttle to take the engine over what he considered the trigger rpm - the results were “inconclusive”. Toaf however is able to active each vis motor even without the engine running.

Nowhere in the Brochure (mines actually called a Tekniskt kompendium which is a far better name) does it mention the mechanical throttle. I would better understand if there’s a direct link between the throttle position sensor and the VIS motors. Is there one?

Dave, where are you?

[stocktake]

Thanks for coming back to us with the outcome of this.

Just to clarify, Cosmin161 has stripped his Vis motor down and correctly diagnosed that the motor itself had failed, After a few Pm's all I did was send him a replacement motor FOC to his home in Romania.

On the subject of the motors operating it is my understanding that the vis motors remain unactivated when less than 31% of throttle is used. Above this then they work their magic working together. There are graphs somewhere on here to support this.

[Cosmin161]

Originally Posted by vitesse

Sorry need a bit of help here as the description I have in Rover’s Technical Brochure doesn’t match that which is given here.

“about 5000 rpm and the tester would not indicate that the vis motors are active” - at 5000 rpm both VIS motors should be active according to Rover.

-not the case because i only touched the throttle as the revs slowly built up to 5000 rpm. if you don't demand power from the engine by presing hard on the throttle pedal, the VIS system will not activate and the engine will slowly and silently rev up without opening the balance flap or bfly valves.

Originally Posted by vitesse

“I could fully press the throttle and the vis motors will instantly go active” - if I fully press my throttle I’d expect the same as the engine is now well over 6500 rpm.

-yes, but they activate right from idle rpm not from 3500 rpm (and you can hear some sweet intake noises ).

Originally Posted by vitesse

When the helpful Rover 54 (Ed) connected his T4 in London to my car in Sweden he tried to test the VIS motors. I followed his instructions pressing the throttle to take the engine over what he considered the trigger rpm - the results were “inconclusive”. Toaf however is able to active each vis motor even without the engine running.

-i think that the tests were inconclusive because of the 31% throttle input that Dave stated. Sometimes you pressed it above 31% sometimes bellow while you where expecting the VIS system to be triggered by the revs.

If interested, i can upload a vid to YT so you can see what i mean.

[SD1too]

I can help here because the discovery I mentioned in my last post was using Ed's (retired member Rover54) T4 and a club member's ZT-T. With the car stationary and the engine speed slowly increased to around 5,000 rpm, the power valve actuator did not move. Repeating the test but by rapidly moving the accelerator pedal resulted in the actuator operating. This was all observed by the three of us on Ed's T4. Therefore as Cosmin161 correctly points out, the assumption that the VIS system works by engine speed alone is incorrect.

Originally Posted by vitesse

Sorry need a bit of help here as the description I have in Rover’s Technical Brochure doesn’t match that which is given here.

Hi Mike,

You say that the document you have is called a Tekniskt kompendium. I'd be interested to know what this actually says. Is it possible to post the actual quote, translated by you of course!
Also, I suspect that there are documents in circulation which resemble MGR publications in appearance but are not genuine (I believe that I have one!). Are you certain that your Tekniskt kompendium isn't one of these?

Originally Posted by vitesse

I would better understand if there’s a direct link between the throttle position sensor and the VIS motors. Is there one?

Yes there is a link. The throttle position sensor is connected to the ECM which also drives the VIS actuators. Software will be involved of course and it is that which we are learning about here.

Originally Posted by stocktake

... it is my understanding that the vis motors remain unactivated when less than 31% of throttle is used ... There are graphs somewhere on here to support this.

Hi Dave,

I believe you're referring to the bar graphs which are not official MG Rover but the interpretation of an unknown person. They don't take account of the speed at which the throttle was opened.

When you kindly lent me your balance actuator & flap test rig I noted that the flap remains open (its default position) unless the throttle angle is changed rapidly. This is consistent with my earlier observations of the power valve described above and with Cosmin161's findings.

The VIS system therefore will operate only if the throttle movement is fast, in other words when maximum torque is required rather than leisurely cruising.

Simon

[stocktake]

Originally Posted by SD1too

Hi Dave,

I believe you're referring to the bar graphs which are not official MG Rover but the interpretation of an unknown person. They don't take account of the speed at which the throttle was opened.

When you kindly lent me your balance actuator & flap test rig I noted that the flap remains open (its default position) unless the throttle angle is changed rapidly. This is consistent with my earlier observations of the power valve described above and with Cosmin161's findings.

The VIS system therefore will operate only if the throttle movement is fast, in other words when maximum torque is required rather than leisurely cruising.

Simon

Thinking about it at the time we communicated about the operation, I believe I posted a short Vid which actually showed the balance flap open at rest and with a short sharp tap on the accelerator snapped shut, so this supports this.

[vitesse]

OK thanks for the replies, not much clearer in my head though.

In the genuine Rover Brochure (197 pages) Rover Service School (translated) there is no mention of percentages of throttle action only rpm. Duncan on the enthusiasts site had an English language version of the same publication, quite rare.
But there is no mention of slow or rapid pedal (TPS sensor) activation although I accept its possible to fool the system. What I really have a problem accepting is the fact that it’s possible to slowly take the engine up to 5000 rpm without any VIS activation, but if several people have observed this then perhaps it’s time to re-evaluate my understanding.

OK bit of translating time. There is a diagram too which shows the position of the various flaps, balance flap, etc.

Then it goes on to say:

The inlet manifold has a variable length in 3 steps and this applies to both engine sizes. It works as follows:

1. At low rpm the balance valve and valve controlling the effect duct is closed. This causes the engine to breath as two 3 cylinder engines each with its own separate mixing chamber and long power ducts, which means that the engine reaches peak torque at 2700 rpm.
2. To improve torque in the medium range the balance valve is opened while the power valve remains closed. Max torque is now reached at 3750 rpm (2.5 ltr) and 4000 rpm (2.0 ltr).
3. At higher engine speeds both the balance and power valve are open. Achieving now a range of torque upwards from 4000 rpm to a maximum of 6250 rpm (2.5) and 6500 rpm (2.0).

The construction of the inlet manifold also gives increased fuel economy at part load. Through the entire emissions cycle the manifold works at part load according to point 3.

Pumping loses (the action of the pistons to suck in air and press out exhaust gases) at sub 4000 rpm has by means of this construction been drastically reduced. This results in improved fuel economy.

OK, perhaps the translation needs some polishing but will have to do. Next question would be, if by not allowing the system to active as designed are you losing out on fuel economy as well as torque?

Keep well

[stocktake]

Originally Posted by vitesse

Next question would be, if by not allowing the system to active as designed are you losing out on fuel economy as well as torque?

Keep well

On all the failed motors I have replaced/repaired it has always depended on what position the valves have failed in as to what the owner experiences, either better/smoother delivery of power, or better mpg, or a little of both. Most common by far is the feeling of no power lowdown in the rev range and this is always the case if the balance vis fails in the closed position.