Lack of power around 2k revs

[Sparkles73]

I’ve had my Mk3 1.5L petrol Leon FR for 4 months and have a problem that’s irritating me. In all gears there seems to be a lack of power around 2k revs and after that the car seems to have a boost of power. I’ve had it fully serviced, new plugs, oil change, new cam-belt etc and the garage found no diagnostic faults. However the problem still persists. The garage said it could be the Active Cylinder Management kicking in, shutting down a couple of cylinders before the revs pick up. I’ve turned traction control off and tried the various driving modes but it doesn’t appear to make any difference. The only way round it is to drive more aggressively keeping the revs up before changing up through the gears. Any suggestions would be welcome.

 

[nd-photo.nl]

How many miles on your engine?

 

[Sparkles73]

Engine is at 37k.

 

[nd-photo.nl]

Could be worth checking the state of the intake valves (carbon deposits). Also, did you check your fuel trims? That could also be an indicator for some strange behaviour.

Especially Long Term Fuel Trim (LTFT).

 

[nd-photo.nl]

You might try to disable the ACT system manually, for troubleshooting purposes:

After carefully reading the 32 pages that explain the operation of the ACT system, I resigned myself to disconnect the connector of each of the 4 actuators that move the cams of the cylinders 2 and 3 to keep the valves closed (2-cylinder mode).

From the start or ignition of the ignition, the system detects that the actuators are disconnected and that's good. Thus, the ACT is deactivated "cleanly".
(I was afraid it would be detected only when trying to switch to 2 cylinder mode, which would have been more embarrassing because possible reduction of the ignition advance and opening of the butterfly before moving the cams .)

Message "Error Start and Stop", which disappears by itself after a few seconds (or by doing OK) then constant indicator EPC orange down to the left, instead of Trip. This witness is of soft intensity so little annoying at night.

So, miracle! I am at the same time rid of the Start and Stop "!

At the 2nd engine start, add the orange engine management indicator (injection pump logo) in the series of indicators at the top of the instrument panel (above the LCD). This light is a little brighter and therefore more visible at night.

More surprising and disturbing, the cruise control does not work anymore: its indicator is orange with an exclamation point, when I try to activate it. This is the ransom of the error "Engine Management". For safety, I guess the controller is disabled.

Apart from that, the 2-cylinder mode is no longer active, Yes! What a pleasure to see the engine always run on 4 cylinders, even when I'm on a gas net. The engine works perfectly: no failures, no softness. I tested from 1,000 to 6,000 rpm. Everything is normal.

I protected the 4 female connectors and the 4 males by a piece of fabric fixed by an small aluminium wire.

I test it last night and today, about 200km. Everything is perfect except the 2 witnesses, the S&S disabled and the speed controller disabled.


Conclusion: for the moment, I will stay like that, without ACT but with 2 error indicators and no cruise control.
I will, however, continue to look for other ways to disable 2-cylinder mode

Source: https://forum.obdeleven.com/thread/5897/disable-system-cylinders-mode-leon