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Artificially / temporarily limiting max rpm of the 2.7HDI
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Paulius   
Tue Dec 05 2017, 09:53pm
Joined: Aug 14 2014
Member No: #1821
Location: Vilnius
 My MOT is about to expire and, since passing it involves them unnecesarily and uncomprehendingly revving diesel engines like crazy, I am looking for ways to get around that. I am looking to preserve my 2.7HDI for as long as possible and this stressful test (revving an engine without load DOES stress it a lot) does not help, so I want to at least try to get away without having it tortured.

I am thinking of tricking the system into limp mode, so the revs would not exceed 3000rpm. I probably could do that by disconnecting some sensor under the hood just before the test.
But that would also probably make the depollution light to show up, which could mean a failure by itself. But, then again, I could try reconnecting the sensor and arguing that there are no faults.

Any thoughts?
Paulius   
Wed Dec 06 2017, 12:12am
Joined: Aug 14 2014
Member No: #1821
Location: Vilnius
 A quick idea - to attach something to the accelerator pedal, so that it would be impossible to floor it.
gmerry   
Wed Dec 06 2017, 08:41am
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Paulius, me too! (I would like a way of reducing the maximum speed).

But the MOT Smoke test in the UK includes a check on operation of the governor, if the governor cannot be observed to be working correctly, its an MOT test failure.

So I suspect the solution will need to be through the engine management software.

However, ask in advance if your MOT testing station will apply the Diesel Fast Pass test procedure

For all private cars and light goods vehicles up to 3500kg design gross weight first used on or after 1 August 1979, a metered smoke test will be carried out.

Before checking the smoke emissions the Tester will firstly ensure that the engine inlet and exhaust system is fully purged, and the engine speed governor is functioning correctly. The engine speed will be raised to around 2500rpm or half the maximum engine speed if this is lower1. Upon reaching this speed, the Tester will hold the engine speed steady for 30 seconds to purge the inlet and exhaust systems, then the engine speed will be slowly increased to maximum to check the operation of the fuel pump governor. Where the engine speed stabilises at its maximum speed indicating that the governor is working, the engine will then be returned to idle speed.

Where it is clear that the governor is not working, the engine will be returned to idle speed and stopped, the smoke test will not be carried out and the Tester will be unable to pass the vehicle.

Provided the preliminary checks are completed satisfactorily, the Tester will prepare the smoke meter and insert the sampling probe into the exhaust tailpipe. Having restarted the engine the tester will start the smoke test.

Diesel Fast Pass

Since 1 August 2002 a metered "fast pass" procedure has been used to help simplify and reduce the time taken for the test, allowing vehicles with low smoke emissions to pass the metered test after one acceleration of the engine. If, after the first acceleration, the meter reading is at or below 1.5m-1, the vehicle will pass the meter test.

The smoke meter will indicate to the Tester to accelerate the engine. The accelerator pedal will be depressed quickly and continuously but not violently, to reach the full fuel position in less than 1 second. After the release prompt is given, the Tester will immediately release the throttle. The meter will calculate the maximum smoke emission during the acceleration and display the result. If the smoke level reading is at or below 1.5m-1, the vehicle has passed the metered test, and a pass result will be displayed on the meter.
 

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