I was having tyres fitted a few days ago in a place that also does MOT`s. It gave me the opportunity to observe a smoke test being carried out. To my surprise the engine did not seem to be given a floored throttle up to the limiter.
It seemed to be given a more gradual application of throttle and slower build up of revs to a lower max revs.
Unlike when I take our diesel to the council place and its really booted up to the limiter.
I have no problem with the latter, but was just interested in what was happening as I thought stamping on the throttle up to max revs was obligatory and monitored by the testing equipment?
Regards
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It's called "fastpass";if it passes on this procedure you go no further.
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I should add that it is a lower (severer) limit.
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Fast pass still requires the engine to be revved to the limiter - the procedure is to steadily increase the revs over about 1s though, then hold it till the analyser gives a signal, the let the throttle off. The tester is not supposed to just mash the pedal to the floor.... Even on a fast pass there should be 2 full speed runs, as the first is to establish that a governer is present. Of course if the presenter has set the max speed down to say 3.5k to get it through.... The fast pass merely means if it comes in at <1.5 on the first run, no further runs are required. However, if the car is pre 1979, then it only needs testing to 2,500 rpm.
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RichardW
Is it illogical? It must be Citroen....
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I can see no mention of GOVERNOR in the Fastpass procedure tho' I may be wrong-checking the pump settings,seals comes before that.
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A lot of testers don't like revving them to the limiter. Taking a diesel to maximum revs with no load on it is just plain cruel - there is no other word to describe it. Diesels are not designed to do this.
I've noticed the tester on the last couple of MOT's on the Mondeo have gone far easier on the revs than they did the first year or two after this test was introduced. I think many testers have gone a bit easier based on the number of engines that blew up during the test.
Cheers
DP
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04 Grand Scenic 1.9 dCi Dynamique
00 Mondeo 1.8TD LX
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I can't see why it should cause the engine any problems, provided it is otherwise in good condition - oil and coolant levels OK, cambelt OK etc.
Afterall the governor is there to prevent damage. If there was any concern then the governor would be set to a lower limit. Wouldn't it?
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No.
The governor is there primarily as an engine safety device and will progressively cut the fuelling when the governed speed is reached. Its other function is to provide closed loop control of the idle speed - a diesel runs on so little fuel at idle that it is not inherently stable. Controlling the idle manually is like balancing a broom vertically with the end of the handle on the palm of your hand.
The problem with the MOT test procedure is one of torsional engine oscillation. Engines are not designed to run at appreciable speeds unloaded and dangerously high levels of torsional oscillation can build up at certain speeds. It is very much a part of engine development to take into account these speeds and ensure that they do not fall into frequently used regions of the engine map.
I temporarily reset the governor on my old PSA car fitted with a Bosch VE pump to 3,500 rpm - I haven't been rumbled yet. The VAG PD diesel will be due its first MOT this year. I'm working on a scheme to reduce the unloaded max speed....
659.
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Thanks for the info. I haven't got a clue what you're on about but I am in no doubt you are right.
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