Diesel failed MOT on black smoke test PART 2

goldspanners

Night-owl wrote: »

I revved my old petrol escort upto 7000 rpm, admitingly the temp counter went right up to high but it passed the MOT

it was a petrol, petrol engines are designed to rev higher than diesels,even 7000 rpm from a petrol would be hitting the rev limiter and not good for any engine,especially for a prolonged period,infact i think this would cause more damage than good to a petrol,theres no need to do this in a petrol engine before mot time.

dieselglider

I would also suspect the EGR valve may be a suspect if the problem seems to be intermittent. If it plays up, you generally get a fair bit of smoke, and maybe loss of power or hesitation also. For the moment, just hope it's working when you go again for the re-test.

inmypocketnottheirs

I too suspect the EGR valve, but not sure if this age of vehicle has one.

I have had the same symptoms on a diesel Saab 95.

Another possibility is perhaps there is an air leak, if air enters a turbo diesel system this will cause over fuelling and black smoke. Check all the visible hoses for splits, even hair line ones.

Have you noticed any increase in fuel consumption or decrease in performance?

If it is the EGR valve, I do not know how accessible is is on the Synergie, but if you can get to it and remove it, they can be cleaned with break disc cleaner (not brake fluid!). This removes the carbon deposits and can provide a low cost solution for a few thousand miles.

HTH

Penny_Farthing_2

Well it passed! And with very low scores. The mean value went down from 5.25 last time to 0.25 this time. The zero drift was 0.19 last time and 0.00 this time. He didn't do the FTP mean value last time but this time it was 0.25. I obviously know nothing about what these things mean but they sound good to me. Fab! Thanks very much indeed for all the ideas. I will get that ERG valve checked out properly when the next service is done.
Or maybe I'll swap the car for one exactly the same that's just 20 days older than mine - then I won't be stuffed for this extra VED next year!
Cheers again everyone.

hewhoisnotintheknow

i always clean my sensors and run some posh fuel through the car a week leading up to the MOT, but this was when i used to drive gti's that would stuggle the emmisons tests. Now i drive a Peugeot HDi i dont see any problems!

cyclonebri1

I think running the engine well up to temp was probably the secret. If you drive like mosdt of us are doing to save fuel at the moment, its really not the best for keeping the engine clean. Imagine static diesel engines, they run at full throttle for hrs on end because they are designed to do. Car diesel engines are similar, and its easy to start looking for sinister faults when just running at "normal" operating temp on a regular basis will rectify the situation.

The suggestion of a split hose on the induction size, as already suggested, would be my first check because its cheap, ie no cost, unless there is actually a fault;)

in2deep_2

You see a good thrashing never hurt anyone.:D