Hi all, recenlty my SDI seems to have developed a bit of a 'knock' which has me a little bemused so wanted to run it by you guys.

The engine just sounds very harsh and diesel knocky particularly in the lower gears and sounds awful (almost like the crank is hanging out of it) by 3ooorpm.

Now there is also intermittently a very distinct tapping in the harshness too but its not always there. In fact the harshness itself is odd as its not always the same severity. It can vary over minutes even. Drive up one road and its okish and drive up the next one and it sounds like the engine is falling apart!

There are no warning lights on the dash.

Apart from its reluctance to rev high, it pulls nice and hard and doesnt seem down on power.

It ticks over nice and clean with no misfires and revs clean when under no load with no obvious noises at all.

It's done it now for around 1000 miles so doubt if its crank or engine bearings (although it sounds like it is) as I'm sure by now it would have actually got worse. I just took it down the bypass at a steady 80mph each way yet it didnt trouble the car and it was still pulling nice and strong. It doesn't sounds overly harsh either in the higher gears, although perhaps the overall cabin noise at speed hides some of that.

I gave it an oil and filters change the other day and it didn't seem to make any difference.

Any clues???

Edited 10 March, 201313 yr by capriman

No replies? Hmmm, I thought that one might have you as baffled as me! lol

anyway, an update. Drove it today (50 miles around town) and the tapping has gone as has much of the heavy knock and harshness although its not totally gone but it certainly doesnt sound like it has done recently.

I'm baffled.

Only difference is the veggie oil. I filled up the day before with straight diesel so i'm wondering if theres an injector issue with one of the injectors or something? I'll run a tank of DERV through it and then runa mix again and see if it reoccurs.

Similar to your engine.

On one of my 1.4 TDI engines, when cold starting after standing all night it has a metallic tapping noise above 1,300 RPM until after 10 minutes of running then it's fine. I always check the MPG at various points when leaving home and when it's cold with the tapping noise the MPG is always lower, but once it's warmed up it's OK.

This occurred after it's 2nd service some 55,000 miles ago and as the years roll by the noise gets louder.

The service intervals are strictly adhered to with the correct oils and filters.

Is this a tappet or injection symptom?

DB.

You say oil and filter change, did you change the fuel filter as a reluctance to rev could be fuel starvation at higher flows. Another forum to join is the biodiesel / waste veg oil / straight veg oil site:- http://www.vegetableoildiesel.co.uk/forum/index.php

I think it's probally more a diesel knock than a engine knock.

Change the fuel filter and run it on diesel only and see if it changes.

Update. The fuel filter was changed when the oil and air ones were.

The car seems to be running pretty well now. It seems a tiny bit louder than it used to be but that could just be my imagination. It still does this occasional two or three quick rev thing if fired up semi warm without letting the glow plug light go out. Also occasionally it will tick over above 1000 rpm for a few mins then stop. Again when its semi warm. Also last 2 days I've noticed just once each day when sat at traffic lights the revs would 'blip' but literally a needles width and no more. Again seems to be when its semi warm.

Something is amiss somewhere but i think its down to a sensor not being sure if the engine is warm or cold if that makes sense?

Oh I ran it down to half a tank on staight diesel and than thres 10 litres of veg in it. Have done 100 miles around town since and no nasty knockings have come back.

If I was running veg oil a lot of the time then

I'd be inclined to run a full tank of super diesel through it

twice a year purely for the cleaning properties of that type of

fuel.

I wonder if you have been suffering from coked up injectors or even valves.

Perhaps continuing to run it on Derv for a while will improve things....grr666 may have a point.

Thanks guys but I've not been using a lot of veg. I use new stuff not waste and run 30% and have only done 4k miles in the car so doubt that would be an issue would it?

Sounds a wee bit harsh again today (but not hideous) so maybe something to your idea. I will stump up for a tank of super diesel n next fill up and see how that goes and report back.

An update on things.

I ran a tank of shell V power through it and all seems good. Seemed to soot a bit during that tank when floored in higher gears so maybe that was it doing a bit of cleaning?

Anyway It did 510 miles on 39.5 litres so good fuel consumption too and no nasty noises from the engine although it still sounds imo to have a little quiet 'tick' in there somewhere but again sounds diesel noise rather than anything sinister.

Today I filled up again but had 15 litres of veg handy so threw in 1.5 litres of unleaded to thin it down and also half a bottle of redex diesel system cleaner. Shook it all up nicely then bunged it in the tank and topped up (using the expansion tank too) with 33 litres of V power. Total cost £54 for 50 litres of fuel.

My theory is that while I'm getting my fresh veg for free then I may as well spend an extra 3 quid to fill the tank with the nice posh diesel to help keep the engine cleaner than using normal diesel.

Anyway, drove 200 miles today on this mix and the car is puliing nice and strong still (I usually notice a drop in power running a 30% veg mix) and the engine is still quiet and sounding healthy.

Thanks for reading and hope my wafflings help someone.

Edited 28 March, 201313 yr by capriman

Good to know its not anything mechanical at least.Glad all is running well

A further update. I hope I'm not just waffling away and this kind of ongoing commentary will be of use to people over time wanting to run a percentage of veg. The car is close to needing fuel and on the 50 litres will have covered 620 miles so a genine 56/57 mpg average which is pretty decent and about what i have come to expect from both this and OH's car.

On both mine and OH's car it is worth noting that power drops when using 30% veg or more. Whilst an SDI is hardly a flying machine at the best of times it really does become a plodder with veg. I've run this latest tank with v power to see what happens. Its down on power on straight v power of course but well up on the usual veg and derv mix and the economy figure suggests I'm not having to floor it so often to make progress. Early days but I think something definitely worthy of note.

The other day it did the very slight revving thing again. Its as if you are literally flicking your foot past the throttle pedal every 7 or so seconds. The revs just blip 30 revs or so thats all. What was worth noting is the temp guage read zero (the car was semi warm). I turned the engine off and restarted it. Temp guage instantly read a quarter and no 'blipping throttle'. The temp guage seems to often read zero when it shouldnt (no water usage or system pressure) so i'm wondering if there is a sensor fault here somewhere??

Anyway the engine continues to runs fine but i'm still sure its not quite spot on. Its a smidgen noisier than it should be and sounds harsher as it revs. Nothing drastically wrong i'm sure but i'm looking forward to a friend pluggin his vagcom in just to see if it shows any codes even though there is no lights on the dash.

Overall though, still very happy with it and almost happy to have a 'challenge'.

Thanks for reading my drunken waffle...................till next time!

edit. The OH's car has now covered 30k miles of which 20k miles have run around 30% veg with no issues at all other than it pulls like a steam train after running a tank of v power through it. I think MY car has a sensor or injector issue which the veg is actually highlighting. I don't think its actually a problem with running veg, just that its highlighting the weakness. I'll have further info once the diagnostics show anything (or not).

Edited 4 April, 201313 yr by capriman