Hi my SDI runs a lot of veg. After a while of veg it develops a tick or knock. Sounds almost like a feint little end or a tappet but clearly isnt either as its done this for 15000 miles and would of course have gotten worse if it was these.

 

Now if I run a couple of tanks of reg derv through it, it really does make it go away almost completely. I'm guessing if I ran derv permanently it would vanish all together.

 

I've just bought myself a VAG401 from the states and plugged it in for codes. Its showing me P1248 but showing as 'sporadic' and hasnt come back on after 30 miles of driving.

 

Also showing in another area was N108 which I believe is associated, says Deviation of injection valve. 

 

Any other channel values I can look at for values that might help me solve this mystery as its gone on for a long time now. 

 

Any help appreciated, thanks.

 

 

http://wiki.ross-tech.com/wiki/index.php/17656/P1248/004680

 

Blockage caused by dirty fuel deposits, this is very common with cars running poor quality diesel or homebrew. Suggest you fit a separate ultrafine filter inline after the standard filter, you also need to change filters much more often.

It's only just had a full service and a service makes no difference at all to it. I don't run waste oil or homebrew either, my oil is straight off the supermarket shelf, clean and unused. I particularly wanted to avoid all the issues involved in running WVO.

 

Now I've said that, do you still think that could be an issue? Thanks for the reply BTW 

Edited 3 June, 201412 yr by capriman

To add, dunno if its any use or not, Channel 4 shows tickover 903rpm and the ign timings are 1.76 and 4.84 and duty cycle 2.79%

It's only just had a full service and a service makes no difference at all to it. I don't run waste oil or homebrew either, my oil is straight off the supermarket shelf, clean and unused. I particularly wanted to avoid all the issues involved in running WVO.

 

Now I've said that, do you still think that could be an issue? Thanks for the reply BTW 

 

Yes, because your 'fuel' contains none of the detergents or volatiles present in pump diesel which keep the fuel system sparkly clean, a separate filter might not make any difference but changing the ratio of veg/derv might help.

But veg oil is thicker than diesel and if a bit of water has got and is emulsifying in the fuel lines, filter or pump that could be the problem.

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I know diesel pumps are usually a 'do not mess' item for the layman, but is there anything on the pump that could be checked and/or cleaned? 

 

Are there any readings I can check on the diagnostics that would give me any clues?

Have you used the timing checker in VCDS?

 

Actually that probably won't work without the full version of VCDS.

No. I was actually going to try just knocking the timing back a smidgen. Its just odd because it does it everytime I run veg or a mix thereof but it wont do it right away, it will very gradually do it over at least a couple of tanks, sometimes 4 or 5 tanks and if I then fill it with nice posh V power it will gradually improve but will take 3 or 400 miles to do so. 

 

I was wondering if there is some kind of auto advance/retard mechanism in the pump which 'learns' so to speak?

 

It certainly doesnt seem to do it any harm as it'll still pull 4000rpm and over 100mph making its racket, just doesnt sound pleasant!! 

 

Is it possible an injector is slowly clogging then clearing allowing a cylinder to run a little lean?

 

One other thing which might offer a clue. When i've been running veg and then run diesel, for a while its power seems down. Only for a 100 miles or so though then it seems ok. Deffo is more powerful and smoother on veg though.

 

Starts first touch of the key rain or shine even on 100%, no cranking whatsoever, doesnt smoke and fuel consumption seems fine.

I would prefer to have VCDS to hand if you are playing with the timing.  You only need move the pump a very small amount to make a big difference to the timing.

 

The ecu does lean to some degree and is capable of adjusting the timing in real time within certain limits.

I can scratch the pulley before undoing the vernier bolts so it goes back. The OH's car a few months ago lost all its power and the diesel knock was very loud. VCDS showed those same errors and as a starting point i checked the vernier. It was at one end of the slots. I undid them  and slid it all the way to the other end as a starting point and tightened them up. No need to alter them further, it runs like a swiss watch now and has done ever since!

 

Im thinking on this now and I wonder if my pump timing is very close to being too advanced and the veg is causing the brain to advance it into the over advanced area?

 

I wonder if when the cambelt was done it was just eeked forward a smidgen too?

 

Gonna get my spanners out I think and have a play! If nothing else, it'll rule it out

On my old TDI, after changing the cambelt the timing was so retarded it didn't show up on the graph in VCDS, I moved the pump about 2mm relative to the pulley and then it was close to the top of the timing window.  Moving the full length of the slots on the pulley will have a massive effect on the timing.

Hers had slipped so was probably massively advanced. It really wasn't nice to drive at all. 

 

Its dry, I have a head torch and its a doddle to do so gonna do it now. It'll bug me otherwise............. BRB

Back. Well the tick is still there but the car has developed a little more pull lower down so I think it benefited from a little retarding. Interestingly the readings in channel 4 have fall substantially too. The ign timings are now 0.00 and 0.88. If I knew what the readings should be at a given RPM I reckon I should be able to tweek the pump timing to be pretty much spot on. 

 

Will keep pondering on this one 

 

Oh one other thing but probably not linked. also got a sporadic on the P1256 coolant temp. Guage does periodically do the 'fabia thing' though so assume thats just down to the usually fabia electrical gremlins.

Edited 3 June, 201412 yr by capriman