Help with an odd engine sound...!?

[numskull]

I've noticed a weird noise that sounds similar to "pre-ignition" or "knocking" in a petrol engine, but oddly, only when the engine is not under load. When I accelerate it disappears; back off and it returns. Any ideas?  

[Supurbia]

Try a different garage for fuel first as you might've got some cut price cut quality cut amount fuel from one of the "erm" less than pukka forcourt owners,

 

You should see it go as the temps come down but tbh the way an engine is tuned these days doesn't help, so long as it's not rattling like a bag of spanners I wouldn't worry too much, Miss Insignia does it at times as well.

Edited 2 September, 2014 by Supurbia

[numskull]

Cheers Superbia...

 

It was filled with Shell so I don't think it's down to the fuel. I wondered if it is a "feature" of the CR system! Guess I'll see if it gets any worse and get it to a dealer in the next couple of weeks if it does...  

[JakeBlade]

Does it make that noise all the time at idle, or just at cold or just at normal operating temp?

[numskull]

Does it make that noise all the time at idle, or just at cold or just at normal operating temp?

 

Normal operating temp and most noticable when cruising...

[JakeBlade]

Cruising as in: clutch down and coasting?

[numskull]

Cruising as in: clutch down and coasting?

 

Nope, as in on the flat and little power required to keep steady forward momentum! 

[JakeBlade]

Hmmm, yours is a diesel, right? The shell fuel does have a high cetane rating, but you'd have to add a lot of extra additive to get pre-ignition. But it could be something in the fuel/air mix. As Sup says above, maybe wait 'til this tank if fuel has been used up, and se if it's the same in the next tank.

[numskull]

Hmmm, yours is a diesel, right? The shell fuel does have a high cetane rating, but you'd have to add a lot of extra additive to get pre-ignition. But it could be something in the fuel/air mix. As Sup says above, maybe wait 'til this tank if fuel has been used up, and se if it's the same in the next tank.

 

Yeah, thats what I'm probably gonna do, but wat to get it looked at before the "real" Skoda warranty finishes at the enmd of the month...

[JakeBlade]

Take it in now, so that your concern gets logged before your warranty runs out.

[numskull]

Take it in now, so that your concern gets logged before your warranty runs out.

 

Yup, now going in on Saturday!

[peterposh]

Have they got a knock sensor?

[numskull]

Yup, now going in on Saturday!

Didn't in the end - too long a story to go into...

Have they got a knock sensor?

No idea. However, now noticed its really awful when cold and under load at about 16-2000 rpm - sounds like a 1971 London Cab....

[JakeBlade]

Didn't in the end - too long a story to go into...

No idea. However, now noticed its really awful when cold and under load at about 16-2000 rpm - sounds like a 1971 London Cab....

 

Have you checked that it's not the rattling air intake box, or the rattling pipe on the bulkhead heat shield?  That's at the same rpm that you describe.

 

http://www.briskoda.net/forums/topic/263477-gruff-exhaust-on-140-estate/?hl=+gruff

 

and

 

http://www.briskoda.net/forums/topic/311004-rattle/?hl=%2Bbulkhead#entry3719983

Edited 8 September, 2014 by JakeBlade

[numskull]

Have you checked that it's not the rattling air intake box, or the rattling pipe on the bulkhead heat shield?  That's at the same rpm that you describe.

 

http://www.briskoda.net/forums/topic/263477-gruff-exhaust-on-140-estate/?hl=+gruff

 

and

 

http://www.briskoda.net/forums/topic/311004-rattle/?hl=%2Bbulkhead#entry3719983

 

Car has gone to the dealer this PM, so I'll certainly look at both when it comes back with "no problem found" matey - thanks!

[numskull]

Car has gone to the dealer this PM, so I'll certainly look at both when it comes back with "no problem found" matey - thanks!

 

....and as I suspected, they can't find a fault, so I'll try and track it down when I get it back!

[JakeBlade]

Give the air intake a wobble to see if there is any play unit, and give the bulkhead heat shield a tap to see if that's the noise you're hearing.

[numskull]

Give the air intake a wobble to see if there is any play unit, and give the bulkhead heat shield a tap to see if that's the noise you're hearing.

 

Yeah, of them both I'm pretty sure it'll be the latter, as the the symptoms decribed in the link to the second thread you gave me (thanks again!) seem to be identical to my issue, so fingers crossed its that and not a CR or other induction/mechanical issue...

[JakeBlade]

Yeah, of them both I'm pretty sure it'll be the latter, as the the symptoms decribed in the link to the second thread you gave me (thanks again!) seem to be identical to my issue, so fingers crossed its that and not a CR or other induction/mechanical issue...

Cool.  If you don't have any insulation, just wrap some foam packing in aluminium tape or kitchen foil.

[numskull]

Yeah, of them both I'm pretty sure it'll be the latter, as the the symptoms decribed in the link to the second thread you gave me (thanks again!) seem to be identical to my issue, so fingers crossed its that and not a CR or other induction/mechanical issue...

 

Checked the pipework on the bulkhead and there are no issues - all tight and no marking on the insulation. So decided to drive with the window down and the noise is really awful - it literally does sound like an old London cab when the engine is under light load. If I give it more welly it disappears, so I presume this isn't normal!? I've also noticed (as did the wife this morning) that the fuel pump is making a terrible whine too. So its back to the dealer which is all rather boring...