Engine surging when de-accelerating

[jimmca]

Hi all

I have an unusual problem with my 06 Superb 130 PDtdi ( AWX ). When I am reducing speed ( engine braking ) by letting my foot of the throttle the car surges like if I was touching the accelerator pedal or touching the brake. It is very noticeable if I am at 70mph and heading down a hill. I checked out the car with a VAG kit but it shows no errors. I even checked the throttle position and injection quantity and they show 0% when engine braking.I have no loss of power,no black or white smoke and I am getting very good MPG.Ticks over very smoothly. I changed the air filter and the fuel filter just in case

I have searched the net for an answer but I have failed to find one.

Its like a petrol engine thats missing.

Help

Jim

[skodanut]

i was wondering if possibly you had a very small amount of unburnt fuel causing the engine to rise is revolutions. Maybe this is due to leakage through the gaskets on the manifold....either way rotodiesel should be along soon for a more pinpoint diagnosis

[rotodiesel]

How much oil does your engine burn?

rotodiesel.

[jimmca]

Hi

It uses about 3/4 of a litre between fixed interval services. I use 507.00 oil. I just noticed another thing this evening. The remaining distance on the computer in the dash is giving me an odd reading. The distance remaining is nearly 300km less than it should be, but the fuel guage needle is in the correct position with the mileage I have covered so far.

I also unpluged the MAF to see if this was the problem but the same problem persisted with alot less power.

I was going to have a look at the EGR valve and hoses but before I start ripping I am hoping for an answer to this mistery.

[jimmca]

Hi

Just to clarify. The surging happens every couple of seconds at random. Its not a continuous surge. Very similar to tapping on the pedal also it occurs when the cruise control is activated.

Jim

[jimmca]

Hi Guys

Update on my problem. Took apart all the pipe work from the Turbo to the inlet manifold and took the manifold of as well.The EGR valve was very dirty but working,the manifold was also coated with 2mm to 3mm of gunk and there was a nice drop of oil in the intercooler. Cleaned all the parts spotless and checked the various vacuum pipes for cracks etc. Reassembled items but the problem still persists.

I also put a blank in the pipe between the EGR and the exhaust to see if this worked but it didnt solve the problem. It generated a EGR fault code so I took out the blank.

So has anybody come across this problem and if they have what was the fix. I have run out of ideas.

[rotodiesel]

3/4 litre of oil between services is too much. I suspect your engine is surging on the overrun because it is burning lubricating oil. Causes will be either excessive crankcase pressure or leaking turbocharger seals. Make absolutely sure the sump is not overfilled.

Eliminate the crankcase blowby by temporarily leaving open the crankcase vent - route it into a tin can to catch the oil.

A pattern or blocked air cleaner element will also cause oil to be drawn into the intake via the compressor seals. Fit a new Mann & Hummel paper element and clean the debris from the housing before condeming the turbocharger. The OE paper element is by far the best.

rotodiesel.

Edited 2 September, 2011 by rotodiesel

[jimmca]

I was thinking about that as well. All the VAG COM readings are showing no diesel injection so it must be burning engine oil

I have excessive blow when I take of the oil filler cap but if I remove the hose that comes out of the top of the rocker cover to just before the turbo,I have very little blow. Is there some sort of a filter inside the rocker cover that can get blocked I was going to take the rocker cover of to see. .

Is the crankcase vent CCV valve for the PD engines built in to the valve cover.

Will have a look at my airfilter as well.

[jimmca]

Checked my air filter which I replaced at the last service,3000 miles ago.Its spotless and its a Mann & Hummel.Also checked my oil level and its a bit low so over filling is not the issue.

Looks like I am removing the valve cover tomorrow.

Jim

[jimmca]

Hi guys

I removed the valve cover this morning to have a look at the breather on it. There is not a whole lot to see,its built into the cover. I noticed that I can blow into that pipe easily enough but if I apply a vacuum it blocks.Seems like there is a one way valve in the cover allowing air in but not out !! It this normal. What that means is the pressure from inside the cover cant get out which makes no sense at all. Am I missing something here or is the crankcase vent somewhere else.

[jimmca]

I cleaned the CCV in the rocker cover as much as I could and put the cover back on. Purchased a new Mann & Hummel airfilter just to be sure to be sure. Ran the car with the vent pipe removed. Very little comes out of the pipe on top of the rocker cover when ticking over but when I take the filler cap of I have a gale coming out. I also checked the dip stick hole and I have very little blow out thereso the sump is not under pressure.Brought the car for a run and the same thing is happening.

So to recap:

All pipework from the turbo to the manifold including the EGR and manifold itself cleaned spotless.

New Mann & Hummel airfilter fitted.

Ran car with vent pipe disconnected.

Removed and cleaned rocker cover as much as possible.

Alot of pressure under rocker cover but very little if anything from vent pipe.

No blow from dipstick hole.

No Vag Com fault codes.

Only started this problem last week.

Car running fine,plenty of power,no difference in MPG etc.

It happens when engine is hot or cold.

The higher the revs the worse it is.

I dont have any white smoke.

Have kept an eye on the oil level since it started but it hasnt changed so its not drinking oil.

I am running out of ideas.

Are my turbo seals the problem

????????????????????????????????????????

[rotodiesel]

If you have excessive crankcase pressure there is a problem. All "waste" air from the vac pump ends up in the crankcase as well as normal piston blowby - so the tandem pump will also pressurise the engine if it is not vented.

A major danger of excessive crankcase pressure is that the oil return line from the turbocharger to the sump (gravity drain) will also be pressurised and consequently prevent proper scavenging of oil from the turbocharger bearing assembly. This will give rise to a leakage of pressure fed oil from the turbocharger via the compressor seals into the engine intake - and the engine will run on this.

Remove the rocker cover again and dismantle the oil trap assembly built into it and see what is causing the excessive crankcase pressure. I've seen pictures of this but never dismantled one - I think there are 2 steel gauze traps in there.

rotodiesel.

I would strongly recommend disconnecting the lower intercooler hose joint and draining off any oil you find there. A little is normal - a lot is bad news...

Edited 3 September, 2011 by rotodiesel

[jimmca]

When I took apart all the hoses from the turbo to the inlet manifold I found about 1 to 2 tablespoons of oil in the intercooler.Some of the joints were wet with oil as well.Would this be the normal amount?

About the crankcase pressure,the vent is built into to the rocker cover which is a big black plastic type.

I tried to access the oil trap assembly but every thing is glued and not removable, seems I would have to break it to get at the valve and gauze.

Should the pressure vent freely out of the vent hole of the rocker cover.

Jim

[rotodiesel]

1 or 2 tablespoons of oil is fairly normal, possibly a little excessive. You don't want to see a cupfull. The lower joints are usually wet.

As far as I'm aware the cover should vent freely otherwise there will be a buildup of crankcase pressure. I've never had one of these apart so I can't offer any advice, but clean it up on the inside and see how it's made. If you can ascertain that there's no valve in there, you could apply an air line...

rotodiesel.

[Supurbia]

You have an airleak from the sound of it, check all pipes to the airbox and also the ones that run along the bulkhead.

[jimmca]

You have an airleak from the sound of it, check all pipes to the airbox and also the ones that run along the bulkhead.

Ok.Will have a look at them.

[jimmca]

Hi guys.

I checked the pipes going to the air box,could only see one 6mm pipe.Followed it along the bulkhead but it is not cracked or disconnected.

So seeing as I was at the air box, I removed it completly and disconnected the air mass meter to get it out. I also disconnected the exhaust at the turbo so I had no exhaust and a straight inlet pipe into the inlet side. I brought the car for a drive but the surging / jumpy hesitation while slowing is still happening. Its exactly like lightly tapping the throttle while slowing down. I noticed with the exhaust off I could clearly hear the turbo speed increase every time this surge happened.

So it looks like I am burning oil or diesel, can the accelerator give signals to the ecu without VAG COM seeing it ?I checked this out but injection quantity and throttle are 0% when slowing down in gear.

I removed the pipe that fits into the EGR and its coated with a film of oil only after 200miles after cleaning it.Is this normal after such a short time

The one question I cant get a clear answer for it how much of a blow should be coming out of the vent pipe on top of the rocker cover.I have very little. If I can get an answer for that I can sort out the crankcase pressure if thats the problem.

[rotodiesel]

Your engine is almost certainly burning lubricating oil on the overrun as the injectors will be at zero delivery under this condition.

You need to find out why - engine runaway will be the consequence of ignoring this problem. Start with the crankcase ventilation.

rotodiesel.

[jimmca]

Agreed.

With the engine ticking over how much of a blow should be coming out of the rocker cover vent?

[jimmca]

Fitted new turbo. Problem solved.

[jimmca]

Another problem with the turbo. Fitted the new turbo and now there is loads of blue smoke on idle. This is usually not a problem after changing a turbo but its not improving after 100miles. I removed the exhaust at the turbo and with the engine idling there is oil dripping out. Am I unlucky enough to have got a dud turbo. The supplier has said that he will change it but cant understand what happened.

I have another topic about very high crankcase pressure on the same car so do I have a bigger problem ?

[jimmca]

Nearly solved.

Still had crankcase over pressure due to blocked CCV valve which caused smoke to blow from exhaust during idle.The CCV which couldnt be accessed so got a second hand cover and problem nw sorted.

[Supurbia]

Mate of mine just had a brand new Garrett for his B5 and it was belching acrid white smoke and blew 24 hours later, replacement seems ok, so you could have a bad new one.