Vacuum Solenoid Block

[fex]

Hi,

 

I was wondering if anyone could help. My turbo doesn't seem to spool up as quick as it should below 2k rpm. I have checked the actuator, it moves fine. I have replaced all of the vacuum lines. I have done the Mr Muscle turbo vane clean. I have checked that the actuator holds vacuum. The car has been remapped and EGR deleted (I removed the EGR components because I thought this may have been causing the problem). I haven't found a boost leak. I am just about ready to give up but:

 

I think I may have isolated the problem now though but I need someone to help me verify something:

 

If I connect a vacuum gauge between the vacuum solenoid block and the vacuum pump, I see a good 25Hg + of vacuum. This implies no vacuum leak(?)

If I connect a vacuum gauge between the vacuum solenoid block and the turbo actuator I do not really see past 17Hg of vacuum at idle. If I press the accelerator it may spike to 20 but immediately go down (like you would expect so that the vanes open turbo spools slower). I have read in many places that is healthy to see 20+Hg down the turbo actuator vacuum hose but everything seems so specific to each turbo that I don't really have a clue anymore.

 

Is this good enough to diagnose that the vacuum solenoid block is at fault? There are different variants of this block (6Q0906625). Mine is a 6Q0906625C (400434D). Does anyone know if they all do the same job? I phoned a Seat parts place and they said the part number has changed to G and quoted £195 for one brand new. There are quite a few on ebay but I was wondering if they all do the same job.

 

I apologise that I do not own a Skoda but I have been trying to sort this problem for 2-3 months now. It is taking a long time for the problem to develop further and I am fed up with the reduced performance and MPG. 

 

Many thanks

 

 

 

[bluecar1]

the actuator works by duty cycle, the more vacuum needed the more time it is connected to vacuum rather than free air

 

it does it a lot of times a second, so the vacuum is a function of the duty cycle, 50/50 gives half the vacuum, that way the actuator on the turbo and EGR can be controlled with a fine degree of accuracy

[Lofty79]

I would think its n75 or maf or map sensor

[bluecar1]

had a similar error on my mk1 Octavia

 

MAF sensor failed, once the car hit about 3000rpm and more than about half throttle the turbo would shutdown, flashing coil lamp and limp mode

 

match what you are seeing?

 

vagcom error was something about boost out of limits

Edited 8 March, 2014 by bluecar1

[fex]

I am not actually seeing limp mode. I am just noticing lack of power til about 2k rpm and a lack of anything on the motorway.

 

Boost log with boost actual/spec scaled near duty cycle. I have been told that high duty cycle means "vanes please open". I have checked that it is not sticky vanes, the lever moves nicely against spring resistance, actuator holds vacuum, replaced all vacuum hoses. Does anyone know if the vacuum solenoid blocks all do the same job, the different variants A-G or so? Maybe I should get a later variant if they are improvements on each other?

 

 

3rd gear 2k rpm WOT

 

 

I don't think the graphs say much except that boost i struggling to be controlled. Many thanks for the replies

[Lofty79]

My money is on maf sensor or n75 then now

when you scan for faults to you get the overboost fault code?

[fex]

No overboost code, just noticed reduced power and mpg. It must be just within the limits ? i've ordered a used vacuum solenoid block off ebay.. did manage to get the C variant but will definitely get a G or something if that just means it's an improved or later model, anyone know?, seat wanted £200 for a brand new one! 

 

 

there is a weird whistle sometimes but I don't know if its related

 and if that were a boost leak it would mean boost would be lost i.e. massive underboost right? I have looked a the piping and it does seem ok. only bit of oil is near the compressor side of turbo Edited 9 March, 2014 by fex

[bluecar1]

any black smoke out exhaust?

 

have you checked all the joints on the big boost pipes are connected correctly

 

when was air filter last changed?

[fex]

No black smoke.

 

Have checked all except the top of the intercooler really, not sure how to get round there. A boost leak wouldn't give overboost though surely?

 

Air filter I changed 3 weeks ago or so.

 

The weird whistle never happens when the vacuum hose to the turbo actuator is disconnected (or the vacuum solenoid block is unplugged). It usually appears in the morning after engine cooling and sitting overnight. You can start the car, wait for a period of time, no whistle, then blip the accelerator and the whistle appears. Not sure if it's related to the boost issues though.

Edited 9 March, 2014 by fex

[Lofty79]

actuator may be duff dude, sometimes the diaphragm chamber inside gets brittle breaks and leaks hence losing boost and leaking causing whistle

 

just a thought

[fex]

I have checked that it holds vacuum and that it doesn't stick when it moves

Edited 9 March, 2014 by fex

[fex]

Bad news, a new (used) N75 didn't fix anything. If anything, the whistle seems louder now. I want to suggest to myself that it is a boost leak but this couldn't cause overboost could it? Don't really know what to try now, finding the whistle is difficult under the car because everything else is so loud.. as in you can hear the whistle away from the car but not really under it.

[bluecar1]

you say the car has been mapped and EGR deleted,

 

when did these issues start ?

 

what was the car mapped to? (assuming it started at the 100bhp of the car in you details)

[fex]

the car was remapped to about 130bhp in June 2013 and issues started in November or December 2013. I EGR deleted because I thought the EGR was the problem but I don't think it actually was. I may remove the EGR delete tbh, waste of dosh.

 

I think if I could pinpoint the whistle, I'd be a lot closer to sorting the problem but I am ready to give up. Any advice on pinpointing a whistle with all the other sounds going on?

Edited 13 March, 2014 by fex

[philhoward]

I think if I could pinpoint the whistle, I'd be a lot closer to sorting the problem but I am ready to give up. Any advice on pinpointing a whistle with all the other sounds going on?

Your only chance is on a rolling road - you won't be able to build up boost any other way..  Put a tube to your ear and start pointing it around the engine bay to find the whistle.

[fex]

Well I'm not sure I see the point in looking for the whistle anymore. It must be a dying turbo? If it were any kind of leak I wouldn't be seeing overboost or is that not true?

[fex]

This new block buzzes after shutdown. Is this normal? Things seem quite a lot better. I haven't had the opportunity to do a boost log yet. Cheers

[fex]

Things feel better sometimes but I am still getting overboost. I don't really know what to proceed with now. duty map cycle is hitting 90+ which is bad right?

please see the boost log graph here:

imgur.com/oHaSrO4,salZT7q

Edited 22 March, 2014 by fex

[bluecar1]

I would say go back to your tuner who did the map for you and get him to check it for you, as you may find changing that vacuum bock has altered things