C5 II 2.0 Ltr Turbo one for Wheeler maybe

cachaciero · Post by **cachaciero** » 18 Mar 2010, 08:39

The Mk II C5 has a modulated Turbo similar but different to the 2.2.
What I want to know is what is the "default" no vacuum regime of this unit.

The 2.2 for no vacuum defaults to an exhaust low /pressure /flow mode which is why it overboosts if there is a problem with the vacuum.

Is the 2.0 ltr the same or is the "logic" reversed i.e no vacuum equates to an exhaust hi pressure / flow mode in which case it would never overboost for vacuum failure just be sluggish at the bottom end.

cachaciero

Trainman · Post by **Trainman** » 19 Mar 2010, 10:24

Found this on another site, may be of some use.....

http://www.eurovan2.com/forum/attachmen ... filter.pdf

Post by **Paul-R** » 19 Mar 2010, 10:41

You have join and then login to access that document. Do you have another link for it?

TopDonkey · Post by **TopDonkey** » 19 Mar 2010, 10:59

the 2.0 hdi with the vacuum controlled wastegate defaults to wastegate open (no boost) mode if there is no vacuum applied to the actuator.

On the 2.0 hdi, if the boost pressure sensor fails or has a wiring fault, then you will see full uncontrolled boost for a few seconds, then no boost, limited revs and limp home mode with the engine management light on until you restart the engine

wheeler · Post by **wheeler** » 19 Mar 2010, 11:45

Im not sure on this one to be honest, is it the RHR engine ?

Top donkey thats certainly true of the older 2.0 HDi's fitted to the xantia & mk1 C5 etc, no vaccum = no boost but the 2.2 16v HDi works the opposite way, with no vaccum applied to the turbo it defaults to full boost. I think the newer 2.0 HDi on the Mk2 C5 that were talking about is more similar to the older 2.2 setup so it may well be the same. best way to check is with a mityvac gauge connected.

cachaciero · Post by **cachaciero** » 19 Mar 2010, 21:15

Yes I believe it is the RHR. To be honest this isn't mine I was trying to help some one else with a post 2005 C5. His problem was that the engine lacked any guts above 2000 rpm but would eventually get to 70 mph where it felt quite reasonable, he said that it felt like the turbo was not coming in.
It had been on a Lexia no fault codes and no warnings when driving.
Then the garage had decided that it was the Turbo control valve and it was changed, that didn't fix it and then they decided that a new Turbo was required so now he was some 2K in a hole and still no fix. At that point I got interested, well it's a challenge isn't it.

Interestingly much of the controls on this engine are true end to end e.g. the Turbo actuator actually has a feedback pot so the ECU can actually read what the Turbo is modulated to unlike the 2.2 where the ECU modulates the control valve but actually has no way of knowing if the Turbo has changed or not except ultimately by changes in manifold pressure.

Any way it did occur to me that if the turbo worked the other way around to the 2.2 then with no vac it would be possible to get the symptoms as described and as under boost is a non damaging condition and probably a non poluting scenario as well the ECU wouldn't raise a fault code.

My guess is that the logic is reversed to the 2.2 that would be the same logic as in the earlier 2.0 except instead of the ECU driving the waste gate valve it drives the Turbo modulating valve. Now coming back to the earlier 2.0 and Top Donkeys description of turbo pressure sensor failure that makes sense but what indications do you get if the vacuum line just "drops off" the waste gate valve? I would put even money on nothing apart from lack of turbo boost.

cachaciero