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Afternoon guys,

I was driving on the motorway this afternoon and activated cruise control at 65mph, and held the stalk up to increase speed to an indicated 80mph. I did this first on the flat, and it was fine, got up to speed quickly and maintained it happily. Anyway I hit the inevitable traffic which was stop and go, but after faffing for a good 20 minutes it opened up again. So got up to around 55 in 5th and pushed up on the stalk which resumes memorised speed (80mph) - this time I was on a hill so I watched the boost gauge and to my surprised it spiked up to 25psi before settling at the normal 20-21psi wastegate pressure. As soon as it hit 25psi I got a check engine light which I knew would be an overboost code. After a few startups, the light extinguished so I thought I would find a long hill and try to replicate the scenario. On level road its fine - boost initially spikes to 22psi then the wastegate starts to open and it settles at 20psi. But as soon as I got onto a hill and tried to increase speed with C/C, the boost spiked to 25psi before returning to 21psi stable which triggered another MIL.

I believe Eric had this issue on his 2.2? The car performs fine with plenty of pulling power and no odd noises, so I reckon a potential vacuum leak. I'm going to remove all but the turbo electrovalve soon and get rid of all those vacuum lines for the air doser and EGR which should simplify the system a bit and make for more immediate availability of vacuum. My suspicion is that when in top gear, once the cruise control detects that the user wants to increase the speed it wants to do that as rapidly as possible, and immediately closes the wastegate to try to generate boost as quickly as possible and sometimes doesn't open the wastegate in time, leading to a transient overboost problem using C/C on inclines. I'm also going to clean the tube that feeds the MAP sensor, as there could be carbon/sludge in there which is restricting the pipe.

Any thoughts?

Overboost fault conditions:



Kind Regards
Benjamin

Yes, more or less.....

It's got a variable turbo & no waste gate. The turbo actuator is vacuum operated and needs vacuum to reduce the boost.

The problem will be down to either a vacuum leak, or something limiting the rate the vacuum can be applied to the turbo.
(Mine was a split diaphragm in the swirl actuator, GingerMagic's was a partially blocked vacuum restrictor in one of the vacuum pipe tee-pieces).

Only trick is finding it - since your's only does it climbing a hill, you have a minor leak / restriction.

Don't forget I have the 110, not the 2.2. I think once I've redone the vacuum system to suit the 1 required electrovalve for the turbo, it should be much better. Is there a restrictor on the 110?

The restrictor is built into the 'T' piece that clips onto the vac pump, and also on the servo end.

Once you have simplified the vacuum system, you only need a 2 way outlet clip on the vac pump ( 1 to turbo EV, 1 to servo ) which will hopefully make things better.

Do you have access to a hand held vac pump? You can measure the vacuum before and after the EVs to eliminate them as suspects

fattail95 wrote:Don't forget I have the 110, not the 2.2

Is it the same on the 110 though? Vacuum to open the wastegate or vacuum to close it?

I believe if you are overboosting, the wastegate isn't opening fast enough, or not at all - the vacuum reduces the boost by opening the wastegate...

One sure way to find out - disconnect / plug the vacuum supply pipe to the turbo/wastegate control valve and CAREFULLY test.
No boost = vacuum need to close wastegate.
Normal/overboost = vacuum needed to open wastegate.

WHen the mechanics accidentally knocked the vacuum line off the turbo on mine it was a slug, so I guess it needs vacuum to close