Wastegate weirdness

[molgrips]

Hi folks, haven't been on for a while but now I have a good one for you.

I've got a 1.9 AAZ in my Passat, and I have a vacuum hose coming from somewhere (presumably some control solenoids or something) that goes to a T piece, one side of which operates the EGR valve and the other the turbo wastegate.  So the other day I noticed that the bit that went to the EGR valve was all broken and not airtight, resulting in no pressure to the EGR valve or the wastegate.  So I assume that means that the EGR valve was shut and the wastegate fully shut all the time.  The car was driving ok, getting about 13psi boost.  I replaced the hose though and it totally broke the car.  I basically had no boost.

Specifically though, I had a fair amount of boost driving up my hill slowly but when I hit the highway something shut off and I then got no boost at all and tons of smoke.  Also a rattling noise that sounded like too much timing advance.  When I'm looking at the wastegate lever with the bonnet open, if I connect the hose it moves to the left, then when I blip the engine it flips to the right for a few seconds (closes?) then slowly goes left again (shuts?).

So I really can't imagine what's going on in there.  Which way does the lever go to open or close the wastegate?  When I hit the pedal it should CLOSE right?  To put more EG through the turbo?  And then it should open when cruising to let the EG flow out better...?

Can someone tell me how it's meant to work?  Thanks.

[molgrips]

Oh, found out something else.  The "electric changeover valve" is turning on boost when I hit the throttle, but only for a couple of seconds then it clicks off again.  I don't think it's meant to do that..?

[molgrips]

Right, I think the timing is too advanced, despite it being perfect before I replaced the hose.  Could it be that now the EGR is working, the timing needs to be retarded?  That would mean that EG in the charge would burn faster, that doesn't make sense at all.

I dunno, it's late.. I need to calm down...

[Vincent Waldon]

Oh, found out something else.  The "electric changeover valve" is turning on boost when I hit the throttle, but only for a couple of seconds then it clicks off again.  I don't think it's meant to do that..?

Yup, you probably have the Eco AAZ with a part-time turbo... the engine control module makes up its own mind as to when you need the turbo... and perhaps for some reason it's confused.

If you track down the wastegate on the side of the turbo you should see two hoses... one that goes back to the intake manifold side of the turbo and the other that goes to a solenoid valve.  Disconnect the one that goes to the solenoid and position it so that it's permanently vented to atmosphere... and you'll have a permanent turbo.

[molgrips]

the engine control module makes up its own mind

Do I have an engine control module?  I thought it was totally mechanical.  Although, the valve is electrically operated from somewhere...

I connected my boost gauge up to the wastegate actuating line (it reads -ve as well as +ve) so I could see what was going on as I drove.  The wastegate only starts working for a bit AFTER I've lifted off the throttle for more than about five seconds.  Then, when I put my foot down again I get a bit of boost for a second or so then off again.  It can't be designed to work that way?

[Vincent Waldon]

the engine control module makes up its own mind

Do I have an engine control module?  I thought it was totally mechanical.  Although, the valve is electrically operated from somewhere...

Yup, it's not a ECU per se, but a big-ass relay-looking module (#136 iirc?) on the fuse panel... kind of a glow plug control on steroids.  It's the controller that listens to the drivers side door and turns on the glow plugs, and it also controls the emissions systems, including the electrical valve that actuates the turbo and the extra solenoid valve at the front of the injection pump.

I've never run a vehicle with it connected personally... my brother had one and it sure felt like the turbo was only on briefly, but we didn't have a boost gauge at the time so I can't say exactly how it felt in real life.  As I understand the system the main input to the emissions part of it's decision-making process is the throttle switch on the top of the injection pump, and the Bentley has the procedure for adjusting when it clicks in.

T'were me I'd pull the vacuum hose off the wastegate and see what happens to my symptoms... if you've got a boost gauge you're in good shape to quickly see if it makes a difference.

[molgrips]

Right, for all 1 of you who're interested I've figured it out (cheers for commenting btw)

With the vacuum hose connected up as it should be, the car's undriveable.  Tons of smoke and literally no power - can't even hit 70mph.  So there's no way VW designed it like that.  But anyway, what I think is happening is that the wastegate is meant to be opened gradually by air pressure from the high pressure side of the turbo.  The vacuum operated actuator is meant to just open for a few seconds to make sure it spins up as fast as possible.  So, my conclusion would be that the hose leading from the high pressure side of the turbo to the wastegate is either leaking or blocked with crud.  So the wastegate closes when the vacuum thing operates it but the air pressure is meant to keep it closed until full boost is reached, but it's not working leaving me with no boost.

Interestingly enough, the car runs smoother with the wastegate fully open - it's got rid of that annoying exhaust resonance I was hearing, presumably caused by higher back pressure caused by the turbo...

This is my theory anyway, we will have to see if it holds up