Weld the wastegate shut?

[sunbeam alpine]

I'm slightly worried that I might be starting an ambiwlans/tyre rating thread here, but I'm thinking of welding/fixing a turbo wastegate shut, and would welcome comments/advice/pisstaking.

The vehicle is a Fiat Ulysse people-carrier - not a high performance beast at the best of times - owned by a good friend, which is seriously down on power. It has no acceleration, gets up to max 60 mph on the flat, dropping seriously when faced with a hill, even with your foot to the floor.

Code reader gives "turbo pressure low" and after removing and testing the turbo, the wastegate is permanently open. It should be closed by vacuum on a pipe (read big mass of spaghetti running all over the engine compartment, with various valves/sensors etc.), and we've been unable to find a fault or a hole in the pipe. The turbo itself seems to be fine - no end float, tiny oil leak, but nothing serious.

Given that this car is mostly used for ferrying his kids to school and local runs, would it be mad to consider welding up/fixing the wastegate closed?

I've been googling but can't find any info regarding the revs at which the wastegate should open to release the extra pressure. I was thinking of suggesting they keep below 3500 rpm for example.

They only want/need to run the car for another year or so, so he doesn't want to spend a huge amount on parts/daignosis, and we've reached the end of our abilities

[hairykrishna]

I'd suggest a replacement wastegate rather than fixing it permanently. A wastegate is a boost pressure regulating mechanism. When it opens depends on the load on the engine (i.e. the volume of exhaust gas) and the pressure that's being developed rather than directly on the revs.

I'm not familiar with that car but, depending on the turbo system in question, fixing it closed might let it develop enough boost pressure to cause damage.

[Mastodon2]

Surely if the wastegat is the issue and you weld it shut, the cat will boost normally, but then will not vent boost when you let off the throttle? Could have an interesting effect on engine braking I'd have thought.

[kambites]

I'm far from an expert, but fixing a waste-gate closed sounds like a recipe for destroying your turbo.

[Ian974]

In my uneducated opinion I'd imagine that would cause as much if not more issues than having it stuck open. It needs to open and close. Not sure of the solution though

[davepoth]

It's likely the pipework or the solenoid. What code exactly are you getting?

[sunbeam alpine]

hairykrishna said:

I'd suggest a replacement wastegate rather than fixing it permanently. A wastegate is a boost pressure regulating mechanism. When it opens depends on the load on the engine (i.e. the volume of exhaust gas) and the pressure that's being developed rather than directly on the revs.

I'm not familiar with that car but, depending on the turbo system in question, fixing it closed might let it develop enough boost pressure to cause damage.

The wastegate itself is fine - my local garage has a turbo tester, and it opens and closes fine on their test bank. The wastegate is open by vacuum which should be supplied by a pipe (but isn't). This pipe runs from under the engine to a sort of switch/valve system above the radiator. There's an absolute mass of pipes/sensors which are difficult to test. What I can say is that there are no holes in any of the pipes.

Interesting comment of yours about revs vs. pressure - I haven't thought it through properly, have I?

[hairykrishna]

Mastodon2 said:

Surely if the wastegat is the issue and you weld it shut, the cat will boost normally, but then will not vent boost when you let off the throttle? Could have an interesting effect on engine braking I'd have thought.

No - that's not what a wastegate does. It's essentially a bypass for the turbo - it's job is to limit the amount of boost pressure developed. Welding it shut will prevent any bypassing and the maximum boost pressure will be determined by something else, probably exhaust back pressure. It'll raise the power until something gives.

[anonymous-user]

"Considering the car is used for the school run" i would suggest it is just left alone and driven as it is.


If you weld the w/g shut, you will very quickly be having to find at least a new turbo, and almost certainly a whole new engine for it.


Either:

1) leave it alone

or

2) Get it fixed by someone who knows what they are doing.


ETA, BTW, the gate is held shut by the spring, and blown open by boost pressure. If the boost control solenoid has failed, the car will be running at the "min boost line" as it won't be venting any pressure off the wastegate capsule.

Edited by anonymous-user on Monday 25th February 18:38

[sunbeam alpine]

davepoth said:

It's likely the pipework or the solenoid. What code exactly are you getting?

Don't have the code any more (and can't run the car at present as the turbo is off). It's a real spaghetti of pipes - I've checked the pipes for leaks and can confirm they're OK.

There seem to be 3 solenoids in a block over the radiator. If I could find that block in a scrappy I swap it over, but I've called all over without success.

[John D.]

Are you going for a qualifying lap?

[EmmaJ]

From my limited understanding once you've built boost pressure and then close the throttle without a wastegate that pressure has nowhere to go and will eventually either force a pipe off or start to despool the turbo. Either way it won't be a good situation, I'd investigate other options before resorting to welding the wastegate shut.

[hairykrishna]

sunbeam alpine said:

The wastegate itself is fine - my local garage has a turbo tester, and it opens and closes fine on their test bank. The wastegate is open by vacuum which should be supplied by a pipe (but isn't). This pipe runs from under the engine to a sort of switch/valve system above the radiator. There's an absolute mass of pipes/sensors which are difficult to test. What I can say is that there are no holes in any of the pipes.

Interesting comment of yours about revs vs. pressure - I haven't thought it through properly, have I?

I'd suggest changing that valve then! Fixing the wastegate closed might be bad news.

It could be that with it fixed that it still doesn't develop enough pressure to cause problems. On the other hand it might easily develop enough boost that the injectors can't keep up and you get catastrophic levels of detonation! It'd solve the power problem, briefly...

[Jonny_]

Would more than likely go like the clappers, at least briefly.

Then it's down to luck as to whether it pops a hose, holes a piston, blows the head gasket...

Seriously, I wouldn't chance it.

[sunbeam alpine]

Max_Torque said:

"Considering the car is used for the school run" i would suggest it is just left along and driven as it is.

This was my suggestion as well, unfortunately my mate persuaded me to help look at it!

Max_Torque said:

If you weld the w/g shut, you will very quickly be having to find at least a new turbo, and almost certainly a whole new engine for it.

This was what I was asking - there are some sites I found on Google which seemed to recommend it (!), others warn of damage.

Max_Torque said:

Either:

1) leave it alone

Too late

or

Max_Torque said:

2) Get it fixed by someone who knows what they are doing.

Unfortunately he can't afford this at present!

[LandingSpot]

Try a new actuator? Look closely at the pipes that connect off the actuaor and he snail of the turbo. They can crack at the ends causing leaks which can be unseen unless removed and unheard because you cannot load the engine properly while stationary without a rolling road.

Plus if you weld the wastegate shut, you'll never have a hope of producing hose wastegate chatter noises

[George111]

Fix it properly or leave it alone . . . bodged things invariably cost a lot more to fix than they would have if done properly in the first place.

[Si_steve]

This better be a wind up?


The heat created in the inlet side of things alone by letting the turbo boost to whatever the hell it can is enough to cause problems (not little problems....big big ones). Once the turbo tries to boost past its efficiency, it in effect becomes a heat pump. Extra (unregulated) heat in the combustion cycle usualy equals new engine.....Seriously if you don't know how to fix it, leave it to someone who can.

[sunbeam alpine]

I'll try to get a price for a new actuator block tomorrow. I've tested all the pipes by disconnecting them and blowing down them (like blowing down a straw) and they're not leaking. I don't know how to test the actuators themselves.

[Noisy]

The engine will probably hit boost cut soon at the turbo spools up with the wastegate stuck closed, the wastegate should be closed until the turbo is supplying the right level of boost then the wastegate will open, it’s not vacuum but boost pressure that opens the wastegate.