How to test a turbo - help please

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Dom-300tdi

Active Member
Posts
181
Hi All,

I've been advised to check my turbo boost pressure to see if it is the cause of my landy being sluggish at low revs.

So a buy a boost guage and tee it in. I get that part, but what about the actuall testing.

Is is possible to test while the vehicle is stationary or do I actually have to be driving with a load on the engine for the readings to be meaningful?

What pressure should the boost gauge read and when should it be present? (300tdi engine)

Is the boost pressure directly linked to RPM? Should the boost be x ammount at 1000 rpm , y ammount at 2000 rpm, z ammount at 3000rpm ? Is there a table I can download somewhere which lists what values I should expect in each case?

At what rpm is the turbo supposed to spin up ? Does it wait until a setpoint has been reached before it energises?

What should I be looking for on the boost guage to tell me if my turbo is stuffed or not ? Ovbiously if its totally shot then there would be no boost at all. But how do I tell the difference between a properly working turbo and a turbo that is not functioning correctly, but still providing some degree of boost?


Sorry for all the quesitons, i've just realised i know sweet f.a about turbos and google hasnt bee much help for me today either.
 
Dom-300tdi said:
Hi All,

I've been advised to check my turbo boost pressure to see if it is the cause of my landy being sluggish at low revs.

So a buy a boost guage and tee it in. I get that part, but what about the actuall testing.

Is is possible to test while the vehicle is stationary or do I actually have to be driving with a load on the engine for the readings to be meaningful?

What pressure should the boost gauge read and when should it be present? (300tdi engine)

Is the boost pressure directly linked to RPM? Should the boost be x ammount at 1000 rpm , y ammount at 2000 rpm, z ammount at 3000rpm ? Is there a table I can download somewhere which lists what values I should expect in each case?

At what rpm is the turbo supposed to spin up ? Does it wait until a setpoint has been reached before it energises?

What should I be looking for on the boost guage to tell me if my turbo is stuffed or not ? Ovbiously if its totally shot then there would be no boost at all. But how do I tell the difference between a properly working turbo and a turbo that is not functioning correctly, but still providing some degree of boost?


Sorry for all the quesitons, i've just realised i know sweet f.a about turbos and google hasnt bee much help for me today either.
Click to expand...


If you slacken off the hose clip where the intercooler pipe joins the inlet manifold (so it is very loose) and break the seal on the pipe so you can twist it you can then start the engine and when you floor the throttle the pipe will bulge and air will rush out of the joint.:)
 
Forget all that boost guage nonsense. At tickover squeeze the rubber pipe between the top of the intercooler and the inlet manifold. Should be squidgy. Get someone to rev the engine, pipe should inflate and go hard. Max boost should be about 2000rpm if I remember correctly.
 
AFIK, there's no table of figures, engines generally are not that 'specific'. When you have your boost gauge fitted, you need to go for a drive. Warm her up then find a bit of a hill where you can drive at a good throttle opening and about 2800-3000rpm in 3rd or 4th gear, you need to get the engine 'working' but not ragging on it of course.

You should then see about 11.5 to 13psi boost on the gauge.

The boost should barely register until about 1500rpm then it should kick in and climb steadily to about 3000rpm where it will level out at max boost.

My one kicks in at 1700 and tops out at 2900 and 12psi of boost now.

If you see the gauge start to climb then stop it may point to the inlet pipes delaminating and blocking the flow or a duff actuator but that is unusual as a busted one would likely jam closed and lead to overboost, on the other hand if the actuator rod has come off the wastegate shaft then it will probably not have any boost at all as the wastegate will just be flapping around in the breeze.

Turbos are pretty simple things as they only have one or two moving parts but they make a massive difference to a diesel engine.
 
The wastegate is located within the turbine housing of the turbo ( you'll see a round cylinder with a rod coming from it to a small arm - thats the waste gate actuator and rod ) when the boost pressure reaches a set pressure the actuator opens the waste gate , so the exhaust gasses bypass the turbine .
 
So you are saying that the turbo is always engaged and the purpose of the wastegate & actuator is to disable the turbo to stop it providing too much boost?

What drives the actuator and where is the pressure set?

Is it possible to adjust the turbo to make it start spinning at lower revs or is it litrally a case of when the revs are high enough there becomes enough exhaust pressure to start spinning the blades?
 
turbos constanly driven by exhaust gases.the faster the exhaust gas the more boost(manifold pressure) =more air forced in the cylinders.

turbos do something called "Spool up" this is the time it takes to spin up. the longer it takes the more turbo lag you have.

the wastegate has a pre-set pressure. this will open at a pre set boost level.

a bigger turbo will produce more power but take longer to spool up and smaller spin up quiker but less power.
 
To make a turbo spin up quicker you are lookikng at fitting a different compressor wheel or fitting anti-lag......this will make the car run rich,spit flames like a rally car and the turbo will last about 5k before failure.:D
 
juiceyv8 said:
To make a turbo spin up quicker you are lookikng at fitting a different compressor wheel or fitting anti-lag......this will make the car run rich,spit flames like a rally car
Click to expand...
Sweet! :D

Thanks for the replys. I think i'm starting to understand this a bit now.

So is it possible to see the wastegate without removing the turbo from the engine and/or dissassembling it? i.e is it possible to check just by looking that the wastegate is operating correctly and hasnt jammed in one position?

Assuming there was a problem with the wastegate or actuator, is that something which can be easily repaired or is it a case of replacing the entire turbo unit?
 
actuators can be replaced. If the turbo has failed then it will need a re-build new bearings etc asuming the casing isnt cracked.

[nomedia="http://www.youtube.com/watch?v=puGCda4ThvU"]YouTube - ford sierra anti lag[/nomedia]

[nomedia]http://www.youtube.com/watch?v=KzG9UGvj-10]YouTube - Audi S2 Coupe [Drag Race 1/8 Mile[/nomedia]

:D:D:D:D
 
Without a boost guage so you can see what the turbo is actually doing you are just ****ing in the wind. All this 'check the air rushing out the pipe' advice is comical :D

Boost is not directly related to revs otherwise when you changed down a gear you would get a massive surge of power :doh: :D

Fit the guage and then floor it in 3rd gear, watch what the boost does as the revs rise if it gets to a point and then keeps dropping off whilst the throttle is open then you may have a boost leak (split pipe, cracked intercooler etc) Likewise if it only manages to top out at a low psi that would indicate a leak or the wastegate is jammed open.
 
I did the 'squeeze the big pipe and rev the engine' test this morning and was happy to see the pipe inflated and that the turbo was in good working order.

Then I got home, read the post above and how i'm back to square one. I have plenty of pneumatic guages lying around that go up to 30psi , however I browsed the haynes manual this afternoon and it said i need a vacuum guage not a positive pressure gauge.

This seems awfully complicated for something that many people say is simple.
 
No, if its a 300/200tdi then you need a PRESSURE gauge not vacuum, 0-20 or 0-30 will do fine, the max boost is around 14psi more likely 12psi so either will work.

Plumb it into the pipe that goes from turbo to fuel pump or for more accurate info, into the plenum / inlet manifold, i think there is a standard threaded hole on the back of the 300 plenum with a blanking plug in it.

Then slap the gauge on the dash or get the wife to hold it like i did and go for a drive, you will then see the relationship between throttle and boost or the fact that you have no boost as i found!:doh:

Dave
 
Dom-300tdi said:
I did the 'squeeze the big pipe and rev the engine' test this morning and was happy to see the pipe inflated and that the turbo was in good working order.

Then I got home, read the post above and how i'm back to square one. I have plenty of pneumatic guages lying around that go up to 30psi , however I browsed the haynes manual this afternoon and it said i need a vacuum guage not a positive pressure gauge.

This seems awfully complicated for something that many people say is simple.
Click to expand...

A proper boost gauge will show the negative and possitive boost because on idle there will be a vacuum. But for temporary checking if boost is achieved then a possitive gauge is fine.
 
You will not get correct boost unless te engine is under load. I would be very suprised if you get anywhere near peak boost at idle.

Turbos work on exhaust gases, so your low power at low revs will be at the point the turbo will be spinning the least. Depends what you mean by low RPM really.

One advantage of using a boost gauge is you can see if it holds boost well - not just the amount of boost reached. A turbo can be pretty shagged and on the way out and give decent boost figures. As mine did befre it virtually exploded.

You could always take the intake pipe and exhaust manifold off the turbo and physically inspect it - check for excessive play in the shafts (both side to side and in-out), broken fins, gauges on the inside of the casing.
 
"a bigger turbo will produce more power but take longer to spool up and smaller spin up quiker but less power"
Click to expand...
- thats a bit of a generalisation really. I have had a larger turbo built for my car, which spools up faster, with more boost, at a lower RPM, than my stock turbo. Its not just about size, it is the efficiency of the turbo, the type of wategate/actuator, the cooler setup, how the boost is controlled etc etc.

Assuming there was a problem with the wastegate or actuator, is that something which can be easily repaired or is it a case of replacing the entire turbo unit?
Click to expand...

Easiily repaired? Not sure about that, depends on your level of skill. If you are looking to get a turbo tested/repaired, I would strongly recommend Turbo Dynamics, who not only repair turbos (from any make or model), but also sell uprated turbos or can build a turbo to your specification for example a turbo that spools at lower RPM, holds boost for longer and higher - but using your original manifold etc - how does that sound? :D

I agree with tuskenraider, squeezing the pipe is not really going to prove much at all!
 
I dont know about Landy turbos but I have found generally you can get a replacement for not much more than getting one rebuilt as well (My experience comes from working with the Garrett T2* series of turbos)
 
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