Thread: Turbo Conundrums

Right. So i checked the boost pressure, measured at the tee where the lines go the injector pump and wastegate actuator - and nothing! No boost at all. Well it creeps up to a bit over zero PSI at about 1500RPM.

So i checked the turbine still has fins, which it does and it looks fine.

I am about to plumb the turbo outlet direct to intake manifold to check if intercooler has a giant leak or something. I have the fan shroud on at the moment so it is hard to find air leaks, but i suspect a big air leak like that would be noticeable...

I blew air the line to the boost diaphragm on the injector pump just to check it wasn't blocked and not letting fuel through.

The engine idles and sounds great, just has absolutely no boost and no power above 1500RPM.

So i pulled the cover off the boost controller on the injector pump and checked the diaphragm for splits, thinking that if it was it would not get enough fuel which would result on loss of power and less exhaust to drive the turbo to make some boost. The diaphragm looks fine.

I then plumbed up some pipe and bypassed the intercooler thinking there could be a hole/split in it. But still no boost.

I also checked that the turbo compressor turbine was spinning when the car was idling and it was - so it looks like it is still connected.

All i can think of now is a fuel problem... Perhaps it is not getting enough fuel at higher RPMs...?

So still chasing down fuel problems; i pulled the pickup out of the tank to check (I have been meaning to do this as maintenance anyway) but it is all clean as a whistle.

Then i swapped out the fuel filter - but still no power at high RPMs/no boost at high RPMs...

Lift pump is the next possibility i presume? I have heard lift pump can fail and not supply enough fuel at higher RPMs. Interestingly this would make it leaner and at mid RPMs (1500) perhaps it would feel more powerful than usual - and maybe that's why it feels like the boost has shifted down to below 1500RPM...

Originally Posted by Finnius

Righto folks, I have an interesting problem for you.

Today the turbo in my 300Tdi has decided to kick in at 1500RPM or even less, instead of 1800-2000RPM.
The result is that you can get up to speed quickly but it cant go faster than 80kmh and when you to put the pedal to the floor nothing happens.

So i immediately thought - the wastegate is seized/stuck open or the actuator is kaput. So I checked it and the wastegate is shut.
I put compressed air to the actuator and it doesn't open.

So pulled it off and you can hear rust or something rattling around inside the actuator.
I will put on a new actuator on of course, but can someone help me understand how having the actuator stuck shut caused the turbo to kick in sooner???
Shouldn't it have just got to peak boost like normal - but then carried on boosting.... Because the wastegate would have been shut at 1500RPM anyway...

Just want to check the actuator is the only thing that needs replacing.

All i can think of is that the actuator has been on the way out for a while, possibly stuck a bit open and that now it is stuck shut i am noticing the difference at the lower RPMs and thinking it is boosting more when it actually isn't. Once i get the new actuator i will put my boost gauge on and check it.

Actuator stuck shut will choke the engine at higher RPM's - not enough exhaust flow.

Did you check the wastegate is free to move when you disconnected the actuator?

Kicking in at lower RPM's is strange, I have had a boost compensator stick partially open, overfuelling it at idle, it will smoke a bit if this is the case. note the orientation of the diaphragm and remove it, if you have to lever it up, the pin below is sticking.

Originally Posted by Finnius

Right. So i checked the boost pressure, measured at the tee where the lines go the injector pump and wastegate actuator - and nothing! No boost at all. Well it creeps up to a bit over zero PSI at about 1500RPM.

So i checked the turbine still has fins, which it does and it looks fine.

I am about to plumb the turbo outlet direct to intake manifold to check if intercooler has a giant leak or something. I have the fan shroud on at the moment so it is hard to find air leaks, but i suspect a big air leak like that would be noticeable...

I blew air the line to the boost diaphragm on the injector pump just to check it wasn't blocked and not letting fuel through.

The engine idles and sounds great, just has absolutely no boost and no power above 1500RPM.

Some of these lines are known for splitting now they are getting old. The wastegate actuator and fuel pump diaphragm should be sealed, run 15psi in from the other end and listen for leaks.
Usually if something like this pops up I look back over whatever I have mucked with most recently to see if I have made a mistake.

Originally Posted by Finnius

So i pulled the cover off the boost controller on the injector pump and checked the diaphragm for splits, thinking that if it was it would not get enough fuel which would result on loss of power and less exhaust to drive the turbo to make some boost. The diaphragm looks fine.

I then plumbed up some pipe and bypassed the intercooler thinking there could be a hole/split in it. But still no boost.

I also checked that the turbo compressor turbine was spinning when the car was idling and it was - so it looks like it is still connected.

All i can think of now is a fuel problem... Perhaps it is not getting enough fuel at higher RPMs...?

The 90 degree intercooler pipe is known for delaminating and blistering on the inside, which chokes the engine.

Originally Posted by Finnius

So still chasing down fuel problems; i pulled the pickup out of the tank to check (I have been meaning to do this as maintenance anyway) but it is all clean as a whistle.

Then i swapped out the fuel filter - but still no power at high RPMs/no boost at high RPMs...

Lift pump is the next possibility i presume? I have heard lift pump can fail and not supply enough fuel at higher RPMs. Interestingly this would make it leaner and at mid RPMs (1500) perhaps it would feel more powerful than usual - and maybe that's why it feels like the boost has shifted down to below 1500RPM...

Originally Posted by SSmith

Actuator stuck shut will choke the engine at higher RPM's - not enough exhaust flow.

Did you check the wastegate is free to move when you disconnected the actuator?

Kicking in at lower RPM's is strange, I have had a boost compensator stick partially open, overfuelling it at idle, it will smoke a bit if this is the case. note the orientation of the diaphragm and remove it, if you have to lever it up, the pin below is sticking.



Some of these lines are known for splitting now they are getting old. The wastegate actuator and fuel pump diaphragm should be sealed, run 15psi in from the other end and listen for leaks.
Usually if something like this pops up I look back over whatever I have mucked with most recently to see if I have made a mistake.



The 90 degree intercooler pipe is known for delaminating and blistering on the inside, which chokes the engine.

Yep, checked the wastegate was free - moves nice and easy.

Yep marked diaphragm when i removed it - I don't think the pin is spring loaded or anything, i think it is just free floating right? The pin moves out when i move the throttle.

I ran 15psi through the actuator, boost diaphragm lines etc. I ran 15psi to the diaphragm when the engine was running, but it made no noticeable difference to the sound of the engine at idle or higher revs?? Should the difference be audible?

Yep, pulled all intercooler hoses etc. They are new silicon ones anyway.

Haven't changed much to do with fueling or trubo recently. Just got back from about 800km trip on the highway never missed a beat, turbo was working fine at 1800RPM. But since then i swapped out the harmonic balancer?!? Cant see that causing this though? Went to start it this morning and revved it up and noticed the turbo kicked in at 1500RPM! Set off down the highway and found in undrivable at highway speeds, no power, foot to floor, it would get too hot running like that and not efficient without turbo so came home...

It baffling me! The engine runs sweet as, no smoke no odd sounds. By the tachometer there is a big jump at 1500RPM BUT by the boost gauge there is basically no boost at all!! Boost gauge tested with another air source and working fine.

I should point out that i think the turbo possibly sounds slightly more whinier/whizzier/whirring than normal.

Originally Posted by Finnius

Yep, checked the wastegate was free - moves nice and easy.

Yep marked diaphragm when i removed it - I don't think the pin is spring loaded or anything, i think it is just free floating right? The pin moves out when i move the throttle.

I ran 15psi through the actuator, boost diaphragm lines etc. I ran 15psi to the diaphragm when the engine was running, but it made no noticeable difference to the sound of the engine at idle or higher revs?? Should the difference be audible?

Yep, pulled all intercooler hoses etc. They are new silicon ones anyway.

Haven't changed much to do with fueling or trubo recently. Just got back from about 800km trip on the highway never missed a beat, turbo was working fine at 1800RPM. But since then i swapped out the harmonic balancer?!? Cant see that causing this though? Went to start it this morning and revved it up and noticed the turbo kicked in at 1500RPM! Set off down the highway and found in undrivable at highway speeds, no power, foot to floor, it would get too hot running like that and not efficient without turbo so came home...

It baffling me! The engine runs sweet as, no smoke no odd sounds. By the tachometer there is a big jump at 1500RPM BUT by the boost gauge there is basically no boost at all!! Boost gauge tested with another air source and working fine.

I should point out that i think the turbo possibly sounds slightly more whinier/whizzier/whirring than normal.

Sounds like the diaphram/pin is working properly. No it shouldnt change anything at idle by putting air in that line. Try it with the engine off to listen for air leaks. Mine split at the Tee giving similar symptoms.

So you can feel the turbo kicking in, but no boost on the gauge?

Have you replaced the actuator already?

Even with the lift pump not working properly you should see some boost, it would be down on power but not absolutely undriveable.

Turbo whizzing/whining means that it is at least working, question is why the engine not getting boost......

My understanding of the lift pump(via info on this site) is that it's main job is to prime the injector pump mainly at startup or steep inlclines(or something like that).
Once the engine is running, the main fuel pressure is via the IP. So apparently you could still drive along fairly nicely with a failed lift pump.

If you have fuel issues, then it could be the IP! (for your wallets sake. . hope not!)

Do you have a boost gauge fitted as an instrument?(or are you using some kind of portable gauge).

Originally Posted by Finnius

....

Yep marked diaphragm when i removed it - I don't think the pin is spring loaded or anything, i think it is just free floating right? The pin moves out when i move the throttle.

....

This bit is a bit of a worry.
Are you referring to the turbo compensator fuelling pin(on the diaphragm). There should be a large spring between it(underside) and the starwheel. It sits in a groove on the starwheel and just sits freely on the underside of the diaphragm plate.
Makes the diaphragm spring loaded(if you push it down, it springs back up).

Thanks guys.

Yes, swapped the actuator out and it works fine when i run compressed air into it.

Yeah the boost gauge is just portable, but works fine when i put compressed air into at at 14psi.

The pin i was referring to is the one that rides up and down on the cone at the bottom of the diaphragm, and yep the spring and plastic collar are all there under the diaphragm.

Yep, tested the lines for air leaks with the car off, no leaks.

And yep at 1500RPM the revs take off all by themselves up a couple of hundred up to 1750RPM, just like the turbo used to do at 1800RPM.

Nothing really makes sense, if the IP is failing why the big whooosh at 1500RPM and everything on the turbo checks out fine. However the turbo runs on exhaust gases, so presumably if there is not enough fuel it wont run fast enough to make boost. Does anyone know if it will make boost even with fuel mix messed up? I.E. With just the capacity of cylinders being blown out exhaust enough to make boost?
That would tell me if it is fuel or turbo i guess?