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Discussion Starter #1
Hi from Denmark.
I have studied turbo and turbo regulation for my VW transporter T4 2.5 TDI ACV a lot the last 2 weeks, and found the most useful information on this forum - excellent forum A:
So I will try to ask some questions here.

I have just cleaned the EGR housing and changed some vacuum and pressure hoses. Did not help. EGR valve goes from closed to open at idle and seam to work fine.
Turbo running fine. Turbo gave lots of air and pressure when I started the engine without EGR valve, inter cooler and piping and let it run at app. 3000 rpm.
Wastegate valve is closed and seam tight. Actuator don't move, and no pressure at the pressure hose, so it is not trying to either. No difference driving the car with pressure hose on or of the actuator.

Is there a limp mode on this old 1998 T4 model?
If yes, something must be telling it to go in limp mode. From reading out the ECM no error codes at all.
Or should I rather look after faults on the fuel pump? Or fuel filter?

As the turbo seam okay, I should not give up - right :)
 

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Yes, your van can go into limp mode.

Are you sure you have connected up the vacuum and pressure line from the N18 and N75 solenoids correctly?

Are you able to move the wastegate actuator by hand?
 

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Discussion Starter #3
Yes, your van can go into limp mode.
Are you sure you have connected up the vacuum and pressure line from the N18 and N75 solenoids correctly?
Are you able to move the wastegate actuator by hand?
1. What can limp mode do? I mean wastegate is closed - especially when I drive without the pressure hose conected to the actuator.
Can the EMC influence the fuel pump?

2. Yes, N18 for EGR is working fine. Also for N75 the hoses are correct cornnected, but a functioning N75 is opening wastegate.

3. Yes, I can move wastegate actuator nicely by hand - although tough spring.

Look like okay boost pressure and nothing is regulating it down, but half power.

Is the fault rather at the fuel system then? Fuel pump? Fuel filter?
The later would be simple, but a bit embarasing :)
 

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Discussion Starter #4
Maybe I should try to connect pressure hose from turbo directly to turbo actuator.
If it moves the actuator we are 100% sure that boost pressure is there.
I will do that.
 

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Discussion Starter #5
Yes, your van can go into limp mode.
Are you sure you have connected up the vacuum and pressure line from the N18 and N75 solenoids correctly?
Are you able to move the wastegate actuator by hand?
Look like one of my posts from this morning has gotten lost, so I write again.

1. What is limp mode doing? I thought it opened the waste gate valve, but that is closed from start, and with no pressure hose on the actuator, the car still only have half power. Can it regulate one something else? The fuel pump?
2. Yes, all hoses are correct connected. N18 and EGR is working. N75 maybe not, but it is supposed to open waste gate valve in order to reduce power - I need the opposite!
3. Yes, I can move the waste gate actuator and valve by hand.

I made a test with the pressure hose from turbo directly connected to turbo actuator, but actuator did not move with engine at 3000 rpm unloaded.

Also made a new test with pressure hose from turbo disconnected from the actuator and I blocked the hose. Engine running fine, but only half power.

Maybe the fault rather is at the fuel system? Fuel pump? Fuel filter?
Last one would be simple - but a bit embarrassing..
 

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If the wastegate is not opening properly, then the ECU will reduce the fuelling to reduce the boost pressure to prevent damage to the engine, and therefore reduce engine performance. This should show a pressure deviation fault code I would have thought though.

Are all your pipes from the N75 in good condition with no splits in?
 

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Discussion Starter #9
Turbo ok - but still half power

If the wastegate is not opening properly, then the ECU will reduce the fuelling to reduce the boost pressure to prevent damage to the engine, and therefore reduce engine performance. This should show a pressure deviation fault code I would have thought though.
Are all your pipes from the N75 in good condition with no splits in?
I see, one more senario where the EUC just cut down the fun - so to speak :)
We are not getting any fault codes. It is not professional cabel and software we are using. It does show a fault code if I drive without air flow messure, and we can delete it, assemble and drive again and now it say no faults found.
Most hoses are changed now - the rest checked.

Assuming you have no smoke at exhaust, I'd guess its the air mass meter, common fault!
No smoke from engine and engine running fine. It has run app. 2500 km the last 3 weeks in this condition - but thats far too slow driving :(
It did smoke a lot when I connected the pressure hose directly from turbo to turbo actuator, and just had no pressure in on N75. With this connection and engine running at app 3500 rpm it did not move the actuator. I guess it need to be loaded before it realy gives presure and is supposed to open the wastegate valve?

I have learned a LOT about VW turbo the last weeks - a lot of it from this forum - very interesting a quite funny

My garage is in Denmark and now I have traveled to Norway to my job - by VW 2.5 (T)DI ;)

Next step should be buying an air mass meter, if that don't help, a new N75.
OR let a pro look at it.
 

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Re: Turbo ok - but still half power

I see, one more senario where the EUC just cut down the fun - so to speak :)
We are not getting any fault codes. It is not professional cabel and software we are using. It does show a fault code if I drive without air flow messure, and we can delete it, assemble and drive again and now it say no faults found.
Most hoses are changed now - the rest checked.


No smoke from engine and engine running fine. It has run app. 2500 km the last 3 weeks in this condition - but thats far too slow driving :(
It did smoke a lot when I connected the pressure hose directly from turbo to turbo actuator, and just had no pressure in on N75. With this connection and engine running at app 3500 rpm it did not move the actuator. I guess it need to be loaded before it realy gives presure and is supposed to open the wastegate valve?

I have learned a LOT about VW turbo the last weeks - a lot of it from this forum - very interesting a quite funny

My garage is in Denmark and now I have traveled to Norway to my job - by VW 2.5 (T)DI ;)

Next step should be buying an air mass meter, if that don't help, a new N75.
OR let a pro look at it.
MAF sensor is the favourite culprit for lack of power and no fault codes. Provided you dont have an air blockage somewhere.
 

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Discussion Starter #12
Really funny now...
MAF sensor is the favourite culprit for lack of power and no fault codes...
"...and no fault codes", that at once changed my mind to buy a MAF T:

Unplug the air mass meter if it runs better the meter is at fault...
WOW, it do runs better!
It continues to take rpm's, and don't have this dead feeling then my foot is half way down.
There still lack quite some hp's, but defenitely it runs better :D
 

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Discussion Starter #14
Update: Turbo ok - but half power

Finally 5 weeks later - all power is back A:
The EGR valve did not close, repair shop say.
Pressure never came over 0,6 bar (total 1,6 bar), but now it is over 2 bar.
Turbo, EUC, MAF ect. are working fine.
I get the car tomorrow - and the bill - I hope the T4 is as good as I have been told.
The plan is to drive with a blocked exhaust recirculation pipe, and ignore the faulty ERG valve. Wonder if that is good or bad?
 
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