help with N75

[georgemckee999]

hello everyone i hope someone can help me with my problem. I've had my leon FR150 about 6 months now and recently my power has been down.
i checked the maf, its good. cleaned the EGR (which was a git to do), but after searching the forum i found a few about the N75 and the N18. after disconnecting the N75 my car runs so well again. it has the power back and is much more responsive.
only problem is its put the engin management light on. Is this going to damage my car in anyway? should i change the N75, or is it something else and that just cured it?
any help would be fantastic

 

[terryliggins]

Loads on here regarding the n75. Although I'd get a n75 j pulls awesome

 

[georgemckee999]

Loads on here regarding the n75. Although I'd get a n75 j pulls awesome

So you think it's a faulty N75? What's different with the N75j?

 

[Lukesmith93]

I'd also like to know the difference with the n75j

 

[georgemckee999]

From looking at videos on YouTube it looks like it boosts harder and earlier on in the rev range.

 

[Lukesmith93]

How come I've seen n75 valves looking different? See ones that just look like a T piece but others have more branching off?

 

[terryliggins]

I would suggest npt running it without the n75. I dont know how you mean disconnected it. I would say it could be n75 but id research on the forum first

 

[Muttley]

N75 controls the turbo boost, by VNT vanes on most of the TDI's or wastegate on the petrol cars. If you disconnect it the turbo will run in lowest boost mode. I expect that you actually disconnected the N18 valve, which controls the EGR. Did you trace the pneumatic lines from the valve to check that they went to the turbo?

The N75 is just one component in the control chain from the ECU so it's hard to understand how changing it will make a difference.

 

[georgemckee999]

N75 controls the turbo boost, by VNT vanes on most of the TDI's or wastegate on the petrol cars. If you disconnect it the turbo will run in lowest boost mode. I expect that you actually disconnected the N18 valve, which controls the EGR. Did you trace the pneumatic lines from the valve to check that they went to the turbo?

The N75 is just one component in the control chain from the ECU so it's hard to understand how changing it will make a difference.

I'm quite sure it's the N75 as I have traced the EGR pipe work to the N18 and this is the valve next to it. See I have heard that it will only boost to 5psi with it disconnected, but mine feels so much better with it disconnected. I wouldn't say it boosted more, or less, but its much more responsive and seems to spool up quicker. The engin managerment light is on though so I'm just worried it might so some damage

 

[georgemckee999]

I would suggest npt running it without the n75. I dont know how you mean disconnected it. I would say it could be n75 but id research on the forum first

I just unplugged the wire harness to it. I left all the vacuum pipes connected

 

[terryliggins]

the car will boost to its minimum value with it disconnected, im pretty sure you cannot damage the car but your car will feel like a bag of s**t. There is a difference between the different N75 valves and a small amount of research on this site will show a lot of experiments showing the pro's and con's of each valve. My N75 was causing my boost to spike to 14-15 psi and then drop to around 8-10 and would continue to pulse under WOT. i replaced my standard valve for the J N75 valve and it runs sweet. i would suggest you change it for either the standard or the J. Just do some research on here and you will find loads.

 

[Muttley]

The vac lines for the ARL engine should look like this:

Of the two valves mounted on the firewall the N75 is nearest to the nearside of the car, N18 further in.

If the N75 is disconnected the vanes will relax to their wide open position, which is the max rpm position and gives poor boost at low rpm. The behaviour you're describing doesn't make sense to me and I'd want to check the vacuum lines to make sure they are in the right places and intact.

Terry, George has a TDI 150 and you have an LCR so the valves will be different: the petrol engines use boost pressure to actuate the wastegate, the TDI's use vacuum to move the vanes.

06A 906 283E for petrol engines, 1J0 906 627B for the TDI 150.

Both valves are performing the N75 function, converting the electrical signal from the ECU into a pneumatic signal to the turbo actuator, but are otherwise different.

 

[georgemckee999]

The vac lines for the ARL engine should look like this:

Of the two valves mounted on the firewall the N75 is nearest to the nearside of the car, N18 further in.

If the N75 is disconnected the vanes will relax to their wide open position, which is the max rpm position and gives poor boost at low rpm. The behaviour you're describing doesn't make sense to me and I'd want to check the vacuum lines to make sure they are in the right places and intact.

Terry, George has a TDI 150 and you have an LCR so the valves will be different: the petrol engines use boost pressure to actuate the wastegate, the TDI's use vacuum to move the vanes.

06A 906 283E for petrol engines, 1J0 906 627B for the TDI 150.

Both valves are performing the N75 function, converting the electrical signal from the ECU into a pneumatic signal to the turbo actuator, but are otherwise different.

wow, i know feel like a right kn*b! it was the N18 i disconnected as from pictures and description i found, i thought the N239 was the N18. that picture you just put up is by far the best one I've seen and shows it all.
after unplugging the N75 it does run like sh*t. but after this discussion and reading up i think i will get hold of a N75 J as they seam to be much better.
is there a reason the N239 leaks air when pushing the plunger on the EGR/anti shudder valve?
thank you so much for your help

 

[Muttley]

George, google for "N75 J" and you will find lots of pictures and descriptions of a valve that will not fit our cars. N75 J is a cobbled together description for the part number 034 906 283J. This is a part that will fit petrol cars and not TDI's.

You need 1J0 906 627B for the ARL TDI 150 engine. Anybody with an ASV, AHF (TDI 110) or ALH (TDI 90) will need a 1J0 906 627A to work with their smaller turbo.