Boost issue

[jamie1]

Im not 100% sure if it would throw a fault code up as im new to these cars and am learning my ways, but it might be worth trying a different n75 as they are fairly cheap to pick up and it does sound to me like an intermittent sticky solenoid?

Im sure someone would be able to tell you if they throw up a code? Even still it might be worth a shot mate.

 

[sambryant]

What u need to do is check for boost leaks, then run with the maf unpluged. Take it from there before spending any money. I dont think its the n 75 as there not prone to die, where as the maf is common to die.

 

[jamie1]

Which is fair enough, but wouldn't maf do it all the time rather than being under load?

Plus, just because n75s aren't prone to failing, doesen't mean they dont.

 

[jamie1]

If floor it in 2nd or 3rd then boost doesn't seem to appear until betweek 3k and 3.5k rpm, then when it does it's very sudden, like someone just switched the turbo from 0 to 100%.

If it had a boost leak it wouldn't do this.

 

[8bit]

a faulty N75 will cause boost problem as it helps contol boost

Read the question again, I asked would a faulty N75 cause a fault code, I already know it can cause boost issues...

 

[Pyro]

Which is fair enough, but wouldn't maf do it all the time rather than being under load?

Plus, just because n75s aren't prone to failing, doesen't mean they dont.

If a MAF is on it's way out the it do it all the time some MAFs will some won't

If it had a boost leak it wouldn't do this.

A boost will do this I'm in the proceses of irradiating mine and ATM I'm get full boost and a nice steady drop then change gear and and it peaks then drop like led so it all depends where the leak is if it's only small then it might no always leak a big one will be constant tho Im with sam in this presure test it try the maf check the spark plugs and if you can swap your N75 with someone to check that if your near Swindon then I have a spare you can try

 

[8bit]

If it had a boost leak it wouldn't do this.

That's what I was thinking, given it's only intermittent and when I do hit about 3200rpm in 3rd the boost comes on very suddenly, like the turbo has just gone from stopped to flat out instantly...

Going to see if I can get the car scanned for codes and logged at the weekend, also will try sambryant's suggestion of driving about for a bit with and without the MAF connected, see if there's any difference.

Thinking about sambryant's limp mode issue (I did read some of your threads on that, glad you got it sorted btw) I guess dying MAFs could possibly give intermittent issues. Just done some searching/reading on N75s tho and looks like a good few folk have had them fail too so I guess that's still a possiblity.

 

[Pyro]

Read the question again, I asked would a faulty N75 cause a fault code, I already know it can cause boost issues...

Again if it shot to **** then nomaly a code but if it's on it's way out then it might not yet there's also a chance the actuator is starting to stick

 

[8bit]

... try the maf check the spark plugs and if you can swap your N75 with someone to check that if your near Swindon then I have a spare you can try

Again, read before posting - in my first post I said the spark plugs were changed recently. I'm nowhere near Swindon, but thanks for the offer.

 

[jamie1]

Keep us posted how you get on mate.

 

[Pyro]

Missed the part about the plugs are you sure the plug gaps are all correct as tgat will cause running issues??

 

[jamie1]

A boost will do this I'm in the proceses of irradiating mine and ATM I'm get full boost and a nice steady drop then change gear and and it peaks then drop like led

This is a dirrerent senario. The car all of a sudden boosts at 3k which would say to me it doesn't have a leak.

 

[8bit]

Missed the part about the plugs are you sure the plug gaps are all correct as tgat will cause running issues??

No idea but it was about 6 weeks ago the plugs were changed and it's been fine until this week so doubt it's that. Still thinking MAF and N75, probably in that order in terms of likelihood.

 

[Pyro]

This is a dirrerent senario. The car all of a sudden boosts at 3k which would say to me it doesn't have a leak.

I do slightly agree but wouldn't rule it out it could be tgat is struggles to get presure ect but tbh I'm starting to think the actuator might be on it's way if it sticks then it won't open the wastegate so it has to wait for a larger build up befor it opens hence the boost lagging

Does that make sence??

 

[8bit]

I do slightly agree but wouldn't rule it out it could be tgat is struggles to get presure ect but tbh I'm starting to think the actuator might be on it's way if it sticks then it won't open the wastegate so it has to wait for a larger build up befor it opens hence the boost lagging

Does that make sence??

No, that's not how it works. Read the thread I linked to in an earlier post, that explains how the turbo, N75 and ECU work together.

 

[Pyro]

Noticed lately that sometimes if I floor it in 2nd or 3rd then boost doesn't seem to appear until betweek 3k and 3.5k rpm, then when it does it's very sudden, like someone just switched the turbo from 0 to 100%. Seems to be more likely to happen when the weather is colder and usually once the car has been warmed up a bit it starts behaving normally again, i.e. it builds from about 2500rpm or thereabouts up to around 3000 rather than just appearing in one big surge.

If the actuator is stickin and requires a higher presure to open it then it will be as if the turbo goes from 0-100% as the pressure has built up but not being used like it would if the actuator opened when it should I have read the post and to ne it makes sence! I could well be wrong but if the actuator isn't opening then it's nit controlling the waste gate properly the N75 also is used in this control process

 

[jamie1]

If the actuator is stickin and requires a higher presure to open it then it will be as if the turbo goes from 0-100% as the pressure has built up but not being used like it would if the actuator opened when it should I have read the post and to ne it makes sence! I could well be wrong but if the actuator isn't opening then it's nit controlling the waste gate properly the N75 also is used in this control process

So what your saying is the wastegate would be stuck in the closed position?

If so then it would boost through the rev range and possibly over boost.

BUT, i am unsure if the ECU will allow it to overboost and chuck it into limp mode?

Either way this theory dosen't make sense to me lol.

 

[leon cupra r]

Well this made me chuckle Niall - I have been thinking long and hard about my issues again, and have realised that when I use my N75 switch (essentially unplugging it) the car is no longer noticeably slower, there is only a very minor change in how much power I have available.... This is making me wonder if I also have an N75, so I did a quick search for 'faulty N75' and see that my 'problem buddy' is thinking the same things haha!

As far as I can see, unplugging the N75 leaves it in its open state, I.E. feeding all the input to the wastegate (effectively bypassing any N75 functionality) and running minimal boost...

I don't know whether or not it is worth trying it with the N75 unplugged if you are thinking it is sticking? as this should leave it in the one state... having said that however, obviously you will run a lot less boost, so if it is something like a split hose creating a boost leak, the lower boost may not escape and you will think the problem is resolved as well....

This may not be of much help but just thought I'd mention the fact that you can try with the N75 disconnected just as another thing to try maybe?

Oh and you won't get an EML from it although it will log a fault code on the ECU showing N75 signal intermittent - scan the car with vagcom before trying this to see if there are any error codes shown with the valve supposedly operating normally, then try it unplugged and clear the code afterwards

Ben

 

[Pyro]

So what your saying is the wastegate would be stuck in the closed position?

If so then it would boost through the rev range and possibly over boost.

BUT, i am unsure if the ECU will allow it to overboost and chuck it into limp mode?

Either way this theory dosen't make sense to me lol.

No I'm saying it won't open as early as normal so the presure will build up be for it gets a to open so when it does open there more boost tgan normal = turbo 0-100% Insted of the uesall steady built up

 

[Cupra_R04]

ill help log your car again if you want. Im in porty and off all day. Have you checked hose from turbo to charge pipe if this has slipped of may be leaking air?