Help with an over boosting issue

[Ibiza2000]

Hi all, just as tittle really, iv had endless problems trying to find out what's causing my Leon to over boost, it's a 1.9 tdi (ALH) engine code so its not a pd, and it's 90bhp waste gate turbo,

So far I have replaced the MAF sensor, had the VNT cleaned out, it has also been on the VAG com but it's giving no hints as to what may be failing I only have fault codes for a coolant sensor, and the positive boost pressure, iv been advised to look at the manifold absolute pressure sensor (boost pressure) but as iv spent a fair few bob I'm a little reluctant to throw cash at maybes without good cause (ie a test)

So has anyone got any advice as to what could be causing my over boost? It tends to cut at around 2100rpm, also of its any clue sometimes my idles a little erratic not all the time but it can sit at 1100rpm 4 out of 7 days a week

I'm a little confused as to what to do next, alternatively if anyone around the Birmingham area has a manifold absolute pressure sensor I could test on my Leon while they was there to rule that out then I would be very very greatful, just a shot in the dark lol

Thanks in advance for anyone's help or replies

 

[Seatmann]

Definitely not a wastegate turbo, that's the earlier ones and the AGR but yours is a vnt 15 turbo.

Anyhoo if the vnt has been all cleaned it should move nice and freely, any sticking will cause overboost. The actuator for the turbo could also be busted, the spring can go weak and also they can and do rust inside and the diaphram comes away from the edge.
Another one would be the N75 valve for the turbo.

Anyway here's some useful limp mode info

http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm

This guy does second hand tdi parts too like actuators etc, you could email him

http://www.darksidedevelopments.co.uk/

 

[Ibiza2000]

The guy tht cleaned the vnts said that all the turbo was absolutley spot on, so maybe the n75? Where's that situated? And how much are they? Also how easy are they to replace?

Thanks for the info on my turbo I'm not very good with them as this is my first, I'll have a quick read on limp mode,

For more info no smoke comes out in limp mode

 

[Muttley]

ALH is the last of the TDI 90 engines, and has a VNT turbo, as Seatmann has already said. VNT is a different way of controlling turbo boost, which by definition does not employ a wastegate.

What's the mileage on your engine? My old Ibiza (with a wastegate turbo TDI 90 engine) began to suffer from overboost, going into limp mode at motorway overtaking speeds (very exciting) at about 85K miles. The cause was the EGR valve sticking open.

EGR is used in the middle of the rev range to keep the combustion temperature down. The EGR valve is closed by the ECU as revs rise, and should be completely closed at full chat.

The EGR system causes a build-up of hard, sooty crud in the inlet manifold. The hot, sooty exhaust gas meets the oily (from the PCV) inlet charge to make this crud. After a while, the valve itself becomes coated, and fails to work properly.

By sticking slightly open as revs rise, the rising exhaust pressure is allowed into the inlet system, resulting in overpressure and limp mode. Turning the engine off resets the ECU, until the next time.

Have a look at the EGR valve and see if it needs cleaning out. You could always try disabling it, which should tell you straight away if that's where the problem lies.

 

[Seatmann]

I reckon yours was overboosting due to the intake being mank Muttley, same as my AGR engined cordy. The egr is pooped on my golf with the ALH and it just causes the car to be wierd a bit when you first press the go pedal.

 

[Ibiza2000]

So what are signs of a egr valve failure? The top end of the egr also had a clean but the bottom end wasn't,

I'm a little confused as to where to head to next on this issue, as I fix one and another pops up can't the egr valve be bypassed in any case? I thought you could get a stainless elbow joint?

My Leon has just topped 100k, it does seem slightly sluggish at times but other times it can really go, it can be worst if I try and push it from a cold start if that gives any insight?

It has a full service history and it has just had another service so I guess it can't be the engine much that's causing me this aggro but the turbo restricting my power, is there any tests I can do for sensors, solenoids or the egr/any thing else?

 

[Seatmann]

Pull the vac pipe off the top and plug it, if the car runs better the egr's a **** like mine lol.

 

[Ibiza2000]

Sorry I'm gonna be really stupid pull the vac pipe off the n75? Which would be the one that's the top right hand side of my engine bay?

 

[Seatmann]

No off the top of the egr valve, there's a big round thing that looks like an alien spaceship lol. The N75 deals with the turbo but the other one deals with the egr, I can never remember the name of the other one lol. Anyway on the intake? The big round thing there? Pull that vac line and plug it, that should help rule out the egr.

 

[Ibiza2000]

Ok do if it is the egr when I unplug and bung then what will happen? And I'm bungin the vac line or the egr hole where the vac line come off?

 

[Seatmann]

Plug the vac line, the turbo on our cars need the vacuum to operate the vnt mechanism and if there's any vacuum leaking it affects the turbo. If that fixies things then you might need an egr or you could just leave it. Some cars get a light on the dash with the egr disconnected but some don't, it wont cause any problems though.

 

[Ibiza2000]

Ok grey thanks for all your help I'll post my results up and see what happens when I bung the line

 

[Ibiza2000]

Hi this is a pic of my egr, which vac line should I pull the one that's on top of the egr or the lower one they both lead to a solenoid, the same one that's closest to the egr....

 

[Ibiza2000]

And also that metal clip that's on top of the egr how can I ensure if that's removed that its tight enough again for no vacuum leak on it?

 

[Seatmann]

The asv one is your anti shudder valve, it works a butterfly type valve that temporarily closes when you switch off the engine, it helps to make the switch off smoother.

The big one on top is the actuator for the egr valve and that's the one you want to disconnect and plug the hose.

 

[Ibiza2000]

Ok crackin, that's easy for me to understand lol ermmm as for the metal clip what precautions should I take to take off and put back on as obviously that clip is made to seal the pressure from the lines

Last thing I want is to remove this and damage it or not be able to remount :/

 

[Seatmann]

Rip it off, you really wont create any major problems, most of them have the clip missing anyway without any bother. You can always replace it with a small jubilee clip if you need to.

 

[Ibiza2000]

Just revisiting this topic as I still haven't got my turbo sorted

Pulling that vac line from the egr, will that not potentially blow my turbo? Or do some kind of damage?

The n75, is that the far right solenoid as if ur looking under the bonnet from the front? Can I just simply unplug the electrics to that to test if that's causing my problems?

These sound simple but don't wana mess if they do damage or won't rule them out the equation

 

[Muttley]

You don't want to disable the N75, that controls your turbo vanes. If you take the plug out of that you will have no boost - the vanes default to fully open.

This is what the ASV engine compartment looks like, yours should be similar

You can pull the electrical connector off the N18 valve to disable the EGR. You may get the engine light coming on, though.

EGR is an emission control device which diverts exhaust gas back into the inlet to reduce the amount of oxygen in the cylinder and bring the combustion temperature down to prevent the formation of NOx, nitrogen oxides. As a side effect it produces more particulates i.e. soot.

I've never heard of any engine damage resulting from the EGR being disabled.

 

[Ibiza2000]

Ok disconnected the n18 the weekend, it is more responsive to say the least and tends to pull more however my turbo is still cutting out at that kind of range as described earlier, what could be the next stage? That's the egr ruled out right?

Also is it safe to keep that n18 disconnected I'm enjoyin that little bit of extra power untill my turbo cuts out lol