Vag-com & Overboost

[Guest DaveS]

I've recently purchased a low mileage (57K) Galaxy (2001 Zetec 115ps TDI). Unfortunately after only 300 miles I have had overboost / limp mode problems. The fault code has been cleared several times now. After alot of head scratching by two other garages I have finally given in and taken it to Ford to break the code down further. They have suggested a process of elimination and that the first thing to be replaced should be the TMAP sensor and then the turbo(!).

 

Something I have noticed is that once the vehicle has gone into limp mode and ECU has been reset by switching the ignition off, there seems to be a very slight drop in performance and the turbo 'flutter' noise on changing gear is barely audible. I can't quite work out why this would be.

 

After all these trips to garages who charge their standard diagnostic fee each time, I'm considering purchase of diagnostic software and interface. I'm hearing alot about VAG-COM. Is this the best / most appropriate tool for me? I really would like to get to the bottom of this myself (I'm an engineer specialising in electronics design).

 

I know there are quite a few posts on this topic already, but I would really appreciate any advice on my situation and what software to buy.

 

Cheers, Dashi

[whitty]

my father in laws golf does exactly the same plugged vag com in to it today and it returned with 0 fault codes we were both surprised! so im gonna take the car out and get it to do it while vag com is running see if a fault code shows then ie before ignition is switched off and it resets itself but if you have any luck on this please do post and i will do likewise if we have any luck but i very very much doubt its the turbo i wouldnt let them replace that unless they can guarantee it cures the fault they too expensive to be replacing on a whim !

[Guest foxy]

I've been down the road of buying a USB cable assembly on Ebay and wasted time (lots) and money. Didn't work on my Sony VA10 and tried all sorts of combinations. (I am an ex computer engineer)

Now purchased the correct cable from Ross-Tech in the USA and using their software which can be downloaded from their web site free of charge. Worked first time and does everything that it says on the tin!!

In my mind worth paying the $286 which includes registerd software and the interface dongle.

I live near Devizes in Wiltshire and am happy to carry out a basic test/fault code reset, at my home, for the price of a couple of pints of local brew. Just contact me via email.

[Jonny75]

I have the same type of problem, took my galaxy 1.9 tdi to garage they replaced MAF sensor but still car loosing power and going to limp mode. other fault that showed up on test was over boost, what do i need to do to cure this? no engine management light is showing up.

Cheers Jon

[tim-spam]

Most likely cause is a sticking VNT mechanism. Does the engine feel rough and sluggish just before tripping into limp mode? If it does, that confirms that the turbo actually overboosting rather than receiving a spurious signal from the TMAP sensor.

 

The posts so far indicate yet again how little the dealers understand.

 

Having said that, the official cure for a sticking VNT mechanism is indeed to replace the turbo - expensive. However, there is an excellent thread (started by dt1) on how to clean the VNT mechanism. Another alternative is to manually give the mechanism some exercise to try and free it up.

[turk90210]

The loosing power/going into limp home mode coupled with the over boost code are related, basically the ECU moniters the turbo boost and tries to keep it at a certain level, if it goes over the threshold then the ECU trips into limp mode to protect the engine and other components from damage. (turning the ignition off /on again and every thing ok again confirms the limp mode and if the ECU see's the same problem on acceleration will trip out again)

As tim-spam has mentioned the VNT mechanism could be the problem like it was on mine, but I didn't get the rough and sluggish bit before tripping into limp mode it just went suddenly. however that said dont overlook the other bits that help to control the boost ie

1/ N75 valve (located on bulk head in the centre usually behind a heat shield)

2/vacuum pipes to said N75 valve (blocked or split)

3/leak around the bowl located at front of engine block with a vac pipe connected to it

 

I did alot of searching on this site and also on www.tdiclub.com to find out the answers I needed, the tdi club site is predominantly all about VW's but the Galaxy diesel is ultimatly a rebadged VW and was very helpful when i couldnt find the answers here

It took me a while to confirm my fault as it was intermittant and I tried the easy bits first and had to wait until it tripped out again before I knew for sure if it was cured or not. Eventually I narrowed it down to the VNT mechanism(located on the turbo) and moving it with a 9/16 or 14mm spanner I found its movement very rough( should obviously be smooth) and after alot of wd40/duckoil and elbow grease moving it up/down I got it moving as it should. I hasten to say that I expect the problem to re-occur as I havn't (due to working shifts) actually regreased/cleaned or stripped down the turbo which I will try first as I was taught to fix/repair cars when i did my apprentaship (yes Im a mechanic of 20+years)

[tim-spam]

Although replacing the N75 valve and/or TMAP sensor are usually tried first by the dealers, I have never yet heard of a case where replacing these parts has cured an overboost problem.

 

As regards the VNT, this is designed to operate without lubrication. Should you use grease or oil on the internal bits after a strip down and clean, this could well lead to it sticking again, due to the deposits left after the oil or grease is burnt off (which it will be due to the high temperature in the turbo). So, if you decide to strip the VNT and clean it, the internals should be assembled dry.