I recently completed a full engine rebuild on my Mk2 Pre-FL VRS (PD 170 - BMN). I replaced both the turbo and the piston rings. The head has been professionally skimmed and rebuilt with all new valves and seals. Also replaced temp sensor on the coolant flange, oil pressure/temp sensor on the head and MAF sensor. Needless to say, I also fitted a new water pump, cam belt, tensioner and aux belt. All parts are genuine from TPS (although I wish I had bought the piston rings somewhere else as they were £70+ a set and appear identical to premium aftermarket ones).  Having recently clocked up the 500 or so "break-in" miles recommended, I've started pushing the car a little harder and a few issues have instantly reared their exasperating heads. 

 

1. There appears to be no, or VERY little, boost pressure before 2000 RPM. I clearly remember the car beginning the build-up right at the bottom of the dial and peaking at around 2500-3500.  Now there is literally NOTHING worth talking about until 2000. 

 

2. The MPG has fallen off the face of the Earth. On a steady motorway run at 60 MPH I could easily reach 50-60 MPG on the dash. Now, no matter how gently I drive, I struggle to get over the 40 MPG mark. Even if these figures aren't entirely reliable, the car is definitely drinking a lot more diesel than it used to judging by the increased frequency of my visits to the petrol station. 

 

I should add here that the DPF was removed (and the EGR deactivated)  a few months ago. This was a temporary measure, taken to avoid serious engine damage as the forced regens were starting to happen almost daily at the end. Not long after that the car started burning oil at a phenomenal rate, hence the rebuild. My guess is that the oil burning issue is what lead to the DPF problem. The irony, of course, is that the DPF was maybe doing its job a little too well? The same company (Avon Tuning in Bristol) also remapped the engine to a reported 200 BHP from 170, which is probably why the oil loss got even worse shortly thereafter. 

 

More worrying still, when I plugged the car into the diagnostics system after the rebuild - expecting to have to clear a whole catalog of fault codes - there were none related to the engine. I even unplugged the MAF sensor to force one, but there was nothing. The system in question is not VCDS, but one made by (or at least marketed as) Snap On. 

 

I have checked the obvious culprits for the boost issue. I've gone over the intercooler pipework from turbo to intake manifold, and all seems well. I've also inspected the vacuumm pipes, and these all appear good too. The actuator on the turbo also moves freely, and does open (close?) under acceleration. 

 

In order to get to the bottom of this I have ordered a VCDS interface from Ross-Tech for my laptop. The Snap On one mentioned above has almost no diagnostic functions, bar one to test various actuators and one to force a DPF regen. i'm not particularly familiar with the VCDS system so it's going to take some learning, but I do have a couple of questions that I'm hoping someone might be able to answer. 

 

1. Is there a chance that whatever Avon Tuning has done to the ECU is behind the mysterious lack of fault codes, or is this more likely to be the Snap On system itself just not being very good?

 

2. If the ECU is somehow corrupted, can I fix this with the VCDS system?

 

3. The main pipe from the vacuum/diesel pump runs off into the firewall and seems to disappear, while only a small branch comes off the bottom to feed the turbo actuator, etc. Where does it go and can there be a leak in the system beyond what can be seen?

 

Any help with these questions would be greatly appreciated.  

 

 

 

 

Clearly something a miss there then.  At least with VCDS you will be able to interrogate various systems such as all the sensors both when the car is running at idle and then again when you are driving. You can run tests on some sensors too.

 

You can map several sensors then go for a drive, such as boost, injection values, MAF sensors for example. This might flag something straight away, if the initial scan for faults doesn't, and then post on here for other PD170 VRS owners to compare with.

 

I've got some logs but they were from a PD140 engine so might not be as useful as someone with the same PD170. You could see when boost was building though, and when it peaked, at what RPM's etc.