O/T 2002 Polo with EGR Excessive Flow Fault

[seventh-heaven]

A bit of a technical conundrum for the collective techie brains to get into on a dull Saturday afternoon!

 

I am looking at a friends Polo - a 2002 1.4 16v 100 bhp. Bit of background - the car has done 92000 miles and is in generally good condition although it is clear that the current owner has taken it for granted and neglected it for the 2/3 years of her ownership - maintenance is done on failure only! She has been complaining that in the last 6 months a number of issues have occurred which have led to it being unreliable including:

 

- poor starting from cold

- Engine fault light (download shows to be 16786 - EGR System P0402-35-00 Excessive Flow)

- occasional breakdown when engine stops but then starts a bit later

- started to need regular top ups of engine oil

 

I have removed the EGR valve and it is sticking and not functioning properly, but it appears to be sticking closed not open. The pipe from the EGR valve to the throttle body looks newer than the rest of the engine bay kit, but once out the carbon in it whilst not excessive shows it has been there a while. Had all the plugs out to do a compression test and they all seem high at around 170-180psi. Now it could be the gauge but I used same gauge on another engine within last 3 months and got more realistic readings. Plugs were very worn and so replaced and now it appears to start much better from cold so that symptom is probably a red herring in respect of the the EGR symptom. I reassembled the EGR valve and pipe with a cardboard gasket to block it off. Sure enough when I go out for a test drive I can get the EGR Excessive Flow fault to reappear - so I know that this is an incorrect diagnosis on the basis there was no flow through the EGR! Now I have never driven this car before (and used to driving a A6 3.0 TDi as well as the 7!) but none the less it felt a bit flat for 100hp. It would rev to the red line ok but not at the pace I expected.

 

So the question is what else could it be. My thinking currently is as follows:

 

- leak on EGR pipe where it goes into the Throttle body. O ring is there but could be leaking;

- Block cat causing excessive back pressure in the exhaust hence causing high compressions and poor air flow through the cylinder - If the flow through the cylinder is restricted then for a specific engine speed and throttle opening the manifold pressure will be higher than the ECU would expect leading it to think that the flow from the EGR is causing it.

- Worn exhaust cam again restricting flow but I would not expect it to be so consistent across all 4 pots;

- air leak in the manifold of vac system - one is not obvious but difficult to be sure. I suppose a Vac gauge could be used to draw a vacuum in the inlet and see if it leaks away. However this would not explain the high compression readings.

 

Any other suggestions or suggestions of how to check the above easily would be appreciated.

 

Thanks

 

Edited by - seventh-heaven on 9 Mar 2013 13:52:55