over fuelling petrol on idle

[lpg boy]

I have a 1995 estate -2e engine with digifant multipoint injection -and has a lpg conversion.
It runs fine on lpg (vcds shows steady ignition timing on tickover) but when hot & run on petrol it runs so badly it chugs and stalls on tick-over , vcds trace shows the timing adjusting wildly to stabilise the tickover but cannot manage it. when really cold it starts and runs fine on tickover. The running is like a carburetter engine on full choke. I don't know anything about the petrol injection system but it must be at fault as lpg is un-affected.
Anybody have any ideas how to sort it please?

[scotty33]

Hi,

Conventional wisdom would probably point to a temp sensor or lambda probe problem. I would suggest you start with the ECU relay, if it is the same part as used in Audi 80 ABK and 2E golfs it is likely to be faulty. this is the item you are looking for:

http://i246.photobucket.com/albums/gg104/scotty33_bucket/SSM10694.jpg

The problem is caused by poor soldering or dry joints on the printed circuit board. Resolder or buy a new relay for approx £14

if it does not have this relay type,

You should be able to see the ECU or G62 temp sensor reading in measuring blocks with VCDS, check it with a hot engine and with a cold engine see if it bears any relation to the actual engine temp? The ECU needs to 'see' a coolant temp of approx 80 deg c before it switches cold enrichment off and starts controlling mixture using the lambda sensor. The ECU temp sensor is purely for the ECU, the gauge value is supplied by a different sensor.

failing that, test resistance of the sensor (blue one mounted on the plastic pipe, front of head) ideally cold and hot readings I don't have the actual values for the 2E sensor, suspect they will be similar to the V6 Audi sensor, if in doubt find the correct values before you change this?:

http://www.12v.org/maintenance/repairs/ect.php

Then test the lambda sensor;

http://justlambda.co.uk/

(go to 'testing sensors')

[lpg boy]

Thanks for instructions scotty,
the temp sender is showing on engine measuring blocks at a 2 or3 degree difference to the dash reading, but increases parallel to it when engine is started.(vcds 10.6)
The relay had one dry joint but I re-soldered them all anyway.
The lambda sensor is behaving oddly in that there is the correct band output when running on lpg measured with a digimeter as justlambda.co.uk suggested but running on petrol it flatlines at about 0.24v.
vcds reads the lambda in 'measuring blocks' and confirms the digimeter readings and if the vag-scope is used the characteristics are shown in graphical form.
Mistake in original message-the engine is running LEAN not rich ,spitting back causing eratic running which is confirmed by the flat low lambda output, but cold starting is very good, hot starting isn't.

It is as though when running on petrol the lambda is ignored and so won't tell the injectors to put in more fuel.:confused:
any help anyone?
thanks