Xantia 1.7l Lpg/petrol Emission Problems.

[bordercollie]

I have had a "W" Reg'd, 2000 Xantia, 1761cc, for the last year, and prior to owning it, it had been converted to run on both Petrol and LPG Autogas.

In case you don't know, after switching on the ignition, the car runs using Petrol for about 3-5 minutes, in order to pre-heat the autogas, which it then automatically switches to, turning off the Petrol.

This means that over the last year, I reckon I have run the car using Autogas 99.9% of the time, and using Petrol, only the other 0.9%.

 

I took it for it's MoT Test today, and was surprised that it failed the Exhaust Emissions Test.

 

The results Print-out read:-

 

NATURAL IDLE TEST- ACTUAL CO 0.413% LIMITS <= 0.500% PASSED

 

SECOND FAST IDLE TEST- ACTUAL CO 0.757% LIMITS <=0.300% FAIL

ACTUAL HC 53ppm LIMITS <=200ppm PASSED

LAMBDA 1.102 LIMITS 0.970-1.030 FAIL

 

FAST IDLE TEST- ACTUAL CO 0.710% LIMITS <=0.300% FAIL

ACTUAL HC 57ppm LIMITS <=200ppm PASSED

LAMBDA 1.213 LIMITS 0.970-1.030 FAIL

 

OVERALL RESULT: FAILED Exhaust Emissions Test

 

Am I right in assuming that normally in a Petrol-only car, a high CO level, coupled with a low HC level, could mean the mixture is too rich, resulting in unburned fuel (HC) causing the high CO levels ?

 

The MoT Tester at the garage, told me that he had met similar emissions problems of this nature, resulting in a failed MoT Emissions Test, with other dual fueled LPG cars- his explanation was that using the LPG nearly 100% of the time, doesn't let the catalytic converter work efficiently, and causes fluctuating emission levels, on the short occasions when Petrol IS being used as the fuel. (Like during the MoT Test itself???)

 

He went on to tell me that before I take the car for a MoT Re-Test, in 10 days time, I should -

(1) Change the air filter, in case this is clogged and reducing O2 supply to the engine

(2) Take the car out for an hour long 'burn-out',(his words) using Petrol supply only, to burn off any deposits in the engine and the catalytic converter

(3) 24 hours before the next MoT Re-Test is due, make sure I only run the car using Petrol only, and don't use the lpg autogas as the fuel supply during this period.

 

Does any of this make sense to you? Is the advice given to me correct and would it 'cure' the emissions problem?

 

Has anyone else any ideas what has caused the high CO and low HC levels, and has this happened to you too?

 

Any ideas and advice would be much appreciated, thank you.

 

David Grieve of Scotland