LPG puts Lambda light on but not petrol?

[capt jack]

Morning all

Over the past month or so, I'm finding that running on LPG puts on the Lambda light on my 97 V70 LPG conversion. The code generated is 231 - 'Long term fuel trim at limits'.

If I clear the code and run on petrol the light stays off.

Things tried so far: Check thoroughly for vac leaks on both petrol and LPG pipework and replace all LPG pipework; Re-map of LPG ECU; replace injection solenoids with new, checked function and resistances of coolant temp sensor and air inlet temp sensor; checked and replaced where suspect all vac hose elbows.

In effect when running on LPG, the engine management ECU 'thinks' that at partial throttle it's running lean, and that the LPG system can't deliver enough fuel.

The car drives perfectly well on both petrol and LPG. It's done 270,000 miles, 220,000 of those on LPG. The O2 sensor was last replaced at 140,000 miles.

My question is, could it be that the O2 sensor is getting tired as it's now done 130,000 miles? If so, is it possible that it's at a point where running on LPG could make it's condition throw a code, when running on petrol doesn't?

The car has the Fenix system and I have been using a home-made Flash Code Reader to read and clear the fault code.

The Lambda light when it does come on, does so randomly. Sometimes just a few miles after being cleared, sometimes only after 200+ miles, but always on LPG, never on petrol.

Is it possible to assess the condition of the O2 sensor by checking resistances and / or output voltages?

Any ideas anyone?

Thanks

Cheers

Jack

[hancym]

I had a load of trouble with the same error on my XC90 when I first had the system fitted.

It was the air con clutch cutting in and out when the car was idling at traffic lights etc. Get someone to take a look at the LPG fuel mapping and bump the mixture up a but on the low end of the engine RPM.

[capt jack]

Thanks - now you come to mention it this has coincided with the warmer weather - and an increased use of the aircon.

I put the same question up in the general 850 / V70 pages, and there were a number of interesting possibilities raised. Thanks for taking the trouble to reply.

I'll be back in touch with the fitting company this week, and I'll see what they think about a re-map with the aircon running.

Cheers

Jack

[classicswede]

It will just be a case of needing to adjust the mapping in the effected area. Best thing to do would be to check the fuel trims with driving normaly and then try with air con on and put on lights, heated rear window etc to load the engine and make sure the trims remain OK. With the AEB ECU the car will be running in a differnt area of the MAP.