2003 H6 3.0 (Romano LPG fitted)
Posting here in the hope someone with a bit of experience on this motor can give a few pointers.

Hi all. Have had this OB for nearly 4 yrs now. Originally got 25-29mpg on petrol driving sensibly
after the first yr this seemed to gradually worsen, so that I now get 18mpg summer/winter (15-16 on lpg, less than petrol as expected) ave 10k miles /yr (13k on lpg so far)
Starts and runs fine, loads of power, just sups like mad No error lights. Won't be a valve regression issue as it started before I had it converted and its only done 13k on lpg with flashlube

Now as I understand, the H6 doesn't use a MAF for A/F mixture control, instead it has a piezo air pressure sensor in the carb. It also has 3 O2 sensors, 1 in each bank exh manifold and 1 nr the cat. I understand these are used for error determination rather than A/F mixture control, but not absolutely certain about this....Does anyone know for certain?

So where should I start to try to improve the mpg? I suspect its running rich, rather like an O2 sensor fault (had this on a previous 2L leggy- silicone blockage for a time). But which one to try swapping first?
Do the piezo sensors in the carb drift off? Can't find much online about these.

Any input welcome

Cheers
Andy

 

Andy

Have you tried on the UK Legacy Forum? Not saying someone here won't know but you might get a better response over there - uklegacy.com

 

Been on there for a couple of years. Plenty of users, but no-one has the in depth on H6 really. Also its very quiet on there at the mo.