Forget references to sensor 2, only US spec cars had post cat sensors, so you are only interested in sensor 1 on each bank. Short term trims will tell you what the fuelling is doing at any particular time. That won't have much affect on the running but if the short term trims are always going one way, the long term will slowly drift away to try to get the short terms back in range. So long term will tell you more that short term if Torque has that option.
Fuel trims are one of those things that confuse a lot of people but are actually simple when you get your head around it. The ECU has a pre-programmed map that adjusts the fuelling depending on load, throttle position, airflow, air and fuel temperature, etc. It adjusts by altering the length of the open time of the petrol injector (as fuel pressure is regulated and the injector has a hole of a set size) which alters the amount of fuel going in. The lambda sensors act as a final check that it has got it right. With manufacturing tolerances and wear in components, the amount of fuel for a set pulse length may be slightly out so the short term trims fine tune the pulse length a bit one way or the other to keep things correct. But, short term trims only have a limited amount of adjustment so if, for example, your fuel pressure is a bit low, then the short term trims will always be going positive to shove a bit more fuel in. If the short term trims are always one way or the other, the long term trims will adjust so that the short term are always hovering around the centre point.
So, if you have a duff lambda sensor, the ECU will see the output from that as showing a lean mixture. Short term trims will always be going positive to shovel more fuel in to correct it. As the output from the sensor doesn't change, it will still keep going positive so the long term will alter to try to get the short term central again but it never does so more and more fuel is chucked in until the car starts to run like a dog as it is being fed far more fuel than it needs. Extra fuel when cold isn't noticeable as extra fuel is needed when cold anyway, but once it warms up it will be like leaving the choke on when it doesn't need it.
As the LPG system slaves off the petrol ECU, then that will suffer too.
Peterborough, Cambs
- '93 Range Rover Classic 4.2 LSE, sold
- '97 Range Rover 4.0SE, in Oxford Blue with a sort of grey/blue leather interior sold as two is plenty.....
- '96 4.6HSE Ascot - now sold
- '98 4.0SE in Rioja Red
'98 Ex-Greater Manchester Police motorway patrol car, Range Rover P38 4.0, in Chawton white - the everyday car
All running perfectly on LPG
- Proud to be a member of the YCHJCYA2PDTHFH club.