I have just completed the installation of a multipoint LPG system to my 98
Cit XM 3.0 V6 auto. It works but roughly, I have found that on petrol the
lambda sensor runs wide i.e. near its max and min range but on LPG its on
the bottom all the time i.e. zero or its not reading at all.
Anyone know what a lambda signal should look like on petrol and or LPG. I
can interrogate both the LPG and original ecu,s.
The petrol ECU is programmed to swing the mixture fairly roughly from rich
to lean and they always overshoot which is why you see both extremes of
voltage. This is normal and how it should work. After a period at idle or
constant cruise you might see it settle down abit better though.
Re the LPG, it sounds like you dont have the ECU responding to a closed loop
system for some reason, either the base fuelling is too rich and the ecu has
gone to full lean (mixture is still too rich) or its ignoring the o2 output,
or the sensor isnt hot enough.
An unlit propane torch /controllable vacuum leak is always handy at times
like this so one can at will make the mixture go rich or lean at will and
watch for a reaction from the ecu.
Would a pair of Mole grips / G clamp on the vaporiser outlet do the same
job? Will give it a go.
I have put a Snap on MT2500 scanner on the original ecu 0.1 - 0.9 on
petrol, when the LPG is running the lambda feed to that is reading 0-1.2
volts (is it a simulated output from the LPG ecu?) but the LPG one is still
0. And it is still rough but it gets better after a few miles, I haven't
tried driving with the laptop connected yet.
The self learning of the LPG ecu is working and its a lot smother can hardly
tell any difference to petrol, an odd side effect! the autoadaptive gearbox
electrically connected to the main ecu and when its running on LPG the box
stays in high longer.
In which case the Petrol ECU isnt "seeing" the engine running as it should
(or being fooled into seeing it properly by the gas ECU) as the auto box
should change just as normal whichever fuel you are usuing.
Sounds like the load signal to the petrol ECU isnt quite being fed to it
My auto control box uses Idle switch, WOT switch, TP Sensor via engine
ECU, Tachometer, speed. Uses throttle position as one of the
parameters and it's bit different with LPG so the shift will change.
It thinks you are driving a bit sportier with bigger throttle openings
so it holds the gear a bit longer.
Its running very well now, tickover a little unsteady but normal driving is
very good. Will give the caravan a tow at the weekend to see what its like
Still haven't stopped the wide swing of the lambda signal between the LPG
ecu and the original ecu.
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