Thinking about it, after my previous checks seemed to show no difference between running on petrol or LPG, those figures were checked with it running on LPG. The engine is going to be sucking in the required volume of air but as I'm running a singlepoint, some of that volume will be the LPG vapour being drawn in between the MAF sensor and throttle body so not measured by the MAF. That might explain why the MAF reading is a touch lower than both RAVE and the Nanocom documentation says it should be.
You'll have to remind me if this is Bosch or Gems, I probably don't fully remember intake ducting arrangement for Gems but all air including IAV passes through the MAF on Bosch(?) and I seem to remember (though now expect to be corrected) it does on Gems? Gas entering downstream from the MAF is still gas, doesn't detract from the air the engine needs.
On quite a few P38 LPG conversions, and in fact on quite a lot of other vehicles too, I have seen engine load decrease at idle running on LPG compared to petrol. Some of this can I'm sure often be attributed to new LPG injectors supplying more equal cylinder to cylinder mixture than old/worn petrol injectors but I think there's a bit more in it than that because the same happens on some engines even with petrol injectors known to flow exactly the same - I believe it's related to the difference in stochiometric ratio. Another advantage (in some cases) of a mixer over injection is that if there's any difference in airflow cylinder to cylinder (which can effect cylinder to cylinder mixture in the same way as worn injector flow rates) a mixer will see that each cylinder gets the same/correct mixture anyway.
It's GEMS, as the thread title says. Yes, IAV air passes through the MAF but the LPG vapour entering the airflow at the mixer between the MAF and throttle body doesn't. So in terms of volume of air the engine requires, the LPG vapour will be added to that volume. The only difference is that there's no petrol being injected and the additional vapour, that isn't being measured by the MAF sensor, is the fuel.
when it came to testing my MAF i made up a wire loom to pin test the unit with a multi meter. you can stick pins in the plugs but that damages the wiring . i just used utilux cable clips , cut and grind them down to fit in the female ends and cut the other in halve and squash together for the male ends. put heat shrink on the open ends so not to short out anything (if you put power though the signal wire on the MAF you will be looking for a new ECU)
from memory their is 3 wires
power wire has 12v runs hotwire
signal wire will vary with load read from .1v to 5v the reading from this should be stable , increase and decrease evenly , not erratic, if it jumps around its likely a faulty MAF
other will have 5v from ECU
do not put 12v through signal wire it will blow up the ECU.
please note that there is alot off variables associated with the maf , it is a trimming devise for the ECU to set up fuel injection rates in association with air temp water temp engine temp etc etc , if you have other influences eg gas injection it will interfere with readings as it calibrates for it
the only way i could test my MAF was with a test cable and a multi meter. well thats my 2 cents worth hope that helps .
It isn't whether the MAF is working or not, I've got two now that both give readings on the Nanocom that are around about correct. The Nano also displays the MAF voltage which, from memory, at idle was around 1V. It's how the Calculated Load Value is worked out and why is it so different to what RAVE says it should be. However, it seems that the figure I've got is almost identical to that shown on a GEMS document relating to the same engine installed in a Morgan. It's looking more like the figure given by OBD2 standard and displayed by the Nano, is calculated differently to how Land Rover calculate it.
Gilbertd wrote:
It's looking more like the figure given by OBD2 standard and displayed by the Nano, is calculated differently to how Land Rover calculate it.
I wouldn't be surprised at that. What diagnostic gear do Landrover use?