GrahamH
8th September 2010, 08:53 PM
Dear Brains Trust
I have this friend. (Honestly.) He has a '91 Range Rover classic 3.9 V8 which recently had LPG fitted. The LPG works fine. The problem is the air-con.
It appears that disabling the injectors using by disabling the EFI relay in the rear of the driver's seat base has caused an issue where the Engine Management Computer thinks that the engine is no longer running properly and therefore it should disable the air-con compressor clutch circuit. So on petrol the air-con works normally. On LPG the air-con does not work at all. I believe that the ECM senses that there is no current being drawn by the injector drive transistors and infers that the engine is not running properly (or at all) and therefore drops out the compressor clutch to reduce the load on the motor.
Apparently in the UK they fit injector emulators between each injector and the loom connector (a set of 4 on each cylinder bank) to control the injectors. When on petrol the drive from the EMC is fed to the injectors normally. When on LPG, 12V from the changeover switch fed to the two emulator controllers opens the circuit to the injector but (presumably) substitutes a resistor for the injector so that the EMC still sees the load it was expecting and thinks that all is well with the engine - and the air-con functions normally.
The LPG equipment supplier knows nothing of this and does not stock the injector emulators (they seem to be quite commonly available for modern EFI cars in the UK though).
Can anyone confirm that I'm on the right track here and suggest a fix? The friend would prefer one that does not involve importing 2 injector emulators from the UK at a cost of around £36 each. Has anyone else struck this? Is there a simple fix?
Thanks in advance for your help everyone.
Cheers
I have this friend. (Honestly.) He has a '91 Range Rover classic 3.9 V8 which recently had LPG fitted. The LPG works fine. The problem is the air-con.
It appears that disabling the injectors using by disabling the EFI relay in the rear of the driver's seat base has caused an issue where the Engine Management Computer thinks that the engine is no longer running properly and therefore it should disable the air-con compressor clutch circuit. So on petrol the air-con works normally. On LPG the air-con does not work at all. I believe that the ECM senses that there is no current being drawn by the injector drive transistors and infers that the engine is not running properly (or at all) and therefore drops out the compressor clutch to reduce the load on the motor.
Apparently in the UK they fit injector emulators between each injector and the loom connector (a set of 4 on each cylinder bank) to control the injectors. When on petrol the drive from the EMC is fed to the injectors normally. When on LPG, 12V from the changeover switch fed to the two emulator controllers opens the circuit to the injector but (presumably) substitutes a resistor for the injector so that the EMC still sees the load it was expecting and thinks that all is well with the engine - and the air-con functions normally.
The LPG equipment supplier knows nothing of this and does not stock the injector emulators (they seem to be quite commonly available for modern EFI cars in the UK though).
Can anyone confirm that I'm on the right track here and suggest a fix? The friend would prefer one that does not involve importing 2 injector emulators from the UK at a cost of around £36 each. Has anyone else struck this? Is there a simple fix?
Thanks in advance for your help everyone.
Cheers