SLROC Forum

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My range rover 1991 3.9 is running like a burst baw
It starts very rough sounds like half the cylinders are not working but as soon as I coax it up to 1800 rpm clicks on to gas and runs as sweet as a nut
I have went through the test in the Haynes manual and all seem well except when I test the resistance for the left and right bank of injectors tested at the plug that goes into the ecu .it has no reading an open circuit so surely the car would not start at all , any thoughts or sugestions please
Thanks Billy

The injector wiring is switched by the gas to turn off the injectors stopping the supply of petrol to the engine. From memory there's a wire for each bank that is cut normally at the ECU,if you find these and rejoin the original wiring this will show if the fault lies within the gas systom or it is a petrol problem. Remember to turn the gas system off on the controller if your trying this.
I've seen this problem on a 4 cylinder engine that would run on gas and not petrol, turned out to be a corroded conection on the emulator box. Depending on your system a V8 has 2 emulator boxes, one for each bank, to shut off the injectors.

Best of luck,
                  Stevie.

Thanks Stevie
I went and had a  lie down and wondered about the lpg
switch set up,that makes sense ,I wonder if I tried to check the resistance with the ignition on it would allow me to see where the faulty injectors lie
Cheers billy

Hi Billy,
          you can't check resistances on a live circuit, a multimeter measuring resistance puts power out from the meter through the circuit being tested, it measures the power that returns to the multimeter and so worksout the resistance. This is why a circuit needs to be dead and isolated to test properly.
If your testing the injectors I would measure the resistance at each injector on it's connections with the wiring unplugged,the wiring for each injector can be tested for continuity from each injector plug to the ecu plug direct(ecu unplugged to test the wiring). The other method of testing the wiring is to disconnect an injector and plug a noid light(led light that plugs into the injector wiring plug) in to the injector plug on the wiring harness. With the engine cranking or running the noid light will flash showing the pulses to operate the injector from the ecu.

Cheers,
            Stevie.

Hi Stevie
What I ment with ignition on was to have the ecu unplugged
I'm guessing the LPG switch is like a solenoid when the ignition is on it will connect the broken wires to each bank of injectors
However I prefer your suggestion of testing the injectors wiring with a light
I will also phone the guy who installed my LPG system 7 years ago I suspect the fault is going to be in the LPG controller switch , when I took all the plugs out for a look one bank was dry the other wet with petrol so I think one bank isn't getting any fuel hence the really rough running
Cheers again Stevie