Thread: Gas/petrol disco cuts out on petrol!??

Check the relay for your injector cut and its wiring. Bridge the relay out of the circuit to test it. Just don't try running on LPG while it is bridged.

Mine did pretty much the same thing. The relay which in my case is in the gas control box was not able to take the full electrical load of the injectors.
The relay still worked according to the multimeter though so I used it to switch a horn relay which now closes the injector circuit.

Also check your fuel pump works properly. I replaced that a few years ago but in my case it ran fine once the engine was running however sometimes it would be very difficult to start. Then one day it never started again. That was prior to fitting gas so it was a show stopper.

The whole petrol injection system gets its input signal from a white/black stripe wire at the negative connection of the ignition coil. If this is loose your vehicle will cut out as you say. It will not affect gas as the gas will have a different connection for its safety cut-out operation.

Then of course with the fuel pump, the connector plugs at the fuel pump and about 1 metre along the harness can melt and connect randomly. If the pump itself is faulty it can be replaced with a VN-on Commodore fuel pump. It's a bit tricky but far cheaper than genuine LR.

Originally Posted by mud

Just bought a 96 disco and really need some help with a problem.
The car is V8i Gas/petrol, runs fine on gas and sometimes runs fine on petrol. When using petrol, the engine will idle fine but when driving it will cut out completely, exactly the same as if I turned the ignition off, but ignition lights don't come on, then it will kick in again and run fine. The cut outs are random. I have driven the car on petrol for 20km or so without a problem except that idle speed was about 1200rpm the whole time. It did not cut out until I had turned the car off for 5 mins, then started it up again, drove 1km down the road and the cut outs were very bad. Switched to gas then the car run perfectly. Anyones help will be much appreciated.
I am also new to forums so bear with me.

The cut outs have now started when driving on gas, not as violent as petrol, tho it is the same. i was still able to drive home 15km with it cutting out while on gas, when it does it on petrol i cannot even build up any speed.
Im not sure now weather your original replies still apply, as the gas system runs of its own pressure. No pump. Could it still be the injector relay opening and closing the circuit? The wires on the coil are ok.

The only common parts to the gas and petrol system are the ignition system and the alarm/immobiliser "spider". The ignition amplifier and coil can be upgraded to Bosch units, thread here:

Lucas ignition amplifier replacement by Bosch 024

The alarm spider has a history of dodgy soldering etc, it lives behind the radio. Base models without security have a bridging plug to bypass it. Do a search on it.

As said the ignition is the common element in LPG/petrol cars.

However in my experience it is the LPG which fails first when your ignition is dodgy as it needs a better spark. However it is possible that it was just coincidence that it only did it on petrol before where it could have done it on either fuel but you just got lucky.

Also it could still be the injector cut relay as it is possible that if it is running very poorly on LPG (as opposed to cutting out entirely) that the relay playing up and is powering up the injectors occasionally when running on LPG. I have discovered when I didn't earth the LPG module correctly that if you try and run your car on both fuels it will idle terribly and not rev.
This is just a theory but so long as you're checking things it is worth a look. Even if just to give you something to do while you stumble across the real answer

hey guys, after i posted the last update she wouldn't start for me at all, cranking over but no start, so i checked the spark at the plugs, and nothing there, checked spark and power to the coil, plenty of spark at the coil. power is dropping from 12.5 to 10.7 when cranking the engine, which i assume is a fairly normal drop, not too much? so then i went to the dizzy where it looks like someone else has had a butcher attempt at levering the rotor button off and cracked the plastic casing inside dizzy. Rotor button is still good tho.. S.o.b i bought the car off must have known about the problem.

Anyway, there is a junction of wires in between the dizzy and the radiator, is this the ignition module? sorry this is my first experience with these. My suspicion is that this is where the immobilizer cuts out the signal to the dizzy as there is two wires going to the dizzy usually there is only one? One is red the other is blue. Or the module is faulty. I tapped into the red wire using a pin and a wire from the negative side of coil to the pin got the misses to crank it over and she fired up! and run for about 2mins then cut out. I was able to do this several times testing with the wire and without, she started with the direct power and would not without it. once it had fired up i had to remove the wire to keep her going. If i touched the pin with the wire after it was running it would stall.

Just trying to eliminate every thing else before i rip the dash to pieces to get at the immobilizer unit. could it be a problem with the dizzy, I'm not familiar with this type of distributor. No points haha

I've ruled out the injector cut relay as i have diagnosed a spark issue.
I really appreciate the help cheers

The coil is a bosch 1 220 522 011. I have changed the plugs and leads, it was the first thing i did after i bought the car because i noticed the leads where cracked and brittle. is anyone familiar with this coil? After reading that thread i think i might change it anyway!?

The distributor contains a magnetic pickup that creates a small voltage every time the teeth of the rotor thingy pass it. That voltage is transferred to the ignition amplifier via the red and blue wires. The amplifier then switches the coil negative side, just like points used to. You can test the pickup with a multimeter on resistance, unplug the pickup from the amp, under 500 ohms and not affected by wriggling any connection.

There is no spider connection here at the amp. If you have no spark, immediately determine if there's a voltage at the coil positive connection. You can wire a small test light in the dash if you want. If that voltage disappears then its likely the spider. If the voltage remains and you have no spark at the coil, it's likely the amp or coil.

If there's spark at the coil but not at the plugs get a new rotor button. They are well known for burning through, especially the cheapies. If you can't find a genuine one you can use an XF falcon one part no. GB864, it looks different but works the same.