Thread: direct injected gas on D2

It is not true that a mixer type system automatically puts the engine into limp-home mode. I have done a few mixer systems and they are reasonably reliable so long as they are fitted properly. Something as simple as a 68 ohm resistor wired across the injector cut relay will allow the ECU to register injector currents and function normally. It is vitally important that the original gas fitter wired the injector cut in the right place in the loom. To do that he would need a wiring diagram as he needs to not cut the power to any of the sensors also on the injector circuit.

See the pic for finding this point.

There is a "crimp" in the engine bay harness right above the inlet manifold. This crimp joins a total of 10 brown/orange stripe wires. The 8 smaller wires feed all the injectors and the remaining 2 are for powering everything else. So the fitter needs to cut off ALL 8 smaller wires and join them to one side of the injector cut relay. The other side if the injector cut relay is connected to the wires from the crimp. Failure to do this will result in engine management issues like you describe. Feel free to print out the pic and explanation and take them to your gas fitter.

The single most important tuning detail I have worked out is that you need to set the plug gaps at 0.6mm/0.024" to avoid back firing on a mixer system.
I have also fitted vapour injection successfully, The performance is better and economy can be marginally better that with a properly fitted mixer system. But expensive unless you do a huge mileage or run consistently high loads on your engine.

I had a venturi system on my GEMS P38A (your Disco is a Thor with Bosch engine management). The Thor engine is reputedly more susceptible to backfiring owing the engine management system.

On my P38A, the fitter had just cut the injector wiring and not fitted any injector emulators so every time the car was switched to LPG, it would log injector faults. It didn't seem to be an issue with the GEMS which has no O2 sensors.

But that wasn't the reason I removed it and fitted a sequential injection system. I had a few backfires which destroyed the plastic airboxes and they cost several hundred dollars each. In the end, I fitted a steel air filter housing from an early Rangie.

My wife would not drive the car on LPG owing to the backfiring and blowing off of all the hoses. One needed to know where the hoses went when refitting them. With the hoses off, the car wouldn't run on LPG or petrol (it would run on petrol but it would rev like mad).

In the end I just removed the LPG altogether. Later on, when I had some engine work done, I fitted sequential injection. That has not given a problem (except for a recent converter fault for which I've been waiting months for a new diaphragm kit).

I have the 02 model with an mixer and lambda control over the converter and main gas tap. I have a scangauge II that logs faults. It does log injector fault when running on LPG, but that does not cause problems, and its an easy reset using the Scangauge. The LPG runs on feedback from the 02 sensor and throttle position sensor. If the 02 is out of parameters that can upset gas tune.

I adopted ute's advice above for the plug gap and it has been a good compromise. If there is anything slightly wrong with the spark (which will often never cause a problem or show up driving on petrol) the LPG will suffer and backfire can occur with a mixer system. A vacuum leak I think would also upset gas tune and could cause backfire. I would be inclined to put anti-backfire spring loaded flaps in the box (or even better get a fabrications place to do one out of alloy - and have the flaps in that) and one day when a coil pack gets weak and you get the inevitable backfire you are not destroying the box - the MAF may or may not die, and in my experience the MAF usually survives backfire events.

Cheers

PS. The increase in power with injection may have as much or more to do with the ability of the engine to flow higher air through a snorkel that has no restriction than the injection itself. Having said that there is not much in it in terms of power economy.

I'd follow b_utey's advise if your handy electrically.

I have an injected system, and it hasnt missed beat.
If u decide to go injection, it shouldn't cost 3500 to get injection, as u already have the tank and lines fitted.

I'v also had 2 D1 on lpg mixer sysems and never had any problems with them either. ( I know there are differences between the D1 and D2 ).

Keep at it.

Rusty