Thread: 1999 V8 4.0L Dual Fuel starting on LPG but not Petrol

Is it a mixer system or an injection system? A mixer system cuts the common positive wire to all 8 injectors. A 330 ohm 1 watt resistor soldered across the injector cut relay allows a small current to flow preventing a dead injector detection. The relay may have dropped a wire. If its an injection system the LPG ECU reads every single injector pulse from the petrol ECU and translates them to LPG injection pulses. You'll need to plug it into the correct diagnostic software to find the problem.

In any case you should find the pressure port on the petrol fuel rail (reach behind the inlet manifold and feel for a Schrader valve) and check the pump pressure. Pumps installed in auxiliary tanks are at higher risk of failure than pumps in their original fuel tank. It may just have a burst outlet hose from a poorly installed replacement pump. You need the proper fully submersible fuel hose at around $30/foot for this application. You should drop the auxiliary petrol tank and extract the pump assembly and inspect it closely.

Originally Posted by bee utey

Is it a mixer system or an injection system?

Thanks for the quick replay mate, it's a mixer system.

Originally Posted by bee utey

You should drop the auxiliary petrol tank and extract the pump assembly and inspect it closely.

The bloke I bought it off said he recently had a new fuel pump installed. As I mentioned in the original post, I can hear petrol mixing in the tank during cranking, so I'm assuming the pump is not the problem. Nevertheless, I'll get around to dropping it out and taking a look if all else fails.

Originally Posted by bee utey

A 330 ohm 1 watt resistor soldered across the injector cut relay allows a small current to flow preventing a dead injector detection. The relay may have dropped a wire.

Where is the common positive wire and the soldered resistor? As I said it's my first car, so I'm not exactly mechanically fluent.

Originally Posted by FirstCarLandy

The bloke I bought it off said he recently had a new fuel pump installed. As I mentioned in the original post, I can hear petrol mixing in the tank during cranking, so I'm assuming the pump is not the problem. Nevertheless, I'll get around to dropping it out and taking a look if all else fails.

Pumps don't "mix" anything, so a noise you describe as "mixing" probably means a burst outlet hose. The correct hose type is essential and someone being stingy will use cheaper hose. Seen it all before.

5 16" Submersible IN Tank Fuel Line Hose SAE30R10 Specs | eBay

Pull the pump out and inspect it after you've tested for the lack of fuel pressure.

Originally Posted by FirstCarLandy

Where is the common positive wire and the soldered resistor? As I said it's my first car, so I'm not exactly mechanically fluent.

The injectors all have brown/orange striped wires to them from the main fuel injection relay. They all join together at the back of the engine inside the loom. To enable the engine to run on gas they must all be cut in the correct place and joined together so as to not cut off any engine accessory other than the injectors. So when the LPG fitter cuts these 8 wires he then has to switch the injectors off with a relay somewhere in the vehicle. You will have to find the relay yourself. Look for electrical tape around the harness and wires running towards some gas control equipment. Then you need to find out exactly which wires are cutting the power to the injectors by measuring the voltage with the petrol on and off. (obviously you'll have to first fix the pump hose if that is indeed the problem) Once you've identified the wires that cut the injectors you need to solder this resistor between the two.

Oh and get yourself a RAVE workshop manual with wiring diagrams ASAP, at the "shop" tag above.

I'll check this out tomorrow and let you know what I find. Cheers.

I'd try pulling the fuel pump relay out and putting 12v across the terminals that power it. That will tell you whether or not the relay, the pump and that side of the circuit work. Then I would put a test light/meter across the terminals that power the relay and try starting on petrol. That will tell you if the relay is getting the signal. With that info you can then start to investigate along the appropriate lines. You are guessing randomly otherwise.

Hey fellas, just a quick update to say that the battery light I mentioned has turned out to be a bigger problem. Turns out the alternator's crook. Not sure whether brushes or regulator so I'm gonna have to strip it down and refit before I continue with the LPG/Petrol problem. I've got a manual, and as soon as this weather clears up, I'll get stuck into it. After that I'll drop the tank out and check that pump. If that fails, I'm starting to think I'll have to take it to an official Rover mob and get them to hook it up to TestBook so that they can reprogram the ECM. After scouring the manual this is pretty much where I'm at. I've tried replacing the gas relay/switch that changes between fuel sources, and it still started on gas, but not petrol, so I'm pretty sure I can rule that out. Bloke I bought it off said that he bought a new fuel pump and had it fitted AFTER this problem reared it's head, so I don't have high hopes about the hose being the problem. I'll let you know how it's going once the alternator's sorted out. Until then, I can't even drive the damn thing.