gq 4.2 tbe starting but not continuing to run???

hi all, having trouble with my sons gq 4.2 tbe not continuing to run on petrol. It will fire and run for about 2 secs then stops and if we crank it, it will miss and carry on but won't run.
I have exactly the same patrol so we have swapped the computer, air flow meter.
Have cleaned the injectors, disconnected the gas system via the relay that switches the injectors off when gas is turned on.
Fuel pressure is a little higher than recommended but we connected my fuel pump to his and ran his return line into a jerry can and got correct pressure in his patrol but still no luck. (we ran his pump back through the return line while doing this test).
We have checked the timing, Ok.
At the end of day we lost pulse to injectors and his computer has died. We put my computer back into his and we had injector pulse back his patrol still only ran for two secs then stopped.
The gas system used to start on petrol and then go over to gas, but we have disconnected the gas system.
It appears I am raving on and I am but we are really struggling at the moment and now we need another computer.

thanks Kevin G

Hi Kevin. When I bought my tb42e it ran rough as guts and everything I did to it gave it minor improvements, but by far the biggest problem with it was the intake gasket. I removed the intake and replaced both the intake and plenum gaskets as they had dried up and cracked and after this it ran like a new engine. I found this by spraying inox around the gasket seams.

thanks, will check that as soon as I get back to it.

Is it a problem related to the ignition key

It starts, Once you let go of the key it stops.

Also partially blocked fuel filter?

We have bypassed fuel filter and no luck, even after it stalls we have an injector pulse and still have spark at plugs.
thanks Kevin G

Has a Fuel line been kinked at all??
Does sound like it's starving, but in a diesel man myself..

hi Westy, Its not fuel lines as I parked my patrol beside the sons patrol and ran fuel lines from my patrol to sons engine, ran mine on gas and checked fuel pressure on sons patrol, good pressure but his would only start and run for two seconds only then stall and not restart.

regards Kevin G

Fuel pressure regulator?
Clean all your earth points aswell.

we tried fuel reg off my patrol, no difference. will check and clean earth points on motor tomorrow night. too flaminin hot here at the moment.

You mention it starts runs for two seconds then stops and will not re-start; how do you re-start it? Do you disconnect all power at battery then re-apply; which I presume resets the computer? If not what process do you use?
If so and it occurred with two computers its getting a dodgy signal somewhere which is telling it to stop and not re-start, or sending incorrect data?
I don't know a great deal about the efi on these and if it will generate a code like the OBD2 stuff?

When did this problem first occur, was it after removing the gas system?

I would start at the beginning. Start the car let it stop then check it definitely has spark and fuel on all cylinders. Check the fuel is actually STILL making its way to the injectors as multiple shut off valves could be added at any point (delivery and return)?

If you are definitely getting spark, fuel and the timing is fine then it would appear that the fuel timing is off or the mixture. Start at the air cleaner and work forward checking and cleaning as you go. Check all connections are clean if electrical, air tight and clean. Check all relays and connections. Have a look at e wry thing such as all vacuum lines for efi, power booster etc

I have seen some complex LPG systems in the past that shut off fuel and adjust timing post start on petrol. I wonder if you have a module somewhere still causing grief?

I would also check if you have a neutral safety switch that its not playing up, sensors for coolant temp, AC, and crank angle (if it has one). Apart from that it should fire up!

It might sound silly but I once worked on a car with a dicky coolant sensor, the efi was set to shut down if the engine over heated! Disconnected and it worked.