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[JamesV6CDX]

For anyone who can't recall, some time ago my MV6 was randomly switching back to petrol when driving. The code logged was "injector number 4 error" in the gas ECU.

In an attempt to work out whether it was the injector at fault, or something elsewhere, I swapped the place of injectors 4 and 6 on that bank. (not physically, but I swapped the loom connectors and lpg feed hoses). This means that, if the fault code moved to injector 6 - it would have been the injector at fault, if it remained at 4, it would be a wiring / loom / ECU issue.

Well... after doing this, do you think I could get it to error again? 2000 miles, and it never happened again - so I pretty much forgot all about it.

So. This morning, I was merrily sailing up lane 3 of the M4 towards London, when... instant total loss of power. Ah, crap, LPG light flashing. It had switched back to petrol, and shamefully I did not notice for what was probably miles, (ignoring the petrol gauge, thinking it was on gas) - and subsequently causing my petrol tank to run dry.

Thankfully someone was looking over me - I was able to get over to the hard shoulder safely. So there I am with no petrol, and a hit and miss ECU system! I managed to force start it on gas, and it drove 20 odd miles or so to the next services (in lane 1!), during which time it died again, whilst on gas, once - and I had to do the same.

When I was safely off the motorway I plugged the laptop into the gas ECU. The error was "injector number 4".

SO it's not the injector at fault as originally suspected. All of the wiring seems to be intact, with no breaks or damage. I've followed it back as far as I practicably could at the time. I guess I'll have to buzz it through from the gas ECU pins etc and properly inspect it all well... would you concur that it seems to be a fault with the wiring to the no4 injectors, or maybe in the piggy back for this injector?

I wouldn't think it would be likely to be an ECU fault with the LPG controller?

Shame it wasn't number 6 causing the problem... I'd have just configured it as a 5 cylinder install, and ran the 1 cylinder on petrol, until the weather warms up a bit

[Kevin Wood]

Did you check the temperatures and pressures to see if something caused it to switch back? Mine is currently doing this due to a problem with the vapouriser temperature sensor. I would expect any other issue to give a warning beep, but this just silently switches back.

Either that or you have an intermittent connection to that injector in the loom.

I think switching a single cylinder over isn't permanent. It's only effective with the laptop connected.

[Lazydocker]

It is, as you say Kevin, only temporary

You have the old, black sensor with the 2 pin plug yes? Do I need to try and get you one from Teilo?

[05omegav6]

I have a couple of spare piggy back connectors with a short section of loom here if that is of any use James

[JamesV6CDX]

I have a couple of spare piggy back connectors with a short section of loom here if that is of any use James

That might well prove to be a godsend, mate

[05omegav6]

I'll dig them out in the morning   let me know if you need them and I'll pop them in the post

[Lazydocker]

I think I chucked all the ones I had in the bin as they had no tails on them anyway. I've done about 3 of those loom mods too

[05omegav6]

I lopped the Stag loom at the plug on the shortest ones, and did the rest at the same point, hence having some 'tails' left

[Kevin Wood]

It is, as you say Kevin, only temporary

You have the old, black sensor with the 2 pin plug yes? Do I need to try and get you one from Teilo?

If you are in contact with Teilo then I would appreciate it if you could ask, but don't worry if not. I've found another supplier online but before spending 20 quid  on one I thought I'd investigate the current one a bit further. Have re-made the connector and that didn't help, so it probably is the sensor itself.

[Lazydocker]

It is, as you say Kevin, only temporary

You have the old, black sensor with the 2 pin plug yes? Do I need to try and get you one from Teilo?

If you are in contact with Teilo then I would appreciate it if you could ask, but don't worry if not. I've found another supplier online but before spending 20 quid  on one I thought I'd investigate the current one a bit further. Have re-made the connector and that didn't help, so it probably is the sensor itself.

I can try for you That sensor is temperamental... I had one fail within the first year The screw in ones seem to be better and more robust

[JamesV6CDX]

On the way back from Sainsburys earlier, on LPG, misfiring badly under load, but this time not switching back.

Had hot pizza in the car, so no time to faff about reading codes. Drove back on petrol, will investigate tomorrow.

Anyone got a match? 

[Kevin Wood]

On the way back from Sainsburys earlier, on LPG, misfiring badly under load, but this time not switching back.

Had hot pizza in the car, so no time to faff about reading codes. Drove back on petrol, will investigate tomorrow.

Anyone got a match? 

That does sound like an injector wiring fault.

[05omegav6]

Have found the piggyback plugs, got three with workable tails of at least 3"

Let me know if they're required

[JamesV6CDX]

I have to be honest in as much as I'm at a bit of a loss with this one now.

I have completely unravelled the wiring for injector circuit number 4 from the ECU pins (the wires that go to the LPG injectors, and the piggy backs) and inspected every mm of them. They are 100% solid, intact, fine. All of the connections into all of the push in connectors are fine, and there is no loss of continuity when wiggling them, etc..

What now? I've ruled out the injector, as I swapped a couple over, and it's still no4 it's complaining about.

It went 100+ miles fine after checking all the wiring, then yesterday kept erroring on gas (fast flashing light) with the only error logged "injector no4). Once you cleared the code, it would go straight back onto gas.

This isn't an issue with pressure/rpm/any other value being dropped. Its the Injector no4 circuit.

I can't see any benefit in re-wiring this circuit, given that it's tested fine both visually and with a meter?

Could it possible be something on the ECU circuit board? 

[Mrs Cakey]

Possible I suppose

Just a thought, as I know he has had this issue in the past, are all the injector plugs sitting home correctly? He had one that seemed to be OK but would just unplug a little periodically, normally when the engine was very hot and he was "making progress" At least, that's the phrase he used to tell me

[JamesV6CDX]

Possible I suppose

Just a thought, as I know he has had this issue in the past, are all the injector plugs sitting home correctly? He had one that seemed to be OK but would just unplug a little periodically, normally when the engine was very hot and he was "making progress" At least, that's the phrase he used to tell me

Yep, all fully home, and no amount of wiggling etc can break the connection... :/

[05omegav6]

Thinking through this, (it's ok, I am sitting down and there's a nurse on hand).

Is it possible that one of the pot 2 valves is sticking slightly open, affecting the gas pressure at the nozzle any carbon build up in the plenum/inlet tract

[JamesV6CDX]

Is it possible that one of the pot 2 valves is sticking slightly open, affecting the gas pressure at the nozzle any carbon build up in the plenum/inlet tract

Nope, because I switched the wiring and LPG feed to a different cylinder for elimination purposes.

Thinking through this, (it's ok, I am sitting down and there's a nurse on hand).

[05omegav6]

Engine valves not injectors pressumed pot2/lpg injector4...

[JamesV6CDX]

Engine valves not injectors pressumed pot2/lpg injector4...

Yeah I get that, but I've moved the troublesome injector circuit to a different cylinder (and hence different set of valves) on the engine... so that would eliminate that...

[05omegav6]

If the nozzles are fitted as per the guide, any blockage of any given nozzle would only affect that nozzle, moving the injector would prove only that the injector is not the problem

[JamesV6CDX]

If the nozzles are fitted as per the guide, any blockage of any given nozzle would only affect that nozzle, moving the injector would prove only that the injector is not the problem

5 o   o 6
3 o   o 4
1 o   o 2

With the above being the numbers of the actual cylinders on the engine, the corresponding LPG injector circuits (on the LPG loom) were originally configured as follows, in relation to the above:

5 o   o 4
3 o   o 2
1 o   o 6

(remember it doesn't matter which goes where, as long as the vapour hoses correspond with the same cylinder that the wiring is set up for)

So looking at the above picture, the circuit for number 4, top right, was erroring.

In order to eliminate the injector from the equation, I swapped the wiring, and vapour hoses, between (LPG) injectors number 4 and 6, so it is now configured as follows

5 o   o 6
3 o   o 2
1 o   o 4

So as you can see, the number 4 circuit now controls the front nearside injector, which due to the swap is now a different injector, different vapour pipe, different nozzle, and different physical cylinder altogether.

This is how a fault with the injector, any specific cylinder on the engine, valves, blockage etc, can be ruled out.

Get where I'm coming from?

[05omegav6]

Ok that now makes sense

Were the injectors new or s/h

[JamesV6CDX]

Ok that now makes sense

Were the injectors new or s/h

Brand new mate... They've done less than 3k I reckon..

[05omegav6]

Doesn't leave much else then

[JamesV6CDX]

Doesn't leave much else then

The LPG loom all seems actually fine... I'm honestly wondering if something is up in the ECU.

And, TBH, taking that to bits is a bit more than I want to do...

[05omegav6]

Are the ecus available as stand alone items