Failed MOT on Gas, had to use petrol to get through emmissions

[Mud_Medic]

Hi Guys

I would like to pick your brains... even if this is a no-brainer

My 4.0 thor engined Disco II just failed its MOT (how many times have I heard that one on here :'( )

Running on gas I had a CO of 8%! Hydrocarbons were 0!

I am currently running a single point injection system with IMPCO emulators. This is not the best setup for this vehicle I know, but it is what it had on it when I bought it, and as it is my plaything, I don't want to spend thousands on an injection system.

The plugs and leads have been changed, and still no improvement. A new MAF sensor, and it passed on petrol, but still 8% CO on gas, even after leaning up the mixture.

Where do I go from here  :-k.

Thanks in advance.

Ed

[Landynuts]

I had the same problem last year, but this year I took it for a really hard blast on the way to the MOT and the co was almost 0.  It may be a silly question but when you did the plugs and leads did you change the cap and rotor arm? I would also change the air filter if it has not been done recently.

[Range Rover Blues]

Change to oil before the MOT too.

But TBH if it's passed then leave it alone, it's running ok isn't it?

Getting a car to run perfectly on both LPG and petrol is not easy, one or the other has to be compramised.

[Mud_Medic]

Thanks for that... It doesn't have a distributor, it is all electronic, with a block which sits behind the engine.... Makes HT cables a pain to change.

Yep, it runs fine now on petrol, but want to run on gas as the fuel is half the price... even if this means reducing the efficiency on petrol.

Ed

[Range Rover Blues]

Ahhh, it finally cloicked what you meant about the LPG not being ideal, it's  a THOR injection (you did say, I din't read it properly).

TBH it's a bit new for me then, but I think yoususpect the same as me, the petrol ECU is way too smart for the LPG setup for a start, how that effects your LPG mix :-k

Unless you have a leaky injector :doh:

[Rossko]

Impossible to say whats going on without some more diagnostics.

I hope this is a closed-loop system, even if it is single point - i.e. stepper motor in the gas feed hose.   If so, the next step would be to hook a laptop up to the gas ECU and see what it thinks.

If its an open-loop system you're on a hiding to nothing, hopelessly unsuitable.  ( whereas a closed loop is just plain unsuitable  ;) )

More than likely it's a tired vaporiser, they tend to go rich at idle with age but perform okay under power.   

cheers, Ross K