1998 V8i Disco Backfiring

Evening All,

I have a 1998 3.9ltr V8i Discovery Automatic gas converted.

When running on petrol the engine backfires between 1000 and 2000 revs, after 2000 revs the engine doesnt backfire as bad and doesnt feel as rough. When I pull up at a junction or roundabout the engine stalls or I loose power and struggle to get going again. However when I switch over to LPG the engine runs like a dream.

So far I have

Changed the fuel filter
Tested the fuel pump (working)
Tested the fuel pressure in the rail, pump (all good)
Tested the fuel pressure regulator (works fine)
Tested the fuel injectors with a stethascope (firing ok)

Tommorow I am going to change the spark plugs.

Has anyone got any other idea's.

Cheers

John

Hi John,

Tomorrow we will disconnect the gas to confirm no gas is leeking in to contaminate the petrol mixture.

Don1 said:

Hi John,

Tomorrow we will disconnect the gas to confirm no gas is leeking in to contaminate the petrol mixture.

Click to expand...

Hi Don1,

Sounds like a plan, how do we disconnect the gas though? do we use the valve on the gas tanks?

John

Thought we might just remove the gas feed pipe from the plenum chamber and plug the connection. Should be no gas coming from the pipe any way but I'm sure we will smell it if any is weeping through.
We could always test with a match, that way if we can't find the problem at least we get rid of the car. Ha Ha Ha.

Don1 said:

Thought we might just remove the gas feed pipe from the plenum chamber and plug the connection. Should be no gas coming from the pipe any way but I'm sure we will smell it if any is weeping through.
We could always test with a match, that way if we can't find the problem at least we get rid of the car. Ha Ha Ha.

Click to expand...

He He I think Sheila likes that idea, I miss my baby though, looking forward to seeing it again tommorow and getting that good old man smell, oil, petrol, sweat n beer.

backfiring is weak spark especially on lpg as it needs stronger spark than petrol

Looks like problem may be solved, tonight I ran home with the MAF sensor unplugged and it ran like a dream on both petrol and lpg.

One last question to finish this off.

Can I run the Disco with the MAF sensor unplugged until the new one arrives.

Thanks

John