lpg backfires on 1991 3.5 v8i disco

[pas]

Help

does anybody have any sugegstions what could be causing back fires when just touching the accelerator (not a problem when accelerator is wide open or shut)

the vehicle has been running on gas successfully for the last 3 years with 2 different engines and I have just finished a full engine rebuild. I have replaced the leads, amp, coil, dissy cap and  rotor arm, I'm getting desperate now as I'm supposed to be doing the mac4x4 challenge in it next weekend so I'm running out of time,

other symptoms include lacking in power to what I would be expecting, or could this be due to the engine still being tight after the rebuild

any help would be greatly appreciated

cheers

Paul

[Eeyore]

How's your airflow meter?

Also check for air leaks into the induction sytem that bypass the AFM.

Bet your bottom dollar that the lambda sensors are seeing a lean mixture in the exhaust and over fuelling to compensate. Lean mixtures will result from excess air entering the system by some means fair or foul. Over fuelling will cause the backfiring. Be carefull it doesn't blow the top of your air box!

Check this out before decidng that the lambdas are broken ('cos lambdas are darned expensive, especially if there's nothing wrong with 'em). A local garage assumed ours were lunched, but it turned out NOT to be the case.

How well is the valley gasket seating?

Hope some of this helps

cheers
Eeyore

[Bush Tucker Man]

Eeyore;
You're not got any caravanners in the family have you?

I ask because there's a lady on 'T&T' whos posts as 'Eeyores Mum' :D

[pas]

well looking at the plugs it is definitely running rich (at least on petrol anyway) but it can't be the lambda sensors as it doesn't have any, althought the airflow meter could be a source(although this wouldn't effect the gas set up) .
 the blow backs on gas are going through the exhaust and back thru the plenum chamber on different occasions (don't have to worry about the air box though as I have the steel cylinder  type and a blow back flap thing in line to stop this ,although I have just had to straighten the flap)

the valley gasket should be ok as I have just fitted it (a composite one at £18 a throw) but I have seen puff of smoke eminating from the valley on back fire and a smell of petrol that I'm not sure about

but i've decided to bite the bullet and am taking it to Rpi in norwich tommorrow to see if they can sort it as I'm running out of time (less than 3 days to sort it )

cheers

Paul

[Eeyore]

You're not got any caravanners in the family have you?

Errrrrr......no, not I. Or not that I know off.

I thought they were dedicated B&B types.......but you never know!!


On topic - can't suggest anything more re the backfiring. RPi should be able to sort it.

Let us know what they say!

cheers
 8)
Eeyore

[Kenny]

Paul,

What have you been doing to that poor car of yours this time.

It seems that you have changed all that I would suggest, however how well does it run on petrol ? What leads do you have ?

Damian

[pas]

well I went to rpi and they found the problem in 5 mins and fixed it inabout an hour, when I refitted the new amp didn't get the signal wires from the dissy the right way round so it was retarding instaed of advancing and causing back fires on petrol and gas, but they sorted it and have just got back from the mac 4x4 where it performed very well (with the exception of needing to bump start it this morning to come home ), so i'm now going to go and veg coz I'm Kna****d after having about 4 hrs sleep between sat am and sun pm

cheers

Paul