Misfire under load - getting worse - help !!

eightinavee said:

Arrrgh - you didnt mention the LPG before,does it misfire on LPG ? What system is fitted ? Normally we ignore the LPG system till it is running 100%on petrol,as the oxy sensors are switching on LPG it means they are being heated and are capable of switching - this means we can believe their outputs and watch what happens while running on petrol.Can you quantify what you mean by all over the place,it isnt the best trying to monitor their outputs with a multimeter - can you get hold of a scope?
It might be an idea to write up a flow chart to remind you what you have checked. Keep going !!

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LPG is the Tartarini system (vapouriser type - not direct injection). Yes, it does misfire on LPG but I think this could be due to the plugs being sooted-up.

Unfortunately I can't get hold of a scope so I will try to describe the typical needle movements on the multimeter:

(in approximate one second intervals)
1st second: Zero to 0.8v to 0.6v to 1.2v to zero.
2nd second: Zero to 0.6v to 1.2v to zero.
3rd second: Zero to 0.8v to zero.
4th second: Zero to 0.8v to 1.4v to 0.6v to zero.

Typically it is as shown in the first second (above). There is almost always a peak of about 1.2v. This is the o/side oxygen sensor.

The n/side oxygen sensor shows a similar pattern.

Whilst opening the throttle I get higher (variable) readings and on the overrun I get zero readings.

Please bear in mind the possible inaccuracy of the old analogue meter I am using.

I cleaned the plugs yesterday and within three miles of running on petrol they were sooty again.

Thanks for the help - I will 'keeg going' with your valuable help.

Alan