Last week I was hunting a CO analyzer and a Gasstaster From Gunson LTD in england was located( it looks like the same one that JC Whitney sells).

I wrote to them to find out about compatibility for this application and here's what I found out:

Question:

"Will the gasstester pro work properly on a '90 Volvo 240 for mixture adjustment?

The CO readings must be taken before the cat converter through a small tapped hole , same size as an O2 sensor hole ."

Response From John at Gunson:

"Regret that the Gastester would require modification for which we have no data to perform in this manner. It could in theory be done, but would call for a lot of research and experimentation. We could not assist with this. It would be better to use an analyser that incorporates an electrical pump."

I wonder if it is possible to calculate the difference in the reading before the Cat and after at the tailpipe?

_Robert