Emissions

I took my 1995 4.0 for it's MOT yesterday and at the time it was running on petrol, the tester has obviously noticed the LPG system and performed an LPG test which means it's the non CAT test.

Since it was the non CAT test even though it was running on petrol at the time. The results though wouldn't have passed on the normal petrol test so I want to try and fix that.

CO: (Limits <= 3.5%) (Value 0.771%)
HC: (Limits 1200 ppm) (Value 891ppm)

For a normal CAT test the limits would be <= 0.200% CO, and <=200ppm for the HC.

Apparently from my friend who was driving behind it a while ago the car stinks under hard acceleration, I know it's an old car (and an even older engine design) but surely it shouldn't be noticeable?

I've checked the MAF sensor and that is outputting the correct voltage as per RAVE, lambdas seem to be OK when looking at them using the LPG software. So what else should I check?

Thanks

You say the oxy sensors are OK,does this mean they are switching at approx once per second between 5 and 0v ? Also where are the fuel trims at ?

Yeah oxygen sensors switch at the correct rate.

I don't have a proper diagnostics machine so I could only take a look using my ODB2 reader. It didn't seem to be able to retrieve the long term fuel trims instead it just provided me with -79.7% for each bank since I can't imagine both would be exactly the same value I assume that means it can't read them.

For the short term fuel trims it hovered between -3 to -7 for each bank, the car wasn't fully warmed up though.

If the trims keep moving around thats a good sign in as much as its clearly running closed loop -ie with feedback from the oxy sensors.
I'd be looking at dodgy plug leads/plugs causing a partial misfire first.

Probably a silly question but what is the best way to check the spark plugs and leads? I replaced the spark plugs a few thousand miles ago so I'll take them out again and check if there's anything obviously wrong with them.

The leads I've got are magnecor ones that were with it when I bought it, no idea how long they've been on.

I replaced the catalytic converters today and the difference is phenomenal, I no longer have a flat spot where it looses power when accelerating, the exhaust just smells like hot air rather than like a steam train.

I imagine the emissions problem is now fixed then. I just bought a cheap cat of ebay for £115 which I didn't imagine would work well but it seems fine for now.