High CO Emissions

I took my car for the annual MOT test today and it failed on CO emissions. The maximum allowed is 0.200 I’m not certain what the actual reading was but it was off the scale on the machine. The Lambda reading was fine at 1.005 (max allowed is 1.030, and the HC was 68 (max allowed is 200 ) Has anyone got any ideas on what to check to rectify this high CO level ?
The car is always regularly serviced, the spark plugs, air and oil filters are less than 600 miles old, it runs sweet as a nut, it uses a maximum of about 1 pint of oil between regular 6000 mile oil changes, no coolant at all, and the exhaust system is all sound and gas tight.
thanks guys.

CO means richer. How much? Does it smell different? As all seems normal, I would first take it to another metering station and see what the level actually is (and back up the previous reading). Before going into anything like cats. Sorry you didn’t pass!

Hi David, thanks for the response. I’m 99% certain the reading was correct. The test station I use are always very obliging, the tester loves old cars and particularly Jags so he was very patient and helpful, when he saw the high reading for CO he tested it again on another gas analyzer just to be sure, both machines gave almost identical readings for CO levels. I didn’t take notice of the actual figures, I was focused on the pointer of the machine which settled hard over to the limit of the red ‘fail’ section on all the tests.

Casso, what’s the status of your MOT and the high carbon monoxide (CO) levels?

I ran across this nugget at:

"There’s also the dreaded catalytic converter – if this is not working effectively then it can cause an increase in dangerous emissions to be released from your vehicle.

If you have concerns that your car may fail its MOT due to emissions you could try Cataclean, a fuel additive which is claimed to reduce emissions by up to 60% by flushing the system and removing any pollutant build-up in the catalytic converter. At under £20 from car accessory shops it may help your car get through the MOT, however the cause of the raised emissions will still need to be looked at."

I have no affiliation with the above-cited Web site or Cataclean etc. etc. etc.

Hi Mike, at the moment my car is parked up on my driveway. I E.mailed the XJ40 specialist at the JEC for advice. It’s obviously a difficult problem to diagnose without seeing the car but he recommended a few things I can try. He suspected it may be down to bad grounding of the EMS because he’s had a couple of cars in his workshop with the same symptoms. He advised repositioning the earth wires on the bulkhead stud to a new location (maybe a bolt on the pedal box) and also adding two more earth wires from the inlet manifold to a good earthing point, then change the Oxy sensor and have the car re-tested. Its been pouring with rain for two weeks so I haven’t done anything yet.
I do use Cataclean, before the last four annual MOT’s I’ve added a bottle to 15 litres of fuel then took the car for a blast on a motorway, it’s always sailed through the emissions testing but not this time. I’ve always been sceptical about fuel additives to be honest, but a few years ago my son was struggling to get his classic mini through the test, the emissions were off the scale, in desperation after replacing almost the entire fuel and ignition system without success we poured a bottle of Cataclean in and without doing anything else it passed easily.
As soon as I’ve replaced the earths and had it retested I’ll let you know, probably early in the new year. cheers.

Thanks for the update, Casso. I hope the new/replaced ground wires work the magic for you. While I believe we all know how important good grounds are to the operation of our Jags this scenario is a new one for me. Thanks in advance for letting us know how this works and merry Christmas to you and yours.

It’s also a new one for me Mike. I have to admit I’m not too optimistic the advice from the JEC will make much difference, I’m aware poor grounds cause untold problems on XJ40’s so I’ve always kept mine clean and I’m confidant they are clean now, also I’ve had NO error messages and the car seemed to be running just fine until the emissions test highlighted the high CO. However, Dave Marks the guy who advised me owns a respected Ind Jaguar garage and has loads of experience with these cars and his advice in the past has always been spot on so it makes sense to do what he said, especially the adding of two new ground leads. Fingers crossed :grinning: Merry Christmas to you and your loved ones Mike.

So today I finally raised enough enthusiasm to start investigating the sky high CO reading that was highlighted at the MOT on Dec 4th. The car has not been driven or even started since that day. I thought I’d start with the ‘hardest’ job first and change the oxy sensor so I took it for a 25 mile drive first, primarily to get the sensor hot to aid removal but also to air the interior after standing so long. I’m baffled to be honest, the car runs so sweet, I selected ’ Fuel Inst ’ on the OBC and monitored the readings as I was driving. It was a still day without much headwind in either direction, at a constant 70 MPH on a flat section of motorway it flickered between 29 - 31 MPG which I think is excellent, on long steady climbs it would momentarily drop as low as 12 MPG as I added more throttle then it would level out to around the 18 - 23 MPG. Travelling downhill with little or no throttle it would jump up to 99. When I arrived home I left it idling for a while, no fuel smells from the tailpipes and both pipes are clean without any soot. I removed the plugs for a check and they are all a very light ‘biscuit’ colour with no build up of carbon to be seen ???. by that time the weather changed and rain was looming so I left the oxy sensor until tomorrow but I’m beginning to think changing it is just a waste of time. I’m thinking I’ll clean all the grounds as the JEC advised and have the emissions re-tested.

Do that.
If the mixture is right (probably is) and the cat isn’t converting as well as it used to it might explain the high readings. Not sure how to test that.