Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing A tale of 3 cats

When we purchased our car I really liked the Plus 4 SS but Morgan would not provide it in LHD so I settled for the Plus 4 with a few options. One was that we had the factory fit what was essentially the same exhaust system as used in the Plus 4 SS.

In hind sight this was really experimental as they had never fitted it to any other standard Plus 4. Almost immediately we started getting engine warning lights and a fault that indicated catalyser failure. In effect, as became evident with the Plus 4 SS, the ECU needed a re-map.

Morgan tried to resolve the problem by replacing the supposed 200 CPSI (Cells Per Square Inch) catalyser with what was said to be a 400 CPSI catalyser and providing exhaust wrap. This helped but we still kept getting fault lights every so often, and a rich exhaust smell until I fitted the throttle bodies and had the new ECU correctly mapped. This will sound familiar to Plus 4 SS owners. There was another downside with the second catalyser by comparison to the first, more open, catalyser and that was there seemed to be a slight loss of mid range torque. The sound level was also reduced, and to be honest the first catalyser was a bit LOUD!

Recently I have become aware of a slight exhaust smell coming into the car and knowing that the pass on the last emissions test was marginal I started to worry that something was not right. A check of the log for the ECU revealed no anomalies and I started thinking of the possibility that the cat may not be functioning as well as it should. I was also interested in the possibility of using a 300 cell cat that Heinz had successfully used on his car in Germany. With a bit of help from him I tracked down the Italian supplier who has a very good name in catalysers. After some discussion with them and sending them my old cat I learned a few things.

Firstly the size of the cat, if it was 400 CPSI was what they would normally recommend for motors up to 1400 cc. If 300 CPSI it would be fine for motors of 1600cc (4/4 for example).
Secondly a cat of this type could have its efficiency reduced to 50% after as little as 60,000 km. I started to think it was quite probable that the early problems of rich mixture may have caused an early deterioration of the cat which has been in use for 50,000 km approximately.
Thirdly, as far as they were concerned, the cat that I sent them as a sample was already less that 300 CPSI probably about 250 CPSI! Regarding this I will try to work out how many cells there are in 1 square centimetre, an area and a number more easily counted than a square inch. From there I can quickly calculate the CPSI figure. In their opinion the original cat, the first one that is, was probably a free flowing, very open, cat suitable only for race homologation and when the CPSI was increased the size of the cat should have been increased to compensate.

I did get in touch with the UK manufacturer of the original exhaust system but after a couple of telephone calls followed by an email they have not given me the courtesy of a reply.

So after all this I ordered a new larger diameter, 126mm as against 110mm (the size of the original), 300 CPSI catalyser with a special coating to the matrix that is richer in the precious metals used by the catalyser. This is expensive but will start to operate at a lower temperature which is important because the system has quite long manifold tubes. At 300 CPSI the 126mm diameter is the smallest size that they would recommend for motors of about 2,000cc.

So far I have only been able to take the car on a 40km test drive. My first impression was that the sound was a little deeper and perhaps a little quieter. During the drive I had no exhaust smell and when I parked in the garage I left the car running for 5 minutes to check something else but on reflection there was no particularly noticeable exhaust smell. Regarding performance I did notice a fractional improvement in mid range torque to the degree that I sensed a little oversteer on some corners where I would not previously had oversteer. This, of course, is quite subjective without a before and after dyno test.

Whilst on the drive I had a computer hooked up to the ECU to log the real readouts of the sonda lambda etc. and I was more than pleased to discover that the map is functioning within the set parameters and this means no re-map is required. All this indicates that the exhaust gas flow is very similar to the that with the previous cat, if not improved slightly, and that the calculations for the new larger diameter cat which has the 300 CPSI core were correct.

All in all the result seems to be satisfactory.

The work was done by Brain Catalizzatori who interestingly also have the capacity to put new cores in used catalytic converters.

If anyone wants further details they are welcome to PM me.

Another stage in your capacity as acting, un-paid and unrecognised MMC Development Driver...

Well done...clearly the engine, exhaust and CPU are now in perfect harmony!!

Cupa a Tea anyone

Wow! Don't tell me you actually read all that

I read the lot - an interesting read and something that many of us may find ourselves returning to as our cars age.

I read it all way above my knowledge .I just worry about balancing my twin 48 's !

Still in sleep mode so speed scan
Wow! Don't tell me you actually read all that [/quote]

Nice informative and forensic summary Peter. Thank you for posting...

Every word...