Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing That Yellow "Engine" Light

They did Peter. My lambda sensor failed again on the way over to the factory to get the throttle bodies fitted and Mark Baldwin told me it wasn't an issue as the new ECU ignored the lambda readings and relied on the mapping for emissions.

Oh so it wasn't that they actually got the cat to work, they just resolved it by ignoring the problem

There never was a "cat problem", let me explain....

Each cat has 2 lambda probes, one on the inlet side and one on the outlet side. Lambda probes measure the amount of oxygen in the exhaust. In a car with a "closed loop" system they also indirectly measure the fuel air mix in the engine.

The right inlet probe gave an out of range reading, indicating that the fuel/air mix went out of range for a moment. The cause? Possibly there is an air leak diluting the gas mix out of range, or the probe malfunctioned or some other cause. Or just some dirt from the exhaust valve came off and hit the lambda sensor for a moment till it burnt off. There are many possibilities.

If the error message is from the downstream sensor then it is possible the cat isn't working. In my case the cat is fine.

Is that all clear?

The correct solution is to clear the error message and see what happens: if the error returns further investigation is needed, if it doesn't come back it is safe to ignore the first error message.

I think Peter (Gambalunga) is referring to Jays 4/4 Sport, which did have a Cat problem...

After 20,000 miles the exhaust on Aldermog has a nice deep burble with an occasional "pop..pop...pop on the over run and a hard snarl at above 5000 rpm. Grgeous.

Peter.....I think I'll wait for a few more miles to build up.....only up to 900 miles now and hopefully the sound will develop!

Graham....my cat never was faulty, the lambda probe was. On the Librands exhaust system you only fit the precat probe, the after cat probe is redundant.

Ah! On the other hand we have what is essentially the Plus 4 SS system plus the second sonda lambda sensor which checks the functioning of the cat (in compliance with homologation regs.). Unfortunately in our case there are times when the cat does not get hot enough to function, or cools down, and after a certain period programed into the ECU the light comes on.

Gas analysis tests indicate the functioning of the cat is marginal and this is in part due to the longer exhaust manifold but I am reliably informed that it can also be contributed to by tiny variations between one engine and another.

One thing that we may try is a faster upstream sensor which may help a little by adjusting the fuel mix a little sooner.

The Service Manager at Williams said that the lambda probes used by Morgan are not the best and they have had a number of failures and a larger numbers of "slow" sensors. So possibly more expensive "racing" sensors might solve most problems.

A week later and the light has stayed off.

Seems it was a one off problem, possibly caused by me moving the air intake?
When I got the car it was pointing down in front of the block, I lifted it so it now sits above the top of the radiator, for some ram air effect.....