620S - odd power loss and misfire over 50mph

[hairyaardvark]

Hey folks, can anyone help with ideas for what could be wrong with my car?

620S (Duratec 2.0 supercharged), with 10K on the clock. Car has generally been behaving impeccably (aside from a dodgy fuel dial and jittery speedo) until the last few days. However now the car feels really low on power and is really juddery (feels like intermittent power loss and misfire) at anything over 50mph. Curiously, this only happens once the car is warmed up - it feels fine before that, cruising in 5th at motorway speeds.

I'm booked in to drop the car off at Caterham South in order to look into the electrical issues this weekend anyway - but now I'm not sure I'm going to be able to drive it there (over 100 miles), for fear of damaging the engine.

Any thoughts welcome

[hp7]

Sounds like the lambda sensor. I am on my third at 13,000 miles.

[mharris]

Change the spark plugs.

The MBE ECU diagnostics lead is a good investment and will more than likely point straight to the problem. It is expensive though.

Could be the lambda sensor. Try disconnecting it and see if the problem goes away.

[hairyaardvark]

Folks, just confirming this issue was indeed the lambda sensor! Now replaced and all fixed. The last one only lasted about 1500 miles though - not too impressive

[hp7]

hairyaardvark said:

Folks, just confirming this issue was indeed the lambda sensor! Now replaced and all fixed. The last one only lasted about 1500 miles though - not too impressive

It's a frustrating issue. On the one hand an easy fix (once diagnosed) but on the other something you wouldn't expect. In over 30 years of motoring and probably over 500,000 miles it's something which has only ever afflicted my 7. I do wonder whether all the pops and bangs on over-run might contribute. I have been thinking of having the "two Steves" re-map thd car. Maybe this winter...

If I was touring, or planning a trip over to the continent, a replacement lambda sensor would definitely be in my bag of spares.

[DCL]

It is simply the position they are installed in the exhaust. Lambda probes are very sensitive to moisture and are designed to be fitted to the top of a horizontal pipe, or at least less than 90 degrees so that they drain any condensate out. Caterham have decided to ignore that recommendation, preferring (one would amuse) the aesthetics. You can reduce failures by never shutting then down without reaching full temperature.

Edited by DCL on Friday 1st June 21:09