Pug 306 oxygen sensor

There is one potential problem. Your car might be fitted with a Marelli 8P engine management system. You can identify it by a label fitted to the engine ECU. It will have a part number IAW8P10. If it is this part number there have been several modifications to the system. Also on this ECU you will find a number of the form 16XXX.XXX. If the first part of this number is lower than 16304 , then there is a replacement ECU available. It is often necessary to fit the updated part in order that cars of this age can pass the MOT. If it is one of the earlier numbers , you made need to change the ECU , the only good news is that you probably do not need to change the oxygen sensor if that is any consolation. You can buy updated ECUs on exchange from

Thanks for the detailed notes Mike - I'll keep a good lookout for all that

Here's his numbers....

Fast idle test: Limits Actual

RPM 2950/3250 3096 Pass CO % VOL 0.30 9.95 Fail HC ppm VOL 200 1264 Fail Lambda 0.97/1.15 0.61 Fail

Natural idle test: Limits Actual

RPM 750/950 849 Pass CO % VOL 0.50 2.91 Fail

That looks like a stuffed sensor to me, I'm not even going to bother checking it since it went though the test last year with flying colours. New sensor is on order...

Hi Group, Those figures sound familier and are consistent with the sort of problems the early type ECU can cause. It ususall;y shows as running lean on the fast idle test which is exactly what the figures show. The problems are , that the early ones have problems with the internal 'adaption strategy' which means at some time in a vehicle's life , this sort of problem occurs. You may be right that it may be just a lambda sensor in this case. I shall be interested to see the new sensor cures the fault without changing the ECU. Regards Mike

I think those figues show it as running rich :-))

Graham

The results are conflicting , The CO is high (running rich) but the Lambda reading is also high which should tell the system to reduce the mixture strength , this is obviously not happening , so something is stopping the control system working. The guess is whether the Lambda sensor is incorrect , or if the ECU is just not responding to lambda. The third possibility is that the engine vacuum is very low (possibly following the head job) and that the engine management system is fine , but I am assuming that this has been checked. Regards

Opened the bonnet and looked in despair at the engine. Couldn't even see the exhaust....:-( so back tomorrow with some stands and a trolley jack.

Could the CHT sensor be giving bad readings (or not even reconnected after the head swap) thus leaving it permanantly in cold-start mode?

It certainly wouldnt remain in 'cold start mode', with an open circuit, short circuit or implausible reading the ECU will substitute either its own fixed value- usually around 80deg (which makes cold starting abit tricky and idle speed will tend to be too slow) OR with more recent ECU's it is clever enough to guess the CTS reading based on air temp, and how long the engine has been running and under what conditions, and fuel accordingly. They are surprisingly accurate to within about 5 deg too!!

Tim..