GEMS 4.6

Engine is perfectly driveable, perhaps a bit of a tappet-like rattle on one cylinder, but notably smelly at idle... I don't have a nose for these things, but it smells a bit rich... Does that mean the cats are up s*** creek (distinctly possible, but sounds expensive), or the MAFs playing up (i haven't removed it/ cleaned it at this point) ? HT leads and plugs are new. All the old plugs looked good on removal too. LH head gasket recently replaced. All injectors resistance tested consistently (although high end of expected range).

Any thoughts from our experts?

Rgds, Rob

I've not known a single P38 that doesn't have a tappet rattle. I replaced the cam followers in mine thinking that would cure it and it made no difference whatsoever. It's never got any worse or better so I just ignore it. You might have a dodgy lambda sensor so one bank is running the default fuelling strategy. Use the Nano to look at the live readings while the engine is running. You are looking for a lambda sensor that switches between 0 and 5V. If the first box shows CL, then it is fine but you may find one bank is reading Open Loop or CL Fault. You'll get no CEL and the car will appear to be running fine. You may also have a fault code for Lambda heater which means one sensor will stop giving an output at idle so it will go open loop. GEMS does benefit from a squirt of MAF cleaner but you'll need to reset the adaptive values afterwards and let it re-learn the trims.

Thanks, yes I forgot to mention the O2 sensors, I had a look in that part of nano the other day and nothing leapt out, but I'll have another look, now that I know what I'm looking for, tnx for the advice

I think O2 sensors look ok? No fault codes

Bank 1
CL. USE O2
pre cat sensor hops around 0-5v (should it hop, or be steady)
LT fuel trim 0 (just cleared it)
ST trim -3.75

Bank 2
CL.USE O2
precat sensor 1.79
LT trim 0
ST trim +3.75

elsewhere:
O2 config is 11
pre cat sensor heater is reading 1.12

Lambdas should flip flop between 0 and 5V or thereabouts. If Bank 2 is sitting at a steady 1.79 and not moving, it's dead. 1.79V is on the low side of centre point so will be telling the ECU it is a touch on the lean side, hence the positive short term trim on that bank.

Just to close this one out for anyone following. Injectors were professionally cleaned, problem solved...

Rob, does lambda voltage flick between 0 and 5v at idle too or only when the engine is under load?

The o2 sensors are hopping around at idle too.

Thanks, has relevance to something me and Gilbert have been talking about.