Technical (adaptives) help for a committed German Cerb owner

[itiejim]

Folks, I'm posting on behalf of my friend Günter from Germany who has a 4.2 Cerb which he has rebuilt over the last 12 months or so. He's had a few frustrations during the engine rebuild but has ended up with a good solid, powerful engine - a GPS verified 286 kph for over an hour on the autobahn seems to confirm this!

Anyway - the car has developed a running fault which makes one bank of cylinders run poorly, particularly at low revs, once the throttle is well open it seems to clear up. He has checked for air leaks, swapped over coil packs and lambda sensors etc, however the problem remains on the same bank.

When plugged into the diagnostics software the only way to get the adaptives balanced is by setting one throttle pot to 19 and the other (problematic) one to 35. Set up like this the car runs fine.

Can anyone shed any more light on why this may be or suggest anything else to check to help him continue terrorising the autobahn

[JensenA]

Faulty throttle pot? He could try swapping the TP leads over to see if the problem jumps to the opposite bank. The worst it can do is to eliminate one possible cause.

[itiejim]

I think that he has already swapped over anything electrical which would move the problem, I'll check though, thanks.

[stuthemong]

Looks like he's done some sensible things.

The fact that @ full throttle it works well (no closed loop control) would suggest the engine is fundamentally OK, but the 'closed loop' lambda/TPot/MAP etc.. control is hiccuping.

To be honest, the easiest way to work out what is going on is to get an airflow meter on the banks, can he get access to one? Ideally he'd just bung an airflow meter on each trumpet and I think it will bel clear as day what's up after he's done that.

If lambdas bounce & balance etc. with throttle at 35, it suggests that bank is flowing a lot more air than t'other. That could be because.

-Link bar set wrong (entire other bank really is flowing that much more air)
-Air link between inlets and head (you'd see this by the flow rates all being equal, but this 'problem' persisting, it's the ONLY otherr place the extra air could be coming from - has he sprayed EZ start around the gasket? If revs blip that's his problem)
-Dodgy inlet, bit of dirt or something could stop one inlet closing properly, or it may be slightly oval etc..
-Drilled bolt in one inlet may be overflowing air - are any of his drilled?
-Air leak in exhaust system (unlikely I think as this would give more weird than consistent results)

So if I were him, I'd buy an air flow meter, the post the results and we can have a think about what it is

[itiejim]

Thanks Stu, that seems like a sensible idea. I'll let him know and see how he gets on.