chudlin

The original sensor was a Bosch. I still have it lying around just in case I ever needed it. It was never bad in the first place, but it did make a bit of a difference when I replaced it

ltooz_a6_a8_q7

I think if you get rid of the MAF error, you'll fix the problem. Check all electrical wiring related to the MAF.

chudlin

I'll give it a try

chudlin

So I took the rocker cover off and there we're no broken pads or slack chains, the cams were in time, according to the dots. Checked valve springs and all seem to be in order. Tried the maf sensor swap and it made no difference. Took inlet manifold to check valves, all seem to be good.

ltooz_a6_a8_q7

I looked at the system related to the MAF, have you check these? I would look at the cleanliness of all the pins to the
connector going to the MAF, make sure no pins is bent or dirty.

Check for the broken levers

Giovanni Giovino 6.0+6.0TT

Hello Louis,
I think everyone is missing that Chudlin stated that "The exhaust on the same bank gets hot like the other bank, but hardly any gasses come from it where as the other side is chuffing as normal", and mainly that "hardly any gasses come from it" and the fact that he has true dual exhaust, as he stated he has no X-Pipe "I have two separate exhausts - one for each bank - no X pipe", now I know this is not what you mean Louis as far as airflow, I know you mean the electrical side of the MAF, but as one MAF and one air filter setup can not starve intake air from just one bank of the engine, and being the 4.2 only has one MAF, and one air filter, not two like the W12 or V-10 which in their case one of either MAF or filter would need to be clogged or closed off somehow to starve intake air, which we know is not the case with the 4.2 setup, and being that he has double check timing of the cams and more, how else would you account for the lack of exhaust gas/pressure flow on the one side of the engine that he is having problems with, he even stated "It does feel like the gasses are much hotter from that side compared to the bank that actually works", again, this leads to a clogged exhaust on the faulty side, when the CAT and or any part of the exhaust is clogged, those are the symptoms, reduced flow, and a much hotter exhaust gas, and YES Chudlin, this situation would cause multiple misfires on the faulty bank.
I suggest you drop the exhaust on that bank to check for a clogged CAT, or that the CAT has not broken down and the particles are not clogging the exhaust further down the line.

ltooz_a6_a8_q7

I didn't pay attention about the modification, I don't believe in modifying the exhaust like people up here. If I read carefully, I wouldn't spend time to try to help. People should accept the consequences when modifying the car.
The MAF error is there, I still think fixing the error will fix the problem, I do not know much about "true dual exhaust".

Thanks for pointing that out, I'm done with this thread.
Cheers,
Louis

dvs_dave

As swapping or unplugging the MAF makes no difference and the other symptoms described I think you've almost certainly got a collapsed/melted CAT on that side. Probably brought on by a combo of a dodgy/intermittent MAF sensor or wiring, a bad oxygen sensor on that side, and the exhaust system modification. Give the bad side cat a tap with a hammer, it should sound the same as the good one.

Either way you need to get that cat out to inspect it as you're only going to cause more damage by continuing to run it. Big job unfortunately....

chudlin

Thabk you very much for the assistance guys, and yes, reading th op usually helps! Thanks for the help. I'll have a look at the cats when I get some time. Would this problem cause a misfire even on idle? I mean, it does feel reasonably smooth on idle but I can feel the slight shudder.

I'll deffinately check out the cats if I can tomorrow.

Giovanni Giovino 6.0+6.0TT

Give us a little info here, did you remove the X-Pipe, or do the UK A8's not have them, not that it matters, just curious, also with a true dual exhaust its easier to know which side is your problem side (old school diagnostics ), I would also think because of improper exhaust flow due to a bad CAT, that the MAF would also throw a code because of improper intake airflow, not enough intake, and the build up of pressure in the four cylinders on that bank, if what I suspect is true (bad CAT) you may also hear popping in the intake of the MAF or the air filter.

Next, please tell us what you mean by this statement, "checked and adjusted timing on all cams and belt", what did you adjust, and why ?