4.2 AUX vs AWN- engine differences?

[S/RConcepts]

Hey everyone, I'm in need of a bit of advice and I hope one of you guys might know the answer I'm looking for.

Here's what's going on. I recently acquired a 2002 A6 Quattro with a 4.2 V8. I got the vehicle after the owner gave up trying to figure out the cause of the misfires on cylinders 6 and 8. It turns out one of the cam chain tensioners decided to spit out the plastic guide. I've done a compression test, and all of the cylinders test above 200 psi, with the exception of #6, which tested at 90 psi. I've looked down the cylinder with a borescope and I see there has been piston/valve contact on the top exhaust valve. So, I believe she needs a new engine, as this seems to be the best route vs. pulling the head and just replacing what's bad.

Now, here's where it gets a bit interesting- I suspect it's been here before, and has had the engine changed previously. It should have an AWN engine, however the block is stamped AUX.

What I'd like to do is put a proper AWN back in, but I'd like to know if there are any differences in external components between the two- i.e. things like lines, hoses, wiring, sensors, etc.- so I can get her back to the way she came from the factory, if need be.

So, is there anything I should check? Also, is there a way I can verify that I still have my original PCM, and not the one out of a donor if I don't have VAG-COM (yet)? I do have OBDEleven, but I did have to enter the VIN, which supposedly the 02's should know themselves.

Thanks in advance for any help you can give me!

[rollerton]

99% sure that the engine itself is pretty much identical. The only real difference I can think of might be the exhaust manifolds? I think the AWN had no tiny upper cats, only the large ones down below in the downpipes. OR maybe it's the AUX. I dunno, but the one thing that they changed that matters was the early V8 had only 2 cats underneath like the S6, they added a pair of small CATs in late 01' If memory serves? That and some can-bus/ hardware changes is why the ECU was changed I think. But there's nothing physical that prevents swapping any of the C5 V8's between chassis.

[Mad Cow]

Keep in mind that the exhaust manifolds have to match the downpipes, they're not cross compatible. I learned that the hard way.

[seishuku]

The engines should be physically the same, biggest change was engine management... Went from ME7.1 to ME7.1.1, which the harnesses aren't compatible IIRC, but that shouldn't be an issue for you (it should already be ME7.1.1).

[S/RConcepts]

Thanks for the responses, everyone!

The car still does have the correct AWN manifolds/downpipes. In fact, the passenger's side cat/downpipe and both O2 sensors were actually replaced about 1k miles ago with a really nice quality pipe and proper Bosch O2s (I have a receipt from a shop with about $2k worth of work that was done to it). So, that part is good news.

I still have to make sure the ECM is the proper one, I figure the easiest way to confirm at this point is to Dremel the 2 ECM 'cage' security bolts, remove the sleeve, and check the actual P/N on the ECM. I'll report back with my findings.

[seishuku]

Pretty sure if the shear bolts are still in place, it's likely still the original ECU.

[rollerton]

I still have to make sure the ECM is the proper one, I figure the easiest way to confirm at this point is to Dremel the 2 ECM 'cage' security bolts, remove the sleeve, and check the actual P/N on the ECM. I'll report back with my findings.

The ECU part# appears in the header any time you scan the module with Vag Com. Easier than going through the trouble of getting to it physically.

[S/RConcepts]

Ok, I was able to confirm that it has the factory ECU, just took a bit of hunting with OBDEleven, so this sets my mind at ease.

On a side note, does the serial number on the engine stamped below the engine code correspond with the original car's VIN? Since I don't have the original engine, I have nothing to compare to.

Thanks for everyone's help here so far, whilst I try to figure out what direction I'd like to take this poor thing in.