When to replace MAFs?

[MoRS6+]

Already had a health check a short while ago there. That's how they identified the boost-leak I had. However, I haven't had a power run since, so will be interesting (and nerve-wracking) to see what the old girl makes. Was a boost hose clip missing - crazy eh? Also identified a small hole in one of the intercoolers which has yet to be repaired. Was gonna wait until the cambelt change so they could do both at the same time. That hole might lose a tiny bit of power but shouldn't be much at all.

Even then though would the health-check identify an iffy or borderline MAF/N75?? Surely the only true way is to change and retest?

[CliveH]

Yes, a proper health check will pick up a dodgy MAF or N75. Change and retest would certainly be conclusive. Another option would be to swap with someone who has confirmed healthy MAFs/N75 - there will be plenty of other RS6s there that weekend

Are you still running the original ICs and hoses?

[MoRS6+]

Are you still running the original ICs and hoses?

Yep.

[CliveH]

Obviously new ICs is an expensive job but would be wise to replace the hoses with some decent ones.

[Shoppinit]

I wonder - if there was no difference, do you reckon Doug would take the new parts back? Or am I being too cheeky there?

You'd probably have no difficulty shifting them on. Or keep them as spares.

[CliveH]

Yea, I'd keep them as spares.

[MoRS6+]

Yes, a proper health check will pick up a dodgy MAF or N75. Change and retest would certainly be conclusive.?

I think I'll do my run and see what she makes before I start piddling around with changing stuff (not that I know how to anyway..). Last time at SRR, it was piss-poor! Only made 436 and 441hp respectively. Charlie said 'summit is up' and he was right - but I'm nervous about my MRC run.

Oh well - will drink plenty of coffee that day

[Shoppinit]

What kind of power are you expecting?

[MoRS6+]

What kind of power are you expecting?

Well fingers (toes, eyes, lips, bollox and tits) crossed, I'll get as near as damn it possible to factory power (473hp). I'm rather hoping that boost-leak was costing me circa 30-35hp. Heeeeeeeeeeere's hoping!

[Shoppinit]

Forgot you were in a plus! Are you going to log your power runs with the vagcom?

Has anyone heard of this place:
http://www.emissioncontrols.co.uk/page. ... wpage=home

[MoRS6+]

Forgot you were in a plus! Are you going to log your power runs with the vagcom?

I wasn't going to, no. I don't have the cable etc. But there will be people there with all the stuff - should I do it? Benefits/reasons for doing this?

[Shoppinit]

Interesting to see what your fueling / ignition is doing under load. Useful as a reference later for comparing to when you had a known power output.

[RS6-4dr911]

Yes, a proper health check will pick up a dodgy MAF or N75. Change and retest would certainly be conclusive. Another option would be to swap with someone who has confirmed healthy MAFs/N75 - there will be plenty of other RS6s there that weekend

Are you still running the original ICs and hoses?

And what exactly constitutes a proper health check? I've done some reading up on the subject and unless the MAF is flat out dead, determining that it's off takes some doing. N75 I think can be checked with VAG and if you see it cycling under boost, it is presumed well, but even then, how exactly do you know if it's truly healthy or like a middle aged man that looks healthy but is a heart attack waiting to happen?

Any diagnostic trickery would be helpful if you'd pass it on.


Thanks

[CliveH]

And what exactly constitutes a proper health check?

Unless you know what you're doing with Vagcom and know these engines, then the best answer is to go to a good independent specialist who really know their stuff.

[Shoppinit]

I've done some reading up on the subject and unless the MAF is flat out dead, determining that it's off takes some doing. N75 I think can be checked with VAG and if you see it cycling under boost, it is presumed well

I'd be interested in determining a method for testing MAFs. They're too expensive to change randomly. These are sensors that send values that can be easily logged with VCDS, so it should be easy enough to compare values with a healthy car up the rev range under full load (WOT). Now, just need to find someone with a healthy car!

I can't help feeling that a bad MAF would throw DTCs on lambda correction or the MAFs themselves, and that if nothing is going out of bounds, the MAF must be good. Am I missing something? I know that the E46 M3 suffers from MAF problems, but I'm trying to get my head around what the failure mode would be and how to eliminate the MAFs from the diagnostics. I know that those guys unplug the MAF to see if the car runs better in limp home mode, but that won't work for our turbo cars. Or rather, the cut in boost from being in limp mode will more than overshadow any improvement due to default fuelling when the MAFs are unplugged.

For the N75, just because the VCDS shows that the part is being cycled, doesn't mean that the solonoid is opening and closing cleanly or at all. There are 2 wires going to it, so the best the ECU can do is determine the resistance of the coil to know if the part is working or not. Please feel free to correct me if I'm wrong on this. The part is dirt cheap and easy to get to, so for me it's a preventative maintenance item. I'll be changing mine soon.