Secondary Air Cleaning - DIY (with DIY tool!)

[Ben1000]

I'm not super active here, but occasionally lurk. Anyhow I had the dreaded P0491/P0492 faults and decided to solve it my own way. I jotted down some notes into a DIY, see link....

https://drive.google.com/file/d/1ttA...ew?usp=sharing

Edit: Updated link with new version

[Shane Horning]

I'm not super active here, but occasionally lurk. Anyhow I had the dreaded P040941/P040942 faults and decided to solve it my own way. I jotted down some notes into a DIY, see link....

https://drive.google.com/file/d/1R5Y...ew?usp=sharing

Nice write up!

[LYKUNO]

Kudos for the impressive craftsmanship and well-documented procedure. Excellent job of thinking through and then creating the tool, providing essential cautionary statements, and thoroughly explaining each step of the process.

[S4'ed]

Ben1000 : Please add the measurements of the tape marks, from the spray hole, so that the camera measurement does not have to be redone by the next guy.

And, consider making and selling the tool...

Thanks!!

[Ben1000]

Thanks all, @S4'ed - good idea, I'll add these soon on another revision. I'd still recommend the camera to verify it worked, but realistically it's probably safe to do it without - once you get all the water flowing through the port (it's very apparent once this happens) at high pressure for a few minutes there's little chance that any meaningful junk can remain. I briefly toyed with the idea of selling a few - if there wasn't pressure involved I might, but too little to gain vs the liability on it. This should be something a local small machine shop or welder can knock out pretty quick though and still come out way ahead vs buying. Another idea for that might be to use an even smaller tube so you can thread both ends directly, no adapter/welding, then just cap one end (but it'd have to fit inside the port) and use some adapter fittings on the other to get it to pressure washer coupler size.

Edit: Instead of a cap, threading the inside of the pipe and using a plug would work even better. I'll add some plans for a version 2.0 no-weld/no-machining version in the next rev also. All that should be needed for that is the tube, a plug, a set of pipe tap/dies, and a micro drill set.

[S4'ed]

You can buy the hose with the sideways nozzle, and the depth scale, for $502....pricey but its not $1000 for the whole kit. This is the only part of the kit you really need, if you can't make your own hose/pipe thingey.

part number VAS6825/8
https://audi.snapon.com/SpecialTools...temId=49450123

[S4'ed]

What is the inside diameter of the port in the head? (the port that runs front-to-back)

[Ben1000]

What is the inside diameter of the port in the head? (the port that runs front-to-back)

Exactly 12mm for the bore itself (don't be fooled by the port, which is a bit bigger). The 3/8" tube (~9.5mm) seemed to be a good match for this, the water that came out when misaligned was forceful, but nothing more than you'd get from a water hose. If the tube were much larger I'd start to worry about making high pressure in the manifold and potentially hurting the combi valves.

With that in mind I think the winning combination for a no-weld version is the following:

- 3/8"OD tube, 0.058" wall, ~1/4"ID (McMaster 89955K118)
- 1/16"NPT plug, allen socket
- 1/8"NPT Female x 1/4"NPT Male adapter fitting/bushing (McMaster 9171K52)

Tap the end of the tube 1/16"NPT and install the plug. Then use a 1/8"NPT die on the OD of the other end of the pipe and install the adapter and standard 1/4" NPT female pressure washer coupler. Drill the orifice on the plugged end.

The only catch here is the 3/8"OD is in-between sizes for NPT threading. The taper will help account for this, but make sure there is good engagement at the adapter fitting. There may be a better way, open to ideas/improvement. Also note pressure limit on adapter, this version may be better suited to lower pressure electric pressure washers. Don't aim any of these at anything important, but this version especially since the plug could become a projectile...


(The crossover pipe arrives tomorrow and I'll be putting everything back together, I'll be able to get the port measurements off the tool then and will update)

[Ben1000]

Doc updated with measurements, first post in thread will be edited soon with updated link. The TSB doesn't give units, but after comparing their #'s to mine it's clear/confirmed they were in cm. I got the same results as them as far as distance between ports, but some offset (likely in their tool) made all the #'s different. My #'s are from the exact edge of the head/port to the center of each passage.

[S4'ed]

Thanks, nice work.

If my 2010 S4 runs into the SAI problem, I am debating if it wouldn't be easier for me to design an add-on electronic device to fool the SAI diagnostic so that the DTC "insufficent flow" doesn't trigger.

[Ben1000]

Update: Back on the road, all seems OK. It'll probably be a few days before all the readiness's come back OK, but so far no pending DTC for secondary air. Only thing of note was that the first start was very odd - the starter ran and it sputtered with misfires and never caught, it did this 3x. Almost sounded like no compression. On the next attempt I hit the gas pedal when starting, it fired up, snapped out of it, and every start since has been totally fine. I'd be interested if anyone can explain this, but I'm not too concerned.

If my 2010 S4 runs into the SAI problem, I am debating if it wouldn't be easier for me to design an add-on electronic device to fool the SAI diagnostic so that the DTC "insufficent flow" doesn't trigger.

Should be possible, having also considered that route and now having done the cleaning I'd say it's probably a wash (pun) as to which is easier; very different kinds of work. Main difference is if you've already ruled everything else out then the cleaning should be pretty much a sure thing fix - a lot of work, but it's done and over with in a few days whereas integrating a bypass circuit could be more of an ongoing project of testing/updating to get it working under all scenarios.

[Ben1000]

One more update for completeness - all readiness's were set (for the first time in about a year probably) after driving around for a while and successfully passed emissions inspection with 2 days to spare. Power seems to be up and it's subjectively smoother/better sounding. Maybe this is placebo because secondary air shouldn't have any effect on this; only thing I can think for that is since the secondary air passages point into the exhaust ports if there was also crud blocking the exhaust it could've been blasted out also.

[S4'ed]

Congrats, sound like a successful fix....but it sounds like the placebo effect concerning "more power, smoother".....like when people say their engine runs better after they change the oil......

[G-Can]

I have a question, why use water, instead of a brush, like the ones you can buy to clean sunroof drains, sink drains, etc. and stuck a vacuum on the hole to suck out all the dust?
like this? https://www.amazon.ca/Bozenu-Flexibl..._source=1&th=1