How to Diagnose transmission slipping on an RS6

[cmore]

Well my problems described in recent threads about my boost dropping off quickly still exists and I've replaced a number of things outside of the MAF. The MAFs seems to be functioning fine, but I haven't ruled them out. The N75 replacement and all vacuum lines didn't make a single difference.

The next steps is to make sure the transmission isn't starting to slip and then tuning back to the engine accordingly. My car has 34,000 miles and an OCT ECU/TCU upgrade with BPs values, downpipes, cats and exhaust.

I am not get any codes in the ECU/TCU after scanning all devices with my VAG-COM.

Is there a measuring block that I can log to review to determine if my transmission is slipping? I want to make sure I am not chasing a transmission issue when looking at the engine.

Thanks,
Chris

[AudiRS4ever]

Check 2 things first.
1. Check to make sure your airbox is on correctly and that the airbox seals aren't ruined.
2. Smoke the engine and see if your intrercoolers are blown (betting they are).

[cmore]

1) I've taken the airbox off about 15 times now and I'm almost an expert on making sure it is sealed.. BUT the seals don't seem very tight around the MAF/turbo inlet. Is that the seals you mean?

2) Not sure what you mean about smoking the engine - sorry for the ignorance.

Thanks!


Check 2 things first.
1. Check to make sure your airbox is on correctly and that the airbox seals aren't ruined.
2. Smoke the engine and see if your intrercoolers are blown (betting they are).

[AudiRS4ever]

1) I've taken the airbox off about 15 times now and I'm almost an expert on making sure it is sealed.. BUT the seals don't seem very tight around the MAF/turbo inlet. Is that the seals you mean?

2) Not sure what you mean about smoking the engine - sorry for the ignorance.

Thanks!

No problem. The seals that the MAF's go into. I replaced mine a few months back just because they were starting to look worn. They are not that tight, but if there is a leak it can make it feel like you hit a wall when you're under boost.

Smoking the engine. Any shop that deals with turbo cars and has a smoker should be able to do it. Airbox off, plug one side, smoke goes through the other side under a small amount of pressure. My car wasn't throwing any codes, but started to cut boost. Smoked car and guess what? Not one, but both intercoolers started smoking right at the seam. When the engine is being smoked you should not see any smoke coming from anywhere. If you do you have a vacumn leak where it is coming out of.

Hope this helps answer your questions.

[cmore]

Ahh, got it. I just called a friend of mine and he has a smoker. I will check that too as that could resolve it all if there was a leak.

Back to the original question, does anyone know if any VAG-COM block can be monitored for transmission slipping? Does the computer ALWAYS set a code as soon as it notices slip that requires the engine to be backed off?


No problem. The seals that the MAF's go into. I replaced mine a few months back just because they were starting to look worn. They are not that tight, but if there is a leak it can make it feel like you hit a wall when you're under boost.

Smoking the engine. Any shop that deals with turbo cars and has a smoker should be able to do it. Airbox off, plug one side, smoke goes through the other side under a small amount of pressure. My car wasn't throwing any codes, but started to cut boost. Smoked car and guess what? Not one, but both intercoolers started smoking right at the seam. When the engine is being smoked you should not see any smoke coming from anywhere. If you do you have a vacumn leak where it is coming out of.

Hope this helps answer your questions.

[DHall1]

The smoker

http://i950.photobucket.com/albums/ad348/03RSTT/RS6pics/blowing-smoke1-505x584.jpg?t=1267467640

Stock RS6 intercoolers suck when it comes to long term reliability. Mine have both started to leak at 30,000 miles. Junk.

[ttboost]

Is there a cost effective (insert laugh here) replacement that is bolt in, requiring no mods to fit?

[DHall1]

Not while my car is under Fidelity. Fidelty can put in 2 sets for all I care.

Mine just started....so the next time its in for any warranty work I will add the ICs to the list.

Out of pocket would be the Wagners but they are not simply bolt in and it takes work to save the factory ducting.

[TozoM8]

If it is slipping it will throw a code (incorrect gear ratio).

[RS6-4dr911]

1. I'll eat my chocolate hat if both intercoolers aren't leaking.

2. If it smokes, it could be vacuum OR boost leak, depends on where in the stream it is as to which it is.

3. Only non-OEM replacements for IC's I know of are Sportec, Wagner and Apikol, all require some jiggering to make them fit. Seems worth the hassle (or your mechanic's knuckles) given the history of the OEM units.

4. To check the transmission slippage, use the Transmission measuring block in VAGCOM, log engine rpm, input shaft rpm, output shaft rpm, TC clutch engagement. Plot them on a graph, they should have linear relationships to each other (a) above the stall speed of the TC (b) when the TCC shows engaged. IIRC, there have been a number of members with slipping trannies but no codes thrown.

5. Two sets of seals to be concerned about. The ones below the MAF's are about $125/pr, but typically are fine. The upper ones the airbox slips into on top of the MAF's are cheaper but more likely to cause problems, replace them, while there, inspect the bottom ones. Smoking will find it as well if it's bad.

6. As for Dave's question, "can I feel it?" You kidding? It's coming out my nose already.


Have fun.

[DHall1]

^^ I hear ya

[cmore]

Re: smoke the engine

Should I do this with the carbon fiber intake system on and the top removed or the while thing off? I've heard of people doing it both ways though with the intake system on would be harder, but would show leaks around the MAF.

Does anyone know someone who made a DIY boost leak tester? Since we don't have a real intake tube it is difficult to do it like other ones I've seen. Unless I do it on the circular intake tubes on the air box.

Thanks!

[AudiRS4ever]

I did mine with the airbox off. The technician that did it had a smoke machine made specifically for this. I don't know how reliable you will be able to get with a DIY kit. We plugged one side and smoked the other side. It took quite a while for the smoke reach the intercoolers, but when it did boy did those Walmart intercoolers show their ugly head. Like I said, I'd be shocked if yours weren't leaking just by the description. Even if it is something else that is causing your car to shut down like that I bet your intercoolers are leaking. Sorry, but I've learned what the weak links on these cars are and that's one of the biggest ones. Good luck to you and please let us know what it ends up being.

[cmore]

Ok, I just completed the transmission logging. You can check out the data and graph here:

http://motorsports.chrismore.com/2010/03/audi-rs6-transmission-logging.html

Doesn't look like any slip unless someone else notices something.

Thanks,
Chris

[p3u]

You should do another log, one that is much longer and that shows the TC in its closed state. With what you posted you can not determine anything.

[cmore]

Ok, here's the pull with the TC closed and held in 3rd gear at the bottom of my blog. engine RPM and input shaft RPMs are right on top of each other.

http://motorsports.chrismore.com/2010/03/audi-rs6-transmission-logging.html

[p3u]

Looks like you can rule out the TC slipping.

[cmore]

Wow... I'm on a roll today. I built a DIY boost leak tester as seen here:

http://motorsports.chrismore.com/2010/03/audi-rs6-diy-boost-leak-tester.html

What I found is that there was a huge amount of air leaking from the passenger side MAF. There was so much air leaking out that I was unable to build any pressure in the system. This could be part of the problem and I am going to look into replacing the seals. It really sounded like the top of the MAF so I will start with them.

Thanks!!
Chris

[hahnmgh63]

Remember, the air going through the MAF's isn't pressurized so it would have to be an obvious seal problem to cause much of a leak.

[JRS-RS6]

? -- Is there normally pressure at the MAF sensors? If the seals are designed to seal under vacuum this may not necessarily be a "real" life test. Did you check the Intercoolers and everything else on the downstream side of the Turbos?

[cmore]

I know - I expected some air to hiss out around the MAF sensors - especially at the bottom. I wanted to do two pressure tests. The first with the airbox on to see if there were any leaks around the MAF that I didn't know about. The second would be with the airbox off, which will be the real test. This test with the airbox on seemed to have been worth it, because air was flowing around very easily around the one MAF, but not the other. If they were all leaking equally then I would say it was probably normal. Previous people said they've had those seals go bad and it throws off the MAF readings. At this point I am just going through the car, part by part and making sure everything is fine. I will replace the seals and move on next to test the intercoolers with the intake removed.

[JRS-RS6]

Makes sense to me but before this your MAFs looked pretty close (Bank 1 was slightly lower over all like all the logs I have seen). It sounds like the seals will need to be done but even if they are leaking your actual boost is lower than the requested and this is measured by the MAP sensor just in front of the Throttle Body at top of the air plenum between the the Diverter Valves. A leak at the MAFs I would think should not have an effect on boost pressure holding they are before the Turbos. What it would do probably is make the car run lean which could than lead the ECU to drop boost if it senses knocking. I would think this could be seen in the requested boost.

[cmore]

@JRS-RS6 - agree! I am not putting money on this will make much of a difference. Since this is a 2003 car and has 30k mile it has sat most of its life. When I replaced all of the vacuum lines the rubber braided lines fell apart in my hands. At this point I am just going through the car step by step. Each diagnosis is just to learn about a particular aspect of the car and to determine if I need to take corrective action. In the end, I will have gone over everything and hopefully figured out this any other problems that may creep up in the near future.

[cmore]

Ok, I've built a new boost leak tester that I hooked right up to the turbo inlet ports. One side is plugged and the another is hooked to an air regulator.

Does anyone know if I should remove the oil fill cap when doing the boost test? I watched a video on a 1.8T doing this same test and they removed the oil cap because they didn't want to pressurize the crank case. I tried it on the RS6 and I cannot build any PSI in the system with the oil fill cap removed. As soon as I put the cap back on, I start to build boost. I've only pressurized the system to about 4psi to test. Am I going to have to go up to 15psi to test for leaks?

Thanks,
Chris