RS6 entering "limp" mode without error codes, require battery pull - Thoughts??

[FUngusmud]

Hi Folks. MTM ECU and TCU chipped car. Every 10/15 drives the RS6 enters a state where the ECU limits boost to about 1/2 of normal ( 7-8 psi). There are no error codes in the TCU or ECU and resetting fault codes does not fix it. Pulling the ECU power for 30 seconds is the only way to bring it back to full power.

All stats in the ECU look perfect except for either the wastgate duty cycle being lower or the throttle position closing to cut power and keep boost much lower than normal.

Anyone ever seen this? Any thoughts?

[gjg]

did you talk to mtm?

[FUngusmud]

Awaiting response from US reseller.

[skiwi]

are you sure there are no other codes?

if it was overboost protection, i would expect a code to be thrown. i would suggest that mtm is your best option as it is their coding.

[FUngusmud]

Definitely no codes. Thanks for the response tho. I'm going to check the SEL block that indicates the ECU being set for a lower % of power output next time just to make sure it didn't get changed somehow (usually only a manual setting tho).

Thanks
--Dan

[Hy Octane]

Mine does this and its stock.. They still cant find out what causes it to think its running to hot when its not and cut the boost..no codes either..However, turning off the ingnition and restarting will reset it..

[FUngusmud]

That's interesting to hear. Do you know where they are seeing the "running hot"? I.e. is it the engine temp sensor, EGT's, Intake air temp? Slight difference tho, I have to pull the battery or ECU to reset it.

Regardless, it gives me someplace to look.

I also think it's happened a few times after a quick start/stop (< 30 seconds run time). I'm still trying to coorelate an event with the onset of the problem.

I'll let everyone know if I ever track it down. MTM is also investigating.
-Dan

[skiwi]

good idea to log the boost blocks. the boost regulation system is supposed to do just that in circumstances where high temps, poor gas, etc. dictate. the boost required and boost supplied blocks would be interesting.

[FUngusmud]

Did it again yesterday. Logged every imaginable block, everything looks perfect and identical whether in busted mode or not. (Except for the boost and throttle cut to 40%).

Isn't related to quick start/stops either.

Waiting to hear from MTM.

[John DNA]

Have you checked for a boost leak? Usually one of the front hoses is the guilty party on this.

On the latter software versions there is an extra boost routine included.

[John DNA]

Did it again yesterday. Logged every imaginable block, everything looks perfect and identical whether in busted mode or not. (Except for the boost and throttle cut to 40%).

Isn't related to quick start/stops either.

Waiting to hear from MTM.

Do you know your ECU code and software version from VAG-COM ?

[FUngusmud]

Boost leak: I doubt it, actual and requested are pretty close.. Actually, actual is a tad higher. I'd expect to see a positive or negative boost deviation if a leak exists. No "rushing air" either as I usually hear on the S4 when I had leaks. I wish I had a way to pressure test the intake tho.

Software version: 4D1 907 558 D 4.2l V8/5VT G01 0003

[jimmy94507]

Just a follow up.
Did you discover what was causing your performance degradation?
Has the problem been resolved to your satisfaction?

Thank you, Jimmy S.

[FUngusmud]

Nope, still haven't figured it out. Not my daily driver, so I just yank the battery and live with it. One of these days I'll bug MTM again. I've troubleshot all I could without replacing the ECU or TCU.

[jimmy94507]

HI,

Really sorry to hear that you're still living with the problem.
From your description, I know of another RS6 with what appears to be the same problem with the MTM chip set. Unplugging the batterywould give him the temporary fix. Then the problem comes back.
Have they offered to trouble shoot the ECU?

Regards, Jimmy S.

[FUngusmud]

Nope. I sent them a few e-mail sometime back. They said they would dig into it, never heard back. I'll start bugging them in a while again.

If you could put me in touch with this fellow, maybe we can find something common, or work together to debug.

[jimmy94507]

Hi _____,

I sent e-mail suggesting he look at this thread. Hope he's not travelling.
Send me an e-mail or PM with your contact info and I'll follow up with him in the next couple days.


Regards, Jimmy S.
jimmys@cableone.net

[42TT]

Fungusmund - I assume your ECU was modified by the way of de-soldering the original chip and either burning that or replacing it with a new chip?

If so i would have them check the contacts as the ecu compartment holds alot of heat and can cause dry joints casuing your exact problem, that is why the factory soldering use's silver solder.

Cheers
42tt

[jonas21]

I know that there are exhaust control units near the turbos which do not log data on the earlier RS6 ones. If one of them has a problem with whatever you will not see any fault log but boost will be limited. Quattro knows about this. Newer cars include units that do log data. You should have your dealer check back with quattro to see if you are affected.

[FUngusmud]

Thanks for the info on the cold solder joints and the unmonitored EGT sensors. I'll see if my dealer can dig anything up to determine if mine of monitored or not.

[chrisTG]

hi im a new member brought a rs6 6 months ago suspension went good job had warrenty now got no turbo boost no leaks no codes can any one help when i get home i will disconnect battery to see if full boost comes back

[Hy Octane]

Its pretty simple really. You chipped it and it is acting up. Remove the chipset and all should be fine. It continues to amaze me that so many folks who chip their cars and have trouble are surprised..
The fact that you send in your ecu and they modify it removes any ability for the tuner to double check that all is well with their work.. thus you get left with these kind of problems. The only way I would do this is if the car can physically be in the tuners shop for the mod. Tuning via Air Mail and email is not an option. Good luck.

[jonas21]

Hy Octane, that is not really that simple. Modifying the ECU doesnt cause any fault logging ability to be lost. Its true that most dealers/repair shops will send you back to your tuner to downgrade to the original software. However some tuners (for example wetterauer) provide the ability to add a second chip to the ECU. You then have a extra "virtual" switch in your car where you can switch between normal and enhanced ECU. This costs some mere 300 Euro extra. (Of course the switch can only be used when the engine is turned off). I can only highly recommend this feature.




Its pretty simple really. You chipped it and it is acting up. Remove the chipset and all should be fine. It continues to amaze me that so many folks who chip their cars and have trouble are surprised..
The fact that you send in your ecu and they modify it removes any ability for the tuner to double check that all is well with their work.. thus you get left with these kind of problems. The only way I would do this is if the car can physically be in the tuners shop for the mod. Tuning via Air Mail and email is not an option. Good luck.

[FUngusmud]

Chris,
What were the results of the battery disconnect?