[Biturbos4] Fw: Detecting "limp" mode?

j y jimnetpa at yahoo.com
Thu Mar 13 21:16:02 PDT 2008

----- Forwarded Message ----
From: j y <jimnetpa at yahoo.com>
To: Chris Newbold <chris at newbold.org>; quickaudi at gmail.com
Cc: biturbos4 at www.audifans.com
Sent: Friday, March 14, 2008 12:13:13 AM
Subject: Re: [Biturbos4] Detecting "limp" mode?

Since you are not a chipped car and you are getting random/multiple cylinder misfires. I strongly suggest that you look at your coil-packs and spark plugs. That's the first suspect on chipped and non-chipped cars, especially a non-chipped car. My mechanic said that the Bosch coil-packs on S4s are usually good for about 85-100k before they start acting up. I was lucky and got over 100k on the original (i.e. "stock") coil-packs with my Stage 1, 2, and 3 S4, but I definitely picked up random misfires with VAG. 
My mechanic said that this was a combination of the mods (X-chip, RS4 MAF, K04s, larger injectors, etc.) and my S4's age (MY 2000, production year 11/99). Personally, I've only gone into (throttle cut induced) "limp mode" as a result of over-boosting (20+ psi) and when the torque converter on my tip tranny died ("tranny limp mode", which is possible on a tip). My S4 has never gone into limp mode under normal (9 psi or less, which is the stock boost level on a non-chipped S4) boost conditions. 
Also, if you have an early S4 (MY 2000, MY early 2001), you should also replace the ignition amplifiers on top of the air-box (if they are the original (i.e. "stock") set), there are two. They are also known to cause random/multiple unexplained mis-fires along with coil-packs. When you change your coil-packs, be sure to put in new spark plugs.
Good luck with your diagnosis.

----- Original Message ----
From: Chris Newbold <chris at newbold.org>
To: quickaudi at gmail.com
Cc: biturbos4 at www.audifans.com
Sent: Thursday, March 13, 2008 11:10:06 PM
Subject: Re: [Biturbos4] Detecting "limp" mode?

On Thu, Mar 13, 2008 at 10:11 PM, Joel Liggins <quickaudi at gmail.com> wrote:

>  Bailey DVs have to be serviced between 15k and 25k miles.  I believe you can
>  find the procedure on their website.  Probably not causing the issue, but
>  couldn't hurt to try.

I'll check it out; good to know that this needs to be done.

>  If you've had the "random multiple misfires" code, then something definitely
>  isn't right.  Those just don't randomly appear.  Is that the code you had,
>  or was it a specific bank/cylinder?

Both, actually. I've got the "random, multiple" code as well as a
cylinder-specific code.

I can imagine how to troubleshoot the cylinder-specific misfires (swap
coil packs, etc.) Any tips on how to go hunting for the
"random-multiple" issue?

>  Random thought: have you checked the brake booster hose that plugs into the
>  accordian hose?  Caused me to run rich and have misfires once.

I'll give it a look in the morning.

>  Are your oxygen sensors stock as well?  (i.e., not been replaced)

Yup; all four are still original. I'm actually surprised that at least
one hasn't gone so far off the map as to trigger a CEL by now....

>  As for a measuring block in vagcom, if you do a 3rd gear WOT run and log
>  block 003, you might see a throttle cut condition (throttle plate should be
>  100% from 4k rpm on), or if you log block 115, you can monitor boost
>  pressure, both requested and actual.

The specified-vs-actual boost graph is pretty much the only one I know
to try. I did a couple of 2nd-3rd gear pulls tonight and the results
didn't look too ratty. Little spikes when lifting and the occasional
one when jumping on the throttle at low RPM. It looked like the ECU
pretty much got the boost it asked for-- no major discrepancy between
the specified level and the actual.

I guess this says that, if there is an issue, it's causing the ECU to
hold back rather than a problem achieving the boost the ECU asked

Thanks for the suggestions.

2001.5 S4 Avant 6spd
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