The dreaded limp mode!

[Verse1]

Hi all,

I've got a little issue that I'm trying to figure out without VAGCOM (as I have a RossTech incoming but it's not here yet: ()

Over the past week my '01 S4 has been going into limp mode every time I drive it. It started out about 5 days ago coming home from work, I accelerated and it felt like it surged then went into limp mode. Parked it up went to work in the morning and it was fine then came home and again on the way home some weird surging and into limp mode. Now every time I drive it it'll go into limp. I can feel when it's about to do it as it will get a little surge/hesitation (unless this is it actually going into limp mode?)

Ever since I bought the car about a month back it's had an intermittent hesitation which would happen sometimes under full throttle and sometimes just part throttle but always under positive boost conditions.

I'm hoping someone may have had similar happen and can possibly point me in the right direction.

Cheers,
Nick

[justinholly]

Any cel? Go to your local vw audi shop an have them do a vag scan. Might just be a boost leak, have u started tracing all the boost an vacuum lines?


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[Verse1]

Any cel? Go to your local vw audi shop an have them do a vag scan. Might just be a boost leak, have u started tracing all the boost an vacuum lines?


Sent from my iPad using Tapatalk

Nope hasn't thrown a CEL ever. I've got a mechanical boost gauge hooked up and it's got a steady 15psi (MTM stage1) and Vac is on 22 without AC or 17 with AC at idle.
My RossTech should be here Monday or Tuesday so I can check it properly then, was just going someone may have some ideas before then.

[justinholly]

Nope hasn't thrown a CEL ever. I've got a mechanical boost gauge hooked up and it's got a steady 15psi (MTM stage1) and Vac is on 22 without AC or 17 with AC at idle.
My RossTech should be here Monday or Tuesday so I can check it properly then, was just going someone may have some ideas before then.

I had a bad egt an that's what would happen under boost it would surge an jump into limpmode only way to know for sure is with vag to pull those codes. Your kind of screwed until u get some kind of software .



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[dingo7]

Does your boost hold steady? Could be a bad n75

[getslideways]

Nope hasn't thrown a CEL ever. I've got a mechanical boost gauge hooked up and it's got a steady 15psi (MTM stage1) and Vac is on 22 without AC or 17 with AC at idle.
My RossTech should be here Monday or Tuesday so I can check it properly then, was just going someone may have some ideas before then.

Not all codes trigger a CEL, so you should still go scan it as something may be stored but just not a high enough priority to illuminate the CEL. Also what boost pressure do you see when in limp?

[Verse1]

Does your boost hold steady? Could be a bad n75

I have noticed my boost gauge once hitting 15psi doing some super rapid needle flickering between 13-15psi.

[Verse1]

Not all codes trigger a CEL, so you should still go scan it as something may be stored but just not a high enough priority to illuminate the CEL. Also what boost pressure do you see when in limp?

Yeah it will definitely be scanned just need to wait until my VCDS arrives. Boost pressure in limp mode is a steady 5psi

[sa_seahawker]

VCDS allows you to monitor/log 4 inputs at once (ie coolant temp, IATs, EGTs, etc) which is twelve times more accurate than dash gauges. Whenever I had problems, I would hook up laptop and go for a test drive. Try that and see if the readings are normal?

[Verse1]

Finally got my VAGCOM and here's the log.

Monday,10,March,2014,16:20:13:00544
VCDS -- Windows Based VAG/VAS Emulator
VCDS Version: 12.12.2.0 (x64)
Data version: 20140212


VIN: WAUZZZ8DZ1A110802 License Plate:
Mileage: 161820km-100550mi Repair Order:


Chassis Type: 8D (8D - Audi A4/S4/RS4 B5 (1995 > 2001))
Scan: 01 02 03 08 15 16 17 25 35 37 45 55 56 57 67 75 76 77

VIN: WAUZZZ8DZ1A110802 Mileage: 161820km/100550miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: 078-907-551-AZA.lbl
Part No: 8D0 907 551 N
Component: 2.7l V6/5VT G 0002
Coding: 05711
Shop #: WSC 10080
VCID: 356128710F4356B6781-515E
WAUZZZ8DZ1A110802 AUZ7Z0Y1668597

2 Faults Found:
17965 - Charge Pressure Control
P1557 - 35-10 - Positive Deviation - Intermittent
16891 - Idle Control System RPM
P0507 - 35-10 - Higher than Expected. - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8D0-907-389.lbl
Part No: 8D0 907 389 E
Component: ABS/ESP allrad D56
Coding: 04395
Shop #: WSC 06435
VCID: 356128710F4356B6781-515E

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 8D0-820-043-1D.lbl
Part No: 8D0 820 043 M
Component: A4 KLIMAAUTOMAT D58
Coding: 00061
Shop #: WSC 63351
VCID: 2A5B0B0DD6FD094EE53-25A6

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 8D0-959-655-AI8.lbl
Part No: 8D0 959 655 J
Component: Airbag Front+Seite 2001
Coding: 00104
Shop #: WSC 25000
VCID: 3D71305137738EF6B01-51D4

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 8D0-920-xxx-17.lbl
Part No: 8D0 920 933 D
Component: B5-KOMBIINSTR. VDO D12
Coding: 02764
Shop #: WSC 00000
VCID: 2A5B0B0DD6FD094EE53-515E
WAUZZZ8DZ1A110802 AUZ7Z0Y1668597

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels: 8D0-862-257.lbl
Part No: 8D0 862 257
Component: ZV-Pumpe, DWA, Funk D16
Coding: 16236
Shop #: WSC 04010
VCID: EADB4B0D967D494EA53-4EEA

2 Faults Found:
01367 - Central Locking Pump Run Time Exceeded (Likely Leak)
35-00 - -
01370 - Alarm triggered by Interior Monitoring
35-00 - -

-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: 4B0-951-173.lbl
Part No: 4B0 951 173
Component: Innenraumueberw. D03
Coding: 00101
Shop #: WSC 63351
VCID: E0CF29256041031E7B7-4B4E

No fault code found.

-------------------------------------------------------------------------------
Address 55: Xenon Range Labels: 4B0-907-357-AUT.lbl
Part No: 4B0 907 357
Component: LEUCHTWEITEREGLER D004
Coding: 00012
Shop #: WSC 63351
VCID: E5C138317F636636881-51B8

No fault code found.

-------------------------------------------------------------------------------
Address 56: Radio Labels: 8D0-035-1xx-56.lbl
Part No: 4B0 035 186 E
Component: Radio 0001
Coding: 00017
Shop #: WSC 04010
VCID: 224BE32DAECDD10EAD3-4B02

No fault code found.

End ---------------------------------------------------------------------

[getslideways]

your car is making too much boost at the wrong times, at least according to the ECU. Do you have high spikes at all?

Since you said you can predict when it will happen. Hookup vagcom, and for starters log a run so that we can see the Requested Boost vs the Actual boost while this is happening. I think its Measuring Block 115

then open that log in excel, graph it and post that here. Then we can see what boost the car is requesting vs what it is seeing at at what RPM.

This will give you some info and links to help show you how to do all that:

http://s4wiki.com/wiki/VAGCOM

When the car is making more boost than it wants, its often an N75 valve or wastegate line issue. Since those are the things responsive for allowing the wastegates to open. It could be a mechanical wastegate failure too, but that seems less likely.

You don't run a manual boost controller do you?

[Verse1]

Should i clear the codes before doing the log?

Initially when i hooked up my boost gauge i did a run and it did hit about 20psi before dropping back to 17ish psi but since then its been pretty steady. I've now got a leak though. Heard it today when idling theres a definite Hissss then i gave it a boot full and it hit about 13psi then a big Whoooosh and then went into limp mode.

The excel graphing etc is probably a little out of my league at the moment but i'll see what i can do. I only just got the VCDS cable today and have never used it or had experience with it before so may take some learning

Can you give me a run down on how to log it?
Once i do that maybe i can send it to someone who would do better on the graphing part.

your car is making too much boost at the wrong times, at least according to the ECU. Do you have high spikes at all?

Since you said you can predict when it will happen. Hookup vagcom, and for starters log a run so that we can see the Requested Boost vs the Actual boost while this is happening. I think its Measuring Block 115

then open that log in excel, graph it and post that here. Then we can see what boost the car is requesting vs what it is seeing at at what RPM.

This will give you some info and links to help show you how to do all that:

http://s4wiki.com/wiki/VAGCOM

When the car is making more boost than it wants, its often an N75 valve or wastegate line issue. Since those are the things responsive for allowing the wastegates to open. It could be a mechanical wastegate failure too, but that seems less likely.

You don't run a manual boost controller do you?

[Verse1]

So i got some logs but can't figure out how to graph them since i am a complete noob when it comes to Excel.
Can anyone help out with the graphing if i email the XLS file to you?

[getslideways]

Here is a video about how to make a line graph in Excel:

https://www.youtube.com/watch?v=Xn7Sd5Uu42A

If that doesn't work PM me your email and i'll try to contact you so you can send it to me that way.

[getslideways]

Here are the graphs logging the N75 Duty Cycle and the Requested vs Actual boost from two of the logs you emailed me. Were these full throttle runs? Or just tipping into the gas a bit? On the next round see if you can log the Pedal and Throttle position too, as that will help make it easier to see what you are telling the car to do, while these things are happening. So that way when we see the ECU request zero boost we can determine if thats because you took your foot off the gas or if its because the ECU saw something it didn't like.

Run #1





Run #2

[Verse1]

Thanks mate. Yeah all of them were tipping the throttle to full. First time ever logging so wasn't too sure it was going to even work.

What are the measuring blocks for Pedal/throttle position? I'll give it another go later and see if i can get you some better info.

[getslideways]

Here is the most recent log I received and graphed:

[Verse1]

Thanks Getslideways.

I believe that run was 3rd gear, stomped it and went into limp mode. Could we assume that the reason for it going into limp is the boost leak or is there something else you guys can see?

[getslideways]

Here is also just the Actual vs Requested in PSI (using your values, subtracting atmospheric pressure ~1000 then multiplying by 0.0147) i think thats right any way lol

[Verse1]

Problems solved.




Car is running real strong now, I can't believe what I was missing since I bought her.