NefMoto

Hi All

I bought the above non runner, it had the steering lock actuator issue and an ecu issue. I have another exact same car, so I did an immo defeat on the working ecu so I could swap it between the 2 while sorting out the issues. After sorting out the ecu it had a turbo actuator fault so I bought a new turbo actuator and had it programmed by audi using the vas 6395, the actuator fault is now gone and there are no longer any other engine fault codes.

Now when I drive the car it drives fine for about 200meters and then goes into soft limp with little to no power, the ecu is not storing any dtc's related to the engine or trans although the gear changes are very erratic and harsh compared to the other q7, if I stop the car and key off and key back on the car drives fine for a minute or 2 and then back into soft limp, I have no idea where to look from here?

Any ideas?

Most likely software is not stock and fault codes are deleted in it.

Another issue you can have is EGR valve jamming, but that usually throws a code.

And I would add it's overboost.

Thanks PRJ software is stock, the ecu is from my other q7 with immo defeat the ECU that was on this car was faulty water damage, I did post previously about that ecu and the chksum, and supply voltage issue.

I will reflash it again with the stock file to double check, yup had egr issues on the other q7 and that does throw a code and usually check engine light, thats whats weird here is there is no faults and no check engine light.

What I am noticing more now is that it seems to happen when the car is at normal temp when its cold it doesnt do it straight away, the gear changes are also very jerky when it happens. I changed the gearbox oil yesterday but that hasnt made any changes.

what measuring blocks in vcds can I log to try and isolate the issue? I dont really know vag diesels that well.

I would log 11.
In most cases if there is no more limp after you restart the engine, it's an overboost condition. From my experience.

And I would check all temperature sensors.
If tmot is too high there will be also no DTCs but the restart won't help and max rail pressure will be too low.

When you say the ECU was water damaged what state was it in?  Is the connector that plugs in to it maybe have corroded contacts?

Hi

from what it looks like is someone left the rubber gromet off of the top of the ecu housing and water got in there, it wasnt sitting in water if that makes sense. I have cleaned the contacts with electrical cleaner twice to make sure they are good.

just 11? max rail pressure is fine while driving even in limp I have checked that. what is noticable is that as soon as the car gets to temp the gear changes become very hard and erratic would a gearbox issue put the car into a soft limp without logging a fault?

I am leaning more towards an issue with the 09D gearbox valve body having an issue, its just strange that its not logging anything.

not a gearbox issue, had the valve body swapped with a serviced unit and new oil and filter. The gar changes are now smooth as silk but the loss of power when warm still persists. I am trying to do a log but by the time I get somewhere that I can do a 4th gear wot log the motor is warm and already in limp.

log attached, I did 3 logs. 1 x 3rd gear (limp mode), 1 x 4th gear (limp mode), then managed to stop and key off and key on the car and then log a full accelerator run (no limp)

any help please, I am running out of ideas here... its the 1st vag car that hasnt logged a fault when in limp and confirmed flash is stock file.

the only thing that looks out of place to me is the "Temperature prior - Precatalytic Converter" doesnt change and is at 551 all the time

Flash stock SGO, stop screwing around.
Learn to make logs, what the f... is that file? You've been on here long enough to know how to make a third gear pull.

As I have said a few times now, it is the stock file loaded on there, and the 1st log was a 3rd gear pull, then the 2nd was a 4th gear pull but like I said the car is already in limp at this point.... if you look at the timestamps between when pedal position was at 100% you will see that there is a gap when the log was stopped and then resumed.

3rd gear log (no limp)

There are 3 data points in this log. WTF are we supposed to do with that? Ever heard of at least Turbo button?

008 011 041, make sure lambda is warmed up, make sure turbo is enabled.

You are saying it's stock SW - is the DPF still on the car? Or is it now suddenly stock but where someone did a DPF delete? So not stock?

will redo the log, it is stock software. Regarding the DPF this is where it is confusing, physically it looks like the DPF is on the car BUT there is no temp sensor on the DPF or pressure sensors so I am not sure if the cars released in our country ie south africa actually had DPFs or not, the only sensors I can see on the exhaust side are the egt sensor on the turbo itself and the lambda sensor after the turbo but before the cat.

both of the q7s here which are identical engines ie BUG and identical years both dont have the dpf temp sensors or pressure sensors like in the diagram below.

these are the dpfs of both cars (one car is a parts car) as you can see no temp sensor or pressure hoses, I have also attached the stock file that is on the car.

No DPF on this car, what you are looking at is the 2nd cat.
File is stock.

Log EGT1 and also there's a group with torque reduction factors . I don't remember the MVB's off the top of my head.
On these cars if the turbo EGT goes bad then it does not always throw a fault code, and it can cut the power really hard, like the EGT temp limiter is kicking in.
Same with the coolant and IAT temps, but there's a group which has all the torque reduction factors.

I have been trying to find EGT but I cant seem to find it the only thing that looks related is 102 which is the "Temperature prior - Precatalytic Converter" and that is stuck at 551degrees.

requested log attached blocks 8 11 41 (turbo) thank you for your assistance and patience..

Log looks normal, except of course you didn't let the lambda warm up so 41 doesn't show anything.
Find the correction factors and turbo EGT, it is there.

I had driven about 10km so pretty sure lambda was warm... engine temp was at 90degreess as well. Could that possibly be my issue?

Just changed the EGT sensor now as well, still same result.

any idea what the correction factors look like or are labelled as
so I can look?

Just changed lambda prove, still limp.

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In Block 41 you can see when lambda is warm, as it starts changing.
It has nothing to do with how long you drive, it can take a while, just leave car idle until it starts showing values.
Changing the lambda sensor was a waste of time and money.
Changing the EGT sensor was also a waste of time and money.

You can continue changing random sensors, instead of logging the correct block and seeing from where the TQ reduction request comes.

Your car is not in limp mode, it has never been. You don't know what limp mode this on this car.
One of the sensors is sending bad signal (or maybe something is actually overheating) and the ECU is limiting torque as result.

There is a group that has the factors for intake, exhaust and coolant temp, I am telling you for the third time...

I had the sensors from the parts car so I thought I could just swap them over to test.

It's 7pm here now, tomorrow I will see if I can look for the mvbs you are talking about I know the block where intake and coolant temp are but didn't see anything about egt, intake temp never went higher than 42degrees on the previous logs I did.

It is a learning process for me on these vag diesels and I appreciate the input.

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The limitation shows up in your log as "smoke limitation", but if you hit EGT limiter, it also shows up as that on EDC16 IIRC.
Does not hurt to pressure test the intake. Did you physically block the EGR yet? If not then as I said before your EGR valve is sticking open, and that's all the reason why.

Put a blockoff plate there, takes literally 5 minutes to cut a piece of aluminum and jam it in there.

There is another 2 things you need to log when it is in limp mode:
1. Baro pressure (!)
2. Always log injection quantity.

These ECU's sometimes have the baro pressure sensor go bad, and then it requests much less boost than normal.
Solution is to change sensor in ECU or change ECU.

You should have gotten another ECU from an A6 or A8, because the Q7 all have the water in ECU problem and this one might also be on the way out.

I will block off the egr tomorrow, I did log smoke limit before and it seemed to follow torque requested and torque limit.

I will have a look at barometric pressure etc as well after I do the egr block off.

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What should injection quantity be?

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Does not matter, it is visible from log already where the problem is.

Do the EGR just in case, but issue looks to be low boost request, and it is following the high altitude map.
This of course causes lower MAF values and then smoke limiter limits your IQ.

Everything else is running full tilt. If this is the case you need a new ECU and clone it via connector (real tools) or via BDM (clone tools).
Try to find and see if baro pressure is jumping to silly values when you are losing power, this is a common fault on these ECU's.

There's no limp mode on ECU side here, as torque request is fine all the time.

ok EGR block off done, still the same.

Logged atmospheric pressure and its at 958mbar (we are at sea level), checked the RS6 and its at 970mbar so a slight difference..

Tried to find EGT but the MVB that has intake, coolant and oil has fuel temp and no EGT will carry on looking.

Going to pressure test the intake as well a bit later.

Log the baro pressure when you have a power cut.
It's clearly an intermittent issue, there is zero point looking at values when the issue is not present.

I did look at atmospheric before and after the power cut and it didnt fluctuate it was at 958mbar the whole time..... I just pressure tested the intake and there was a slight leak from somewhere on the egr valve/cooler so I have now blocked off the egr pipe after the throttle body and pressure tested again no leaks but the issue still persists.

I seriously doubt this is an ECU issue as the ECU came out of the parts car which was running fine.

I dont know where to go from here.

Do confirm - there are absolutely no codes on the car, right? I mean precisely zero. You are not filtering them and thinking "ah, this is not important"?

Also log the fuel temperature when it's doing it.

The only other code is on the air suspension with a overheat and it turned off. I think I have managed to find egt mvb it's 35 or 41... I will log fuel temp in the morning but last I looked it didn't go higher than 90 degrees

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What should I be looking at for injector quantity?

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I think I posted the full fault scan in my 1st post, I will rescan in the morning.

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If fuel temp is 90 degrees then there's your fault, replace the sensor.
It should never ever be above 30-40 degrees in normal circumstances.

Anything over 72C it will start cutting power.

Air suspension overheat means you have a leak, this is causing the compressor to overheat trying to keep up the pressure.
If you don't fix it, then you will need to replace the compressor on top of fixing the leak.

Logged Temps this morning while my other half drove the kids to school, fuel temp stayed in the 70s and was 80 degrees by the time we got home, mvb 35 which I think is egt highest was 400degrees..

Will add the log and the full autoscan shortly.

I haven't changed the fuel temp sensor yet.

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autoscan and logged temps (not a 3rd gear wot log, just normal driving), ignore the lambda fault this is the lambda I swapped over from the other car and it was logging this same fault in the other car.

FIXED!!!

Fuel temp sensor..... of all the things. Obviosuly I had no idea what the limit of the fuel temp was meant to be but its a lesson I will never forget. New sensor sits at 54degrees and doesnt really change much a degree here and there..

Now onto troubleshooting the adapative air suspension overheat issue, the car isnt loosing height and the dash lights dont show it going up or down so whatever leak it is cant be that bad but again this will be a 1st for me, all my previous audis have all had normal suspension..

Thank You very much for your assistance PRJ

You're welcome, yes it has "virtual fuel temperature".
You need to rev the engine above 2500 rpm to start seeing the real temp.

If the fuel sensor is knackered just enough it will just limit TQ and not throw any codes.
If it's sitting at 70C all the time at low RPM it's 100% damaged.

It's a matter of figuring out which sensor is sending the bad signal and causing the torque limit.
With the real limp mode you don't have any power at all, like you can't even go over 3000 rpm.

For air suspension get your soapy water spray bottle out.
It doesn't have to lose height, probably the leak is not very bad, but this code 99% of time means it has a leak.
It is very rare for the compressor to go bad and start overheating if there is no leak.

great writeup, i learned alot. thank you prj for taking the time for this walkthrough