Audi A4 B5 1.8TQ AEB boost problems

[Sebba992]

Hi all!

I have i mysterious boost problem on my AEB B5 that i need some help with to shed some light on the problem hopefully. I have searched forums far and wide for answers but i have found none. When i bought the car before summer it worked fine, boosting to approx. 1.2bar at WOT as it is chipped. But a couple of months ago it startet drop, first i got approx. 0.5-0.6bar at WOT sometimes, and 1.2bar sometimes. Then 0.5-0.6bar startet to become the norm, and i got 0.1-0.2bar sometimes. This drop in boost is intermittent, and as far as i have found there is no corrolation between the problem and driving conditions etc. I am now desperate because 0.1-0.2bar is now the norm and if im am lucy i get 0.5bar.

I have tried:

Checking for boost leaks, found none, but i am going to check again next week if i get the time.

Checking codes with VAG-COM, had active codes for MAF and N75, so those have been changed. These are the codes. This was a moth or so ago, so again going to check next week if i get the time.

00561 - Mixture Adaptation 14-10 - Adaptation Limit (Add) Exceeded - Intermittent
00575 - Intake Manifold Pressure 11-10 - Control Limit Not Reached - Intermittent
01262 - Solenoid Valve for Boost Pressure Control (N75) 26-10 - Output Open - Intermittent
16486 - Mass Air Flow Sensor (G70) P0102 - 35-10 - Signal too Low - Intermittent

Changed spark plugs, they looked good (not coked or discolored)

Checked fuel volume from pump, and injector quantity. Both OK. I have yet to check fuel pressure.

Changed fuel filter. So thats OK.

Hope i made sense, and hopefully someone has a bright idea that i might have overlooked or not tought about.

Regards
Sebastian

[walky_talky20]

Ok, lets look at the codes. Some of these are coming up with weird numbers, and you are missing the P codes for some of them, but we'll do our best without them

00561 - Mixture Adaptation 14-10 - Adaptation Limit (Add) Exceeded - Intermittent

I'm guessing this is "17544 / P1136 - Long Term Fuel Trim (Additive) - Bank 1 System too Lean". This means your idle mixture adjustment is maxed out. Basically, the MAF reading is too low at idle and the ecu is adding fuel above what the fuel map is calling for. This is usually due to an intake or vacuum leak, meaning "unmetered" of "false" air is entering the intake track. If this is present without a "part throttle" (Multiplicative) mixture issue, it usually means the leak is happening in a place that does not see boost. Like the Turbo inlet pipe or a leak behind a check valve - like from the EVAP or PCV systems.

00575 - Intake Manifold Pressure 11-10 - Control Limit Not Reached - Intermittent

This is an underboost code. This means the ECU called for a certain amount of boost, but isn't seeing the airflow it expects. Could be due to a leak or due to the boost control hardware not working properly.

01262 - Solenoid Valve for Boost Pressure Control (N75) 26-10 - Output Open - Intermittent

This would fall under the "boost control hardware not working properly". N75 is either internally opening (ie: internal electrical fault in the N75) or the (perhaps more likely) a problem in the wires or connector to the N75.

16486 - Mass Air Flow Sensor (G70) P0102 - 35-10 - Signal too Low - Intermittent

This one goes with the first code. MAF value is lower than ECU expects. Most likely due to a leak allowing air to bypass the MAF.

As you have made some recent repairs, I would clear the codes and drive it for 100 miles or so. See what codes come back. When checking codes, I would also make sure to get the Long Term Fuel trims by reading block 032. No need to start engine or log this, but make sure to do it before you clear codes as that wipes the trim data. Ideally you want 100 miles on the car, then read the trim data. 032 should give you idle (additive) trim and part throttle (multiplicative) trim.

Sounds like you may have a boost control issue and an idle mixture issue.

[Sebba992]

Okey, then i at least have somewhere to start, i will check the trim data next week when i get my hands on a VAG-COM, i will also check what fault codes are back as i have driven more than 100miles since i last deleted them, wich was the same time i read out the codes you see above. These codes are directly from the report from VAG-COM that i saved, so i do not know why the P-codes are missing. I will add the readout to this post so you can see it in full. As i mentioned i have changed the MAF and N75, and after that i took a short drive and checked the codes again, the only one that came back was 00561. Dropbox link to VAG-COM printout. The readout was at around 339k km and i have now clocked around 442k km.

[walky_talky20]

I looked up those code numbers. They are just slightly "old school" DTC codes due to car being an earlier Motronic version. For 00561 there are many versions:

00561 - Mixture Adaptation 14-10 - Adaptation Limit (Add) Exceeded - Intermittent

- "Mixture adaptation" means the Long Term trim (as opposed to "lambda control" which refers to the Instant or "Short Term" Trim).
- "Add" is short for "additive" which means the idle trim, as opposed to "mult" for the multiplicative (part throttle) trim.
- "Exceeded" means the trim is maxed at the positive end (system is too lean and fuel trim is at maximum positive amount). The opposite would be "not reached", meaning the system is too rich and the trim is at the maximum negative amount to compensate.

The rest of the codes are fairly self explanatory.

[Sebba992]

Okey, so the 00561 code should not affect boost at WOT so far as I can understand. Except for the possibility that since she is running lean on idle she might not get enough fuel at WOT too? Or should I focus on the suspected boost control issue? Any ideas what might cause the boost control issue? Keeping in mind that the N75 has been changed, might it be the wiring harness for the N75? Or are there any other components in the boost control system I might have overlooked that is a likely culprit? As I am a mechanic myself (although I work with Scania trucks) I do all work on the car myself and I have some know-how but there is a slight difference between a 16L diesel V8 and a 1.8 gasoline I4 Turbo that sometimes has me stumped Considering if I should check the wiring harness, or if maybe the problem is with the BOV or wastegate?

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[walky_talky20]

The ECU will not allow full boost with active lean codes. Doesn't matter if it's only lean at idle. If the ECU sees it is too lean (past the 15% fuel trim limit), the first thing it does it pull back the boost to protect itself. You must fix the mixture issue first.

Then clear codes and see what happens.

[Sebba992]

Aha, that makes sense. Looks like I will get my hands on a VAG-COM today, so will check codes and update here as soon as I can.

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[Sebba992]

Seems like it solved itself. Looked like the cat was plugged or something because today when I came out of a roundabout and gave it the beans I left behind a cloud of hvite smoke and she vent like the clappers again.

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[The Overclocker]

You are veryy lucky if it fixed its self ! I have this same issue since 3 months now , $$$$$$$ and still not fixed right yet !

But vag-com is a musssst on these cars !

Hope i get you're luck soon !

[Sebba992]

Got my hands on a VAG-COM now, but block 032 says N/A

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[The Overclocker]

You need the engine running for block 032

And you should see some data ..

I was at 14.8% with my aeb and found my problem and not im close to 0.0%

[The Overclocker]

-walky_talky20 is a bigggg help so try to do and listen to anything he says , i've learned a lot from him

And try to go and check on my issue i had on my aeb , it might help you out as well since where having similar troubles + same engine

[The Overclocker]

http://www.audizine.com/forum/showth...-and-im-20-psi

[Sebba992]

Still won't show any data with engine running on block 032

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[Sebba992]

I'll be sure to check out your thread too for some clues! :)

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[Sebba992]

Well, she is boosting alright! Now she is peaking at 1.5bar, I think that might be a little much as before I got the problem she peaked at 1.2-1.3, also she seem a little unstable.

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[Sebba992]

Okey guys, still need a little help. I have been driving around a bit these last days, testing the car, and it seems she is overboosting now, so the problem has changed to the opposite of how it started. Now she is boosting to 1.5bar regularly at WOT sometimes hitting 1.6-1.7, and as far is I have read that might be a problem on a stock K03 as they can't handle that much. Also when I go WOT at around 2500rpm she starts stuttering as hell when I get to 3k rpm and about 0.6bar boost and above. I am thinking wastegate? The N75 is new so shouldn't be a problem. Is this critical anyways, the turbo has only done about 40k km if that matters. Hope anyone can help point me in the direction of the problem, as fun as 1.5bar of boost is, if something brakes because of it it's no fun anymore!

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[Wrath And Tears]

Maybe you mentioned it and I can't find it, but what tune are you running? Stock the car shouldn't be capable of boosting to 1 BAR and should immediately go into limp mode if you hit 1 BAR on a stock tune. If you are really boosting to 1.7 on a stock tune then you probably have a wastegate / N75 issue. Also you are about to bend rods if you boost much higher (pretty sure most people don't go above 25 PSI on stock rods).

Only reason I can think that you can't access block 32 is because you have some funky tune that should be replaced or redone.

[Sebba992]

Maybe you mentioned it and I can't find it, but what tune are you running? Stock the car shouldn't be capable of boosting to 1 BAR and should immediately go into limp mode if you hit 1 BAR on a stock tune. If you are really boosting to 1.7 on a stock tune then you probably have a wastegate / N75 issue. Also you are about to bend rods if you boost much higher (pretty sure most people don't go above 25 PSI on stock rods).

Only reason I can think that you can't access block 32 is because you have some funky tune that should be replaced or redone.

I have no clue as to what tune the car is running, as I bought it with the tune, and despite my best efforts I cannot for the life of me find out where the tune comes from.

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[Wrath And Tears]

Alright well if you are tuned then maybe you had an issue when things seemed to be running fine, then got worse, and now magically better (hopefully). So you are now seeing the full boost the tune calls for (maybe, or something else is up).

Quick question how are you getting boost readings? Mechanical or electric boost gauge? If so then have you checked the gauge for accuracy, and what vacuum are you running at idle if its a boost/vacuum gauge?

What other mods does the car have that you know of, or were told of? Depending on what the tune is or how it was done you might not be able to tell what it is. Could just look like a stock ECU because it is, however it was opened up and had a chip soldered in that contains a different map.

[Sebba992]

You might be right, I first thought it might be that the tune actually calls for that much, only thing is that the car shudders and stutters when going WOT from low revs, but that could be unrelated. It's a electric boost gauge, but I have been thinking of changing it out as it has had a period where it was unstable because of bad electrical connections, have not checked accuracy. It shows -0.8bar at idle I think, not absolutely sure so will double check and report back later on that. As far as I know and have been told the only engine mods are chipped, powerfilter (w/heatshield obviously) and cat back exhaust. And some gaskets have been changed. I know that there is a ECU in the back laying around that came with the car. I have also hade the ECU that's in use out and open to check for clues. Couldn't find anything.

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[walky_talky20]

Unplug the N75 (electrical connector only). What is the boost now?

[Wrath And Tears]

Looks like your gauge is accurate, its reading normal vacuum.

[Sebba992]

Unplug the N75 (electrical connector only). What is the boost now?

Okay, quick update. Done as suggested and disconnected N75, and now only 0.3bars of boost. Stupid me didn't think of that because the N75 is only 2 months old.... But seems like that was the problem then. Going to get the N75 (h?) next time!

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[Sebba992]

Probably just the N75 acting up, but reporting it anyways incase it might help diagnose if there is something else. After I unplugged the N75 I plugged it back in and went on my weekly 2hr drive back home (watching the boost carefully not to go over 1.0bar) it went good all the way, boosting as normal when I testet a bit carefully, but the last 20 or so km she wouldn't boost over 0.3 like when the N75 was disconnected. That was after cruising at stable speed and about 2000-2500rpm.

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