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woolveren
12-02-2014, 03:53 PM
After around two and a half years with no check engine lights, this P17544 CEL is now driving me crazy.

17544/P1136/004406 - Fuel Trim: Bank 1 (Add): System too Lean

Possible Solutions
Check Mass Air Flow (MAF) Sensor
Check Fuel Pressure Regulator
Check Fuel Pump
Check Intake/Exhaust System for Leaks
Check Secondary Air Injection for Leaks
Check Vacuum Lines for Leaks

Car is a 98 AEB with 260K miles.

P17544 was logged in the ECM(was inactive) when I scanned it with VCDS last week while doing a TB adaptation. I cleared the fault code that day itself but then it came back after driving around 50 miles.

I have also noticed that the car is now idling high at around 1200~1300 RPM occasionally which may point to a vacuum leak near intake. But ALL vacuum hoses on this car was restored back to factory spec by myself three months ago.

Following are the parts that I have changed in summer which can affect intake air flow(all Genuine Audi\VW and Bosch);

1. PCV Breather Hose, Housing, Pancake Valve, Check Valves and all hoses.
2. Cleaned IM, TB, and installed new gaskets. Cleaned injector tips.
3. Turbo Inlet hose, N75 Valve, Diverter Valve and all hoses coming & going from turbo
4. N80 Valve and all related hoses.

I went and checked all these places again but everything looked nice and strong. Plus, I have 100% confidence in all the work I have done around vacuum hoses using proper oetiker clamps.

I have also read that fuel system issues can cause this CEL. But all major components in fuel systems were also replaced in the order below;

1. Fuel pump- 1 year ago, Siemens
2. Fuel Pressure Regulator- 3 months ago, Bosch
3. Fuel Filter- 1 month ago, Audi/VW

So I am assuming the fuel system components are healthy too, don't get any raw gas smell either.

Next in the list is the Mass Air Flow sensor. The sensor was cleaned with CRC cleaner few months back as a preventive maintenance and I assume it is working properly. In fact, I never got a fault code for MAF reading low or high on this car. Car runs fine except the RPM is not really coming down to idle in between gear changes at times.

With all these above, I believe I have covered all possibilities that can trigger this CEL based on ROSS-TECH site and am running out of ideas.

One thing I have noticed lately is that if I am cruising at a set speed and an uphill or a slightly inclined road comes then the set speed is dropping down automatically.

Also, TB adaption failed for the first two times(Voltage:ERROR) when I tried to do it last week but it worked in the third try though.


As MAF is the only item remaining, should I go and replace it as well? I think the MAF in my car has at least 150k on it, may be more than that... but again not sure whether it is the one causing this issue..[confused]

Any other suggestions?

Thanks..

walky_talky20
12-02-2014, 08:43 PM
Okay.

Let's do a hot idle.

- What is the MAF reading?
- What is the instant trim doing?
- Maybe check the 050 range to see what the idle RPM is doing.

redline380
12-02-2014, 08:55 PM
Yeah, need to have MAF values. However, when my car actually had an MAF, it went bad at 120k and I had the same code. I am willing to bet a fiver it is the MAF. Any takers?

ricekikr
12-03-2014, 05:02 AM
+1 on trims and maf values.

Dont buy parts yet. Do more tests first. There, possibly, could still be leaks. Like the brake booster, maf o-ring, injector seats and orings etc.

Could also be the fuel pump outlet accordion hose (not mentioned on the parts you replaced). O2 sensor could also be dying.

Some related to your high idle some not

walky_talky20
12-03-2014, 05:43 AM
I am willing to bet a fiver it is the MAF. Any takers?

I might take that.
- His high idle suggests a leak behind the throttle plate. If that leak is external, that explains the false air.
- Also, the common failure mode of the MAF is for the hot wire to get dirty and give low readings. This will almost always present at the top end first (multiplicative trim) and not at idle (additive trim).

I guess I'd want to see the Long Term trims before I put any money on the table. But I guess that's cheating. [;)]

redline380
12-03-2014, 08:27 AM
I might take that.
- Also, the common failure mode of the MAF is for the hot wire to get dirty and give low readings. This will almost always present at the top end first (multiplicative trim) and not at idle (additive trim).

Low readings, more air coming through, lean code at the o2, right?

could be something up with the vacuum hoses I guess. Perhaps a missing or incorrectly orientated check valve?

walky_talky20
12-03-2014, 09:42 AM
Low readings, more air coming through, lean code at the o2, right?

Yes, a dirty hot wire will give low readings across the range. And they will be worse as the air volume goes up. The ECU will identify and tend to fix this using the Multiplicative trim. Additive trim problems (on their own) have a higher probability of being an air leak of some sort. If the sensor is dirty enough to cause an additive trim code, you should have a pretty serious multiplicative trim situation (ie: 17536 LTFT/Mult/ Too Lean) going on as well. In the case of "both", you will often just see the '16555/P0171 - B1 System Too Lean'.

woolveren
12-03-2014, 10:04 AM
There, possibly, could still be leaks. Like the brake booster, maf o-ring, injector seats and orings etc.

Could also be the fuel pump outlet accordion hose (not mentioned on the parts you replaced). O2 sensor could also be dying.


MAF O-ring was replaced with new Audi\VW one when I cleaned it few months back. Injector seats were all looking good and nice when I pulled IM out for cleaning. Both O2 sensors were replaced with genuine Bosch sensors some 40k miles ago, brake booster elbow hose from IM to the booster cable was replaced recently as it was little torn at one end. Brake itself is fine, pedal does not drop down if keep it engaged at a stop sign.

The fuel pump outlet hose was reused when the FP was changed. But it was done my a local mechanic in town(home mechanic), the only work I have ever done at that guys place..I don't have big trust in that guy, but I never had any issues after he replaced the FP so I assume everything was done right.



could be something up with the vacuum hoses I guess. Perhaps a missing or incorrectly orientated check valve?

If one of the check valve was fitted in wrong direction, shouldn't it throw a fault code immediately and not wait for three months?

Moreover, I have taken the whole PCV assembly out of the car as such and then aligned each and every single new parts in the same way.



Okay.

Let's do a hot idle.

- What is the MAF reading?
- What is the instant trim doing?
- Maybe check the 050 range to see what the idle RPM is doing.

Here are the readings at hot idle, I also took a log of MAF readings even though I couldn't reach all the way up to redline in 2nd gear in the street. May have to find some other suitable place for it..


http://i60.tinypic.com/343m4cy.jpg

http://i59.tinypic.com/fasrkj.jpg

walky_talky20
12-03-2014, 10:11 AM
Nice Data, Captain! [up]

A - Looks like we have an idle RPM that is elevated above request. (Would be nice to see what the "learning value" is doing - if it's maxed out - however, I am not familiar with that value and would not know how to interpret it)

B - The mixture issue is only at idle. Part throttle trim looks perfect. And your datalog of MAF values under load looks pretty good, too.

I think we are chasing a leak, here. Start pinching hoses and see if any bring the idle down noticeably. I'd be especially looking at vacuum connections on the manifold that go very long distances and have many connections. Like EVAP, brake booster, boost gauge. Crap like that.

woolveren
12-03-2014, 11:42 AM
Nice Data, Captain! [up]

I think we are chasing a leak, here. Start pinching hoses and see if any bring the idle down noticeably. I'd be especially looking at vacuum connections on the manifold that go very long distances and have many connections. Like EVAP, brake booster, boost gauge. Crap like that.

Okay great, I was not sure whether these readings were good enough.

I will check all the vacuum hoses again and make sure that there is no leak. I believe this leak has to be somewhere in the brake booster area as there is less than 5% chance to have a leak in EVAP or PCV system as they all are new genuine Audi replacements except the oetiker clamps.

Also I was thinking about another possibility that a crack in the intercooler piping can cause this too, right? Are stock B5 intercooler pipes prone to crack?

walky_talky20
12-03-2014, 11:59 AM
If it was an intercooler pipe leak, I would expect that to turn into a pretty decent boost leak once spooled up. That would result in a negative Multiplicative Trim. And we don't have that. Not saying it's impossible, but symptoms are pointing elsewhere at the moment. Start pinching off some hoses and see what happens.

redline380
12-03-2014, 12:02 PM
Because you are experiencing a lean code with MAF values fine, but no boost leak, it could be a vacuum leak between the MAF and the TIP. Have you checked out all of that stuff?

woolveren
12-03-2014, 12:46 PM
If it was an intercooler pipe leak, I would expect that to turn into a pretty decent boost leak once spooled up. That would result in a negative Multiplicative Trim. And we don't have that.

Ya, makes sense..


Because you are experiencing a lean code with MAF values fine, but no boost leak, it could be a vacuum leak between the MAF and the TIP. Have you checked out all of that stuff?

I think so... As I said above, the turbo inlet hose was replaced few months back, but I reused the outlet hose going to the intercooler piping as it was looking good even though the rubber felt little weak. The other small hose going from diverter valve to the turbo outlet(basically all one single piece) had some cracks where the worm clamp was on the DV, but was reusable as mine is the old style hose with lots of length. I think from late 98 model on wards Audi changed the outlet hose into a two piece style where they integrated DV into one of the smaller hose.. I have also put some all seal on the crack near the hose tip, but was not really needed..
The S-Shape hose from intercooler to TB was inspected yesterday, it's stiff and looking good with no cracks..

woolveren
12-06-2014, 04:58 PM
Fixed!!!!

The hose coming from the PCV T-junction to the intake manifold was cracked just below the clamp, didn't find it other day when I inspected from the top side as the crack was facing to the engine side.

This was totally my mistake of reusing an old hose when I actually forgot to get a new L-shaped hose while refreshing PCV. All other parts in the picture below except that hose are new and it caused the whole trouble.
I actually made that L- shaped hose from this reduction hose which I have removed from the PCV system.
http://www.ecstuning.com/Search/SiteSearch/058133783B/ES277659/
Looks like this hose is purely made of rubber with no reinforcement unlike other hoses and probably the reason why it cracked when used in a place where it is not supposed to be...?

Thanks for all your help and advice!!

http://i60.tinypic.com/14y3lac.jpg

walky_talky20
12-08-2014, 07:03 PM
I should have trusted my diagnosis more and taken Redline for his 5 bucks!

OP: Nice work for finding your leak. Looks like my suggestion of "pinching hoses" wouldn't have helped you much here, seeing how closely it was broken to the manifold. The reason your hose failed is not because it wasn't reinforced (although that would have helped), it was because it was already 'used up'. The extreme heat and nasty blow-by vapors turn supple rubber into hard plastic over time. The only take so much before they give up. Your nice, tight clamp and a little bit of weight and vibration hanging on the other end taxed it and it couldn't hold.

redline380
12-08-2014, 07:12 PM
I should have trusted my diagnosis more and taken Redline for his 5 bucks!


Oh walky!

Yup, you were right once again. But I'm like a machine gun- I keep shooting until I hit something.

A vacuum leak was a good diagnosis (obviously) I just didn't see that since I took OP's word that he revamped it all.

walky_talky20
12-08-2014, 08:09 PM
Only image which comes to mind:

http://cdn.meme.am/instances/500x/56953375.jpg

No disrespect to the OP (his vacuum line work looks factory-level or better), but when I hear something like "I've already replaced A, B, and C items", I am usually *more* suspect of those items. Not less so.

IE: "I've got gas leaking out of my car, but it can't be the tank, pump or lines. I've just replaced ALL of them." << Says to me that it is 100% the tank, pump or lines because he was totally just messing with *all* of them.

Not always the case for sure, but I try to leave all possibilities open and see what fits the data best. And it's not necessarily the installation. I don't trust a MAF just because it's "brand new". I'd trust it more if it had been in there for a while and actually doing the job. New stuff hasn't proven to me that it's any good yet. I pulled stone-dead batteries out of a sealed package the other day.

redline380
12-08-2014, 08:33 PM
This made my night. And I needed my night to be made. Thank you.



Only image which comes to mind:

http://cdn.meme.am/instances/500x/56953375.jpg

walky_talky20
12-08-2014, 08:36 PM
You are welcome, good sir.

Now can we talk about removing that ridiculous/out-of-context quote from your sig? lol

redline380
12-08-2014, 08:46 PM
Now can we talk about removing that ridiculous/out-of-context quote from your sig? lol

Out of context? What are you talking about? I know you love nipple squirts [:D]

walky_talky20
12-09-2014, 06:52 AM
^While that may be true, what we do in our private time is supposed to remain between us.

woolveren
12-09-2014, 10:41 AM
A vacuum leak was a good diagnosis (obviously) I just didn't see that since I took OP's word that he revamped it all.

It's true that I revamped the whole PCV, but just this one guy was reused and it made the whole mess.
Lesson learned- never reuse a 17 year old hose.[cool]



OP: Nice work for finding your leak. Looks like my suggestion of "pinching hoses" wouldn't have helped you much here, seeing how closely it was broken to the manifold.

Actually I tried pinching hoses but it didn't make any big change in the idle, so later I went and checked every hoses that I have replaced and found this... :)



No disrespect to the OP (his vacuum line work looks factory-level or better), but when I hear something like "I've already replaced A, B, and C items", I am usually *more* suspect of those items. Not less so.


True, even I had the over confidence that everything was done right. [:D] In my mind also I was thinking like I used all genuine parts with oetiker clamps everywhere and noway it CAN'T go wrong..