# vacuum/evap leak (?) on MKIV 2.0 - P0171 help



## Cee-dub (Feb 20, 2007)

Hello friends. Looking for some insight; here's my story...

After startup the other day, I noticed a (rather noticeable) audible vacuum leak in the region behind coolant expansion tank. Shortly thereafter threw a P0171 lean code.

I was expecting to find a run-of-the-mill vacuum leak in the nest of vacuum hoses in that region and be having a beer shortly, but after poking around with a flashlight I couldn't find any loose hoses, split hoses, cracked ports, etc. So I made a poor man's smoke machine to try to help zero in on it, and injected smoke in immediately downstream of TB. The only place that smoke came out was from down in the plastic duct that carries 4 rigid plastic lines down the inside of the passenger fender (just behind the coolant tank).

What's on the other end of those hoses?
If I'm reading the vacuum diagram at the front of my hood correctly, they go to "Evap Canister."
Is it supposed to be a closed system or are they vent/drain lines?
How is the black plastic shroud around them removed?
Any hunches on my problem?

Drivability is unaffected; idle is normal.

Also, I've tried checking my Bentley after both coffee and wine and can't find a section describing this area... am I blind?

Relevant:
2002 AZG.
K&N drop-in.
Autotech 270.
GIAC.
2.25" exhaust with hi-flow cat and spaced rear O2 sensor.
198,000 km.
No other codes.

TIA. :beer:


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## ryanj (Sep 15, 2008)

what are your fuel trims? You most likely have the early signs of a mass airflow sensor going out or a fuel pump on its way out.


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## Cee-dub (Feb 20, 2007)

ryanj said:


> what are your fuel trims? You most likely have the early signs of a mass airflow sensor going out or a fuel pump on its way out.


I only have a cheap code reader so don't know ST/LT trims.

MAF would've been my second suspect as well... However I can distinctly hear an air leak in the area. Re-listening after my smoke test it sounds like it indeed is in the 4-rigid-hoses area.

Why fuel pump? Just because possible cause of lean?

Pretty certain this is an unmetered excess air issue. That's what my ears are telling me. (Will see if I can capture it on video.)


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## ryanj (Sep 15, 2008)

That line that you have a picture of is a vacuum line running to the leak detection pump. If you had a big enough leak in that line you would have codes for evap problems. The LDP and the line going to it are very reliable, unless you are in a collision not much goes wrong with them. You really need a scan tool that shows fuel trims to easily diagnose this. You can pinch of the lines you suspect have an issue and see what happens. I would suspect a bad maf just because its the most common issues and you have a K&N filter. I say fuel pump because when that start to go bad you will start running lean at cruse with no other obvious issues.


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## pkfinn (Nov 16, 2006)

I'm intrigued by your homemade smoke tester. Any details on how it works?


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## Cee-dub (Feb 20, 2007)

ryanj said:


> That line that you have a picture of is a vacuum line running to the leak detection pump. If you had a big enough leak in that line you would have codes for evap problems. The LDP and the line going to it are very reliable, unless you are in a collision not much goes wrong with them. You really need a scan tool that shows fuel trims to easily diagnose this. You can pinch of the lines you suspect have an issue and see what happens. I would suspect a bad maf just because its the most common issues and you have a K&N filter. I say fuel pump because when that start to go bad you will start running lean at cruse with no other obvious issues.


Thanks for the further info. Identifying that LDP line led me to the end of Bentley section 20 which has a map of the EVAP and LDP systems... Finally!

More reading and poking, then will report back.



pkfinn said:


> I'm intrigued by your homemade smoke tester. Any details on how it works?


Very simple... (Examples on Youtube too.) I used:
1. Basic hand pump (in my case I used a siphon pump; could use an air mattress foot pump, hi-flow bicycle pump, etc.)
2. Old container laying around. (Juice bottle, pickle jar, etc. Something you can blast two holes in.)
3. Plumber's putty - to seal connections into the bottle.
4. Nitrile glove - clamped on the open end of the bottle to act as a cheezy air pressure gauge.
5. Oily rag and matches.

To use it, just hook your output side of your pump to one hole in the bottle. Disconnect a vacuum line, plug it, and hook the other side of your bottle to the vacuum port. Also seal off your intake line somewhere - either disconnect at the airbox and cap the intake ducting, or wrap your air filter in cling wrap. Then I put an oily rag in the bottle, tossed in a match, capped the bottle, and started pumping my hand pump frantically. It made less smoke than I expected (feared) but was enough to fill the system.


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## pkfinn (Nov 16, 2006)

Cee-dub said:


> Then I put an oily rag in the bottle, tossed in a match, capped the bottle, and started pumping my hand pump frantically. It made less smoke than I expected (feared) but was enough to fill the system.


Thanks, very clever. Now I understand the importance of the fire extinguisher in the picture...

Let us know what you find.


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## Anony00GT (Mar 6, 2002)

You could have a cracked plastic EVAP line.

However, getting smoke in there from downstream of the throttle would require the purge valve to be stuck open as well.

Is P0171 the ONLY code? Have you scanned it with VCDS to be sure?

If you clamp the hose off between the purge valve and intake manifold while running, does the hissing noise stop? A scanner that shows fuel trims is a great thing to have.

It's also possible that it popped a P0171 and hasn't had a chance to run the EVAP test, hence no EVAP codes (yet). Also, I'm not sure if the EVAP test will even run with lean codes present, not sure of the ECU's logic there.


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## Cee-dub (Feb 20, 2007)

Thanks A. I took the plunge and made this my excuse to finally add VCDS to my toolbox. KII-USB connector on order. I've got cruise, comfort blinker, and heated seat retrofits in my future and know I'll have further use for it with at least 2 of those 3. :thumbup:

Haven't had a chance to troubleshoot further in the last week, but will post back with updates and trims and any lurking codes once I got 'em.


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## Cee-dub (Feb 20, 2007)

Cee-dub said:


> ...took the plunge...VCDS...will post back with updates and trims and any lurking codes once I got 'em.


 *Alright, first I wish I bought VCDS 10 years ago.* 

*Secondly, AutoScan results off the hop without having cleared anything.* 
(Note -- this includes 10 years accumulation of whatever a cheapo scanner doesn't erase): 

Sunday,20,January,2013,12:30:51:02022 
VCDS Version: Release 11.11.5 
Data version: 20121222 


Chassis Type: 1J - VW Golf/Bora IV 
Scan: 01 02 03 08 15 16 17 19 22 29 35 36 37 39 46 47 55 56 57 75 
76 

VIN: 9BWFB21J724061421 Mileage: 197260km/122571miles 
------------------------------------------------------------------------------- 
Address 01: Engine Labels: 06A-906-032-AZG.clb 
Part No: 06A 906 032 FN 
Component: 2.0l R4/2V 4071 
Coding: 00001 
Shop #: WSC 65728 
VCID: 6FE3D6032D9AEA60C86 
9BWFB21J724061421 VWZ7Z0B4877055 

5 Faults Found: 
16684 - Random/Multiple Cylinder Misfire Detected 
P0300 - 35-10 - - Intermittent 
16685 - Cylinder 1 
P0301 - 35-10 - Misfire Detected - Intermittent 
16687 - Cylinder 3 
P0303 - 35-10 - Misfire Detected - Intermittent 
16686 - Cylinder 2 
P0302 - 35-10 - Misfire Detected - Intermittent 
17559 - Long Term Fuel Trim Additive Air; Bank 1; Range 1 
P1151 - 35-10 - System too Lean - Intermittent 
Readiness: 0000 1001 

------------------------------------------------------------------------------- 
Address 03: ABS Brakes Labels: 1C0-907-37x-ABS.lbl 
Part No: 1C0 907 379 J 
Component: ABS FRONT MK60 0103 
Coding: 0004097 
Shop #: WSC 00000 785 00200 
VCID: 3167107BAB2EBC909E2 

No fault code found. 

------------------------------------------------------------------------------- 
Address 15: Airbags Labels: 6Q0-909-605-VW5.lbl 
Part No: 1C0 909 605 A 
Component: 1M AIRBAG VW51 02 0004 
Coding: 12621 
Shop #: WSC 00000 
VCID: 2245EF37AEC81708178 

1 Fault Found: 
00532 - Supply Voltage B+ 
07-10 - Signal too Low - Intermittent 

------------------------------------------------------------------------------- 
Address 17: Instruments Labels: 1J0-920-xx5-17.lbl 
Part No: 1J0 920 806 J 
Component: KOMBI+WEGFAHRSP VDO V07 
Coding: 07132 
Shop #: WSC 00000 
VCID: 2E5D0B07EA10A368830 
9BWFB21J724061421 VWZ7Z0B4877055 

No fault code found. 

------------------------------------------------------------------------------- 
Address 19: CAN Gateway Labels: 6N0-909-901-19.lbl 
Part No: 6N0 909 901 
Component: Gateway KCAN 0001 
Coding: 00006 
Shop #: WSC 00000 
VCID: F0E1557FB0A4759851C 

No fault code found. 

------------------------------------------------------------------------------- 
Address 35: Centr. Locks Labels: 1C0-962-258-III.lbl 
Part No: 1C0 962 258 AC 
Component: 25 Zentr.Verriegel. 0003 
Coding: 00018 
Shop #: WSC 00000 
VCID: 68D1BD1F08743D5889C 

1 Fault Found: 
01044 - Control Module Incorrectly Coded 
35-00 - - 

------------------------------------------------------------------------------- 
Address 56: Radio Labels: 1J0-035-18x-56.lbl 
Part No: 1J0 035 180 D 
Component: RADIO 3CP 0002 
Coding: 01401 
Shop #: WSC 00000 
VCID: 2041E53FA0C4051801C 

1 Fault Found: 
00856 - Radio Antenna 
36-00 - Open Circuit 

End ---------------------------------------------------------------------​ 


*Thirdly, fresh AutoScan results 160 km after clearing all: 
* 
Friday,25,January,2013,15:18:14:02022 
VCDS Version: Release 11.11.5 (x64) 
Data version: 20121222 


Chassis Type: 1J - VW Golf/Bora IV 
Scan: 01 02 03 08 15 16 17 19 22 29 35 36 37 39 46 47 55 56 57 75 
76 

VIN: 9BWFB21J724061421 Mileage: 197420km/122671miles 
------------------------------------------------------------------------------- 
Address 01: Engine Labels: 06A-906-032-AZG.clb 
Part No: 06A 906 032 FN 
Component: 2.0l R4/2V 4071 
Coding: 00001 
Shop #: WSC 65728 
VCID: 6FE3D6032D9AEA60C86 
9BWFB21J724061421 VWZ7Z0B4877055 

2 Faults Found: 
17559 - Long Term Fuel Trim Additive Air; Bank 1; Range 1 
P1151 - 35-00 - System too Lean 
17704 - Error in Mapped Cooling System (check Temp-Sensor and Thermostat) 
P1296 - 35-10 - - Intermittent 
Readiness: 0000 1100 

------------------------------------------------------------------------------- 
Address 03: ABS Brakes Labels: 1C0-907-37x-ABS.lbl 
Part No: 1C0 907 379 J 
Component: ABS FRONT MK60 0103 
Coding: 0004097 
Shop #: WSC 00000 785 00200 
VCID: 3167107BAB2EBC909E2 

No fault code found. 

------------------------------------------------------------------------------- 
Address 15: Airbags Labels: 6Q0-909-605-VW5.lbl 
Part No: 1C0 909 605 A 
Component: 1M AIRBAG VW51 02 0004 
Coding: 12621 
Shop #: WSC 00000 
VCID: 2245EF37AEC81708178 

No fault code found. 

------------------------------------------------------------------------------- 
Address 17: Instruments Labels: 1J0-920-xx5-17.lbl 
Part No: 1J0 920 806 J 
Component: KOMBI+WEGFAHRSP VDO V07 
Coding: 07132 
Shop #: WSC 00000 
VCID: 2E5D0B07EA10A368830 
9BWFB21J724061421 VWZ7Z0B4877055 

No fault code found. 

------------------------------------------------------------------------------- 
Address 19: CAN Gateway Labels: 6N0-909-901-19.lbl 
Part No: 6N0 909 901 
Component: Gateway KCAN 0001 
Coding: 00006 
Shop #: WSC 00000 
VCID: F0E1557FB0A4759851C 

No fault code found. 

------------------------------------------------------------------------------- 
Address 35: Centr. Locks Labels: 1C0-962-258-III.lbl 
Part No: 1C0 962 258 AC 
Component: 25 Zentr.Verriegel. 0003 
Coding: 00018 
Shop #: WSC 00000 
VCID: 68D1BD1F08743D5889C 

No fault code found. 

------------------------------------------------------------------------------- 
Address 56: Radio Labels: 1J0-035-18x-56.lbl 
Part No: 1J0 035 180 D 
Component: RADIO 3CP 0002 
Coding: 01401 
Shop #: WSC 00000 
VCID: 2041E53FA0C4051801C 

1 Fault Found: 
00856 - Radio Antenna 
36-00 - Open Circuit 

End ---------------------------------------------------------------------​ 


*Fourthly, here's my trims from block 032:* 











*And lastly, I logged this 2nd-3rd WOT pull to check peak measured airflow*. 










Have I read correctly elsewhere that I should expect a peak flow [g/s] of HP*0.8? If so, then I'm depressed (85.7/0.8 =107), but maybe I should take it with a grain of salt. Road salt, that is. (Well, road gravel.) I'm choosing to chalk up my result to a lack of available traction... :what: 

*My conclusions* (please comment)... 
- Additive/Idle Trim being the troublemaker confirms vacuum leak 
- MAF looks fine 
- I may want to find the spare thermostat I bought awhile ago 
- (Airbag supply voltage happened to be shortly after a frozen/dead battery -- no worries there) 
- Nothing else significant appears to be going on 

(What does the "engine load" signal actually mean, and why is my ceiling apparently 80%?)


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## Anony00GT (Mar 6, 2002)

As for 17704, just replace the temp sensor and thermostat at once. Both are cheap items and common failures, drain the coolant once and do both. 

MAF numbers are low. I'd say you need to repair a vacuum leak first and re-test, but bad MAF is also a possibility. Repair all vacuum leaks, clear faults, run the readiness script and report back. 

If you do have a bad MAF, dump the K&N filter and install a fresh paper filter (should do this anyway). Cut the airbox if you want more flow.


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## Cee-dub (Feb 20, 2007)

Just to close the loop on this for any future searchers, the culprit turned out to be twofold.

The P0171 was indeed a vacuum leak from a chafed EVAP line in the tunnel near the front passenger wheel well. (Pic below.)

The misfires were a failed coilpack. (The original 3 mounting bolts had actually backed out loose from the block, leaving the coilpack semi-loose to vibrate to death.)


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