AndrewDickerson

Hi all,

I am at my wits end this p0171 issue, I have tried pretty much everything and do not know where to look further.

Model: 2007 C180 Kompressor Auto
VIN: WDC2030462R261104
Engine Number: 27194630861788

The history:

1. About 3 months ago I had rather high Long Term Fuel Trim Values of about +16.8 that would occasionally trigger the check engine light. When putting the engine under load it would subtract up to -7% and when at idle it would shoot up to around +10%.
2. The fuel system would stay Closed loop most of the time but when moving the throttle it would bounce to Closed Loop Fault and occasionally Open Loop Drive.
3. About a month ago the Long Term Trim numbers suddenly started getting worse, they went up to +17.2% and the 18.4%, This brought on the below work:

• Fuel System: New Fuel Pump and Sender Unit (Pierburg), New Fuel Pressure Regulator (Merc Original), New Injectors (Merc Original)
• Intake System: New Manifold Seals (Merc Original), New Throttle Body (Bosch OE), New Throttle body Seals (Merc Original), all pipes ion the system where then removed, cleaned, checked and refitted.
• Exhaust System: Flange was resealed, New o2 Sensors (Merc Original) and the manifold was checked by two shops for leaks.
• Ignition System: New Spark Plugs (Merc Original), New Ignition Coils (Beru OE)
• Sensors: New Cam Position Sensors (Bosch OE), new MaF Sensor (VDO OE), new MaP sensor (Merc Original), new Altitude Sensor (Merc Original), New Air Temperature Sensor (FAE)
• Miscellaneous: New Evap Solenoid (Merc Original), New PCV valve and piping (Merc Original)

After all of this work the problem is now even worse, the long term trim sits at +21.1% and the short term trims are even more erratic. Fuel system status does dit on CL most of the time, but moves to CL-Fault under load and OL-Drive when freewheeling to a stop. The o2 sensor reads between 0.300v and 1.200v normally, it then occasionally shoots up to around 4v for a few seconds when putting the car under load and accelerating aggressively.

I have propaned the engine bay thoroughly and cannot find any air leaks, what could be causing this problem?

I would love to save someone this horrible ordeal, any good information will be acted on and I will keep the forum updated on any progress made.

Any required live data can be arranged, just let me know.

tjts1

Your O2 sensor is giving false readings.

AndrewDickerson

Hi Tjts1, thanks for the reply.

I have tried putting the original sensor back in and the trims/o2 readings do not change.

I have also put a brand new FAE sensor in to see and it too does not affect the trims or o2 readings.

The new sensor is 4 months old and a Mercedes original, it was my first suspicion.

RedGray

Wow, you have a great informative first post, except you never say WTF the P0171 code stands for. So close!....
I'm on my tablet, so short post, and you use Google etc. :-)

It's great that you said that you have an M271. That makes ALL the difference!

Search for something like
m271 $11 hose fix


Very common problem. Cheap fix. But, it takes a good amount of time (man hours).

Since someone always says that they can do some complicated repair in 10mins. I'll say that I did the repair, and cleaned up every street in the world,and it took me 0.00090001 seconds. So, screw you pathetic sloth humans!!!!! ;-)

Good Luck!

RedGray

https://mbworld.org/forums/c-class-w203/233246-diy-m271-12-hose-replacement.html



https://mbworld.org/forums/c-class-w...placement.html

Good Luck!

AndrewDickerson

Hi RedGray, thanks for getting back to me.

The 12$ hose is part of the PCV system, Positive Crankcase Ventilation, it is three rubber hoses and a valve. I have already removed the supercharger and replaced those hoses and the PCV with Mercedes originals.

At the same time I resealed the Supercharger Gaskets.

I went so far as to remove the airbox, fit all the sensors and propane the PCV and supercharger area while watching my live Data just to make sure, no pickup in short term trims.

The ECU is running 21% longer fuel trims permanently and yet I am getting a lean code (P0171)

RedGray

I agree that it sounds like you have a vacuum leak. Those can be *extremely* hard to find.
You need a smoke leak test machine. Thankfully, you can get one cheaply now.
Like just about all modern engines, there are a _lot_ of places on an m271 where a vacuum leak can occur.


Below are some very quick suggestions:

https://www.amazon.com/STINGER-Smoke-Machine-Adapter-Manifolds/dp/B0758ZRBT7/








https://www.amazon.com/Vacuum-Smoke-Machine-Detector-Automotive/dp/B0746SL9D6



Those were quick to come up from a search. There are a few sellers that have a very good reputation.
Buy one from amazon, or eBay.

Good Luck!

mtnman82

Yep, $12 hose would have been my first guess too. I paid the stealer something like $500~$600 to replace years ago before we knew that hose was a bad part. I know there have been several upgraded part #'s for that hose since and am wondering if I don't need to replace it again. I keep going thru upstream O2 sensors and my gas mileage is not that great. I also smell gas sometimes.

Smoke detector is the way to go on vacuum leaks. Vacuum leaks can be a ***** to find. One of my other cars is a late 80's turbo and I've had to deal with them more than I care to admit. It does very much sound like a vacuum leak the computer is trying to compensate for. Good luck with it and please post any info or links to procedures you find on vacuum leak testing these cars. I fear it's something I'm going to need to do in the near future...

AndrewDickerson

Hi all,

Been compiling info from a few different forums, few suspects below:

1. There is apparently a second crankcase breather, trying to get some info on this, does anyone know more?
2. Getting a smoke machine either today or tomorrow to do another vacuum leak test, will update after that.
3. Apparently, there is a way to reset adaptations with STAR, does anyone know if this could be causing the issue?

Thank you all for the help so far, really appreciate the assistance.

AndrewDickerson

Okay, so I will have compression tester later today and a smoke machine.

I'll be rechecking the engine bay for leaks, after which I will perform a compression test on all cylinders.
Once all cylinders are tested Ill be testing the pre cat o2 sensor for the exhaust pressure as per another forums suggestion.

Ill write back after all has been done, hoping to find something.

The forum won't let me upload pictures, I have a pile of live data shots that I wish you all could see, does anyone know a way around the uploading bug? I select photos but it just sits at 0% indefinitely? Really annoying

mtnman82

Any updates? Really hoping you find/post a smoke test procedure for the intake.

AndrewDickerson

Hi Mtnman82,

I tried to smoke the engine with a conventional smoke machine, couldn't find any leaks though.

To do this I used a conventional event smoke machine and attached a pool hose to the nozzle allowing me to shoot a concentrated smoke burst around the engine bay.

I am now working between either the front SAM being faulty or the superchargers gasket having gone, should have stripped the supercharger out by this weekend.

I'll try post some pictures here, I'm sure there are a few people who would like to see the steps for supercharger removal on a m271 engine.

mtnman82

Did you pressure test the intake with the smoke machine? The smoke machine you posted earlier uses the regulator to regulate pressure to something less than 5 psi. You seal up the intake tract and inject the low pressure smoke to find the leaks, which should be easy to spot from the smoke leaking out. The hard part is knowing how to cap off/seal up the intake tract to perform the test.

Are you saying you just waved the smoke around the engine bay to look for leaks?

AndrewDickerson

Hi Mtnman82,

I think you are confusing another members post, I do not have a specialized smoke machine, only a standard event machine.

If you wanted to cap off the intercooler loop you could disconnect the right angle that comes up from the intercooler to the intake manifold/throttle body, it sits right under the air filters intake. I would then use duct tape to close that and seal the MAF feed pipe that sits on the back of the airbox to the smoke machines outlet, that should get you a testable setup.

Have you tried doing a propane test and having someone watch the short term trims?

Diego Schnorr

hi andrew I'm following your problem I'm with the same code. Have you made any progress?

Alaqil

These readings indicate lean in the exhaust and being compensated by higher fuel trim which makes the mixture rich resulted in non burned fuel. However, the amount of ingress air in the exhaust could still able to mislead the O2 reading to be lean instead of rich.
Since The intake has been checked with no leaks, I would suggest to check for leaks into exhaust manifold. The first suspected is air secondary injection circuit and I suggest to check for all tubes that connected to both switchover and recalculation valves as maybe the intermittently stuck at open position.
For me, I found a vacuum line from throttle body to control solenoid severely torn at the area that directly contacted hot engine parts. Also, lean faults used to be triggered from time to time. I just jumped the damaged area and all is fine for now. Precautionary, I sprayed some WD40 lubricant inside bleed connectors on both valves as this may help if there is a jammed component somewhere.

shan

I had the same problem recurring again and again even after changing the $12 hose together with the valve. After deleting the code and ECL with a scanner, it will reappear whenever I was caught in a bumper to bumper crawl on my way home from work. I read someone had suggested that the gas filler cap can also give this code P0171. I had my filler cap seal liberally sprayed with silikon and the problem has disappeared at least for the last 2 months. I am keeping my fingers crossed.

slammer111

My car threw the same code recently. I found a vacuum line (#5) had popped off a nipple, in the lower R corner of the diagram.

While you're at it, check all vacuum lines for cracks and leaks. There are 4 lines in total (Part #5 in diagram). Also check Part #20. Not sure about #20, but #5 seems to go bad at the 12 year mark or so.

The hoses should be ID 3.5mm iirc. My local parts store didn't have it so I went with 4mm, which would explain why the hose wiggled itself loose after a few years.

sajo1973

Just wondering if you solved the problem.

You can reset adaptations and all learning processes using das.

Oliverm271

Wow I am glad I stumbled upon this!!! I am a mechanic by hobby and have worked on close to around 50 different cars thoroughly and this one has me stumped! You have no idea how much all this information of the parts you invested is going to help me because I am having the same exact problem I changed everything! And it still keeps on giving me the same damn error but I am really starting to suspect that it is electrical I will read through all of the posts and leave up any information which can be pertinent and helpful as I have had this problem for near 2 years and it has been progressively getting worse as you stated also so the next step that I will be taking will be to clean the walls and or change them if necessary because it appears that even a slightly can cause major problems in these engines since they are high compression and especially mine being the c230k has a higher compression ratio than yours

shan

After a lot of hassle with P0171, changing a number of parts, one indie here found that it was the long vacuum hose 5 going out of part #50 in Slammer's diagram that had caused the problem. It was brittle and showing cracks near the far end which is not very accessible. Now my CEL is gone for good.

Phil Brewis

Had this code for a while now ! Noticed egr valve hose was split ..... no codes anymore , when air leaked in it affects quite a lot of things ! Maybe this could help

Rull-

Hello everyone,

I'm facing the same issue and replaced everything listed by Andrew, is any solution found?

Thanks in advance!

Aggelos katerin

Hello from Greece. I have an slk r171 with m271 engine.i have the same issue with fuel trims. Ltft are +25 and stft are almost 0 at idle but goes up to +25 at part load of the engine. I have change all vacuum hoses i have smoked the engine for leaks 2 times i have changed maf map lambda sensors i have checked the pressure in fuel. Rail but the problem is still there. I don't know what else to do. I would appreciate any help. Sorry for my bad English ! Thanks in advance

slammer111

Did you change all 4 sections of hose (part #5 in the diagram)?