High Long Term Fuel Trims with ROW Airboxes
 

Anyone else seen this - was trying to isolate why my LTFT was 25% at idle, a bit lower when driving. Thought it was the tune, Jerry says it should look normal, he thought maybe intake leak, so checked that and no leak to be found. Put my stock airbox lids back on and magically normal fuel trims.

Drove it for a week and fuel trims stayed consistent, thought maybe a leak at the airbox lid clamp to intake or something, put the ROW airboxes back on and fuel trims go right back to 25%.

Anyone else seen that - is that normal? I would not expect that much more airflow to need that much more fuel at idle, but maybe it is normal?

Thanks

Rob

DIY ROW? or are they MB Factory parts?

Thanks

Dave

MAFs are all interchangeable. Same part numbers across all the C63 models. They're not "recalibrated" for the immaterially increased airflow as someone incorrectly pointed out recently.

I got high ltft after ROW install too, very similar.
I sold the mafs off of the factory ones, so now I Have to check part numbers.
If the mafs are indeed the same, what we are seeing is the US tune and it compensating for ROW. As the load increases, the volume of metered air becomes unchanged ROW/US.

https://cimg6.ibsrv.net/gimg/www.mbw...01d7d0fe9a.jpg
Hey there. These are the factory MAFs you sold. I was the buyer :-) I never used them, and have since sold the car (upgraded to a W205 C63)

I will double check the MAF part numbers to confirm if they are the same or different for science.

do you have logs? fuel pressure and long term fuel trims have a direct relation with one another.

I haven't had a chance to check the part number for the new maf yet. I normally check them in the first place, but with these you have to really dent those steel brackets to get them out, I didn't want to do this.

As far as fuel pressure, it shows in the Xentry line up of tests and mine is fine. Xentry does not log it, to my understanding.

from my own logs variation of 1-2 psi of fuel pressure has caused my LTFT's to swing from 40's to 20's and everything in between.

I had the same exact thing happen to me with the ROW airboxes. I even swapped the MAFs from my original airboxes to the ROW airboxes and it made no impact on the high LTFT readings. I believe the MAF part numbers were the exact same, but the date stamped on the ROW MAFs was more recent.

I've replaced my intake manifold gasket, smoke tested for leaks (none were found), replaced the airbox bolts, and nothing has made any difference. No matter what, with ROWs I get LTFT readings in the 20%-25% at idle, while with US airboxes and charcoal filters I get 0-1% at idle. I'm using OEM paper filters in both scenarios. Furthermore, with the ROWs, my car eventually starts to have strange hesitations in acceleration under low RPMs. I've put about 500 miles on with the ROWs and called it quits with them. It seems like YMMV as far as whether or not they work in your car. I have a P31 tune as well.

I added ROW Airboxes and K&N filters to an otherwise 100% stock 24,000 mile 2012 Edition1 and noticed the same hesitation. Come spring let me know what you guys figure out. :D

Ahhh oh yeah, Rob you reminded me of something which I've been meaning to post for ages now, but it slipped my mind.

I was experiencing somewhat high fuel trims too and deduced that the aluminium inner sleeve of the airbox lid wasn't sitting 100% flush with the outer plastic skin which slides into the Y-pipe at the back of the intake manifold. When I held the airbox into the light, I could actually see right through to the other end. I instantly thought....right...so this is how I'm getting unmetered air, which is in turn pushing the fuel trims up.

I carefully blobbed some clear epoxy over the perimeter, particularly where there were the big gaps and wouldn't you just know it....average LTFTs of around +10-12 and STFTs of around 7-8 at idle, have now become as close to zero as anybody would be happy to have. Needless to say drivability and fuel economy were improved afterwards.


https://cimg0.ibsrv.net/gimg/www.mbw...d47056a416.png
https://cimg6.ibsrv.net/gimg/www.mbw...486f6fb325.png
https://cimg3.ibsrv.net/gimg/www.mbw...5d193504b3.png
https://cimg1.ibsrv.net/gimg/www.mbw...1cf5cad39a.png


Although pics shown are from one box, there were similar gaps on the other box too. Mine is a 2010 E63 UK/Euro model with....yep, you guessed it - ROW boxes. I don't know if this is a ROW-only issue, but mine is now sorted. Maybe this remedy might work for your cars too guys.

https://cimg0.ibsrv.net/gimg/www.mbw...24ad62a5d1.jpg


so what you're telling me you've been holding out on this valuable information for years...i see what has become of our "friendship"

So celicasaur, when the time comes to pull the air box lid off to clean the filters, will that epoxy easily peal off from the lid so you can you re-apply a new layer?

So, was the plastic deformed preventing the clamp on the Y pipe from creating a seal? That gap where you put the silicone is inside the Y pipe so I'm not picturing what you fixed.

EDIT: Wait... was air actually flowing between the metal and plastic on the INSIDE undetected by the sensor?

High guys, off topic but can you guys tell me what i need in order to find out the fuel trim recording? I believe i needcan app, an obd2 scanner... but what else?

i have been noticing high liter/100 gas mileage at idle and i want to find out if could be some similar issue.

thank for any help.

Fuel mileage at idle would be an infinite number. Assuming you're referring to idle as being stationary.

Sounds like it.
I thought maybe the computer had to relearn, but unmetered air sounds like a likely culprit.
I wish this thread would have been a week or two ago, we just got 7inchs of snow today or I'd pull it apart and check. It would be easy enough to compare the ROW airboxes to the US ones.

Can we just take the metal out?