Lets see what you guys think.. Current engine mods are dp back exhaust (no 2nd cat), RMW Tune, intake/stock intake

Roll back to May, got my RMW Tune with exhaust and alta intake. Everything runs great, strong car. Previous to tune, getting about 28-29mpg on a heavy foot. After tune, getting about 27-28mpg, from a heavier foot.

Fast Forward to mid June. Theories of Stock intake producing more power, so thought I'd give it a try. Took off Alta, cleaned MAF, swapped to stock, but after 3 days (200 miles) decided to go back to alta intake. 100 Miles later, CEL, limp mode. Read code, states engine too rich at idle. Swap back to stock intake, clean MAF thoroughly, and reflash my tune to stock file. (Should of tried just the intake swap first for results to control variables). CEL gone, car is out of limp mode and driving great.

Since then (mid June to present, over 1500 miles) stock intake has been on, no CEL returns. The last 5 or 6 fillups I've noticed my hand calculated MPG (not read on the car's computer), has gone down to 24, then to 22 most recently. So, safe to say its steadily dropping. I've even been conscious about my foot and watching my instantaneous mpg readout, trying to keep it as high as possible and lowering my cruising speed on the highway. I've been driving the same route to work, 70 mile round trip, 50 miles worth is highway. Driving style has become more conservative, etc etc. Its not the AC or windows down or all those petty mpg variables, as its a 5mpg drop. 5mpg may not be much to some, but to me is pretty dramatic, as I can drive the car hard for a whole tank and get 28mpg still, even with the AC on/windows down etc. Deviation was only 1mpg, 2 at most.

Right before the CEL, I did have a fair amount of backpressure/backfire on rev match downshifts, if the exhaust temp was right. Usually I have some burble anyways just from running a 2.5" exhaust and no 2nd cat and no resonator, but the backpressure pop's i'm referring to are rather large pops. After reflashing the ECU and CEL went away, it did not pop nearly as much anymore. So, there is definitely an indication it was running rich, but not at idle. This is like 5-4 shifts on the highway, or 6-5.
Over time, the pops have slowly been coming back, but still sparse, it happened on one drive twice (loud backfires) on rev match downshifts in a week.

So, my thought is a bad O2 sensor.. sending my AFR off (possibly being too rich) and sending my mpg plummiting. Another thought is the amount of air going into the intake, and the tune expecting to see more (to run a 10.5 AFR that I saw on the dyno from the tune).. causing the mixture to be too rich. I know at stock the ecu will adjust for this, but not sure how this changes with the tune.

What would you think this is? Mind you from 08 when I got the car new that I averaged 28-30mpg throughout the year, driving styles, weather, etc. So 22 is a new low that is causing worry.

 

c'mon guys, this is a forum to contribute to, 30 views and noone has an opinion? I don't believe 30 car enthusiasts are all car illiterate..
just looking for opinions.. please share your thoughts

 

No one has had coffee yet! Sorry, I'd contribute if I had anything helpful to suggest. I'm sure the thread will pick up, there seem to be a ton of knowledgeable helpful car guys around here.

 

Mini keeps trying to get me to pay $600. for a fuel system cleaning. Maybe yours needs one?

 

SEAFOAM IT!

I may not be much of a help but understand your concerns.

I too went from a Aftermarket Intake (Forge) back to stock intake with K&N filter and Alta turbo inlet hose. I have the Canned tune, w/DP 3"back (catted). If i understand you about the "burble" I to have random "burble here and there. But not all the time?? My car does run rich from looking at the exhaust tip but it also ran rich when it was all stock as well. I to have a O2 sensor (DP related) causing a cel but has seemed to go away now for the last 3-4weeks with the stock intake? Please stay off so i can pass emissions

I have lost about 4-5 mpg with my current setup. Could be due to the heavy foot syndrome brought on by the RMW tune?

 

Thanks for the input, Its been seafoamed 2 months back, i have a stock dp so the o2 sensor isnt being tripped by the aftermarket cat (as mines stock).Our cars run very lean when stock, ~14.5-15.5 afr.. yes your tips will still be black but its running lean. Jan trims the afr down to about 10.5 or so to make it more rich, as a turbo wants to be at. The burble I'm talking about is a backfire, not the backpressure burble from when letting off the throttle with a larger exhaust. The backfire sounds almost like a pop from antilag (not as loud but much louder than any burble).. my thoughts still point towards a o2 sensor. hmmmm

 

You won't like my guess. I suspect you were so rich that it melted your cat.
If it is too rich, the cat is working too hard to do it's thing and they can actually melt and bock most of the flow. What little gets through now is still cleaned up so the downstream O2 sensor is not throwing a code.

10.5 all the time is WAY too rich. Heck, I did not even run my old Triumph's that rich. At WOT ( where it is legal to go open loop) it would give you the boost and power you want, but if off the stop, it had better be way leaner that that. I can easily see that as the cause of a cat meltdown. IMHO.

I hope I am wrong.

 

Although a clogged cat would be a problem that could cause a decrease in gas mileage, you would notice a big drop in power as well.

given that your first CEL came after cleaning the MAF, and then a more thorough cleaning seems to have made it worse, I would try to get my hands on another known-good MAF and see if your problem clears up. My guess would be that somehow in cleaning your MAF, you threw off its calibration.

 

TVR, maybe someone with a RMW tune could chime in with a AFR dyno graph. I know it runs 10.5afr at WOT in 4th gear for the dyno run, but do not have a gauge/scangauge for afr's when cruising. I als agree with splattj that i'd notice a large decrease in power if my cat/exhaust was clogged. This is probably actually just me more hoping that its not a bad cat... lol

Splattj, the MAF does seem plausible... don't those run a pretty penny too?

And, are all R56 MAF's interchangeable? Maybe I will try switching with someone local and see if there is a difference.

I should probably throw in also that I had a dyno tune file from Jan, but then got a reworked one for a hesitation issue, and that second tune was loaded around the time that the intakes were changed...
blah, that just hit me, and now it throws in another variable too.

I may try to reflash to my original dyno tune file on my next tank and see if it makes a difference.

Thanks for the continued input guys, much appreciated.

 

So a small update.. I changed from the stock intake box to an AEM dryflow filter yesterday. I originally was running the Alta intake, but due to finding oil in the intake tubing I didn't want to go back to an oil filter. The reason I changed it away from stock again was because talking to Thumper he said he had his car tuned on an aftermarket intake and when he swapped to stock intake his car did not react nicely. So I thought I'd give it a try for a tank and see if theres any change in fuel econ.

The MAF idea seems plausible too as I did get the cel after cleaning it. Maybe I touched the sensor or something accidently..

 

Wow, I fail, I didn't even give an explanation as to why I posted about the intake change. So, One thing I've noticed with the intake change is that the stock DV recirculating is not nearly as loud as it used to be with the alta. Could this be due to the different material? The AEM is definitely smaller, 5" long vs the alta which was probably more like 9.. but I feel as though an open intake is going to give you a fairly loud "blow off" sound regardless. This lead me to believe a possible boost leak? I really wish I had a boost gauge right now. The car still feels pretty strong (I can't really tell its lost much power if any).. which would null the leak. I've never actually gone looking for a boost leak before. Anything more to than checking hose connections being clamped tightly? Is there a way I can do it by listening to sounds at idle? Or does it have to be under load?

Or would this possibility not be feasible at all?
Usually I can hear the DV when lifting off throttle for shifts, for rev match downshifts etc over the exhaust, but I can barely hear it over the exhaust now, unless i'm really on the throttle.

 

Oil, cleaner, fingers, MAF. Bad combination.
How did you get oil in it? Over oiled K&N? I blot mine before running them.

I believe there is special cleaner safe for MAF sensors. Don't know what it is though. Sure beats a cat issue! Best of luck.

When you get the problem fixed, Thumber is right on having to match the tune to the intake. Specific tune to a specific intake.

"but I can barely hear it over the exhaust now," Well, to me that means your exhaust is too loud.

 

Well Cat vs MAF... MAF is 400$... Cat is definitely up there too.. so not sure its 'that' much better lol. Rather it be neither.
The car does seem to be behaving better now with the open intake on again.. While I only have a 35mi commute from work to home, I reset it and got a steady 27mpg, with a mixture of heavy and soft foot. I'm trying to drive it the same as I normally would and see if there are improvements. So far it seems good, and there are less hesitation with boost hitting compared to with stock intake (with the tune that is). I feel much better with a non oil'ed filter on now. Just refilled, so we will see what the mileage reading in a few days is.

Plan of attack...

-Filter (current test)
-Clean MAF again, along with intake tube, and possibly MAP (though shouldnt affect it)
-Oil Change (almost due anyways)
-Swap MAF with another R56 and see if improvements are there, if so, approach dealer for a new MAF (yes i know warranty issues ensue here)
-O2 Sensor
-Cat

 

One question, what are you cleaning your MAF with? I've read the CRC Mass Air Flow Sensor Cleaner works pretty good, but I have not tried it.

 

probably a silly question, but have you been pulling your battery w/ each intake change? or have I been pulling my batter cable for no reason each time i make a change like i did with my integra.

 

That's what I used

 

$400 for a stinking MAF? This is a $20 part. Borderline extortion. See what Napa has. I'd be ticked if it was $80. BMW should be embarrassed, but it seems they have no shame at all. The probability I will ever buy another goes down every day.

 

I used the CRC MAF cleaner.
tvr... I've had a MB and Audi before this, so I know how expensive these german parts are... ridiculous

However..
For an update... Tried the intake for one tank.. 23mpg, so, no improvement essentially. One thing I remembered... Jan had sent me an updated tune file for the hesitation issue around this time. I just swapped back to my original dyno tuned file two days ago and I reset my mpg counter. So far, (even though its only been 90 miles), it reads 29mpg avg... thus, so far it looks like that MAY have been the problem... maybe some value was skewed in the file, not sure. We will see after hand calculations of mpg after this tank.

Update soon..

 

MAF sensors do not like oil. I only use oiled filters on cars that do not utilize MAF sensors. Paper elements work just fine and also filter better.

 

It is not fair to say "paper is better, foam is better, gause is better". It depends on each individual element. The testing David Vizzard did clearly showed the K&N filtered better than the foam and paper he tested at that time, and it did not reduce it's flow as much as it got dirty as the paper did. It was not lower restriction to start with as is sometimes claimed. One test, one point in time. It was also clear that all paper is not created equal. If I remember, Autolite came out on top for the paper, with Fram the worst. As all foam is not the same.

I run the K&N and still get 31 to 32 MPG based on odometer and gas pump. (the computer says 34)

 

You did good to change from the foam oil filter. You've cleaned your MAF, now you need to clean the other two sensors along the intake track that oil from the foam coated. One is on the left and side of the engine and easy to see, the other is kinda under your intake on the backside of the engine.

AEm also makes a 8-9" filter which works great on the Alta setup.

 

OK. One thing I do know though...is that most paper is NOT oiled and no oil is a good thing with these modern, computerized machines. MAF's are easily contaminated and can greatly influence your economy. I would recommend, from my personal experience, to stay away from oiled elements on cars that utilize MAF's.