car reporting 6mpg ... stuck injector? or o2 sensor?

[kolosy]

I've got an o2 sensor code (274a) that keeps popping up, and I plan on replacing those in a weekend or so. In the meantime, I noticed that the car sucked down a tank of gas in ~190 miles, so i flipped into the mpg display and reset it (it was showing ~18, but that included the ride from DC to Chicago when I brought it back). It sat at 6mpg just tooling around down. Then after a few miles it started ramping up from 6 (it was pegged at 6.0 and not moving).

i know bad o2 sensors will make it run rich.. is that what i'm seeing? or do i have a stuck injector? is there anything I can do to test for that short of pulling them out and actually testing them?

car has ~60k miles on it.

[NiBe]

6 mpg 274a should be precat O2 sensor in bank 1. I would start with replacing it. It would be interesting to see your STFT and LTFT. Problems with O2 can and typically will result into rich/lean. Btw if you are running so so rich then I would not drive until this is resolved because you can damage your catalyst. Do you smell fuel from exhaust gases?

[kolosy]

Originally Posted by NiBe

6 mpg 274a should be precat O2 sensor in bank 1. I would start with replacing it. It would be interesting to see your STFT and LTFT. Problems with O2 can and typically will result into rich/lean. Btw if you are running so so rich then I would not drive until this is resolved because you can damage your catalyst. Do you smell fuel from exhaust gases?

I can try pulling those numbers (i assume ISTA?)

Car is running test pipes and I do smell some fuel from the exhaust but hard to tell if it's just because it's missing the primaries...

[NiBe]

Originally Posted by kolosy

I can try pulling those numbers (i assume ISTA?)

Possibly something like this:

Or INPA: https://bimmerprofs.com/stft-and-ltft/

Or Carly, CarScanner, ScanMaster-ELM

etc.

[amrazM]

IIRC you bought the car with a tune on it already no? to really have a baseline you should flash it back to stock, correct the errors and go from there.

If there was a stuck injector you would know. fwiw my supercharged e90 gets like 15mpg driving normally shifting at 3500RPM.

[kolosy]

Originally Posted by amrazM

IIRC you bought the car with a tune on it already no? to really have a baseline you should flash it back to stock, correct the errors and go from there.

If there was a stuck injector you would know. fwiw my supercharged e90 gets like 15mpg driving normally shifting at 3500RPM.

yeah, and agree that would be best. problem is that it's got test pipes so flashing it to stock would also throw a CEL.

re: "you'd know" -- is it sudden death in that scenario? not sure how long it takes to get to bore wash / hydrolock

[amrazM]

Originally Posted by kolosy

yeah, and agree that would be best. problem is that it's got test pipes so flashing it to stock would also throw a CEL.

re: "you'd know" -- is it sudden death in that scenario? not sure how long it takes to get to bore wash / hydrolock

The smell of the car at idle with a stuck open injector would make your eyes burn and the car will also misfire extremely bad. It sounds like your car runs normally.

A primary cat O2 sensor would throw the fuel trims way off, it could explain what youre experiencing here.

[spammysammich]

Originally Posted by kolosy

yeah, and agree that would be best. problem is that it's got test pipes so flashing it to stock would also throw a CEL.

re: "you'd know" -- is it sudden death in that scenario? not sure how long it takes to get to bore wash / hydrolock

Depending on the severity of the leak, borewash can take a while or happen relatively quickly. You can verify by pulling plugs and getting an endoscope in to inspect the cylinder walls for signs of bore scoring. You would probably experience black smoke on start up if there was significant enough wash to score the cylinder walls.

RE: hydrolock, it typically happens quickly. See examples of water ingestion when driving a car with a low cold air intake through a body of water. You'd hear rod knock immediately if it didn't kill the engine. It doesn't take much water to beat the bejeezus out of bearings, you could pull an oil sample and pan for gold to verify.

Amraz sounds like he's got you on the right track.

[kolosy]

me again.

replaced the precat O2 sensors with shiny new bosch ones. The ones that came out were completely black (not sure if that's a bad thing necessarily, though) and not OE. dropped in the new ones, and decided to not reset adaptions but just drive it for 50 miles. here i am, ~60 miles later. Haven't gotten a CEL since doing this, but mileage still sucks. Now getting ~8 in the city, low teens highway.

The car does have an Evolve Stage 2 tune from the PO, but a little bit of research shows that that should still be in the mid teens combined.

I've got new plugs and new injectors sitting here that I'll throw in because I already have them, but ... other thoughts?

oh and as someone else pointed out -- car sounds and behaves great otherwise. just keeping an eye out for what's happening.

[torrque]

The tune. Remove it.

[kolosy]

Originally Posted by torrque

The tune. Remove it.

Can you be more specific? Are you saying that as a diagnosis step or that it’s causing the mileage directly?

I don’t much care what the mileage is, I just view it as a potential symptom of a problem I’d like to understand.

[tbuck]

Are you saying that you are manually figuring mileage, based on actual gas used and miles driven, OR are you saying this is what the on-board comp is telling you? I can tell you that once you move away from stock (tune, intake, exhaust, etc.) the on-board comp loses its mind and is all but useless. Just saying, not sure it would be this far off, but still...

[kolosy]

Originally Posted by tbuck

Are you saying that you are manually figuring mileage, based on actual gas used and miles driven, OR are you saying this is what the on-board comp is telling you? I can tell you that once you move away from stock (tune, intake, exhaust, etc.) the on-board comp loses its mind and is all but useless. Just saying, not sure it would be this far off, but still...

i'm using the reported mpg value from the comp, BUT it does seem to track with how often i'm filling up.

... that said, since i've only done 60 or so miles since changing the sensors, i haven't gone through a tank and haven't thought about what you're saying. i'll keep a manual eye on it for a bit then and see what happens.

[e90335e36m3]

Originally Posted by kolosy

i'm using the reported mpg value from the comp, BUT it does seem to track with how often i'm filling up.

... that said, since i've only done 60 or so miles since changing the sensors, i haven't gone through a tank and haven't thought about what you're saying. i'll keep a manual eye on it for a bit then and see what happens.

6mpg x 16 gallons = 96 miles. If you were filling up that often, you'd notice.