[FIXED] P0171 - 2008 Mazda 3

YAY! Finally, we hit paydirt with our testing, lol.

I'm pretty sure that the regulator in the fuel system on your Mazda is integral to the fuel pump assembly in the tank. No external regulator, or fuel filter (as you noted). It's possible that the filter in the pump assembly is clogged, but I think your best move would be to replace the assembly at that point.

The foggy fuel IS somewhat suspicious. If you're going for the pump assembly, then it may still be a good idea to test for ethanol contamination. If it fails that test, then you might consider draining/refilling the tank.

Totally agree about the MAF. Really, that was my mistake, not realizing the implications of the 100% Load reading That was the big clue to move away from air measurement and onto fuel delivery, but I missed it. Lesson learned there - sometimes you just gotta trust the data

Many thanks for keeping us updated on this one, sir. Let us know where you go from here!

Found a picture of a flow chart I found in a training manual, thought I'd post it in here for anyone following along. I really like this chart, because it takes the WOT O2 test that ScannerDanner uses, and adds Load and MAP PIDS into the equation.



My thought process was following the 'Oxygen Sensor Low' path, but it was challenging for me to 'see' that in the data captures. Not that you were doing anything wrong, I'm just used to working with enhanced OEM data, instead of Generic OBD. That's why I had you working with the Equivalency Ratio and such.

But with the high Load reading, the chart points directly to a fuel delivery issue

I like that flow chart! I saved it for future reference.

So I replaced the fuel pump and I've been running on the new one for about a week now. No engine light. I cleared the codes. The car's ECU seems to have re-learned with the new pump. I have been monitoring my LTFT through out the week and it seems to stay in the range between positive 3 and 9. Only once have I seen it go up to 13 but then it quickly dropped. Knowing from past experience that anything between plus/minus 10 is acceptable, I feel that the new fuel pump has fixed the lean condition. When I am on the highway, I can see that the fuel pump is able keep up with the demand of air and is no longer running lean like with the old pump. I'm thinking that the slightly high LTFT might be due to other small things which is something probably not worth chasing.

On the other hand, I managed to take apart the old pump and take a picture of the old fuel filter. I don't know if this is what caused the low fuel pressure but it definitely was interesting. The picture is attached.

Also the tank was much cleaner than I had expected. I have attached a picture of that as well. The picture doesn't do so much justice, but it looked real clean.

I just want to thank everyone who has given me any help/tips or advice along the way to help me fix this problem! I've been chasing it for over a year now and I wouldn't be able to fix it without the help from you guys.

So the file sizes of the pictures are too big so you'll just have to take my word for it. I can't make them small enough for the forum unfortunately .

This thread might help you with reducing picture size.

link to Forum Thread on Picture Size & Formats

YAY! :woohoo: Thanks for getting back to us, sir, very glad to hear that everything worked out. If you're willing to resize your pictures, I'd still like to see the old filter you got out of the tank.

I'm OK with those fuel trims, too. Like you said, there may be room for improvement, but likely not worth chasing.

Again, I'm really happy you brought this issue to us, happy to help. For my part, I feel better about working with Global OBD now, instead of relying on OEM stuff. That'll absolutely pay dividends later.

I'm gonna slap a [FIXED] label on this one