I've been struggling with my 2013 Mazda 2. CEL has been on for a long while for p0171, lean condition. Done all the basics: check for external and internal vacuum leaks and found none, replaced the MAF with a non-OE unit and things got worse for about two weeks, cleaned and reinstalled the original MAF and things went back to "normal" (that is, p0171 is still there with an occasional misfire about 2500-3000 rpm but no misfire code), disconnected the crank vent tube from the valve cover and plugged the port on the MAF housing, verified no issues with the MAF housing and SRI from Corksport, purge valve working correctly, pcv valve is not leaking, MAP sensor vacuum good as is vacuum reading for the intake, even went so far as to rotate the MAF housing to change the clocking position of the sensor relative to the throttle body on recommendation of a friend. The OEM Denso MAF is about $100 after discount from Advance Auto. Do I take the plunge again but with the OE part?
The only thing I would use a non-oem maf for is a tire chock.
Ugh. Sme thought on mine but with oe vs denso purge valve. I'd go oe
Don’t they have a return policy?
I'm not familiar with this model, but here's what I would try before spending the money.
Is fuel pressure good?
Does unplugging the MAF help or hurt?
Do you have a way to get a known good sensor off of another car and try it?
Did you change the air filter?
FP is unknown. I have gauges but need to hook them up. Considering how well the car runs otherwise my guess right now is not pressure, but you are right in that I need to verify.
Unplugging MAF makes no difference.
My impatience got the better of me so I bought the Denso MAF. We'll see if that has any effect.
Has Corksport SRI.
Fuel filters are generally cheap.
grover said:
Fuel filters are generally cheap.
Not on these and it's in the tank to boot!
It reads lean because of O2 readings, yes? Do you have something that can read O2 signal real time to make sure that it makes sense?
When is it lean? Hot? Cold? Idle? Cruise? Loaded? You need to monitor fuel trims and diagnose.
In reply to mazdeuce - Seth :
Don't think so. Watched readings in real time while heading home. AFR was generally just rich except when closing throttle or under full decel. So as expected.
In reply to Streetwiseguy :
As soon as starts up it's lean. Always. Long term is near 19%, while short term moves around quite a bit based on load and demand.
19 percent is huge. Are there any times the short term goes negative teens? The two are added, so you need to watch the pair.
Do you have the original air intake? I have seen situations where airflow differences will make the maf read wrong. Might be worth swapping back if possible.
In reply to Streetwiseguy :
When ST goes negative it rarely gets to -10.
No on original air intake. The Corksport SRI has been installed for at least three years.
Fuel pressure good. Over 50 psi. Only thing left to check is EGR and valve clearances.
You know, occasionally I have run into situations where everything on the inlet side is correct, but the O2 sensor is a bit off. Not enough to set a sensor code, but enough to drive the mixture a bit out of range. Without a tailpipe sniffer, its pretty hard to pin that down. What I have done, is reset the KAM memory, unplug the front sensor, and see whether it runs bad, or better. 20% lean will make for a reasonably unhappy idle and part throttle, so if the sensor is not there, your car should run a bit badly. Plug the sensor back in, and if it starts to run better as the fuel correction comes back, you know you are chasing an actual lean condition. Unplug and it runs well, maybe you are a bit off on the O2 sensor. Plugs black at all with the current code? 20% added fuel, if it doesn't really need it, should make them a wee bit darker than normal, I would imagine. Cat might stink a bit, too.
In reply to Streetwiseguy :
These numbers were taken at idle. Perhaps I need to disconnect the battery to reset the long term fuel trim and see if things are different with the AFR disconnected.
Lord, man, that's 43 percent total trim. That's huge. If the oxygen sensor is reading wrong, it should be black and stinking out the tailpipe. Does the short term stay positive like that at higher loads? If it heads to negative numbers at higher air flow, there could be a fairly big vacuum leak somewhere. If it stays positive, maf? Low fuel pressure? High resistance in the injector power supply? Plugged injectors?
It's not a flex fuel vehicle, is it? The alcohol sensors can get stupid sometimes, but that generally drives trims way negative.
Did it accidentally get a load of e85?
This is probably a long shot, but the 2500-3000 RPM misfire got me thinking. In a 1.8 Miata, there can be a stumble around those RPM when the engine hasn’t warmed up yet, and the usual cure is new coils/plugs/wires. It doesn’t always fix it, though. The next thing to do is replace the leading O2 sensor, even if it’s not throwing a code. That fixed the issue on my Miata. I know a Mazda2 is going to be a lot newer tech, but it might be worth a try.
I'm not used to looking at afr on a scan tool. 14 to 1 is lean, right? The rear sensor is reading rich while front is lean. That's wrong, although seeing a snapshot like that isn't as useful as seeing it in real time. Maybe try to unplug front sensor, reset Kam and see if it runs like crap with B1S1 unplugged.
In reply to Streetwiseguy :
No, It's stoich- 14.6 for gas, 14.3 for E10- but I'm betting the scan tool has no clue about the fuel, so assumes gas- and I'm 100% sure that this car uses a WB sensor. So that's stoich in the exhaust.
The plugs confirm that it's not running super rich, too- so it's either a massive air leak or very short on fuel. I would not suspect the MAF as failing, as they are very robust and simple- but perhaps getting some spray MAF cleaner might help. It's a very mild wire cleaner.
Back in my FWD OBDII Mazda days P0171 was nearly always a vacuum/exhaust leak or a bad oxygen sensor. I had this code more times than I could count on my old turbocharged Protege5. Most were vacuum leaks and for some reason Mazda's control system seems to be VERY sensitive to those. Isn't the Corksport intake silicone? Perhaps it's developed a leak due to age. I've experienced two situations where a large exhaust leak (e.g. exhaust sheared off at flex joint) caused the upstream primary oxygen sensor to read lean. I've also encountered exactly two "bad" oxygen sensors. I don't know what exactly was "wrong" with them but replacing them with an OEM unit, and not a universal aftermarket one, fixed the problem. Only once have I had it occur due to a fuel issue and that was because I managed to screw up a fuel line connection.
Streetwiseguy said:
I'm not used to looking at afr on a scan tool. 14 to 1 is lean, right? The rear sensor is reading rich while front is lean. That's wrong, although seeing a snapshot like that isn't as useful as seeing it in real time. Maybe try to unplug front sensor, reset Kam and see if it runs like crap with B1S1 unplugged.
This. I reset KAM (disconnected the battery and left it off all day at work) then left work. Drove poorly. After about ten miles I decided to disconnect the AFR sensor (aka front o2). Ran like crap the last 15 miles home. Did not have my tablet with me to verify while driving.
To others, I have replaced the MAF with an OEM Denso unit. I've pulled the Corksport SRI and verified it's fine. I also cleaned the old MAF with CRC Mass airflow cleaner (generous plug for a fine product!)
There are no vacuum leaks. I've used carb cleaner and propane to look for leaks and found none. The exhaust note has not changed at all and I can find no leaks in the manifold at or near the AFR.
Fuel pressure is good (see gauge reading above).
I will view the gauges again tonight under various load conditions and report back.
