[FIXED] P0171 - 2008 Mazda 3

Hi,

I have an '08 Mazda 3 2.3L engine. It's giving me an engine code P0171 Lean in Bank 1 that I have been trying to diagnose. I have two scanners (a Scangauge 2 and a cheaper odb cord that hooks to the laptop - OBDWIZ) that I have been using to do my diagnosis. The freeze frame data shows that the lean code is detected at higher loads, around 50% - 60% with a long term fuel trim at around +20%. I only seem to get the code at high speeds, like on the highway, especially on hot days. Now when I monitor my o2 sensors at idle, I see that my upstream sensor is running rich for the most part with small dips to low voltage but then back up to higher voltage. My downstream sensor is steady at around 0.7 to 0.8 volts, which I believe is good. What is confusing me is that my o2 sensors are reading the mixture rich, for the most part, but the code is tell me that the mixture is lean. Is the o2 sensor detecting the adjustment that the engine is making to the engine?

I also noticed that my Manifold Absolute Pressure is at around 4.3 PSI which seems low and tells me that there is a vacuum leak. I had the car sent to two different shops and both told me that the smoke test came back negative and that there were no leaks detected. One of the shops was actually my Mazda dealer.

I plan to test the following, but still have not executed any of them:

- fuel pressure
- MAF sensor
- IRMC solenoids
- MAP sensor

I have attached screenshots of the o2 sensor graphs.

Any suggestions to what this may possibly be?

Thank you in advance

Hey Mazda3GT! Welcome to the forums!

First off, love that you've got some graphing capabilities! That'll make diagnosing this one a lot easier. A question about your OBDwiz captures: The top graph is always labeled Bank 1 Sensor 2, and the lower one Bank 1 Sensor 3. I doubt your 2.3L has two different downstream sensors, so I'm wondering if the top graph is actually the upstream sensor?

If the top graph IS the upstream sensor, then it's worth mentioning that the upstream sensor isn't a conventional O2 sensor, but a 'wideband' air/fuel ratio sensor. They don't behave like normal zirconia O2's, but the Global OBD data will show you a 'converted' value on a 0 - 1V scale. Basically, trying to make the sensor data friendly for anyone not familiar with A/F ratio sensors. Looking at the captures, I'm not sure if rich/lean is being represented correctly. Not saying I think the sensor is the problem, just trying to account for the O2 readings you're seeing.

About the MAP sensor, I'm not sure I'd read too deeply into that data PID yet. With the MAF sensor in play, the MAP isn't a load input, and shouldn't have much say on fuel trims. If you have the chance, could you take some shots of the MAP data next to the engine speed on a test drive? That'd help us check the sensor's performance.

The fact that your code sets under higher load conditions (good catch, BTW) tends to suggest a fuel delivery issue, so I'm not surprised that the shops didn't find a vacuum leak.

My first suspicion is a misreporting MAF sensor, as this is somewhat common, and neatly accounts for your symptoms. One of the best tests I can think of for this is the classic WOT fuel delivery test:



Your ODBwiz probably won't have the same data available, so I'd suggest watching the upstream A/F sensor, LOAD, engine speed, throttle position, and MAF if available during your WOT run. If we're on the right track, then we'll see a lean upstream sensor, along with low LOAD %.

Try that test, post up the results, and we can go from there!

Hello guys hope this help, on mazda 3 the pressure should be around 55 to 70 psi at idle and soon you turn the car off should drop no more than 38 psi ! I did a mazda pick up b2300 returnless system have the same problem and symptoms high fuel trims at high speed ! Good luck also like tyler said check flow meter! Good luck!

So I did a few WOT tests on a back road and recorded load %, the same o2 sensor signal (sensor 2 in OBDWIZ), MAF rate, MAP pressure, Vehicle Speed, and throttle position. I have attached a few graphs I put together from the data that was recorded. OBDWIZ has a neat feature that will record all the parameters I choose into an excel document. Unfortunately I cannot attache the excel document of the data collected due to the format.

I also have another set of data with a slightly longer pull at WOT (about 9 seconds long). That pull is not reflected in the attached graphs.

Also, when I went to collect data, I noticed that there was new engine code. I still had the P0171 but I also had a P0113 - Air Intake Temp. Circuit High Input. This gives me another reason to suspect the MAF since the IAT sensor is integrated with the MAF sensor. However, A few days ago i was playing around with my MAF sensor connector. I was trying to fit paperclips to see if I could back-probe the sensor to test it. I don't think this would have anything to do with the code since I was trying to probe the 12V and ground terminals. But I thought that this was interesting. I also cleaned the MAF sensor one more time before the run.

Hey Mazda3GT, thanks for getting back to me with the data! My sincere apologies for not getting back to you sooner.

First off, I really like the Time Vs. Speed Vs. MAP capture, as I think it shows the MAP working correctly. At WOT, the MAP swings up to slightly above 14 PSI, which is pretty close to atmospheric pressure. At idle, the reading is closer to 8 or 9 PSI, which works out to around 17 inHg, normal for a running engine in gear with some accessories on. It's confusing because the data PID reads in pressure compared to a vacuum (psi-a), instead of compared to atmospheric pressure (psi-g).

Second, I see the Load PID going to 100%, which kinda surprises me! That would tend to suggest that the MAF is working correctly, but let's not rule it out yet.

Looking at the O2 Vs. throttle position is a bit confusing. I'm still not sure that the O2 voltage PID is working correctly, or at least representing the sensor signal correctly. Any chance that there's other upstream O2 data PIDs available? I'm thinking of 'equivalence ratio', AKA lambda or air fuel ratio. That would really spell out what the sensor is reading.

The other issue is that we could really use a WOT run through first, and maybe second gear, from a stop. This will really load the fuel system, and give the data a chance to expose an issue. A run like that while watching the upstream O2 (or equivalence ratio), MAF, engine speed, and throttle position would be ideal.

It would also be beneficial to have a look at your fuel trims during a drive. Your freeze frame indicated a Load of 50 - 60 % when the code set, so I'd be interested to see what the trims are doing around that range.

Again, my apologies, I don't mean to make you drive all over town! Thanks for working with us, sir.

No problem. We all get busy. In fact, thank you for helping me thus far! I really appreciate it!

The MAP reading makes more sense now. I was worried because I saw around 4.3 psi at idle and immediately thought vacuum leak. This does make sense now. Is this almost like the difference between gage and absolute pressure?

Now that you mention it, there is a PID that is called "equivalence ratio" in OBDWIZ. I looked it up briefly and google told me that its the deviation ratio from the ideal air/fuel ratio of 14.7:1. I didn't use it previously because I didn't think it would help me. I also have a "lamba" PID and a "wide probe" PID (if I am remembering the name correctly) for both o2 sensors. Should I perform the new tests with all of those PID's for the upstream sensor? I can also throw in the short term and long term fuel trim PID's in the data.

I think I may do a separate test with Time vs. Load vs. STFT/LTFT.

Also. I went out to Harbor Freight to but a fuel pump tester. I bought the cheaper one. Link below:
www.harborfreight.com/fuel-injection-pump-tester-92699.html

I'm itching to test the fuel pump to see how the pressure compares to spec. Just to rule that out if I can. What do you think?

Andyford,

Thank you for those specs by the way! I might be testing the pump soon. Hope for the best.

The MAP reading makes more sense now. I was worried because I saw around 4.3 psi at idle and immediately thought vacuum leak. This does make sense now. Is this almost like the difference between gage and absolute pressure?

Exactly! Why did they choose to do it that way? Who knows. Like this Civic I saw yesterday, with an A/C pressure sensor reading in inHg. Just... why? lol

Now that you mention it, there is a PID that is called "equivalence ratio" in OBDWIZ. I looked it up briefly and google told me that its the deviation ratio from the ideal air/fuel ratio of 14.7:1. I didn't use it previously because I didn't think it would help me. I also have a "lamba" PID and a "wide probe" PID (if I am remembering the name correctly) for both o2 sensors. Should I perform the new tests with all of those PID's for the upstream sensor? I can also throw in the short term and long term fuel trim PID's in the data.

I think I may do a separate test with Time vs. Load vs. STFT/LTFT.

Yeah, that'd be perfect. No worries about not using it previously - I actually forgot it existed on the Global side, lol. I was trying to think of other PIDs for you to watch, ended up checked Global ODB data on a customers Corolla (with a similar upstream A/F, downstream zirconia O2 setup), and saw the equivalence ratio PID. Perfect for our purposes!

Also. I went out to Harbor Freight to but a fuel pump tester. I bought the cheaper one. Link below:
www.harborfreight.com/fuel-injection-pump-tester-92699.html

I'm itching to test the fuel pump to see how the pressure compares to spec. Just to rule that out if I can. What do you think?

Hmmmmmm, I'm not sure that the tester you got will adapt to the fuel system on your Mazda. It's returnless, with quick disconnects and no Schrader valve You'll be able to adapt to the male end of a quick disconnect, but the female end will be tough. Not saying you SHOULDN'T check fuel pressure, I was just trying to avoid it given the challenges involved.

Yea those MAP readings are misleading.

I'll re-do the test with equivalent ratio and try to perform the testing in 1st or 2nd gear, from stop. I'll also do a running test measuring load and STFT and LTFT against time.

I figured that that tester won't be the best. I was going to use the t-connector to tap into the quick-connect on my car. I would have to use the small rubber hose to connect one end to the male port on the car. But I'm not sure if the hose is the right size. I think I may need one like in the link below:
www.harborfreight.com/master-fuel-inject...-test-kit-97706.html
Harbor Freight brand is probably not the best but I just need something cheap that will do the job.

I'll post back my results as soon as the tests are done.

Mazda3GT wrote: Yea those MAP readings are misleading.

I'll re-do the test with equivalent ratio and try to perform the testing in 1st or 2nd gear, from stop. I'll also do a running test measuring load and STFT and LTFT against time.

I figured that that tester won't be the best. I was going to use the t-connector to tap into the quick-connect on my car. I would have to use the small rubber hose to connect one end to the male port on the car. But I'm not sure if the hose is the right size. I think I may need one like in the link below:
www.harborfreight.com/master-fuel-inject...-test-kit-97706.html
Harbor Freight brand is probably not the best but I just need something cheap that will do the job.

I'll post back my results as soon as the tests are done.

I think that's the same set as my $450 OTC set (very similar anyway). Same gauge and everything, just in a red box. I wouldn't hesitate to drop $80 on that!

Is it just me or did the o2 voltage kind of trend lean against the TPS voltage PID in capture 3?
I'm curious to see how the data pids Tyler mentioned check out during the WOT run. Most of the cars I see still have old zirconia sensors.

I saw the same thing, Noah. But the reactions of the A/F sensor still don't make sense to me

Which got me thinking about this Mazda 3, and if Mazda3GT owns a California emissions vehicle. Those models actually DO have three O2 sensors in them, one upstream A/F and two downstream sensors. I initially thought the OBDwiz software was misnaming the upstream sensor as B1S2, but it may actually be telling the truth, and we're not yet looking at the upstream sensor!

Tyler wrote: I saw the same thing, Noah. But the reactions of the A/F sensor still don't make sense to me

Which got me thinking about this Mazda 3, and if Mazda3GT owns a California emissions vehicle. Those models actually DO have three O2 sensors in them, one upstream A/F and two downstream sensors. I initially thought the OBDwiz software was misnaming the upstream sensor as B1S2, but it may actually be telling the truth, and we're not yet looking at the upstream sensor!

I had considered that possibility myself Tyler, I've seen these with 3 sensors. Most cars I see are California compliant.

Noah wrote: I had considered that possibility myself Tyler, I've seen these with 3 sensors. Most cars I see are California compliant.

See, that's an interesting difference in experiences, 'cause I almost never see Cali emissions vehicles out here! Probably something I should keep in mind more often.

Massachusetts is kind of funny, I'm pretty sure all new vehicles sold in the state are California compliant. But they only need to pass emissions for 15 years. After that, safety inspection only.

Back with the results....Finally haha. Sorry for the delay. Was in the process of packing things to go back to school and unpacking. Hate this time of year.

Anyway. I was able to hit WOT in first gear. I did it from a stop sign, turned and floored it but couldn't hold it as much as I can in 3rd or 4th; so the pull is short. Hopefully it is enough to see a trend. I also collected some data on the highway (when I usually get the MIL) at WOT in 5th gear. I took LTFT and STFT data vs. Throttle Pos. The graphs are attached. The equivalence ratio seems to decrease when WOT is hit. On the highway, It doesn't seem to dip too much at first but slowly starts to decrease.

However, Let me know what you think.

Thanks.

These are the other charts

Back again, finally!

I think you can really see the issue in how the short term trims react to throttle position. Even some light throttle application results in big fuel trim changes. This *seems* like an air measurement issue to me.

My only problem with that is how we were seeing 100% Load in previous captures. By itself, that tends to suggest the MAF is measuring correctly. Every time I've seen a MAF problem, it's always resulted in a low Load calculation. This is why I have a hard time suggesting parts replacement, lol.

Like you noted in the opening post, fuel pressure is still on the table. Any luck finding a different test kit? Speaking of fuel, there's also ethanol fuel to consider. This page does a pretty good job of keeping the procedure simple. If we're on the right track with fuel quality, then this test will show FAR more than 10% ethanol.

EDIT: There are also test kits available online, though I've never used them before. If you go this route, let us know what the results are? I've always been curious how well they work.

Check pcv elbow hose under intake plenum, they collapse and start leaking.you barely see it,almost not but famous water bottle test works great.

UPDATE!

So I went ahead and tested the fuel pressure on the car and sure enough the pressure was low when running. KOER showed no more than 40 psi, when the normal range is between 51 and 59 psi. After running for 10 mins at idle, the pressure dropped down to 34-36 psi. After the car was shut off, I waited 5 mins to see how the pressure would react. It rose from 36 psi to 46 psi. After another 5 mins (a total of 10 mins) the pressure was up to 49 psi. If I am correct, I believe this result can confirm that there aren't any leaks in the system since the pressure not only did not drop but went up. However, I know that I have a fuel delivery problem, most likely from a bad pump. However, I am not sure if this would signal a bad regulator.

In addition, I do not have a fuel filter on the car, instead I have a strainer at the pump. A really stupid thing that Mazda did here. But it could possibly be that the strainer is dirty and clogged up. I did bleed the line a few times to make sure there was no air in the line and when I did I was able to retrieve a bit of fuel. The fuel did look a bit foggy so it does lead me to think that it could be just a dirty strainer.

Good thing is that I know which way to look now. MAF sensor is most likely out of the question. This would support the fact that I was getting a high load value at WOT, signalling that the MAF is most likely good.

What do you guys think?