P0172 runing rich on bank one issue. 2005 matrix, 1.8l 4cyl (FIXED)

Hey all I'm new to the forum but a long-time scanner danner fan. Forgive me if this has been discussed before, but i have not seen my specific question asked..........SO in the pursuit of solving my P0172 problem I came across a suggestion to create the opposite condition (make the car go lean). So I pulled off the PCV hose just a little and started to notice that my short-term fuel trims were getting closer to 0 (where it should be) and the maf's grams per second reading started to go up to around 1.8 - 2.0. All this is done at idle of course and my readings before doing this was...... short term fuel trims bounced between -20 and -21, MAF would read 1.2 - 1.4 grams per second. My question is this, did I reveal a clog in my airway or did I reveal a lazy maf?

Given that you have a P0172 your LTFT must be around 21+ as well. By inducing the vacuum leak you drove the 02 lean indicating that the 02 and circuit are working. 1.4 g/s at idle is not an issue. You can inspect and clean MAF but I don't believe that's the problem.
I would start testing the fuel delivery. Check fuel pressure and fuel regulator. I believe psi should be 44-50 at idle.

 Faster response than i had expected! Thanks! and yes with the P0172 condition my LTFT would hover around -18 to -20 and sometimes drop all the way down to -28. I have cleaned that thing like a million times already, checked voltage, ground, and signal and all seems to be within range, at idle of course. I don't have access to a dedicated pressure gauge to test the fuel but I have recently done some work on the pump in solving a hard start problem, there was in fact a leak in the filter and the hard start problem went away.

Hi guys, There is a detail which doesn´t make too much sense to me.

If you pulled off PCV, you are forcing air bypass Maf, so readings should go down, since air passing through Maf sensor is reduced.

My little experience tells me at idle minimum reading should be above 1.8gr/sec (Don´t you think scannerJhon?. could be you know that engine better than me (i don´t know it at all). I Suggest you unplug Maf sensor at idle and see where fuel trims go (so that you can rule Maf out (only for idle condition)

 

Perfect! that was my understanding as well, maf readings should go down, but in fact, they went up and the idle smoothen out. I have also read that maf readings should be in relation to the engine displacement.....1.8l = 1.8g/s

Can you give me an idea of what i should look for when i do the unplugit test?

When you unplug Maf sensor, your are "forcing" PCM to work with pre-programed values (factory values programed in dyno). Then PCM looks for TPS, Map and ECT and ignores Maf sensor (off course).

If Maf sensor is bad (or dirty but i don´t think is the case), you should see fuel trims changing (STFT going to +28% (or the opposite LTFT value). If fuel trims don´t change after some minutes, i would say Maf is not the root cause.

Rich mixture could be caused by:
*Leaking injectors (you can unplug one at a time and watch fuel trims PID´s)
*Fuel pressure too high
*PCM is not "seing" the real operating conditions (load (Maf or Map), ECT, IAT)
*Contaminated oil (you should not smell too much fuel on it)
*Fuel vapors coming to intake manifold from fuel tank through evap valve (purge valve canister). You can unplug evap hose at idle and watch fuel trims PID´s


 

Thanks...those are some more tests that i can do...i was just watching one of scannerdanner's vids that detailed the unplugit test and it turned out to be the booster, not the maf. I'll run these tests and let everyone know...Thanks guys.

I forgot you must keep an eye on O2 uptream sensor voltage. Once engine is at operating conditions (and closed loop), you should see sensor voltage going back and forth between 0.2v and 0.8v

You can test O2 sensor by making a vacuum leak (voltage going down to 0.2 or below) and by enriching mixture (adding some gas) and seing O2 sensor voltage going up. There is another test to check O2 sensor agging (which depends on respond timing), but i think we need to check first sensor activity.


 

wrote:

Hi guys, There is a detail which doesn´t make too much sense to me.

If you pulled off PCV, you are forcing air bypass Maf, so readings should go down, since air passing through Maf sensor is reduced.

My little experience tells me at idle minimum reading should be above 1.8gr/sec (Don´t you think scannerJhon?. could be you know that engine better than me (i don´t know it at all). I Suggest you unplug Maf sensor at idle and see where fuel trims go (so that you can rule Maf out (only for idle condition)



 

So then if logic and design dictates that maf readings should go down......why then, did they infact go up?

Hard to say without test it first, but i guess is a Maf sensor or Maf ground or power issue.


 

Pcv is attached to intake for vacuum to operate the valve. At idle vacuum is high so valve is shut. Pulling hose at idle would cause a vacuum leak and a lean condition.
G/S should be equal to engine L. 1.4g/s instead of 1.8g/s I did not think was that big of a problem for 20 or higher rich condition.
I am leaning to the fuel problem.

scannerJohn. Mate, Actually i have never read about PCV operating conditions. I would say the more vacuum inside intake manifold, the more open PCV is (my homework to know about that).

Anyway, let´s wait for tests from John side, hopping they give us a direction. Thanks




 

Hey guys, so i had enough time to do just one test, to disconnect the maf, im going to attach a screen shot that. I will get the results of the other tests tomorrow when i should have more time. 

wrote:

wrote:

Hi guys, There is a detail which doesn´t make too much sense to me.

If you pulled off PCV, you are forcing air bypass Maf, so readings should go down, since air passing through Maf sensor is reduced.

My little experience tells me at idle minimum reading should be above 1.8gr/sec (Don´t you think scannerJhon?. could be you know that engine better than me (i don´t know it at all). I Suggest you unplug Maf sensor at idle and see where fuel trims go (so that you can rule Maf out (only for idle condition)

 

So then if logic and design dictates that maf readings should go down......why then, did they infact go up?

This may shed some light on why the MAF reading can go up when creating a vacuum leak:

www.scannerdanner.com/forum/scannerdanne...ith-vacuum-leak.html

How are the fuel trims behaving at different rpm and load conditions??
The scan data shows 0% STFT, probably the ecm entered open loop mode due to the disconnected MAF?
 

Hey guys, good morning. So i just came home from a test drive and here are some scans that i took some screenshots of....

MAF is connected and codes were cleared.

I must also mention that yesterday when i was testing with the maf off I took another look at my vacuum lines and noticed quite a few cracks right at the ends, some of them weren't holding air when i blew through them, so as a temp fix until i could get some tubing I wrapped up the ends with some electrical tape nice and tight and I have to say that my G/S rose from that 1.2 - 1.4 that i reported earlier, to between 1.8 - 2.0. I'm going to attach some recorded data as well as some live data. Based on what I'm seeing here I'm starting to lean more to what scannerjohn said.....for me to look in the area of fuel.....furthermore, I'm starting to think that MAF isn't my problem but the O2 is still seeing a rich condition so that tells me that combustion isn't being completed.....I'm thinking I need to put my focus in the area AFTER maf and BEFORE O2S1 which would mean plugs, coil packs, and fuel injectors. Let me know what your brilliant minds come up with as my solution.          

This may shed some light on why the MAF reading can go up when creating a vacuum leak:

www.scannerdanner.com/forum/scannerdanne...ith-vacuum-leak.html

Juergen.scholl. That make sense to me. you should see rpm going down for few seconds once you make the vacuum leak and then IAC opening to compensate rpm. Thanks.

John1920. I guess you have found root cause for Maf readings (nice). I would say now we don´t need to keep an eye on Maf as a problem now.

As i understand, LTFT is affected no matter PCM is on closed loop or open loop, so by unplugging Maf, LTFT on -35% is still telling us there is too much fuel

What the other tests are telling me is the amount of fuel that is leftover at idle, is becoming diluted at higher rpm (fuel trims going to less negative and O2S2 going to little leaner). 

BTW. it would be great to have O2S1 readings instead of O2S2, since upstream sensor is not affected directly by CAT. Also fuel tank pressure and Map. 

I´ll be pending on the other tests we suggested because we have not found root cause for excess of fuel.

 

Ok here's a shot of both O2 sensors, but i as im watching it i have some questions. I had always thought that the voltage on the upstream (O2S1) was between 0.1 and 0.9, not the downstream (O2S2). Was i thought wrong about the voltages on the O2's or is my scanner screwy? 

O2S1: It should be hot and on closed loop to start operating. the oscillation (between 0.1v and 0.9v) is due to PCM adding and extracting a little amount of fuel from stoichiometric (O2 sensor voltage at 450mv). 

O2S2: When CAT is cold, you can see a voltage similary to O2S1 because CAT is not able to use oxygen passing through it. Once CAT is hot, you can see a steady voltage (depending on CAT efficiency between 0.4v to 0.6v). That steady voltage means CAT is using oxygen to convert CO into CO2 and HC into H2O. That voltage also means absence of oxygen (or at least there is less oxygen than present in atmospheric air).

If you have more oxygen than CAT can storage, It passes through CAT and O2S2 voltage drops.

About O2S1 screenshot, I´m not seing it bouncing and based on time you recorded, it should jumped into closed loop. Have you tested it? 

Test O2 circuit integrity by unpluging the sensor and watching PID (should be 0.45v). Also you can check O2 sensor (plugged) making a vacuum leak and watching voltage droping.

Good day guys, FIXED!
So no more scans to review because I believe I solved the P0172. I took the advice of looking into the area of fuel and cleaned up my old injectors....thank goodness I make the habit of keeping old parts......I cleaned them, tested their spray pattern and nothing told me that they were bad, so my youngest daughter and I popped them back in and fuel trims started to fluctuate closer to stoichiometric. They are more on the leaner side than I would want but that's because I'm still waiting on a throttle body gasket to come in and I still need to change those vacuum lines that I had mentioned.....EVAP line to the intake and PCV hose. I'm sure after taking care of those my trims will be spot on. 

Thanks, Scanner John for sticking your ground and pointing what you know. I was getting ready to replace a MAF that cost $300 where I am when all I need was to give my OEM injectors some lovin. Not sure if I had mentioned but I did put in some new injectors that I got off of amazon, it goes to show you....new isn't always good. 

Finally! I went for a 30 min drive this morning and NO CODES.  Thanks guys! really mean it