2002 Forester code P0172 System too Rich

[travisriggle]

Hello all, 

I'm new to the forum, but need help.  I don't wont to replace my Forester but I might have to due to the new emissions testing laws.

Background:

Bought this car in 2006 from a dealer with 60k miles. 4-cylinder 5 speed manual ("L" class)

At 105k replaced the clutch

Has run and preformed above and beyond for years,  great MPG and other than the clutch no major repairs.

Car now has 206k miles...

10 months ago failed emissions testing in Colorado for high Knox   Got a check engine light after that for a P0172 System too rich.  Replaced the upstream O2 sensor (before cat.), ran AMS oil injector cleaner, used premium gas, and passed emissions.

 

Check Engine Light is still on for system too rich, idle is getting rougher by the week and has started to "bog down" when starting from a stop  then suddenly finding it's power and surging forward.  If i run the RPM up to about 3.5k and let the clutch out slowly it dose not "bog down".  

         By "bog down" I mean the peddle is to the floor and it dose not go,  engine has a 'putting sound' real dull like there is no spark.

 

Shortly after the low end problem started things got worse.  One or more cylinders started pre-firing and the car began to jerk front to back, changed gears and it happened again within 10 sec.  Limped the car home and did some digging.

Replaced the MAP Sensor and reset the on-board computer by unplugging the battery.  No change, replaced plugs and wires, no change.

On a suggestion from a friend, unplugged the O2 sensor I replaced 10 months ago, when the car is cold there is no change, still rough idle and still a wild ride.  When the engine reaches normal temp, the idle gets better, still not factory smooth.  The engine stops pre-firing but still cuts out ("boughs down") every now and then.

Sorry for the log post but here is my question.  I have been to Auto Zone and they provide me with the code P0172 and a list of parts to replace including O2 sensor, MAP Sensor, Fuel filter, Fuel ejectors and a few other things.  I don't have the money to just go replacing things and hope it works.  Can anyone point me in a good direction or have any ideas?  My other thought is I have to get emissions tested again in 14 months and I have had some people suggest my Cat. converter is "burned out", is this related to the other problems I'm seeing or is this different?

 

Thank you in advance.

 

Travis

[Legacy777]

Travis,

 

Welcome to the USMB.

 

I would recommend taking it to a good reputable Subaru shop.  This thread has some similar issues, they mention spark plugs and just crud build up.  http://www.subaruoutback.org/forums/66-problems-maintenance/8563-p0172.html

 

I think spending a little money for a shop to do a good diagnostic check/tests is probably worth the time and money rather then just replacing parts.

 

Hopefully others can chime in with some additional info and maybe recommend a shop in the area.

[1 Lucky Texan]

perhaps a slipped TB? it's almost due for its second one.

 

vacuum gauge test can look for clogged cat conv, sticking valve or vacuum leak

 

(i THINK hi NOX is a lean burn problem - though I don't know how to correlate that with a rich condition ECU code ???)

[Legacy777]

NOx emissions are caused by high heat and typically only present in high quantities if the catalytic converter is bad.  CO emissions are caused by low heat or incomplete combustion.  HC emissions are unburnt fuel.  Typically CO & HC emissions will typically go hand in hand.

[travisriggle]

Thank you all for the quick replays.  I have been reviewing the data I have about the emissions and the CEL.  The emissions was high in NOx, but just barley.   When I pass the emissions NOx had only come down 10%.  But the CEL print out that Auto Zone gave me is P0172 System to Rich, 1) High Fuel Pressure, Possible causes 1)Faulty fuel pressure reg, 2) MAF/VAF sensor faulty 3)Faulty HO2S Bank 1

 

If I'm not mistaking the HO2S bank 1 is the O2 sensor I replaced.  I'm hopping the MAF = MAP sensor.  Could be a fuel reg, only thing on their list I haven't replaced.

 

I thought of a slipped timing belt, but the engine gets better and worse depending on temp, RPM and if the O2 sensor is plugged in or not.  Would a slipped TB give the same symptoms all the time?

[ivans imports]

maf ? or leaking injector if feul reg is bad will be gas in vacume line or pluged feul fillter if pluged the pump makes more psi than normal and can over feul

[1 Lucky Texan]

bad Engine Temp Sensor (not the gauge sensor, though newer soobs use the same 3 wire unit for both) could easily cause a car to run differently based on temp.

 

vacuum leak will throw off the A:F mixture.

 

 

many possibilities. Some scanners can retrieve short and longterm fuel trims - that might tell us if the ECU has had to make drastic adjustments.

[Fairtax4me]

Second Texan's suggestion, it sounds like the temp sensor for the ECU could be bad.

 

What brand of O2 sensor did you install?

 

Could also be a vacuum leak, but that would usually cause a lean condition.

 

Also wonder if the timing belt was replaced at any point in the last 100k miles. If not its 100k miles overdue, and a very serious and costly potential problem.

[travisriggle]

Thank you all for your input.  I have posted on two other forums and this is the only community that has responded, THANK YOU.  

 

Fairtax4me - I have been unable to find my warranty paperwork for my O2 sensor (still digging), don't recall what brand.  And to the best of my knowledge this it the factory original timing belt.

 

I looked for the engine coolant temp sensor on the car and I believe it is a 3 lead sensor, would this drive the temp gauge on the dash?  If so, the operating temp has not changed.

[1 Lucky Texan]

Thank you all for your input.  I have posted on two other forums and this is the only community that has responded, THANK YOU.  

 

Fairtax4me - I have been unable to find my warranty paperwork for my O2 sensor (still digging), don't recall what brand.  And to the best of my knowledge this it the factory original timing belt.

 

I looked for the engine coolant temp sensor on the car and I believe it is a 3 lead sensor, would this drive the temp gauge on the dash?  If so, the operating temp has not changed.

Well, keep in mind we are throwing out 'educated guesses'. The 'mechanical housing' of the sensor likely has 3 wires because its electrical 'guts' contains 2 thermocouples or similar type devices. So, it could still be bad I'd guess. Someone else here may know how to use an ohm or voltmeter to test it.

 

I think I can safely recommend a shop that may be only 40 miles or so away; http://retroroo.com/why-retroroo-subaru-service-repair-denver-colorado/

 

if you end up needing a pro

Edited April 29, 2013 by 1 Lucky Texan

[ivans imports]

Doubt coolant senser only because have never seen one fail but low coolant level whould do it or shorted o2

[travisriggle]

Thank you for your help.  I am planning to take my car to a Subaru dealer for diagnostics however they need the car for 3-5 days, I can't rent a car nor have a loner car for the dealer for another couple of months (age related).  In the mean time I am trying to limp this car along and not make it any worse.

 

Over the weekend I replaced the coolant temp sensor and the engine is running better at temp, still will not idle or run when it is cold.  Now the temp gauge on the dash is not correct.  When the car is started the temp gauge moved to the "regular" position within 20 sec or so.  The gauge will stay there 3 to 5 min then move rather quickly to off scale high.  I opened the hood and the engine was not burn your face off hot.  It has been running so I could not touch it but nothing to indicate the engine was over heating?  I double checked the coolant level and the fans are cycling on and on like it is at temp?

 

Can a car really over heat in 5 min when left over night and lows overnight where mid 40's??

your guess is better then mine right now.

[1 Lucky Texan]

weird, even a stuck thermostat would be unlikely to cause heating like that. Almost seems like combustion gasses are gathering around the sensor or some weird voltage problem.

Maybe put the old sensor back in to confirm there's really a difference in the way they behave - maybe you got a new one that is the wrong part or is bad?

 

2002 is old enough to have bad wires or coil. They sometimes cause some of your symptoms and especially in damp or 'cold/dew-y' conditions. You can spray the wires/coil with a mister bottle when it's idling to see if idle get worse. (if done at night, you can sometimes see and hear arcing)

Edited May 6, 2013 by 1 Lucky Texan

[Fairtax4me]

Either the new sensor is bad or there is damage in the wire harness for the sensor.

Can't rule out a mechanical condition causing it to run rough when cold, but the temp needle wouldn't react like that. Even with a bad head gasket.

[1 Lucky Texan]

even a bad ground might have different behavior with temp/moisture. Start refreshing every ground connection you can find and confirm the battery cables are not corroded inside the insulation.

[travisriggle]

I am under the imprecation there are two temp sensor on this motor.  The one  I replaced has a triangular plug and was located on the water pipe running across the top of the block under the intake manifold.  I believe the gauge sensor is on the top of the block next to the crack shaft position sensor and only has one lead on the top (assumable grounds to the block).  Am I on track or did I replace the wrong sensor for my problem?

[1 Lucky Texan]

I am under the imprecation there are two temp sensor on this motor.  The one  I replaced has a triangular plug and was located on the water pipe running across the top of the block under the intake manifold.  I believe the gauge sensor is on the top of the block next to the crack shaft position sensor and only has one lead on the top (assumable grounds to the block).  Am I on track or did I replace the wrong sensor for my problem?

did it have 3 wires? that sensor does both jobs, ECU and gauge info.

 

at opposedforces it seems 22630AA161 is the part, that is the 3-wire unit.

 

 

maybe someone with more experience can confirm.

Edited May 7, 2013 by 1 Lucky Texan

[Fairtax4me]

The one next to the crank sensor is the oil pressure switch.

The cars with 2 temp sensors have them right next to each other on the water crossover pipe.

 

Grounds can cause some funny issues, might check the main ECU ground where it attaches to the intake manifold. That probably won't help the temp gauge issue any, but it might help the running issue.

[ivans imports]

is the water pump sticking or not turning have had this make them over heat fast also check main engine harness conectors are pluged in all the way and check grounds

[travisriggle]

Checked all the grounds and connections over the weekend, no change.  I drained a little coolant from the radiator and marked the level on the over flow tank.  After driving for about 10 min the level in the over flow tank dropped about the amount I drained.  This means coolant is still flowing and the temp gauge on the dash is just wrong?

[Jg02legacy]

I am having the exact problem with the heavy bogging... Did you ever find out the source of the problem???

[DanForest]

My 2010 Forester also has a recurring P0172 code. Got the car from my father who tried its best to get rid of it for three years, but never could fix it. I thougth I succeeded this winter after I changed the oversized exhaust lines and aftermarket silencer the first owner had put on, but after a month, the P0172 Bank 1 too rich code came back.

My father had changed the upstream O2 sensor many time and both the upstream and downstream sensor at the same time once (there are reports of code appearing after changing just the front sensor), but still the same problem came back soon each time. He also had the mass air flow sensor replaced once.

My trusted mechanics's son also had a 2010 Forester and had the same code over and over. They rebuilt the entire engine (gasket, O2 sensors and other things he didn't mentionned), and the code came back a year after.

He's educated guess is that Subaru has programmed the ECU for way too narrow specs for the O2 sensors readings. In other words the margins of tolerance for the O2 sensors value is too small before it triggers the code. In that case, many unperfect things can trigger the code, including vacuum leaks, mass air flow sensor getting older, wiring imperfections, air filter clogged, fuel filter getting old, in addition to actual O2 sensor defects. About the fuel filter, it is located inside the gas tank in the 2010 models, so changing it is not an option.

Sometimes last winter (I live in Canada), the dash lights on my forester (check engine + loss of cruise control + loss of traction control) would come on and off several times within the same week. Usually dry cold whether would help get rid of it while slushy humid temperatures would trigger the code. Correct me if I am wrong, but this is impossible to get from a bad O2 sensor as these do not come back when they are toasted.

I was hoping to get more info about this on the web and on this forum, but it appears I already know as much as there is to know. Please throw in all additonal info if I am wrong.

Since this is a very common problem on these cars, I am surprised nobody can say more about it. To finish, I found this site is of some help:

https://repairpal.com/subaru-forester-2010/problems

 

[GeneralDisorder]

It's a system rich code. It's only going to trigger if the system is pulling like 25% fuel for a period of time. You need someone that's familiar with interpreting live data and has an in-depth understanding of closed loop fuel control. It's not that complicated to troubleshoot. And no - the ECU isn't "just too sensitive". That's a cop-out from a mechanic that doesn't know his business. 

GD

Edited June 13, 2020 by GeneralDisorder