Any One know what will cause the P0172 & P0175 Codes on a 2002 XJ8. I have researched and found that this is a "too rich Fuel " in Bank 1 & 2. The things I have done or seen say to replace the MAF sensor. I did that. Still having the problem. I dont think it is the O2 sensors because they cause a diferent code to appear. Any ones help would be appreciated.

 

Check the MAF connector pins, also check you cam cover vent tube for blockage and connection. Make sure your air filter is clean and unrestricted also.

 

Thanks, I'll try all your suggestions. I'll also let you know how it turns out.

 

One of the most common causes of rich running is an Engine Coolant Temperature Sensor (ECTS) that is stuck at a "cold" setting, which causes the Engine Control Module (ECM) to continue applying cold-start fuel enrichment even after the engine reaches full operating temperature.

If your scanner can view Live Data, you can watch the ECTS signal to see if it is plausible. I just replaced the ECTS on a Honda that was telling the ECM that the coolant temperature was ranging from -14F to 35F with our weather in the 60s. Also check your Intake Air Temperature Sensor (IATS) and Throttle Position Sensor (TPS) signals for plausibility.

A failed Fuel Pressure Regulator (FPR) can cause high fuel pressure and rich running or allow fuel to leak past the diaphragm into the intake manifold. Leaking fuel injectors can also be a cause, but it's less common to have injectors in both banks suddenly leak simultaneously.

Please keep us informed - this is how we all learn.

Cheers,

Don

 

I'm having these same problems right now with my car.

 

I'm getting P0172 on both banks with restricted performance, too. My IATS seems real when it happens (30 degrees C) and my temp gage seems spot on so I would think that rules out the ECTS.

My fuel pressure was 38 psi when I checked it a couple weeks ago.

I guess I could swap the MAF from my XK8 and see what that does.

 

Hi Ungn,

I assume you mean P0172 on bank 1 and P0175 on bank 2? You can't really judge the health of your ECTS by the temperature gauge in the Instrument Cluster because the gauges are notorious for being inaccurate and indicating "Normal" temperature over a very wide range of actual coolant temperatures. If your scan tool can read Live Data you can monitor the coolant temperature more accurately.

Other possibilities include a dirty or malfunctioning MAFS, clogged air filter, stuck-open coolant thermostat, leaking fuel injectors, leaking fuel pressure regulator, worn or oil-fouled spark plugs that are not burning the fuel completely, leading the O2 sensors to report rich running, problems with the TPS, carbon/varnish buildup in the throttle body, etc.

Cheers,

Don

 

To add to Don's suggestions, check the cam cover breather tube for blockage also....but as Don also states about a faulty MAF, I'd try cleaning that with a MAF only cleaner and see what you get. If your values are fluctuating on your real time monitoring at idle, I'd be leaning on a MAF going south. But be sure to check what else he's suggested before shelling out that money.

 

The temp gauges are out of wack as Don said
they are so cheep to replace as well
I like the idea the fule being rich because it thinks its cold engine that would explain why changing the MAF made no difference.
breather tubes seem to be an issue I see regularly on the forum, plugs well we are getting deeper now you could pull some at random out and have a look ,what plugs are you using?
how old and do they need replacing anyway.
Live reading a must and freeze frame or save data
all the best dutchy

 

Was there ever a solution to this?

 

Great info. Thanks

 

Reviving this thread to get some insight into my situation. I had one of the rich running codes for one bank (can't remember which came first) with CEL and intermittent restricted performance that was ultimately resolved with a new upstream O2 sensor on that bank. Other than the restricted performance issue, the car ran fine. Now the code has returned within 2 months for the other bank along with rough idle, occasional raw fuel smell, and it has stalled once at a light. In the process of dealing with the first too rich condition, I replaced the fuel pressure regulator, air filter, and cleaned the MAF. Plugs are less than 2 years and 10,000 miles. I'll need to get ahold of a scanner to monitor the engine coolant temp sensor.

 

Have you changed the opposite side O2? Unburnt fuel is ECM default map to protect the engine.

 

This seems to be a recurring issue. The original posting was four years ago.

 

Not yet, the other side looked quite a bit harder to access based on a thread I found here so researching on the forum to rule out other, simpler possibilities first. But given the age and parallel symptoms, the O2 sensor is the most likely culprit.

 

Yep...MAF sensor and O2 sensor are among the most prevalent causes.

 

Hi CvryanWRX,

A scan tool will help reduce the amount of guesswork involved in diagnosing your rich running, but some possible causes like an out-of-spec MAFS or leaking fuel injectors are more challenging to diagnose. The MAFS signal can appear plausible but actually be far enough out of range to cause the ECM to over-fuel.

A scan tool that can show Live Data in graph form is helpful for comparing the O2S signals for both banks (upstream B1 vs. upstream B2 and downstream B1 vs. downstream B2). Often, a lazy O2S is obvious when viewing the signals from both banks in line-graph form.

See other possible causes I listed in post #7.

Cheers,

Don

 

I've had the same issue as in the title of this thread only it happens pretty random, like every other month and will be one bank or the other or sometimes both. So following the thread, I hooked up my scan tool, set it to capture data on a DTC trigger and drove it several times like that till I finally captured one. I'd clear the codes and try several times but fail to capture anything. Then I'd grow complacent thinking it was another fluke, stop trying for a couple of months till it did it again and then I'd try some more to capture it. Finally!

I'm not an automotive diagnostician, I just restore old pre-emissions cars, so I could use a little help interpreting. Sorry, my scan tool doesn't graph or export so I typed these into Excel for easier comparison. I just wrote down some of the seemingly relevant values from the trigger frame and the previous frame. I probably should have written down the RPM and a few other fields, but if it helps, it triggered while sitting at idle. Seems like the message always comes up while sitting at idle but could be that's just always when I happened to look down at the instruments and noticed it. This particular time it was just one bank and didn't show restricted performance.


Looks like its just one value O2S B2 S1(mA) that changed to trigger it. Which rabbit hole should I go down first?

 

Clean the MAF, clean the throttle bore and plate, tighten all fittings from the air cleaner to the throttle, clean the part-load breather; if you have an OBD reader, what is the engine temperature (if it is out of wack, look to the ECT -- see some of the earlier inputs to this thread). Run a can of GUMOUT or SEAFoam through a tank of gas (most likely your injectors are dirty and are spitting instead of spraying). And let us know (see Don's #4).

 

I had a problem with my 2001 XJ8 (P0172/P0175) and I have several 'parts-cars' so I checked STFT and LTFT.
First I cleaned the MAFS. (no change)
Replaced the O2 sensors. (no change)
Swapped intake manifold with injectors from a spare engine. (no change)
Swapped MAFS with 'known-good' car. (better but still flagged rich codes after a while)
Swapped in ANOTHER MAFS from another AJ27 car. (no change)
Bought a 'Rock Auto' MAFS (WALKER BRAND) and the fuel trims were within spec immediately.
Swapped MAFS again just for fun. (rich codes AGAIN)
Put Walker MAFS in another car that was running fine and the fuel trims were 'off' a little.
Put Walker MAFS back in the problem car and it has been there for a few years now with NO ISSUES.

I have NO IDEA why the car likes the WALKER MAFS and no others.(I don't care and am not going to tempt fate)