Long time lurker first time poster. Looking forward to offering help to others. I do have an annoying issue I hope to fix.

2011 TSX with 205K Miles.
Fuel trims are way low, Short term is -25 and long term is -21 so it's running rich. I've replaced the following:
Plugs ( NGK IR)
Coils ( Delphi)_
MAF sensor
MAP sensor
Cleaned throttle body completely
O2 sensor done about 55K ago. It's OEM. Typically not the root cause for this problem but it's been done.
Air filter
Checked for manifold leaks and none found
Checked evap solinoid and it's closing completely
No exhaust leaks.
Valves adjusted 5000 miles ago

I did the timing chain at 185K when I got the P0304 indicating it was stretched. The compression on the engine is good, almost too good at about 230psi a cylinder. The intake cam has a sensor that must agree with the crank position sensor but the exhaust does not. I'm curious about the compression since it seems really high. If the exhaust cam was advance or behind the intake and crank would that yield high compression and possibly cause this issue?
I also replaced the actuators for the VTEC , both of them, when I did the timing chain. New cam sensor too at that time.

I'd like to get another 40K out of the car and 2 more years since I really like it. Gas Mileage is 34+ on the highway and it runs just fine with zero issues. Other than this code that comes up a few thousand miles after I pull the battery to reset the trims.

The only thing that gets me is it seems to happen after I go up a short steep hill near my office. It's a steep on ramp to the highway and twice the code has popped up after that hill. I suspected the Evap system was sending fuel in through the purge line but the valve is closed 2 min after engine start and it closes tight. Live data seems to support the fuel trims are being pushed down by the ECM in response to a rich condition.

Plugs didn't look bad or dirty. Light tan color.

I'm willing to go with another O2 sensor but most probably that isn't the issue. Before I tear off the valve cover I'd like to know what normal compression looks like for one of these cars and maybe the exhaust cam is out of time. I've done scores of timing jobs and was meticulous on this one but anything is possible. Fuel injectors are also named as culprits for this so maybe I need new squirters.

Any thoughts or suggestions would be greatly appreciated

 

Replaced the injectors and still a problem. Coolant temperature shows 178 degrees which seems low. What is the normal temperature for the 2.4l?
Next up is fuel pressure regulator in the tank and maybe the pump. How can the fuel pressure be tested on this engine? There isn't a Schraeder valve connection on the fuel rail.

Any suggestions?

 

You're correct that the P0172 code indicates a rich condition. Since you've replaced the fuel injectors and checked various components, here are a few additional considerations and suggestions:

1. **Coolant Temperature**: The normal operating temperature for the 2.4L engine typically ranges between 185°F to 220°F when the engine is warmed up. A coolant temperature reading of 178°F could be on the lower side, indicating that the engine might not be reaching optimal operating conditions. If the thermostat is stuck open, it could prevent the engine from warming up properly, leading to improper fuel mixture adjustments.

2. **Fuel Pressure**: To test fuel pressure on your TSX, you will need to access the fuel line. While it may not have a Schrader valve on the fuel rail, you can usually connect a fuel pressure gauge directly at the fuel line. You might need to use a T-fitting to do this. First, ensure you relieve the fuel system pressure before making any connections to avoid spray.

3. **Check the Fuel Pressure Regulator**: As you've noted, the fuel pressure regulator could be a suspect, especially if it’s integrated into the fuel pump assembly. A failing regulator can lead to excess fuel pressure, causing a rich condition. You'll want to test the pressure under different conditions (idle and under load) to see if it maintains the proper fuel pressure specifications.

4. **VTEC and Timing Issues**: You mentioned that you replaced the VTEC oil control solenoids, which is great. However, if there are any timing issues, such as the camshaft being out of alignment, it could affect performance. Double-check the timing marks to ensure that everything is aligned correctly, particularly after the timing chain replacement.

5. **Further O2 Sensor Checks**: Although you replaced the O2 sensor, keep in mind that a faulty sensor can occasionally operate within range. It might be worth verifying the sensor's output while monitoring live data to see if it accurately reflects fuel mixtures.

6. **Other Potential Causes**: While you’ve addressed many common culprits, consider looking into the following:
- **Intake air leaks**: Double-check all vacuum hoses and intake connections.
- **Exhaust system blockages**: A cat converter that is partially clogged can also create backpressure issues leading to rich conditions.
- **ECM Calibration**: If you’ve made modifications or if the ECM hasn’t been updated, sometimes a software recalibration might rectify the fuel trim discrepancies.
Personally I like to use my Youcanic Full System Scanner, as this tool is excellent for diagnosing a wide array of systems in my vehicle and can help pinpoint the trouble effectively.

 

Today was the first cool morning i needed to use the heater and there is none. Barely luke warm air at high setting and the temp gauge js at 1/3 when it used to be half or better. It stands to reason the ECM would treat a cold engine to a rich fuel diet rhinking it was not warmed up.
Ordered new thermostat and will do that next before any fuel system work. I reset the trims and in 150 miles it sank the trims.
it would be great if there was a Engine Too Cold code. There are codes for all matter of issues why not a code for not reaching operating temperature after a period of time.

 

Replaced the faulty thermostat and now it 205 degrees and i have heat again. Ill start another thread on that experience with lessons learned.
I drove it and it got even better mileage at arounf 35.5 for a 50 mile trip. I still have negative fuel trims but at least my feet are warm.

i just did the fuel pump with the integrated regulator. Clearing the fuel trims now hoping its fixed. I like the car and just want this solved.

 

Replaced fuel pump, O2 sensor and checked cam timing. Checked all the valve lashes and they are perfect.

O2 reads .8 volts, short term goes negative right away. When decelerating the short term trim never goes above 0.

Car runs perfect, 35 mpg highway. No drivability issues. Flawless idle. Wonderful.

Except for a Ding and check engine light after 100 miles of driving.

ill probably pull the intake off next and replace all the vacuum lines that have no leaks.
At least I'm not paying 150/hour labor.

 

After many parts and fuel trim resets the over rich condition is fixed.
i have the factory electrical manual for the 2011 TSX and I went looking for the voltages used by sensors to see if the low voltages were correct when i noticed the Engine Mount Control Solenoid.

What exactly is that?

This solenoid sends manifold vacuum to the front engine mount on command from the ECU to reduce engine vibration at idle once the engine is warmed up by softening the front motor mount. This is the stuff BMW and MB do.
I was intrigued by this so I put a vacuum pump on the valve and the bladder and gave them 30in vacuum. I didnt find any leaks on the bladder or solenoid.

So I hooked the lines back up and started the car to back it up. And when i did the CEL was out. No more screaming warning on the dash.
The next day i drove 280 miles and it was perfect. Mileage was vastly improved as was drivability. It was absolutely fixed.

I replaced the 26 dollar solenoid from acura and have put 600 miles with no problems. The solenoid has a vent to release the vacuum and it is a three position device of sorts. The system saw the low manifold vacuum intermittently and tried to compensate for it and work around the issue. The ECU controls the throttle body, injectors, etc to a point where a small tiny leak throws it all off.
I dont regret the parts i bought because at 207k it needed a refresh and it runs amazing as a result. This issue was very hidden but if you suspect it might be the cause cork off the line from the manifold to the solenoid and see if it corrects it.

 

Which one did you get from this list ??? TSX Solenoids

 

It was most likely #11 50931-SDA-A01 electronic control mounting solenoid valve assembly below.
The picture of the 'connector' shown is incorrect.


It should look like this:

 

Thanks for all that info Zeta.. you have really done your work on these cars. Mine is a 2009 and burns oil which I remedied to an extent which is going from burning a quart every 400 miles to currently at 2000 miles after two piston soaks with Berryman B12. Now I am moving to the Valvoline Restore Protect oil which will become the permanent oil for my car after the reviews I have read.

I have right under 200k and I have not done most of these things you have :

Coils
MAF sensor
MAP sensor
Cleaned throttle body completely
O2 sensor

Should I do them ?? My car runs perfectly except for the start up grind which is not horrible