Need some help with diagnosing CEL codes P0172 and P0175

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Mike Z

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2002 Jeep TJ 4.0, 79,000 miles

Check engine codes P0172 and P0175 (bank one and bank two running rich)

Ok, so replaced the coolant temperature sensor today and the plugs with XP 985's in the hope that it would be a quick fix. No such luck. Still getting P0172 and P0175 codes. The jeep is running great. No loss of power, no hesitation. If the CEL wasn't coming on, I would not know there was a problem based on how it is running. The only abnormal issue I have is a bit of a hard start when the engine is cool, but that makes sense to me since the jeep is losing pressure at the fuel rail schrader valve.

Have cleaned the IAC valve, replaced the purge valve, TPS, MAP, IAT sensor, coolant sensor, thermostat, plugs, upstream O2 sensors, air filter and cleaned the throttle body. All sensors are Mopar, plugs are XP 985, purge valve is Mopar, 02 sensors are NTK and thermostat was an OE 195 degree.

I have not installed anything on this jeep from Autozone.

What am I missing?

The only problematic data I have is a bit of an extended start when cold, P0172 and P0175 codes (both banks running rich) and fuel pressure that drops at the rail after priming (not starting).

43 PSI at the schrader valve on the fuel rail after priming
33 PSI after 1 minute 30 seconds (still with engine off)
23 PSI after 4 minutes and 30 seconds
0 PSI after 25-30 minutes

49 PSI at idle

Please respond with advice. Love this old TJ, but seriously considering lighting it on fire.
 
Mike Zimmermann said:
2002 Jeep TJ 4.0, 79,000 miles

Check engine codes P0172 and P0175 (bank one and bank two running rich)

Ok, so replaced the coolant temperature sensor today and the plugs with XP 985's in the hope that it would be a quick fix. No such luck. Still getting P0172 and P0175 codes. The jeep is running great. No loss of power, no hesitation. If the CEL wasn't coming on, I would not know there was a problem based on how it is running. The only abnormal issue I have is a bit of a hard start when the engine is cool, but that makes sense to me since the jeep is losing pressure at the fuel rail schrader valve.

Have cleaned the IAC valve, replaced the purge valve, TPS, MAP, IAT sensor, coolant sensor, thermostat, plugs, upstream O2 sensors, air filter and cleaned the throttle body. All sensors are Mopar, plugs are XP 985, purge valve is Mopar, 02 sensors are NTK and thermostat was an OE 195 degree.

I have not installed anything on this jeep from Autozone.

What am I missing?

The only problematic data I have is a bit of an extended start when cold, P0172 and P0175 codes (both banks running rich) and fuel pressure that drops at the rail after priming (not starting).

43 PSI at the schrader valve on the fuel rail after priming
33 PSI after 1 minute 30 seconds (still with engine off)
23 PSI after 4 minutes and 30 seconds
0 PSI after 25-30 minutes

49 PSI at idle

Please respond with advice. Love this old TJ, but seriously considering lighting it on fire.
Click to expand...
Welcome!

What brand/temp thermostat did you choose?

If you have an OBDII reader, what does the coolant temperature reading show after fully warmed up?
 
I bought an OEM
RMETeeJay said:
Welcome!

What brand/temp thermostat did you choose?

If you have an OBDII reader, what does the coolant temperature reading show after fully warmed up?
Click to expand...
I bought an OEM t stat at NAPA specific for 195 degrees. Problem? Should I get a Mopar? The reader shows right around 196 for the temp.
 
CharlesHS said:
Do you have an exhaust manifold leak ?
An crack in the exhaust manifold can make the ECU believe the engine is running lean and increase the fuel injector pulse.
Click to expand...
I don't hear any leak at the manifold. I printed out the diagram yesterday of the manifold bolts and checked them for tightness. They all seemed snug. Any other ideas? Does the idea of a leaky injector seem possible? Someone mentioned to me that a leaky injector in the number 3 spot or 4 could actually leak into both banks...one common intake chamber feeds all six intake runners.
 
The leak that I am referring to would be a crack in the exhaust manifold tubing where you could hear escaping exhaust. While the injector(s) can be leaking... it is doubtful they can leak into an additional cylinder. The loss of fuel pressure you are identifying after priming can be a leaking fuel injector, but can also be caused by a leaking check valve in the fuel system.
Do you have a OBD Scan tool or know someone that owns one ?
You can connect the scan tool and check the system operating temperatures when warmed up and check the O2 sensor voltages to verify what is going on. Check to see if the fuel system is transitioning from Open Loop (Default ECU program) to Closed Loop (O2 sensor voltages to ECU). Normal O2 sensor voltage when warmed up should be 0.4-0.7; more than 0.7 is rich and less than 0.4 is lean.
 
Got it. Thanks for the clarification on the exhaust leak. I will listen for any escaping exhaust.

I do have a OBD scan tool. I will check and see what the operating temp is and the O2 sensor voltage.

What reading do I look for in my scan tool results that shows if the fuel system is transitioning from open to closed loop?

As you can tell, I'm not a mechanic, but I want to learn.
 
Yes...Listen for an exhaust leak which can sound muffled or a slight ticking depending upon how bad and where it’s located.
Readings will be O2 bank 1 and 2 upstream and the Closed Loop. These descriptions could vary slightly depending upon Scan tool firmware.
 
Update...

Went ahead and installed factory Mopar fuel injectors tonight. Finally solved the issues with the Jeep. Immediately, I noticed the hard start was gone, then noticed the idle was smooth and steady. I took it for a ride and the Jeep accelerated beautifully. No hesitation or stutter.

I hooked up my OBD to get live data as I drove and checked the ST and LT fuel trims. All now within factory ranges. Prior to the installation of the fuel injectors, the LT fuel trims were -33%.

No more P0172 and P0175.

Happy again.
 
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