P0172 Issue
 

Question on an engine control issue:
I've been consistently getting a P0172 code (Bank 1/1 Running Rich) for a few months now. That is the only code present. Other symptoms are that it runs pretty rough at cold idle, but is fine at running temp.
According to Freeze-Frame data (idle conditions) the Short Term Fuel Trim was at -3.1%, and the Long Term Fuel Trim at -32.8%.
I replaced the MAP sensor and cleaned the throttle body, but the code still shows up. All fuel injectors were recently replaced, and I haven't found any vacuum leaks, so I'm a bit lost as to what is causing the rich condition. Any ideas?
Thanks!

Do you have California emissions exhaust system (dual upstream Cats)?

It has standard emissions (single cat before muffler).

Probably un-metered air intake (leak) that self resolves as things warm up and expand.

A cold vehicle smoke test is probably the most efficient way to find the source. You could continue to poke around with something like propane to try and detect a leak, but you'll probably only be able to catch it when the vehicle is dead cold.

This might be one of those times when letting a shop do the smoke test pays off, just to help reduce the amount of guess work, so that you can get to fixing it.

It could also be the excuse you've been waiting for to buy (or build) your own smoke tester.

One other question: The head was cracked when I bought it; could the cat/O2 sensor being fouled by the cracked head cause this problem?

If by cat/O2 sensor you mean the downstream sensor (the one furthest from the motor), then no, probably not. It is used for emissions monitoring, but it is not used by the ECM to make air fuel adjustments.

If instead you mean the upstream sensor, nearest the motor, then yes possibly. If it were reading (or reporting) high remaining oxygen in the exhaust then the long term fuel trim will keep adjusting upwards to compensate.

Do your fuel trims change or start to go down once the vehicle is hot?

tvcfcc

If anything, it would be the upstream O2S causing the problem.


The heater in the O2S may be shot.

I haven't been able to look at fuel trims in real time, but I would assume the Long Term drops after startup. If I can get my hands on a better scan tool, I'll see how it acts when it's cold.

Diagnostic data.




P0172-1/1 FUEL SYSTEM RICH

WhenMonitored: With the engine running in closed loop mode, the ambient/battery temperatureabove 20 deg. F and altitude below 8000 ft.

SetCondition: If the PCM multiplies short term compensation by long term adaptive and the result is below a certain value for two trips, a freeze frame isstored, the MIL illuminates and a trouble code is stored.

POSSIBLE CAUSES

INTERMITTENT CONDITION

RESTRICTED FUEL SUPPLY LINE

FUEL PUMP INLET STRAINER PLUGGED

FUEL PUMP MODULE

O2 SENSOR HEATER OPERATION

O2 SENSOR

EVAP SYSTEM OPERATION

O2 SENSOR SIGNAL CIRCUIT SHORTED TO VOLTAGE

O2 SENSOR SIGNAL CIRCUIT OPEN

TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED

TP SENSOR SWEEP

MAP SENSOR OPERATION

ECT SENSOR OPERATION

ENGINE MECHANICAL PROBLEM

FUEL FILTER/PRESSURE REGULATOR (HIGH)

PCM