Hi Scotty I have 2004 Jeep Liberty 3.7 190,000 miles on her. I keep get the P0172 code. I've replaced lots of parts fuel injectors, spark plugs, coil packs, pvc valve, purge valve, intake thermostat sensor, map sensor, idol air control valve, air filter, both 02 upstream sensors and thermostat. It has a rough idol when it get to operating temperature but drives smooth. Pre emissions test on obd scanner says catalyst and oxygen sensor not ready. Please help what am I missing???
Maybe take a look at the fuel trims.
The P0172 code says bank 1 is running rich.
It would be useful to see if bank 2 is also running rich but maybe just not rich enough to set a P0175 DTC.
Check the fuel trims at (warmed up) idle and then hold the engine at 2500 rpms for a minute or so and see what the fuel trims do.
Anyway, other things like a leaking EGR valve could be the problem. Or, with a twenty year old vehicle, check for oil contaminated with gasoline. Smell the oil to see if it smells like gasoline.
Also, when it's running rough at "warmed up idle", try removing the fuel injector electrical connectors one by one. See if there's one cylinder that doesn't make the engine idle worse when you cut off fuel to it. That could point you to a cylinder that's acting up and give you a direction to troubleshoot.
Fuel trim at idle bank 1 - long term is -32.81% short is at -10.16
Fuel trim at idle bank 2 - long tem is -21.09% short term is at -3.91
So it's running really rich on both cylinder banks
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What happens to the fuel trims when you hold the engine at 2500 rpms for a minute or so?
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Do the short term fuel trims start pulling down the long term fuel trims, or does the rich condition get even worse (even higher negative fuel trims), or do they stay the same?
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Maybe do an oil change so you can smell the oil. Does it smell like gasoline?
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Also, like I mentioned, an EGR valve that's stuck open a little will cause a rich condition on both cylinder banks. It will be worse at idle than at high rpms so check the fuel trims after holding rpms above 2500 for a minute or two
Unfortunately the 2004 Jeep Liberty 3.7 does not have an EGR valve. I'm starting to wonder could a vacuum leak cause this ?
Maybe, because your 3.7 uses speed density (MAP sensor) to calculate air volume but those fuel trims are really high for a vacuum leak to be causing them. Usually with a vacuum leak with a MAP sensor you'll experience High idle rpms. But it wouldn't hurt to check for a vacuum leak
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That's another reason to hold the rpms above 2500 for a minute or so to see the effect of the engine load calculation on the fuel trims
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Also hook up a scanner and make sure the IAT sensor temperature compares close to the actual outside air temperature because the speed density system uses IAT to calculate the density of the air
Is there someplace I can send a screenshot of the freeze frame reading ?
Freeze Frame Data when thrown..
Engine load: 31.4%
Engine rpm: 612.0 rpm
Eng coolant temp: 203.0 F
Fuel system status: closed loop, using 02 sensors for feedback
Intake Air Temp: 129.2°
Intake Manafold absolute press: 70 kpa
Long term fuel trim:
Bank 1 : -32.81%
Bank 2 : -22.66%
Short term fuel trim:
Bank 1 : -11.72%
Bank 2 : -0.78%
Throttle position: 16.5%
Timing advance: 8.5 degrees
Vehicle speed: 0.0
Has new fuel injectors how would I check to see if one is leaking would it be noticeable
By Letha290 Topic starter 13/07/2023 4:07 pm
- Connect fuel pressure gauge to fuel rail.
- Run engine to operating temperature.
- Turn off engine.
- Fuel Pressure should not fall below 30psi for 5 minutes
This will tell you if an injector is leaking or not.
OK going the check it tomorrow and let you know what I find thank you
"idle".
idol is something you worship.
Run through the "possible solutions" on this page:
https://www.obd-codes.com/p0172
Unfortunately the 2004 Jeep Liberty 3.7 does not have an EGR valve. I'm starting to wonder could a vacuum leak cause this ?
A vacuum leak would have the opposite effect, you would see positive fuel trims as the computer attempts to compensate for the overly lean mixture. Given that you're talking about a nearly 20 year old vehicle one suspect would be leaky fuel injectors. There are some fairly detailed discussions about P0172 here:
https://www.carparts.com/blog/p0172-code-fuel-system-too-rich-bank-1/
https://eeuroparts.com/blog/p0172-code-fuel-system-too-rich-bank-1/
Has new fuel injectors how would I check to see if one is leaking would it be noticeable
One way is to pull them out right after turning the engine off, they should not be dripping. Are they OEM injectors?
Freeze Frame Data when thrown..
Engine load: 31.4%
Engine rpm: 612.0 rpm
Eng coolant temp: 203.0 F
Fuel system status: closed loop, using 02 sensors for feedback
Intake Air Temp: 129.2°
Intake Manafold absolute press: 70 kpa
Long term fuel trim:
Bank 1 : -32.81%
Bank 2 : -22.66%
Short term fuel trim:
Bank 1 : -11.72%
Bank 2 : -0.78%
Throttle position: 16.5%
Timing advance: 8.5 degrees
Vehicle speed: 0.0
I don't know what all this means or if it can lead to a possible clue into what is wrong ? Help
The fuel trims confirm that the engine is running too rich, Bank 1 being the worst.
So should I look for leaking fuel injectors on that side ?
Have you run through the diagnostic steps in the links previously provided?
Yes I have
Then I'd go ahead and check the fuel injectors. If that's not the problem and all of the items in the links check out I'm out of ideas - maybe someone can chime in with something not already covered.
OK I found out it's the PCM...
Can I by a used one and replace it without having to get it programed or flashed ?