2003 3.7L - RPM drop when throttling

tester

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Started having a problem where it would lose RPM (gradually drops down to around 1000) and get shudders even though my foot was on the throttle. If I let go of the throttle for a few seconds and then re-press, it would have some power, or if I press the throttle harder. I replaced a dead fuel pump+filter (this was happening before that), a coil pack that the coolant bottle was leaking on (along with the bottle), IAC and TPS. No codes have popped up.

Jeep idles fine, and drives normal for the first 2-3 min, and then all of the above starts happening. Would anyone have any idea what this might be?
 
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tester

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Is it possible that O2 sensors could cause this? I would think it would throw a code (although its probably a good idea to change them out anyway since I dont know when the last time they were changed, if ever).

Im going to try and get it to do it in the drive way tomorrow, that will atleast be a bit easier to diagnose instead of driving it.
 

Artart

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I would rather look at the fuel pump first. That's fuel pump overheating symptoms. Next it's going to cut out when driving. Following. Pump not pushing enough fuel now there is air bubbles in the fuel line causing the shudder. Idle smooth because you basically just need fumes to idle. Most people would say check the sensors first but I would put my money on the fuel pump. Also check for fuel leak.
 

LibertyTC

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Did you buy a Mopar IAC or an after market? & did you clean the port inside of the IAC with throttle body cleaner?
Yes test the fuel pressure.. ignition on-psi reading- running psi and key off for 15 minutes psi reading is?
Rich Condition, See this link: https://www.700r4transmissionhq.com/p0172-jeep-liberty/
 

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tester

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Fuel pressure was one of the things I was more leaning towards, as it has all the symptoms of not getting enough juice. Ill check fuel pressure tomorrow once I can find my pressure tester. I hope it isn't the pump as its literally brand new.

IAC was aftermarket, but I can pull one from another Liberty I have to test.
 

Ksat

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To answer your question, yes, bad O2 sensors could cause your problem. After your first 2-3 minutes, the PCM could be switching from open to closed loop, where it starts relying on info from the sensors to make mixture adjustments. If one (of both) of your sensors is faulty and misreporting it's easy to guess what happens.

Pull the electrical connectors to both sensors, it should force the PCM to stay in open loop. Drive the vehicle and see what happens after your 3 minute window.

If you end up replacing them, NTK brand sensors are the only ones you should be buying.
 

tester

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Tried swapping out the IAC with another one from another Lib, no change (I did clean out the IAC port when I did swap it out the first time).
Unplugged the O2's, and it did the usual just faster.
Couldn't find my fuel pressure tester, so ill pick up one soon.
 

Ksat

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If the problem is pump-related, it might help to check that you don't have power or grounding issue. When testing pressure, make sure to check what it is when the engine is under load, as well.

Even though you said you don't have codes, if you have a live data-reading scanner, it would be prudent to look through the (mode 1) list and see what some of the sensors are reporting.
 

tester

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Been busy as hell the last week, will be able to work on it in the next few days here.
If the problem is pump-related, it might help to check that you don't have power or grounding issue. When testing pressure, make sure to check what it is when the engine is under load, as well.

Even though you said you don't have codes, if you have a live data-reading scanner, it would be prudent to look through the (mode 1) list and see what some of the sensors are reporting.
Yep, ill check when its under load and all also check the live data.

What year is it?
03, also in the title
 

tester

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Jeeze "next few days" turned into over a month.
Anyway, tested the fuel pressure, priming is 45psi, running is 50 (above 50 when giving it some throttle). Holds pressure for a good 10+ min. Going to dump some injector cleaner into it tomorrow, since it wouldn't hurt in case they are gummed up.
Ill also check driving sensor data tomorrow once I can get a copilot.
 

tester

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Back again with some logs. I am using Torque pro for logging, so it outputs a CSV which I have attached.
You can view the logs in excel (I think) or use: https://limonte.github.io/csv-viewer-online/

At 13:09 is when it started doing its thing; lines 184-217 in the CSV you can see the RPM dropping.
Fuel trim Bank 1 long is weirdly at -10.156 along all of that, and Bank 2 Long at -9.375, im not sure exactly if that has anything to do with it or not.

At 13:11 it also happened, and coincidentally at @ line 268-300 its the same fuel trim as above, not sure if there is a correlation or not.

Minus trim means the computer is leaning out the fuel I would assume? If so, would -10 lean it out so much it would kill performance, and drop RPM?

Are there any wizards can decipher this better than me?
 

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Ksat

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Fuel trims, at least at idle, should quickly switch between +/-5%. The reason the mixture goes from slightly rich to slightly lean like this is so the catalyst can do its job properly. The -10.156% and -9.375% fuel trims you reported are excessive, especially if they stay at those values and do not change. If that's the case, it's happening because the PCM has detected a rich condition on both banks (via info it's getting from the O2 sensors) and is commanding less fuel go in to correct it. An easy way to interpret positive and negative trims is to remember negative trim means fuel is being removed because of a (perceived) rich condition and positive trim means fuel is being added because of a (perceived) lean condition.

Reasons for a rich condition vary. As I mentioned previously in this thread, the O2s may be faulty as well, which may be making the PCM think there's a rich condition when there really isn't one.

It's hard to say how an engine will behave exactly based on the fuel trim %. It's safe to say, however, the more skewed the numbers are, however, the more likely it won't be running correctly.

By the way, kudos to you for using live data to help diagnose your problem,
 
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tester

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Thats my thinking as well for why the PCM is thinking its a rich condition and leaning it out. Im sure the O2's were from when the vehicle came off the line, so its already going to be a good idea to replace them anyway.
I just threw in an order for both upper banks, ill post back here whether it worked or not.
Of course if anyone has any other ideas im all ears.

And thanks everyone for helping!
 

Ksat

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Remember, only buy NTK brand and make sure it's from a legit source. No ebay and amazon only if it's being sold by them directly.

In the meantime, you may want to disconnect the electrical plugs on both O2s just to see if your problem improves. That should keep the car in open loop mode, where it relies on (mostly) pre-programmed data to set the trims.
 
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tester

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Yep, I only get NTK o2's from reputable sources. Im not driving it currently, so it can wait.
 

tester

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Got them installed and logged the run, and its still thinking its in a rich condition (lines 183-215) and leaning it out.
What else would cause it to think its in a rich condition like this?
 

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Ksat

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Sorry for the delay. Can u copy/paste what's in that file to this thread here?
 

tester

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Had to chop up the file to be under the 10k character limit, but should have all the parts needed. Each line is 1 second interval.

EngineRPM(rpm)Fuelflowrate/minute(cc/min)FuelTrimBank1LongTerm(%)FuelTrimBank1ShortTerm(%)FuelTrimBank2LongTerm(%)FuelTrimBank2ShortTerm(%)FueltrimBank1Sensor1(%)FueltrimBank2Sensor1(%)O2Bank1Sensor1Voltage(V)O2Bank1Sensor2Voltage(V)O2Bank2Sensor1Voltage(V)O2Bank2Sensor2Voltage(V)
1966.75146.31-15.625-5.46-12.50-1.56-1.560.10.120.060.1
140287.68-15.6253.125-12.53.903.903.1250.060.080.060.08
1339.7576.85-15.625-0.78-12.50-0.7800.890.880.880.30
1274.570.81-15.625-3.90-12.5-3.125-3.90-5.460.920.920.920.86
1210.7567.37-10.15-7.03-9.375-6.25-7.03-8.590.920.940.920.94
113771.23-10.15-10.93-9.375-13.28-10.93-12.50.880.920.890.94
1063.567.06-10.15-14.06-9.375-16.40-14.06-15.6250.860.890.880.92
1011.7574.95-10.15-19.53-9.375-20.31-19.53-18.750.660.860.830.88
917.581.21-10.15-17.96-9.375-22.65-17.96-20.310.10.750.140.86
1070.571.60-10.15-17.96-9.375-20.31-17.96-24.210.10.750.750.81
931.574.43-10.15-20.31-9.375-21.875-19.53-21.8750.080.470.080.80
919.7579.97-10.15-18.75-9.375-21.09-18.75-21.090.060.120.060.75
916.7578.96-10.15-14.84-9.375-20.31-14.84-20.310.060.080.060.5
937.2578.70-10.15-13.28-9.375-18.75-12.5-19.530.060.060.060.16
899.2580.46-10.15-10.93-9.375-16.40-10.15-15.6250.080.080.060.08
944.7575.44-10.15-12.5-9.375-14.06-12.5-15.6250.690.340.20.12
871.7579.26-10.15-10.15-9.375-11.71-9.375-12.50.160.10.10.1
87877.09-10.15-10.15-9.375-13.28-10.15-14.840.280.10.680.14
850.2576.96-10.15-12.5-9.375-13.28-11.71-14.060.080.10.120.1
849.2574.652-10.15-14.06-9.375-15.625-12.5-15.6250.630.20.770.14
86569.59-10.15-14.84-9.375-17.18-14.84-18.750.570.540.740.22
863.2569.19-10.15-15.625-9.375-17.18-15.625-19.530.160.400.800.23
86164.00-10.15-17.18-9.375-17.18-17.18-17.960.080.10.080.08
828.7554.97-10.15-14.84-9.375-19.53-14.84-18.750.10.080.660.12
78754.24-10.15-15.625-9.375-15.625-15.625-16.400.080.080.080.1
770.555.28-10.15-14.84-9.375-14.06-15.625-14.840.880.080.080.08
1255.566.14-10.15-9.375-7.81-12.5-12.5-14.060.660.570.860.69
1061.7583.28-10.15-14.84-9.375-15.625-14.84-16.400.830.800.830.72
932.7576.43-10.15-11.71-9.375-17.18-12.5-14.060.540.380.160.62
822.569.11-10.15-14.06-9.375-17.96-16.40-14.840.360.720.220.63
805.2569.00-3.90-14.06-4.68-17.96-14.06-15.6250.060.10.140.62
798.7569.13-3.90-12.5-4.68-14.84-11.71-13.280.060.060.040.47
795.570.13-10.15-10.15-4.68-11.71-13.28-15.6250.770.830.880.77
80479.26-3.90-9.375-4.68-9.375-9.375-9.3750.060.060.040.04
793.2567.45-3.90-10.15-4.68-7.03-10.15-7.030.080.10.060.04
790.7566.55-3.90-8.59-4.68-4.68-7.81-3.900.140.120.060.06
786.2566.34-3.90-10.15-4.68-3.125-10.15-1.560.060.060.060.06
802.2565.96-3.90-7.81-4.68-3.125-7.81-2.340.060.060.560.12
79066.28-3.90-6.25-4.68-0.78-6.25-1.560.080.080.160.1
78166.02-3.90-3.90-4.68-1.56-3.90-3.1250.310.140.720.14
795.7564.00-3.90-10.15-4.68-4.68-10.15-1.560.720.690.570.14
780.2565.21-3.90-9.375-4.68-6.25-8.59-7.030.120.160.460.22
783.7563.94-3.90-13.28-4.68-5.46-10.93-7.810.160.300.680.34
778.7563.73-3.90-13.28-4.68-7.03-13.28-6.250.770.690.140.36
782.7562.29-3.90-11.71-4.68-7.03-11.71-7.030.10.120.10.22
782.7562.61-3.90-14.06-4.68-7.03-13.28-9.3750.080.180.660.14
78562.61-3.90-15.625-4.68-10.93-14.06-10.150.140.250.740.16
772.562.79-3.90-14.06-4.68-7.81-16.40-10.150.690.300.770.12
773.7561.79-3.90-13.28-4.68-6.25-14.06-7.030.10.10.060.06
759.2564.91-6.25-11.71-3.125-4.68-7.81-10.930.880.880.860.74
2067.25269.93-0.782.34-2.348.593.1254.680.080.080.060.06
 

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