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P0122,p0171 having trouble getting engine running properly

4x4JeePmaNthINg

NAXJA Forum User
Location
Colorado
As the title says I've got an engine I've swapped in that is giving me p0122,p0171 codes. The jeep starts fine, but runs terrible once warmed up.


I've tested injectors, all are between 12.5-12.9 ohm
The TPS checked out good on the multimeter for all 3 tests and sweep is smooth. (Can it still be bad?)
I've tried spraying crv carb cleaner around all vacuum lines and connections with no response.
I've tested 02 sensor ground from battery negative to 02 sensor ground inputs, my meter did not register any ohm on any setting, have i done this improperly?

Here is what the scanner I'm using is showing:
gYABnVO.jpg

WSAos1R.jpg


I don't understand why it idles fine until it's at operating temp, then starts sputtering and sounds like it's going to die?
I've researched testing for leaks with propane, does anyone not suggest this method?
 
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Have you replaced sensor 1 o2 sensor? The computer runs on its own programming cold and once warm it factors in that o2 sensor data. Could be that simple.

Sent from my SM-G950U using Tapatalk
 
Use the trouble codes to guide your diagnostics. The reason it idles fine until warm is because it is in open loop mode and using pre-programmed data until warmed up when it begins closed loop mode and uses the engine sensor inputs.

What brand of O2 sensors are installed ?

Are you installing genuine Jeep OBD engine sensors ?



P0122 JEEP - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes
•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection


P0171 JEEP - Fuel System 1/1 Lean


Possible causes
•Intake air leaks
•Faulty front heated oxygen sensor
•Ignition misfiring
•Faulty fuel injectors
•Exhaust gas leaks
 
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Use the trouble codes to guide your diagnostics.

What brand of O2 sensors are installed ? are you installing genuine Jeep OBD engine sensors ?



P0122 JEEP - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes
•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection

what should've I seen if the sensor harness was open/shorted, or poor connection?

P0171 JEEP - Fuel System 1/1 Lean


Possible causes
•Intake air leaks (Is propane a good way to find these?)
•Faulty front heated oxygen sensor ( I'm uncertain if I've performed something wrong here, no readings on the meter)
•Ignition misfiring ( Can a distributor fit well and be off a tooth?, the retaining bolt lined up well)
•Faulty fuel injectors ( is there test beyond ohm reading?)
•Exhaust gas leaks



Tim,

Currently upstream and downstream 02 sensors are aftermarket Bosch. The upstream was removed completely for the engine swap, then reinstalled.
Are bosch not sufficient replacement, you mention jeep obd sensors??
Tim I've tried testing the 02 with a manual range digital meter, am I performing this test incorrectly if I'm not getting an ohm reading?


Should I be finding readings from the harness?

Slowxj,

No I have not replaced the upstream 02 sensor yet, ide hoped to get some readings to test if it was bad or not. I had good connection to battery ground, but the meter didn't register any ohm reading while probing the sensor.

Thanks guys, I'll do everything I can to perform these tests. I've got a free manual downloaded, but there's a lot left out for testing and I'm really relying on those of you that know better.
 
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It is well known that the Jeep 4.0L and Bosch O2 sensors do not play well together. You should ALWAYS use NTK O2 sensors. It is very highly likely that the Bosch O2 sensors are the root cause of P0171 code.

Use the volts/ohms multi-meter to check O2 sensor voltage, O2 sensor function, and for wire continuity of the O2 sensor wire harness. Make sure there is continuity to ground also. Look for corrosion and bent or pushed back pins in the O2 wire plugs.

TPS failure is somewhat common, test/inspect the wire plugs and wire harness. Be sure to install a genuine Jeep replacement TPS if necessary.
 
Looking on rockauto I notice Ntk sensors are about the same price as Bosch, 30$. Mopar 02 are 89$, are these rebaged ntk or why do ntk seem to work better?

I'll recheck the 02, should I be backprobing the sensor for readings, or to the harness pin inlets? 200ohm setting?
 
A basic Google search finds this:

1991-2001 HO

The O2 Sensor is also the main sensing element for the Catalyst and Fuel Monitors. The O2 Sensor can fail in any or all of the following manners:

slow response rate
reduced output voltage
dynamic shift
shorted or open circuits

Response rate is the time required for the sensor to switch from lean to rich once it is exposed to a richer than optimum A/F mixture or vice versa. As the sensor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas.

The output voltage of the O2S ranges from 0 to 1 volt. A good sensor can easily generate any output voltage in this range as it is exposed to different concentrations of oxygen. To detect a shift in the A/F mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.

For the HO years, 91-02, the O2 sensor has 4 wires. One wire is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall (unless they moved them in later years to the relay & fuse boxes?), and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immediately after start up. Loss of that power will hurt gas mileage even with a good O2 sensor.

Two black wires are grounds for the heater power and O2 signal to the ECU. A poor ground will limit current to the O2 sensors heater or cause an error in the O2 sensor output voltage read by the PCM (ECU) causing poor mileage even with a good O2 sensor. Test the 2 ground wires with power off. Test between the wire end at the sensor and the battery negative ground post. It should read less than 1 ohm.

The last wire, #4, is a signal feed wire, 0-1 volts, from the O2 sensor to the PCM (ECU) sensor. The O2 sensor is an O2 concentration sensitive variable voltage generator. At optimal O2 concentration the O2 sensor puts out 0.45 volts.

At idle that voltage should read 0.1-0.9 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 0.4 and 0.5 volts max (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the grounds and the 12-14 volts to the heater. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth.

If the O2 sensor readings are not right, say they read .1 volts or .8 volts steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 on one, and ensure the ground wires (power off) reads less than 1 ohm to the battery negative post.

If any one of the grounds or the O2 sensor to ECU/PCM wires reads a high voltage chances are the wiring harness is damaged and the 12-14 volts for the O2 sensor heater is getting through a bad spot in the wires insulation and contacting a ground wire or the O2 sensor wire feed to the ECU/PCM. This is not the O2 sensors fault, but a wiring problem.


A leaky exhaust system or leaky fuel injector(s), or bad compression or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.
 
Yes that is the same instruction i used from another thread on naxja.
"Test between the wire end at the sensor and the battery negative ground post. It should read less than 1 ohm. "
Is where I'm getting confused, on inlet of sensor or backprobing????

I do appreciate you looking all that up though.
 
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"Test between the wire end at the sensor and the battery negative ground post. It should read less than 1 ohm. "
Without doing a heavy read, I'm thinking that refers to the resistance in the wiring harness.

The only resistance test for an oxygen sensor, is for a heated oxygen sensor. You don't have that.
 
Yeah this is where I'm really hitting walls here. I'm asking in between questions that most here know better about, but I'm highly unkowledgable on the small details that make a huge difference! It seems like most on here could build an xj from the ground up, with their eyes closed. Most take this information for granted and assume folks understand what they are writting about. I'm Researching and reading I swear, but a little clarity goes a long way when your as new to this as I am. For instance, which ohm setting on a meter I should use, the small stuff gets lost in translation....


Still haven't heard anyone chime in on testing leaks with propane( good, bad, safe/unsafe,do/dont)

Tim mentioned Ntk sensors, does anyone know if Mopar is worth the extra money, or just added $$ for the name on an ntk manufactured sensor?

The manual I downloaded has almost nothing in the intake/ exhaust section so I'm leaning on diagnosis methods from the knowledgeable on here.


I Greatly, Greatly appreciate the patience and effort those here have taken to help me. To those I say Thank You!
 
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Jeep O2 sensors from the Dealership are NTK sensors in a different box.
 
I'm just going to throw this out there -- I didn't want to when this thread 1st popped up but it may be becoming relevant

Here is a link to what may be my 1st thread on NAXJA -- Basically a bunch of unexplained codes
https://www.naxja.org/forum/showthread.php?t=1137127

I didn't re-read the whole thread but I'm basically looking for solid,exact answers to how to test and diagnose some of the sensors, mainly the TPS -- pretty much what this thread is doing

In that whole thread -- I don't believe I ever got an exact black and white answer -- I'm not sure one exists

In the end, all my codes meant nothing -- a simple compression test found my issue -- it was a bent pushrod and exhaust valve stuck open -- I spent a lot of time and money chasing a gremlin that didn't exist

Your problem may not be electrical at all...
 
Still haven't heard anyone chime in on testing leaks with propane( good, bad, safe/unsafe,do/dont)

Leaks as in vacuum leaks? Smoke test is going to be your best bet on that. They do have DIY ways to make one.
 
Without doing a heavy read, I'm thinking that refers to the resistance in the wiring harness.

The only resistance test for an oxygen sensor, is for a heated oxygen sensor. You don't have that.

I take that back, you do have a heated oxygen sensor.

That said, I would trust a real-time scan more than a spot reading. With the engine warmed up, idling, in closed loop, the oxygen sensor output voltage should fluctuate as described in Tim's post. If it works, don't fix it!
 
I ran it again today before work, here is what the scanner reads once it's running bad.
vUH8Ba8.jpg

h9B7u0D.jpg

I may try a new 02, some have said the body, which I have, do not work well with jeeps idk.
 
Leaks as in vacuum leaks? Smoke test is going to be your best bet on that. They do have DIY ways to make one.

I'll see what I can come up with this monday-tuesday. I feel like my stomach is in my throat everyday trying to get my only wheels going man. This has been quite the journey taking on a job like this for my having practically no experience with engines. :wow:

My hats off to anyone doing this regularly.
 
I'll see what I can come up with this monday-tuesday. I feel like my stomach is in my throat everyday trying to get my only wheels going man. This has been quite the journey taking on a job like this for my having practically no experience with engines. :wow:

My hats off to anyone doing this regularly.

I hear ya man. Mechanical stuff I have no issue with but electrical things are a bitch. DIY smokers aren't hard to make. Just take some basic things and a compressor. Wish I knew more to help a out, but I'm even greener in this arena than you are right now!
 
First and foremost, I want to give a shout-out to Matt! He did a great job on the many "first time ever" tasks that went into this engine swap.

The stars aligned, the clouds parted, I was able to help another COLORADO CHAPTER MEMBER sort out some problems with his XJ.

The purpose of writing this out is to illustrate a systemic approach to diagnostics, that seems to be absent from many internet threads.

Drill-Down List:

Visual Inspection:
All electrical and vacuum systems hooked up, general condition?
Any loose or missing fasteners?
Any gaps, misalignments, or witness marks indicating loose assemblies?

Confirm Observations:

Matt had already confirmed the TPS Low and High Voltages were within prescribed limits. Without having specific knowledge of the software’s terminology, I wanted to do a “sweep” test on the sensor. Having some working knowledge of Rheostats and Potentiometers, and not having a DVOM with the capability of measuring for “drop out,” I brought an analog Ohmmeter. Alas! I could not reliably connect to the pins, so we opted for the OBDII reader. With the Key On, Engine Off, we checked the TPS for dead spots. The display did show two spots with no reading from the TPS, but, not at idle. The question remains: Are the dead spots the reason for the “TPS Low Voltage” code?

Since I am not familiar with the scanner software, I wanted to take another approach to the “Bank 1 lean” code set by the scanner.

While we tested the TPS, the ECU set another code, something about no signal from the CPS. Go figure!

Active Investigation:

After attaching a Vacuum Gauge to the manifold, and pressure gauge to the fuel rail, we started the engine. I noticed a slight misfire, and rough idle. The vacuum gauge registered 14” at idle, with minor, rapid, fluctuations. I thought this was a low reading, which could be an indicator of a few different problems. There were no sounds indicating mechanical problems inside the engine. I attributed the rapid fluctuation and low vacuum to the cylinder misfire. Fuel pressure was within spec, and consistent.

In an attempt to track down the misfire, we started by disconnecting the plug wires, one at a time, with the engine running. Each time, the rpms dropped, with no other changes. I touched each injector to find the solenoids cycling. In spite of Matt’s diligence in labeling and keeping the under hood organized, I wanted to try swapping injector connectors on cylinders 1 & 2, 5 & 6: No change. When we shut off the engine to swap the first pair of injector connectors, I did monitor the pressure on the fuel rail. After waiting 30 minutes, we had a slow and consistent 50% bleed down, which I believe is acceptable.

Through my process of looking for the big AHA! The scanner software on Matt’s had shut off a few times. At this point, I wanted to see the real time output from the oxygen sensor. Matt found the bar graph, with a voltage reading. As we watched, the graph went flat, the voltage went to zero, and stayed at zero. We had our smoking gun! When Matt pulled the oxygen sensor, it was covered with black soot.

After installing a new oxygen sensor, we started the engine to record the same low, unstable vacuum reading that we had already documented. I held the throttle open long enough to clear unburned fuel from the cylinders, no change. Time to look at the spark plugs.

attachment.php


All six spark plugs were covered with black soot, except where the arc was jumping from electrode to ground strap. All six plugs were properly gapped. All six spark plugs are platinum tipped, the manufacturer specified standard plugs. I wanted to do a compression test while the spark plugs were out.

Matt held the throttle all the way open while cranking the engine. While cranking on the first cylinder test, there was a strong fuel smell that was not present when we tested the rest of the cylinders. Results are as follows:
Cylinder 1-130 lbs.
Cylinder 2-130 lbs.
Cylinder 3-128 lbs.
Cylinder 4-135 lbs.
Cylinder 5-132 lbs.
Cylinder 6-130 lbs.

After recording the readings on my phone, I observed that all cylinders held their pressure until I released it.

At this point, we decided to install the used plugs from the old engine. We pulled the used plugs from the old engine, verified the gap and installed. The engine started easily and idled smoothly, the vacuum reading was more stable at 14”. As a cross check, I put the vacuum gauge on my engine: 14” vacuum. I guess that is all we can expect at his elevation.

 
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