Loss of power / high fuel trim / stall under load

[Juggernaut]

I’d now consider the trims and o2 voltage a symptom and not the cause. An exhaust leak wouldn’t cause the TPS and IAC codes so I’d turn my attention to the both of these sensors.

A few quick checks:
What is your TPS voltage at idle and does it change once the vehicle reaches operating temp and starts to run rough?

Also does your scanner show “desired idle” as well as engine rpm? Try to understand what the PCM is seeing. Does the scanner allow you to increase the idle to test the IAC stepper motor?

Digging deeper with just a multimeter you need to again confirm the reference voltage for the IAC and TPS and more importantly resistance test the ground on these sensors. On the 05/06 they share a common ground (which is a dark blue wire green stripe IIRC). Yours may vary. An error in the reported signal of these sensors would confuse the PCM and it would not be able to model the airflow and the fueling would be off as a result.

 

[A.leese]

@Juggernaut I think you’re spot on!

I just started it to look at the specific data points you referenced. For reference I have the Innova 5210 (V2).

I’m not sure if I can get the voltage for the TPS on my OBD reader (unless it’s user error) however it stays consistent on the percentage value even when hot ~18% at idle. When I graph it the sensor responds correctly and there doesn’t seem to be any lag.

Unfortunately, I don’t think I can change rpms through the scanner either. However, when I start it, it’s around 800rpm and then settles in to 660-680 rpm (until it jacks up the trims and starts to sputter) I also don’t believe I’m able to test IAC.

HOWEVER… when it stalled this time it dropped two new codes:

P0171- system too lean bank 1
P0174- system too lean bank 2

I’ll be using the multimeter now and get back with the resistance.

 

[macleanflood]

Use the multimeter to get the voltage going to the TPM. Should be around 5v. It helps verify the supply voltage from the PCM and wiring.

We've seen issues where that supply voltage was shorted to ground elsewhere...in one case a clock spring... causing system wide havoc.

-Mac

 

[A.leese]

@macleanflood

Are there any resources you have that could help me make sure I’m doing it correctly in the first place? I’m starting to think some user error may be involved with my multimeter trouble shooting.

 

[macleanflood]

I think @hear made some troubleshooting videos...or posts...

-Mac

 

[A.leese]

@macleanflood

Right now from left to right I’m getting

1- 0v (ground)
2- 4.63v (sensor signal)
3- 5.17v (supply)

 

[macleanflood]

And that sensor signal voltage varies as you rotate the slot?

Looks good to me.

-Mac

 

[Juggernaut]

@macleanflood

Right now from left to right I’m getting

1- 0v (ground)
2- 4.63v (sensor signal)
3- 5.17v (supply)

The readings for the TPS look normal, however when taking reading for the reference voltage and signal voltage make certain you are taking the reading with the multimeter using the sensors ground wire. If you attach the mulimeter positive lead to the sensor but attach the negative lead to any available ground such as a engine bolt instead of the sensors ground, you’ll get a correct reading but miss a potential problem with the circuit.

 

[Juggernaut]

The readings for the TPS look normal, however when taking reading for the reference voltage and signal voltage make certain you are taking the reading with the multimeter using the sensors ground wire. If you attach the mulimeter positive lead to the sensor but attach the negative lead to any available ground such as a engine bolt instead of the sensors ground, you’ll get a correct reading but miss a potential problem with the circuit.

@macleanflood

Right now from left to right I’m getting

1- 0v (ground)
2- 4.63v (sensor signal)
3- 5.17v (supply)

Nvm- looks like you have ~18% at idle

 

[hear]

I think @hear made some troubleshooting videos...or posts...

-Mac

I only ever did the cam position sensor, but I really want to complete the project for all the sensors. Maybe this summer??

 

[A.leese]

The readings for the TPS look normal, however when taking reading for the reference voltage and signal voltage make certain you are taking the reading with the multimeter using the sensors ground wire. If you attach the mulimeter positive lead to the sensor but attach the negative lead to any available ground such as a engine bolt instead of the sensors ground, you’ll get a correct reading but miss a potential problem with the circuit.

I learned something new! I appreciate the advice. When I get home I’ll take a look and see if any of the voltages change.

 

[A.leese]

And that sensor signal voltage varies as you rotate the slot?

Looks good to me.

-Mac

@macleanflood
It appears to respond appropriately voltage wise when the slot rotates!

However, the readings I could get when graphing the O2 sensors after seeing your previous images looked like this on my upstream sensors.

These definitely aren’t looking quite right. While the upstream sensors are the correct NTK parts, something doesn’t seem right.

When the sensor flat lines at the end of the graph is the voltage when it stumbles and eventually stalls.

 

[A.leese]

@Juggernaut

I appreciate your help with this. I’ve been learning a lot from everyone!

 

[macleanflood]

Your upstream is working. Mine is dead. I've got a replacement on order. We'll see if a cheap Walker will work.

-Mac

 

[A.leese]

To update…

I took a long shot after testing every sensor that has to do with the fuel delivery system and went after injectors just for the heck of it. After getting lean codes for both banks, it’s possible it actually is starving it of fuel.

Either I’m not doing it correctly or I have a short in the wire harness. After reviewing the manual, I am under the impression I should be getting 12v from the PCM to the injector connection. I’m not getting a single volt. The key is in the “on” position.

Any guidance on testing these further would be much appreciated.

 

[Juggernaut]

I wouldn’t jump to the injectors yet.
Based on your info, what appears to be happening is that you cold start the jeep it will run ok in open loop until it warms up and starts using feedback from the certain sensors in closed loop. Once in closed loop, the upstream o2 sensors begin switching between rich and lean as normal but then peg lean, the pcm responds with positive trims adding fuel to the lean condition. The p0171 and p0174 codes you received will be triggered when trims exceed roughly +25%.

If the earlier FSM have a trouble shooting tree similar to the later models, did you follow this while testing? If you’ve tested the various sensors and grounds and all appear correct, we need to look for correlation in the data (the IAC, TPS, engine temp and MAP readings) at the point in time when the O2s flat line. If you clear the codes and restart cold, do the IAC TPS CPS codes trigger with the Key on Engine off, does it only occur once up to operating temp when it starts to run rough? Does your scanner show fuel system status Open Closed?