Hello all,

First time poster/member, but long time reader here.

After going through Multiple forums and posts the past couple days, I have been unable to find a thread that fully describes my issue.

217k miles, 4.0, AW4, no major performance mods. The only mods I have done is upgraded injectors, K&N Cold Air Intake, Relocated Intake Temp sensor, and Oil Filter relocation Kit with inline Oil temp sender/gauge.

Recently replaced Fuel Pump. Had replaced Radiator within the past 6 months. Replaced Idle air control valve. I have hood vents to help with temps.

Also, I live in Southern Arizona, so 100+ temps are common of course.

Before anyone says anything about this, I have come to the conclusion that I am not experiencing Heat Soak/"vapor lock". I have determined this by the fact that i can turn off the vehicle, and it will start, no matter how soon I restart it or let it sit to heat up the fuel rail.

So here's the rundown. Engine will start up fine, regardless of temperature. Coolant temperature never goes above 210*. However, Whether it be that I am out wheeling on the trail, Or a long trip across town, When my oil temperature gauge reads around 225-230, The engine begins to Bog down, loose power, and misfire. Idle sits around 250-300 once the issue starts (numbers taken from OBDII B/T adapter and app). I can smell un-burnt fuel at idle. When giving it gas, The motor will not rev above 2000, but will when I give it full throttle and it shifts down. If I turn off the vehicle, and then restart it, it starts just fine, but begins the harsh idle. If I let the motor sit turned off for about 15-20 minutes, it will be back to normal once started.

Today the computer tripped codes once I arrived at work and the issue was occurring.

P0171 - Powertrain - System too Lean (Bank 1)
P0705 - Powertrain - Transmission Range Sensor Circuit Malfunction (PRNDL Input) (this would be my Neutral Safety Switch if I am to understand correctly)
P0455 - Powertrain - Evap. Emission control System Leak (i know this is my gas cap. the sensor or something is bad.)

So, after some searching, I have come to zero conclusion, only speculation:
1: My Crankshaft Position Sensor could be getting too hot.
2: A Piston ring is failing
3: Crack in block
4: Ignition Coil is becoming heated and improperly providing voltage
5: Some unknown form of heat soak
6: Black Magic
7: I'm an idiot and don't know what I'm doing anymore.

So. that's my issue. Tomorrow, i'm going to go through and check EVERYTHING. Everything short of pulling the motor apart.

As far as fixes go, if I can make it last another 2 months, I have a 4.7 stroker build I am in the middle of.

Anything helps. It really can't get much worse for me right now.

 

Also, Just because, I am putting thermal protection on the fuel rail. Even if that isn't an issue, I will for sure be able to rule that out as a cause. And It will look better that way once its in the stroker.

 

Have you checked fuel pressure at the rail when the issue is happening? I would also check compression after it's warm.

 

I don't have a compression tester, but that is on my to-do list for Thursday if I don't find anything tomorrow.

As for fuel pressure, it sits comfortably at 39ish psi Whether it is running normally or when it is doing the sputtering.

 

What year is your Jeep?

 

Yeah that would have helped. 1999

 

Much better. How's the coil, distributor and rotor look? If there's any cracks in the coil's housing, it could be arcing against the block... try checking next time it's dark.

 

Good call. See? I'm overlooking things.

Distributor and Rotor were replaced within the last month, cause I thought that could have been the cause. Obviously, it wasn't. Checked them today, Still look new.

 

Just checked the Coil. Looks fine, No cracks, no sparks.

 

Wires good too, I assume?

Reviewing your original post regarding the lean bank 1, I would assume spark isn't the issue. As far as the input signal, I would definitely pull the NSS and open it up if you haven't done it. Clean it real good and see what you get. I don't think that's going to fix your issue, but since the computer is throwing that code, you may as well clean it anyway.

 

I just keep forgetting things don't I? I did replace all of the Spark Plug wires as well as the coil wire. Getting great and even spark out of each.

Yeah I'm going to clean out my NSS tomorrow. Too dark and too heat exhausted (I have no A/C) to do anything at the moment.

Quick question. Could my Injector Wiring Harness be the issue? The plastic cover gets a little toasty once the issue is occurring, so maybe a resistance change in the wiring causing the misfire?

 

Anyone else have some input? I'm pretty much out of options here.

 

Although you didn't mention getting a code for it, I keep thinking upstream O2 sensor. It sounds like the problem starts when the engine computer tries to go into closed loop. When was the last time the front O2 sensor was changed?

 

P0171 - Powertrain - System too Lean (Bank 1)

This is the code I got which made me think that it was the upstream O2 sensor. or a vacuum leak. Ill take a look at that too today.

 

Alright. So upstream O2 sensor is a little cooked out (cables are really heat rotted). So I have one coming in tomorrow. Also, ordered a new Crankshaft Position Sensor. The CPS is working, but not as well as it should. readings are a little low, and vary as the motor turns. Checked all my injectors, things look fine. Covered the fuel rail with Heat reflectors, and those stay nice and cool once motor is hot. Cleaned out my NSS.

Its raining today, about 75* outside right now. Can't get the oil up to the temperature required to re-create the issue i'm having, so no idea if anything changed.

anybody else have something to say about my issue?