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O2 Sensor Issue!!


WackoRanger

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Hello,

Shortly after I fixed the same 1997 Ford Ranger 3.0l Engine, the same problem came back after I replaced the PCM. For about 3 days I was able to run the truck completely normally and reliably. When I got in the truck to head home after work last night, it started having the same issue. The engine would start immediately, jump to 2K RPM, fall down to 1K RPM as it warmed up then eventually die. If I tried to apply any throttle, the engine would sputter and misfire as if I had a crossed spark plug wire (which I don't). When I applied the gas, it was like the engine was hitting the rev limiter and killing the ignition.

Anyways, I nursed it home without any throttle and I was able to get a read on the codes it was throwing.

P0174: System too Lean (Cylinder Bank 2)
P0171: System too Lean (Cylinder Bank 1)
P1445: Purge Flow Sensor Circuit High Input (To be expected, this engine is equipped with an EGR delete)

I also did a live data reading and found that as soon as any throttle was given to it, the O2 sensors would immediately die / give no output to the PCM.

So here's where I'm stuck. Previously, I was able to just let the engine warm itself up and it would mitigate this issue, which was annoying but I dealt with it, but now I have no ideas. With it being 25 degrees outside right now this truck really doesn't want to run and I don't really have any other reliable cars to use which makes this kind of urgent. Tomorrow I plan to check the junkyard for a new wiring harness from another 3.0. If that doesn't work, I'll check with some starting fluid for vacuum leaks and try and fix them. After that, I might throw the EGR system back on the engine and try it from there. Otherwise, I'm completely out of ideas. I have no explanation for why this stupid engine keeps killing PCM computers and I could really use some help.

__
WackoRanger
 


franklin2

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On the oxygen sensors, they may be telling the truth or they may be lying. You can disconnect them temporarily and see what the engine does after that. When it sees the sensors not there, it will avoid going into closed loop and instead run the engine off the fueling charts in the computer memory. If it still won't run that's more verification there is something else going on, like fuel pressure or a vacuum leak. Water in the fuel is going to freeze at those temps, and may cause a fuel restriction.
 

DILLARD000

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Your prior posts noted you did install new OxSensors; did you use Ford\Bosch (MotorCraft\OriginalMaker)?
Offbrand OxSensors are notorious for "infant mortality", not lasting more than a few months before they die.
 

Blmpkn

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Your prior posts noted you did install new OxSensors; did you use Ford\Bosch (MotorCraft\OriginalMaker)?
Offbrand OxSensors are notorious for "infant mortality", not lasting more than a few months before they die.

This.

Brand new eBay o2s lasted me about 2 weeks in my old crown vic.
 

19Walt93

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Lean codes are seldom O2 sensor failures, they're telling you there's likely a vacuum leak or possibly fuel supply problem. The Autozone near our dealership was famous for selling sensors when their Mickey Mouse tester displayed "O2 sensor lean/rich". O2 sensor rich/lean isn't a diagnosis, it's a symptom.
 

WackoRanger

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Having just unplugged the O2 sensors, the engine still does the exact same thing. As for the brand of the sensors, the shop said they were Bosch / Ford sensors but I couldn’t read anything off of the sensors themselves. The shop is pretty high quality so I doubt they’d use cheapo off-brands. But- I didn’t install them so I guess there is a slim possibility. Of course they did start doing this immediately when they were installed.

I’ve checked all over for any vacuum leaks and I just can’t find anything. I’m planning on picking up an IR thermometer then testing the catalytic converter to see if it might be clogged up. If so then it gets a straight pipe :)

If that still fails, maybe I’ll slap the EGR system back on and see if that fixes anything. Any more ideas would be great help!

__
WackoRanger
 

Craig0320

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When you check the cats make sure the engine is full temp and set the engine to 2000 rpms. Pull a temp right at the entrance and exit of the cat. You should have at minimum a 100 degress hotter on exit temp. If the the system is already lean idling when you rev it up all the sensors are going to show is lean(no movement at all). Sounds like the canister purge valve for the fuel tank is stuck open feeding unmetered fuel vapors to your intake causing the lean issue. Which would make sense showing lean on both banks.
 

franklin2

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When you check the cats make sure the engine is full temp and set the engine to 2000 rpms. Pull a temp right at the entrance and exit of the cat. You should have at minimum a 100 degress hotter on exit temp. If the the system is already lean idling when you rev it up all the sensors are going to show is lean(no movement at all). Sounds like the canister purge valve for the fuel tank is stuck open feeding unmetered fuel vapors to your intake causing the lean issue. Which would make sense showing lean on both banks.
That might make sense, seeing he has a P1445 code. That would not have anything to do with the EGR, that is the EVAP system like you said.
 

Craig0320

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That might make sense, seeing he has a P1445 code. That would not have anything to do with the EGR, that is the EVAP system like you said.
Funny I literally just fixed an 07 escalade doing the same thing. Other symptoms it has was dieseling after shutting the key off and a ton of back pressure when you opened the fuel cap.
 

WackoRanger

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I am now at a complete loss.

I have completely redone the EVAP system, that CEL cleared and never came back, but the lean codes are still there.

In terms of tests that I've done since the EVAP rebuild, I've checked TPS (came back fine, all voltages in tolerances), Vacuum Leaks (Starter Fluid method, no response with sprays), IAC solenoid (Idled at 500rpm until plugged back in, came back fine). The only thing that's changed since redoing the EVAP is that when the MAF sensor is unplugged, the engine runs smoothly and normally.

I don't really have any more ideas on what to do with this. I've noticed that on some drives, the accelerator will have a "dead zone" where I'll have to push the pedal forward more than I was expecting to get it to kick in, which it does. Otherwise, I've noticed that I've got TERRIBLE gas mileage just going to and from work every weekday and 1 or 2 other places during the week, I've gone through almost 2 tanks full. No additional CELs either, which I am so puzzled by because it's obviously more than a vacuum leak.

So, if you come across this post and have even a slight thought of what could be causing all of this, please just take a minute and write it down. I have no idea where to go next and this engine is just driving me crazy.

__
WackoRanger
 

Craig0320

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Forgive me if i've skipped over reading something. Have you checked the coolant temp sensor. It sends data to the pcm and the pcm uses this info to determine fueling(among others).

Check your maf readings. It is directly responsible for sending the amount of air going into the engine to the pcm which in turn adjust fuel.
Leave the maf plugged in and tap it with the rubber end of a screwdriver to see if the engine runs rough. Check the maf reading on a scanner with the engine off. The reading should be stable and not bouncing/moving(if it is it's bad).
 

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