1995 f150 5.8 code 172
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From: New Sharon, IA
1995 f150 5.8 code 172
Howfy folks I'm trying to track down a 172 code HEGO lean- o2 sensor reading lean.
My truck is a 1995 f150 with the 5.8 and speed density.
I havent replaced the sensor yet because I have read many other posts that say it's other things and I've checked them. I need help!
I've checked for vacuum leaks with carb cleaner, replaced all hard plastic lines with rubber, replaced my throttle body gasket, checked pcv valve and made sure it was sealed well, and checked egr. I am at a loss and don't know where to go from here.
Am i able to check resistance in the o2 sensor wiring or something? Could it be shorted out? I have an oil pan gasket leak and my wiring and sensor is covered in filth, could that be causing it?
I havent checked fuel pressure but I put a new pump in a few months ago and figured it would be good. Also I get a faint gas smell from the fuel pressure regulator vacuum line.
Thank you Tye
My truck is a 1995 f150 with the 5.8 and speed density.
I havent replaced the sensor yet because I have read many other posts that say it's other things and I've checked them. I need help!
I've checked for vacuum leaks with carb cleaner, replaced all hard plastic lines with rubber, replaced my throttle body gasket, checked pcv valve and made sure it was sealed well, and checked egr. I am at a loss and don't know where to go from here.
Am i able to check resistance in the o2 sensor wiring or something? Could it be shorted out? I have an oil pan gasket leak and my wiring and sensor is covered in filth, could that be causing it?
I havent checked fuel pressure but I put a new pump in a few months ago and figured it would be good. Also I get a faint gas smell from the fuel pressure regulator vacuum line.
Thank you Tye
Last edited by 1993_f350_2013; Nov 18, 2016 at 12:54 PM. Reason: More info
Lead Driver
Joined: Jul 2007
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From: Rhode Island
Start by checking the fuel pressure. Should be 34-36 PSI at idle and go to 40-42 PSI if you snap the throttle wide open.
However, O2 sensors don't last forever, and they usually fail "lean". If the sensor has over 100,000 miles on it, it should probably be replaced.
However, O2 sensors don't last forever, and they usually fail "lean". If the sensor has over 100,000 miles on it, it should probably be replaced.
Senior User
Joined: Jan 2016
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From: Oregon
Clean up the connector real good with non contact electrical cleaner. I had the same issue with the leaky gasket and dirty connector. Replaced the sensor with no luck. Cleaned up the connector real well and the CEL finally stayed off.
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Posting Guru
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From: New Sharon, IA
clean the o2 sensor plug? also what gasket are you referring to?
i replace the o2 sensor about 60,000 miles ago so it could be bad?
Senior User
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From: Oregon
oil pan....same situation that resulted in a dirty connector/plug.
Fleet Mechanic
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From: Candy Mountain
My experience.
https://www.ford-trucks.com/forums/1...hego-lean.html
I had a new Ford unit go bad after just a few months, and went through extensive diagnostics because I figured the new unit being bad was the least likely scenario. Found a few problems, but in the end the new Ford sensor was bad.
Oil can and will penetrate and corrode seals and connectors.
Get your hands on a Fuel Pressure gauge and Vacuum gauge and get some real numbers.
https://www.ford-trucks.com/forums/1...hego-lean.html
I had a new Ford unit go bad after just a few months, and went through extensive diagnostics because I figured the new unit being bad was the least likely scenario. Found a few problems, but in the end the new Ford sensor was bad.
Oil can and will penetrate and corrode seals and connectors.
Get your hands on a Fuel Pressure gauge and Vacuum gauge and get some real numbers.
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Posting Guru
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From: New Sharon, IA
I will do all you guys mentioned! Thank you much for all the help! I'll get a couple testers and throw the readings back up here!
How big big of a pain is it to do the oil pan gasket? Also would it be good to do the rear main seal while I'm in there?
How big big of a pain is it to do the oil pan gasket? Also would it be good to do the rear main seal while I'm in there?
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Lead Driver
Joined: Jul 2007
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From: Rhode Island
Oil pan gasket is a hassle since the cross member is in the way and you can't take the oil pan out. You basically have to fish the new gasket around the oil pump and pickup.
Fleet Mechanic
Joined: Aug 2015
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From: Candy Mountain
It is not difficult, but a pain and to get the clearance you need you have to take quite a things loose or completely off.
You can actually stretch a one piece gasket around the pan from the bottom and not have to fish around the pump and pickup tube.
You can actually stretch a one piece gasket around the pan from the bottom and not have to fish around the pump and pickup tube.
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Code 172 fix
I fought with a check engine light and excessive spark knock for months. I replaced the o2 sensor twice, mass airflow sensor, temp sensor check for vacuum leaks, inspected wiring, cleaned and inspected connector till I finally decided I would replace the ecu. I checked for discount codes online for Advance Auto and found one for 30% off for orders bought online over 50.00. I replaced it and havent had another CEL since. Also the truck runs much better and the gas mileage is much better.
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