CEL/CODES questions
Fleet Owner
Joined: Aug 2005
Posts: 23,666
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From: Easton,Ks
Code 312 is a code that only comes up on the KOER self-test. This can happen if someone puts on headers and the O2 sensor is no longer in the cross pipe and now is only on the pipe that both exhaust manifold feed into.
It can also be caused by a bad or missing O2 sensor or O2 wiring.
During the KOER self-test the computer will switch air into one bank only and then switch air back into the other bank only. It then looks for a change in the O2 readings between the two banks. If it does not see one it flags the 312 code.
Or to get technical what it does is:
The test first enriches up the mixture, and then sends thermactor air upstream of the O2 sensor and checks that the O2 sensor indicates LEAN. If that test passes, then it sends the thermactor air downstream of the O2 sensor and checks that the enriched mixture indicates rich on the O2 sensor.
If not, it sets code 312, presuming that the air was not diverted, and was therefore sent upstream, as in the previous test.
You have no sensor called IME.
I think he was just giving his opinion in that statement.
It can also be caused by a bad or missing O2 sensor or O2 wiring.
During the KOER self-test the computer will switch air into one bank only and then switch air back into the other bank only. It then looks for a change in the O2 readings between the two banks. If it does not see one it flags the 312 code.
Or to get technical what it does is:
The test first enriches up the mixture, and then sends thermactor air upstream of the O2 sensor and checks that the O2 sensor indicates LEAN. If that test passes, then it sends the thermactor air downstream of the O2 sensor and checks that the enriched mixture indicates rich on the O2 sensor.
If not, it sets code 312, presuming that the air was not diverted, and was therefore sent upstream, as in the previous test.
You have no sensor called IME.
I think he was just giving his opinion in that statement.
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
I am sitting here laughing my fanny off. You see, I work in food processing and we do use IME sensors and they are uber expensive. I could not for the life of me figure out how they would have adapted one to work in an automotive vehicle!
Sounds like the first step is a replacement of the O2 sensor. Would it be advisable to clean the throttle body and the TPS also?
Sounds like the first step is a replacement of the O2 sensor. Would it be advisable to clean the throttle body and the TPS also?
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
I am sitting here laughing my fanny off. You see, I work in food processing and we do use IME sensors and they are uber expensive. I could not for the life of me figure out how they would have adapted one to work in an automotive vehicle!
Sounds like the first step is a replacement of the O2 sensor. Would it be advisable to clean the throttle body and the TPS also?
Sounds like the first step is a replacement of the O2 sensor. Would it be advisable to clean the throttle body and the TPS also?
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 12
From: Sand Lake, MI
LOL Yup I should have made that more clear I guess, should have just spelled it out not like it was a huge time saver that way!
I think the O2 sensor is highly suspect and wouldn't hurt to change it regardless, adaptive strategies should have kicked in saving on fuel but again IME that is not the case.
O2 sensor fails and fails 172 "system lean", gas mileage takes a header with it as computer continuity tries to swing "rich" in some attempt get a rise out of the sensor, rather than flag as bad disregard it turn the MIL light on use "adaptive" its built over time for fuel.
Static pressure test, connect fuel pressure gauge to fuel rail cycle the key on and off couple times to allow build pressure then turn off the key and watch the gauge. A healthy fuel system the pressure will hold for quite a while before even starting to drop but passing test results = "holds within 5 psi of spec for 1 minute".
If holds then no further testing is required, if drops right away and value drops fast continues to do so right to zero then other testing is required get an idea where the fault lies. For example might be leaking injector/s.
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
LOL Yup I should have made that more clear I guess, should have just spelled it out not like it was a huge time saver that way!
I think the O2 sensor is highly suspect and wouldn't hurt to change it regardless, adaptive strategies should have kicked in saving on fuel but again IME that is not the case.
O2 sensor fails and fails 172 "system lean", gas mileage takes a header with it as computer continuity tries to swing "rich" in some attempt get a rise out of the sensor, rather than flag as bad disregard it turn the MIL light on use "adaptive" its built over time for fuel.
Static pressure test, connect fuel pressure gauge to fuel rail cycle the key on and off couple times to allow build pressure then turn off the key and watch the gauge. A healthy fuel system the pressure will hold for quite a while before even starting to drop but passing test results = "holds within 5 psi of spec for 1 minute".
If holds then no further testing is required, if drops right away and value drops fast continues to do so right to zero then other testing is required get an idea where the fault lies. For example might be leaking injector/s.
I think the O2 sensor is highly suspect and wouldn't hurt to change it regardless, adaptive strategies should have kicked in saving on fuel but again IME that is not the case.
O2 sensor fails and fails 172 "system lean", gas mileage takes a header with it as computer continuity tries to swing "rich" in some attempt get a rise out of the sensor, rather than flag as bad disregard it turn the MIL light on use "adaptive" its built over time for fuel.
Static pressure test, connect fuel pressure gauge to fuel rail cycle the key on and off couple times to allow build pressure then turn off the key and watch the gauge. A healthy fuel system the pressure will hold for quite a while before even starting to drop but passing test results = "holds within 5 psi of spec for 1 minute".
If holds then no further testing is required, if drops right away and value drops fast continues to do so right to zero then other testing is required get an idea where the fault lies. For example might be leaking injector/s.
Senior User
Joined: Aug 2013
Posts: 262
Likes: 1
From: Cherryville, NC
As far as vacuum lines go, here are a few things that will make life a little easier in this regard. Much cheaper to buy the rolls on Amazon than by the foot at the parts store. You can cross-reference the Gates part number on the Gates web site to determine the sizes, Amazon doesn't document them well. The comments sections help. Here is what I bought.
Rather than just change vacuum hoses you can test with one of these:
That's just an example, there are many out there. Some include the accessories to bleed brakes.
Rather than just change vacuum hoses you can test with one of these:
That's just an example, there are many out there. Some include the accessories to bleed brakes.
Thread Starter
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
As far as vacuum lines go, here are a few things that will make life a little easier in this regard. Much cheaper to buy the rolls on Amazon than by the foot at the parts store. You can cross-reference the Gates part number on the Gates web site to determine the sizes, Amazon doesn't document them well. The comments sections help. Here is what I bought.
Amazon.com: Gates 27043 Windshield Washer and Vacuum Hose: Automotive
Amazon.com: Gates 27044 Windshield Washer and Vacuum Hose: Automotive
Amazon.com: Gates 27050: Automotive
Amazon.com: Dorman 47380 Vacuum Connector Value Pack, 65 Piece: Automotive
Rather than just change vacuum hoses you can test with one of these:
Amazon.com: Actron CP7830 Hand Vacuum Pump: Automotive
That's just an example, there are many out there. Some include the accessories to bleed brakes.
Amazon.com: Gates 27043 Windshield Washer and Vacuum Hose: Automotive
Amazon.com: Gates 27044 Windshield Washer and Vacuum Hose: Automotive
Amazon.com: Gates 27050: Automotive
Amazon.com: Dorman 47380 Vacuum Connector Value Pack, 65 Piece: Automotive
Rather than just change vacuum hoses you can test with one of these:
Amazon.com: Actron CP7830 Hand Vacuum Pump: Automotive
That's just an example, there are many out there. Some include the accessories to bleed brakes.
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
So we tested fuel pressure and it is okay. Replaced O2 sensor this morning and a difference is noticed right away. Held fast idle on start-up (was surging) and dropped to ~650 after a few minutes. Hopefully that takes care of the issue. BTW, where can I find the MAF sensor? It was suggested to me that I should probably clean it.
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
You do not have one. You have a MAP sensor instead and you do not clean them.
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
Thank you Subford. I really need to stop listening to this guy. He told me I had to clean my TPS also, and I was told here that you can't clean them either.
Laughing Gas
Joined: Nov 2013
Posts: 871
Likes: 6
From: Orcas Island, WA
Thread Starter
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Senior User
Joined: May 2014
Posts: 139
Likes: 0
From: N.E Oregon
Just tell him you got the problem fixed. It turned out that the muffler bearings were corroded and were causing excessive back pressure. You took them out, cleaned them up, and greased them with the new Techatron XL+ lubricant and the truck is now running better than it ever has before.
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XionTheBrony
1987 - 1996 F150 & Larger F-Series Trucks
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Feb 28, 2013 10:59 AM