o2 sensor problem?
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o2 sensor problem?
i have a 1994 ford f150. 5.0 motor. i have replaced the maf sensor and egr valve. checked all vacuums and scanned it many times. pointed to o2 sensor. replaced oxygen sensor. when vehicle runs well, o2 sensor shows voltage readings between .2 and .7 when idling rough and no throttle the o2 sensor shows invalid. what the heck does invalid mean and how do i fix it? i have tried to get it fixed for two weeks now. no check engine light. have gotten numerous codes from scanner. knock sensor, egr valve, o2 sensor, maf sensor. fuel pumps are fine. have dual tanks and it does same thing with either tank. any help at this point is greatly appreciated.
Elder User
Joined: May 2012
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From: Covington VA
This area is for 80-86 f150s.
Welcome to fte. I am sure the guys in the newer section would be a big help.
On a side note my first thought is a intake leak past the maf sensor. The maf obviously reads airflow determining how much fuel to inject. Then the o2 reads how much fuel got burned. Comparing these 2 figures then gets the computer to either alter the a/f ratio or timing. It may even be oxygen being introduced at the exhaust manifold throwing the system a crazy figure.
Again this is just what jumped into my head. I honestly have no clue if this is right.
Welcome to fte. I am sure the guys in the newer section would be a big help.
On a side note my first thought is a intake leak past the maf sensor. The maf obviously reads airflow determining how much fuel to inject. Then the o2 reads how much fuel got burned. Comparing these 2 figures then gets the computer to either alter the a/f ratio or timing. It may even be oxygen being introduced at the exhaust manifold throwing the system a crazy figure.
Again this is just what jumped into my head. I honestly have no clue if this is right.
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From: Denver Metro Area, CO
You really need to get yourself a Ford factory service manual, it lists the exact procedures to diagnosis problems like this.
Pretty cheap on eBay:
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1994 Ford Car Truck Powertrain Control Emissions Diagnosis Service Manual | eBay
I'm also moving this thread to the proper forum....
Pretty cheap on eBay:
1994 Ford Car Truck Powertrain Control Emissions Diagnosis Service Manual | eBay
I'm also moving this thread to the proper forum....
FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
Post up the exact code numbers you're getting, what a lot of people are calling O2 codes are not specifically referring to the O2 at all and that could explain why your codes come back after replacing the parts.
What are you using to read the codes as well?
What are you using to read the codes as well?
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From: Denver Metro Area, CO
There are often different procedures used to diagnose & correct problems depending on those attributes.
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thank you all. truck will idle better and respond when cold. as it warms up it starts to get worse. have received codes all over the board. 16, 72, 116, 157, 172, 225, 327, 332, 536,556 ,636. all with koer test. dcl mode is where i get the consistent running voltages and temps. am using autoxray scanner. tested and works on other vehicles fine. found no vacuum leaks. only consistent code is 111. koeo test. replaced o2 sensor only because of the invalid message from scanner during dcl test. when running, voltage from o2 working, runs fine. when no voltage and invalid showing on tester runs like crap. still doing it after replacement. could it be the ect sensor? no leakage aroung intake or exhaust manifolds. all rubber hoses are good. just not sure how to test this sensor. your ideas are great and i will try all. if i could, i would have the garage test it. cant get it down there. wont run good long enough.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
You will get either 2 digit codes or 3 digit codes, not both. Your 1994 model year should have 3 digit codes.
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Elder User
Joined: Dec 2003
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From: Northern California
thank you all. truck will idle better and respond when cold. as it warms up it starts to get worse. have received codes all over the board. 16, 72, 116, 157, 172, 225, 327, 332, 536,556 ,636. all with koer test. dcl mode is where i get the consistent running voltages and temps. am using autoxray scanner. tested and works on other vehicles fine. found no vacuum leaks. only consistent code is 111. koeo test. replaced o2 sensor only because of the invalid message from scanner during dcl test. when running, voltage from o2 working, runs fine. when no voltage and invalid showing on tester runs like crap. still doing it after replacement. could it be the ect sensor? no leakage aroung intake or exhaust manifolds. all rubber hoses are good. just not sure how to test this sensor. your ideas are great and i will try all. if i could, i would have the garage test it. cant get it down there. wont run good long enough.
If I were in your position, here's what I'd start with......JUST TO MAKE SURE.
First, clean and examine all grounds and both battery cables and their connections.
A poor block ground will relay bad information from the sensors back to the computer.
Second, pull the computer/EEC/PCM/ECU (use your favorite term) and check for leaking/failed capacitors, cold solder joint(s), burned components or anything awry.
Just my thoughts on how I'd tackle this one.
Bob
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From: Denver Metro Area, CO
Yes, you should have all 3-digit codes, never a mixture.
Cleaning your connections and grounds is a good idea as they can cause weird problems with electronics, and looking inside your computer for leaking capacitors and burned components is also a good idea. It doesn't happen often that these computers fail but it's not unheard of.
Not from a car computer but some good illustrations of what can happen:
Cleaning your connections and grounds is a good idea as they can cause weird problems with electronics, and looking inside your computer for leaking capacitors and burned components is also a good idea. It doesn't happen often that these computers fail but it's not unheard of.
Not from a car computer but some good illustrations of what can happen:
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