Hi folks
I have a '96 F150, I6 engine. Auto parts store tells me there is an upstream and downstream O2 sensor. There is one towards the front of the engine and one towards the back, how do I tell which is which? Neither one seems further away in the exhaust stream, so both seem to be upstream.
Maybe there are two upstream and then another downstream?
Thanks!
-ben
What there really is, is one before the CAT and one after the CAT.
The exhaust comes out of the engine and into the exhaust manifold. There is a sensor mounted to the exhaust manifold, this is upstream of the Catalytic Converter (CAT). There is another sensor mounted after the CAT to judge if the CAT has cdone its job, this is the down stream sensor.
Depending on the configuration of the exhaust system, the number of sensors can vary. If the exhaust manifold is split so that 3 cylinders flow into one section and the other 3 flow into another section, then you can have two sensors upstream of the CAT. If the two manifolds come together ahead of the CAT, then they normally put the sensor just after (from the perspective of the flow) the point where the manifolds combine into one tube, and this allows 1 sensor to be used. If each manifold feeds the CAT separately, then there will be two upstream sensors, and if there are two CATs, then there will also be two downstream sensors -- a sensor for each CAT.
Ah, got it. Thanks. I have a split exhaust manifold, so two in there and one after the cat.
-ben
Jeff Strickland wrote:
Now, your '96 is OBD II compliant, and there is a data port along the bottom edge of the dash board, generally where your left leg rests while driving, and your local autoparts store (and eBay) offer code readers for a reasonable sum.
The computer will spit out codes that will tell you what sensor is giving readings that are outside of the expected range. If you haven't got a code reader, AutoZone will let you use theirs for free, or (depending on what state you are in) they will use the scan tool for you.
The upstream sensors are refered to as Bank 1 Sensor 1, Bank 2 Sensor 1, Bank 1 Sensor 2, etc. Bank 1 is the bank that contains the #1 Cylinder, and Sensor 1 or Sensor 2 defines the location in the exhaust system, with lower numbers being closer to the front, and higher numbers being towards the rear.
If your computer is not throwing codes, your sensors are okay and do not need attention.
Yep, checked this out. Advance Auto read them for me, though I was told by a mechanic they read the codes incorrectly. All three O2 sensors read a 'too lean' condition. The guy who read the codes told me all three sensors were bad - but a mechanic told me this is fine, it's a different problem altogether.
I took the mechanic's advice and pulled the fuel injectors. Replaced one and cleaned the other five. It's running better but not 100%, so I expect the remaining five need to go for better cleaning or replacement.
Thanks again for the help,
-ben
That is certainly possible. If ONE sensor read bad (only one code came up), I'd not hesitate to suspect a bad sensor. But, when all three sensors throw a code, I'd have to look at different stuff.
It isn't clear, does your truck currently have a lit Check Engine light?
On Mon, 04 Jun 2007 16:13:58 -0400, Ben Snyder rearranged some electrons to form:
Could also be a vacuum leak somewhere.
Good call!
A vac leak in the right place will cause a lean condition ...
On Tue, 05 Jun 2007 02:17:22 +0000, Jeff Strickland rearranged some electrons to form:
Yeah, it seems unlikely that 3 O2 sensors are bad. Then again, the OP might be burning lamp oil instead of gasoline.
They sometimes tend to shoot the messenger instead of trying to figure out the message.
If you have not already done so, you may get some improvement by cleaning the MAF sensor. It should be in the air pipe from the air cleaner to the throttle body. You will need an inexpensive set of tamper resistant torx bits to remove it. You can get 'em at Advance. Use a good residue free electrical cleaner and a cotton swap to clean the wires. Pictures are found on the net. The MAF is a component of mixture control by sensing the amount of air entering the engine. If it is sensing low because it is contaminated by the film produced by crankcase vapors over time, it will cause a lean mix and, many times, pinging like the timing is too far advanced or low octane fuel. Should take you about 10 minutes to clean it. You may also want to look up cleaning the throttle body and IAC while you are doing this. All free DIY work for the cost of a couple cans of spray cleaners.
Lugnut
Yup, it's on.
I can pretty much guarantee it's gasoline, but who knows. Local station skimping on real gas...
Anyway, thanks for the info guys. I'll check into vacuum tests, my father in law hopefully still has some equipment for this.
-ben
Awesome, thanks! I'll be able to do these this weekend.
-ben
Did you reset the codes then see which ones popped up again? Or are you working from the code list that you got from reading the codes the first time the light came on?
Sometimes a sensor will note an out of range condition and post a code but not set the Check light on. When the Check light finally comes on, you pull all of these codes and set to work fixing each of them. It might be better to write a list, reset the codes, then if the Check light comes on again, compare the codes you get at taht time with the ones you got earlier. Then set about to repair any code that is on both lists.
Since you are getting a lean condition from three different sensors, odds favor an actual lean condition more than a failed sensor. But, we been over that before ...
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