So i had a whole new exhaust system put on my 89 F150 w/351W and I'm running MAJORLY rich now. Plumes of smoke on hard acceleration RICH. And Major decrease in already pathetic gas mileage. I had new flowtech shorty headers put on, new "highflow 3-way cat" and a 40series flowmaster muffler. i brought it by my mechanic and he told me that the position of the 02 sensor was causing it to not get enough gas flow by it.
this is a sketch of the set up.
http://http://i113.photobucket.com/a...uastlayout.jpg
this is an exploded view of where the O2 sensor is.
http://i113.photobucket.com/albums/n...nupexhaust.jpg

The muffler shop tells me that they DID NOT move the 02 sensor to it's current position, rather they modified the stock set up and that the 02 sensor was in the same position as the factory set up. I don't recall how the factory set up is. I'm fairly certain it is not how it is now. If someone could please upload a picture of where their O2 sensor is i'd really appreciate it. I need to get this figured out, so i can go get my emissions done, and also so i don't have to stop by the gas pump every day! HELP ME PLEASE!

 

That's how the stock system is setup, but how far from the engine is the sensor now? Is the crossover tube actually getting exhaust gas? Is the sensor plugged in and not damaged? There's no need really for the sensor to measure both banks of the engine, it will work just fine plugged into one of the main sections of the Y pipe, but it should be as near the head as possible.

 

when measured the O2 sensor is withinline normal limits. It's t ofactory specs. But it reads LEAN, thats why it's dumping excess gas into the engine. it's not far from the engine, i'd say about the same as before.

 

I say replace that sensor and your problem will go away. When was the last time it was replaced anyway?

 

replaced march 07, the sensor reads within normal limits. it's resistace is fine, it's getting refrence voltage. why replace it?

 

yeah i agree, check to see if that crossover tube is even getting exhaust gas..

 

Here's a picture of a F150 with 351 factory exhaust. I've circled where the oxygen sensor is. It's hard to see the crossover tube so I've also posted a pic. of the exhaust on the Econoline. In that pic. you can see the crossover tube.

F150 with 351


Econoline with 351

 

could i check by removing the O2 sensor and running the engine and seeing if i can feel exhaust flow through the crossover tube? is that how i'd check the flow?

 

also why wouldn't it get axhaust flow?

 

Maybe the exhaust shop didn't drill it out, or drill it out enough.

 

When you first start the engine the oxygen sensor has to reach a certain temperature before it will give off a stable reading that the computer can use to adjust the fuel mixture.

Your truck uses a heated oxygen sensor so it heats up more quickly rather than waiting for the exhaust gases to get it hot. Probably takes a couple of minutes before the computer goes into closed loop.

So on a cold engine does you engine run rich?
Does it blow smoke out the exhaust?

If it does, it's not an oxygen sensor problem.

In open loop the computer adjusts the fuel mixture from a calibration table.
It does not use the feedback from the oxygen sensor until the system goes into closed loop mode. You can keep the computer in open loop by unplugging the wire connector at the oxygen sensor.

I'm not sure on your vehicle, but a code might set if the computer doesn't go into closed loop mode after the engine has been running for a certain period of time. Just ignore the error code. If you disconnect the oxygen sensor plug you can at least eliminate the oxygen sensor as being the problem causing the rich condition.

If the engine runs fine with the plug disconnected, then you could have a problem with the sensor, sensor wiring or the exhaust gas flow at the sensor.

 

F150xlt---- That is a very fine trouble shooting process you explained. Anytime you can eliminate a potential cause you are making progress.
Frank

 

Could their be a ground fault to the O2 sensor?
Did the shop reset the old codes out after completeing the work? That is all I know about it...
Brent

 

F150xlt. thanks so much for that help, i'm on my way outside to try that right now! keeping my fingers crossed!

 

well it smokes unconditionally. i start it up cold she smokes under hard throttle, she's warm and she smokes under hard throttle. Why would the O2 sensor read lean if it's not an O2 sensor problem. the crossover pipe is factory so it couldn' have been something the muffler shop did. unless the angles of the pipes somehow created an air pocket that just isn't getting flow. PLEASE any suggestions are very uch appreciated!