So i installed a midpipe and got rid of the stock cat, i already have a down pipe and cat back and i have a cheap bastard intake setup. I installed a PFC with a base map and i also installed a PLX WB o2. When i fire up the car it idles great and warms up and idles sweet at 1000rpm with 20 inches of vacuum, BUT the o2 states that it is running at 20 afr and the speedo jumps up to 20mph at an idle until it warms up then the speedo will stay at 0 ?? When i rev the engine the mph goes down to 0 and the PLX o2 will come down to 13 or so? There is no exhaust leaks! I do however have the air pump still hooked up. I am assumed that it only pumped air into the converter?? Am i wrong?? Is that why the afr's are way off or is the gauge wrong?? why is the speedo jumping up at an idle??

Thank you in advance this site rocks!!

MIKE

 

speedo can jump because of a bad ground, my tach does the same thing and it's irritating.
where did you plug in the wb sensor at? perhaps it needs to be callibrated or set differently, I know with the AEM unit you can have it set to a few different settings, check the instructions for it, it'll probably explain how to change this. did you join chuck's PFC group? You'll get a great set-up guide for the PFC, I highly recommend it.

 

Unless your air pump is somehow plumbed back into your exhaust, that shouldn't have anything to do with it. You're getting air somewhere though as it shouldn't idle at all that lean. Where's the O2 sensor installed?

 

My o2 is where the factory o 2 was installed at....

 

Well it looks like i did figure out the speedo part of the problem...... there is a ground that hooks on to where the factory ecu is mounted and i had just everything setting there for testing and that ground was the culprit for the speedo issue but the afr gauge does have me stumped?? I did check the settings over on the plx gauge and everything is in the proper setup?? and there is no exhaust leaks...further more when the throttle is just tapped to briefly rev the engine the afr goes richer where as a piston engine woud have had a breif lein spot ??

 

I just got a PLX A/FS and was told that installing the o2 sensor in the downpipe is to hot and would kill the sensor quick. Have you heard anything about this? I am planning on putting mine in the midpipe.

 

Wow, can't believe no one has had the right answer yet.

The factory airpump injects air to the main cat via the air tube and also into the stock exhaust manifold. At any time that the air pump runs, you will get crazy readings on your O2 sensor. The air pump runs at idle and light load.

If you're doing any tuning with the PFC, you can unplug the airpump. Actually, you can really just unplug the airpump since you have no cats any more.

To get rid of the airpump all together, you'll need to get an airpump idler pulley. Yes, you can do it with just underdrive pullies, but that's not the right way to do it. You get less contact on the water pump's pulley with underdrive pullies, which can lead to the airpump slipping and not running at 100%. Also, if you tighten the belt up enough so it won't slip, you will prematurely wear out the front stationary gear's bearing, which is also bad.

Dale

 

Yes it does say to run the sensor at least 24" away from the exhaust outlet but I cant understand why the stock sensor can live but the wide ban will not?? im going to give it a try for a bit but my plans are to take out the down pipe when i am going to have to port the waste gate and put one in the lower part of the down pipe out of the way.....

 

Ahh dammit. Guess I shoulda paid more attention to the stock setup.

 

i would also like to know why the stock o2 sensor can alive and well in ths stock location but a wb o2 sensor cant.. anyone have pictures of theirs mounted on the mp?

 

IIRC a WB O2 has to be around a certain temp. It has a heating element to regulate that. I don't know what kind of range that is, but being it's more sensitive, I believe this is the reason. A NB O2 on the other hand is a pretty dumb sensor relatively speaking and simpler in design.

Don't quote me, but IIRC that's pretty much the reason. I don't have pics, but mine is located about 8-10" from the front of the pipe as straight up as I can make it between the tranny and chassis.

 

WB's are significantly more sensitive than the POS stock narrowband. That said, my WB sensor is also in the stock location, but that's gonna get fixed once I can take the car out to an exhaust shop, ******* shitty weather.

 

When I had my O2 bung installed, I made a mark at the tail end of the downpipe just before the flange where I wanted it to go - checked on the car, made sure it would clear everything.

Took the downpipe to an exhaust shop, said "put an O2 bung here", $20 later I was out the door with a bung welded on. Easy as pie.

Also, I had that done before I sent it to Jet-Hot for the 2000 degree ceramic coat. Highly recommend that, BTW - makes a big difference in temps.

Not sure as to the "why" of it, but widebands can't live in the stock O2 bung. A few full throttle runs and you'll have error messages. Put it at the end of the downpipe and you'll be good to go for a loooong time.

Dale