So I've decided to mount my LS4U sensor after the turbo (and not in the crosspipe) after hearing the effects high pressure has on them, as well as too much heat.

...my question is can I get away with mounting the sensor on the downpipe, or is that too close to the turbo (will the turbulence from the hotside throw off readings)? The reason I ask is because I will be getting a new exhaust from the downpipe back, and don't want to have to go to the trouble of mounting a bung twice...

 

Did you see my post in the other thread? I provided pics of all the possible locations. My thinking is that directly after the turbo may be a tad bit to hot, but I have no real world data. The spot my sensor is mounted seems to work. I haven't compared it to a dyno though.

 

The only thing I'm concerned with in remounting is the distance away from the pistons. I know that has to be a factor, but I just don't know if it is a sizeable problem or not. Does anyone know the effects associated with O2 sensors and distance from the combustion chamber? If it is mounted too far away, I would think the ECU would be working with "old" readings, as the sensor would read the conditions in the engine much later than realtime (I assume it could be as great as 3 seconds depending on location). In that case, you would be running very rich the very lean for 3 seconds each transition; an example of that would be:

1. the engine is receiving too much fuel
2. 3 seconds later, the ECU gets the signal
3. the ECU leans the mixture
4. the engine leans out
5. then 3 seconds later, the ECU gets the signal, and the process starts over again

The ECU will always dither, but the faster the dithering, the better - right?
Maybe my 3 second rule is a bit exaggerated, but you get the idea. Am I out of my mind or is this a concern?

 

Oh and I forgot to mention that my WBO2 sensor will be driving my ECU.

 

as will mine...

 

Anyone on this topic?

 

I would strongly recommend that you keep the NB O2 sensor connected to the DME/ECU. The WB sensor is more fragile and doesn’t have the sharp response curve at Lamda=1.

Bosch did a far amount of testing to determine the correct location of the NB on this engine to pass emission tests. The correct location of the NB is not the same as the correct location of the WB.

 

beab951,

The WB setup I got from PLXDevices has a NB output that simulates the giant delta at 14.7, just as the ECU expects to see. I ended up mounting the WB sensor just a few inches past the downpipe, and so far so good! As far as I can tell, the response to change is immediate. When I'm cruising and take my foot off the accelerator, the signal goes to "air". As soon as I touch the pedal, I see the reading pop right back up to in the 14's. So I can't notice any delay at all.

 

Good to know it works...
But the accelerator test doesn't work through the O2 sensor... It goes through the TPS IIRC. I think the only way to tell the difference, would be to datalog the two signals (stock O2 sensor and the WBO2 sensor) then graph their signals vs. time. Do you still have the stock one in place?

BTW - How did you run the 6 wire cable into the cab?

 

I think the original NB sensor is more reliable. Why replace it with a simulated WB output if the NB signal already exists?

 

koolbeenz, I think you mistook my comment...or more likely I typed sloppily (sp?)

I just mean that as soon as I give the car gas, the change is immediately shown in the WB signal....when I'm off throttle but in gear (injectors turn OFF), the WB shows 'air'....I quickly floor it (injectors turn ON), and the WB immediately shows correct a/f ratio.

I use this bit of info merely to disprove the statement you made:

"I would think the ECU would be working with "old" readings, as the sensor would read the conditions in the engine much later than realtime (I assume it could be as great as 3 seconds depending on location). "

My WBo2 sensor seems to realize the fact that the injectors have been turned back on immediately after they turn on. Of course this is not measured, but just my human judgement call...as soon as I mash down on the pedal and hear the engine jump up...the a/f is reading the correct reading (i.e. not reading 'air' anymore).

I am in no way trying to point fingers or say "you are wrong"...I just wanted to share what information I have gathered and noticed. I am definitely learning here and am positive that I know nowhere near what others know on the subject

Oh, and I pulled the cable into the cabin right along side the DME wiring harness...fed it right into the DME/KLR area.

 

Oh yeah MB... I did read it wrong. That makes sense now. I'm glad you are proving me wrong - that is what I want to hear!

I have heard problems with some V8 turbo's that have miles of exhaust to reach the turbo. Thats why I brought it up.

When you said you passed the cable next to the DME harness, did you cut off the large connector, feed the cable through, then solder it back together? I'm having a hard time trying to visualize how you did that with the connector still on.

 

hmm okay...this time it's my poor descriptive typing....I just fed the line up into the cabin NEXT TO where the DME wire bundle enters the cabin....like...next to it...side by side my bad :-)

and beab, I don't know about reliability, but the WB is more accurate, and can simulate the 0 - 1v NB flip flop more closely to where it is supposed to happen (14.7)

 

LOL Sorry- I must be a little slow!
So you are saying you fed the connecter with the wire through with the DME wires. So the way I see it, you either passed the white connector in, or the black connector out... right?

 

Chris, great pics! yes I passed the white connector in. The black connector wouldn't reach all the way through, as I took care to keep far away from hot engine components.

Do you have the PLX Devices unit as well?