tveltman

I recently bought one of the motorsport X-pipes, and I noticed that there are two welded threaded bungs (one on each pipe) which I would guess are for oxygen sensors. The unit came with a plug so that you could hook your sensor up to one and plug the other hole. However, I am concerned that monitoring only one side of the engine might result in damage to the other if there is some unforseen problem with an injector or something. Can anyone think of a way to use two oxygen sensors (and thus be able to monitor both exhaust banks independently) while averaging them into one voltage for the sake of the LH unit? I won't be putting on the X-pipe for a while, since I am presently sorting out some unrelated engine trouble, but the pipe is just chilling out in my living room, and I was looking at it and got curious...

James Bailey

Given that the 928 batch fires all the injectors it makes little difference which 1/2 the engine it gets a reading from. The extra bung is for an aftermarket air fuel meter...

Mike Frye

I'm thinking if you lost a whole bank you'd know about it.

Jim, is the batch firing for all 8 or 4 at a time?

I don't know how you'd do it with a stock setup, but you can set it up in another way if you want to get tricky.

Maybe put in another bung after the 'x' for the stock setup and then monitor each of the individual banks with an aftermarket WBO2. Then you could have a gauge for each one or monitor them with a logging setup that would have an output trigger an LED or something if one bank suddenly went lean on you.

tveltman

Well, I was thinking that you would definitely KNOW if something was wrong with one bank, but the computer *wouldn't*, and so might not adjust the A/F mixture properly to prevent overly lean or rich conditions. Seems to me that overly rich causes a cat fire, and overly lean runs risk of knocking, neither of which you want to happen, hence my curiousity about averaging signals. Incidentally, I found a way using an op-amp. Evidently you can use them to add, subtract, and average. You can check out the google books link here: http://books.google.com/books?id=STz...ltages&f=false

9x8

AFAIK, injectors are organized into 2 quads.
At least it looks like that in the electric schematic.

Mike Frye

That's what I thought (which leads to the 'limp home' mode possibility in the S4s)

EDIT: READ Jim Bailey's post below, this is not limp home mode).

I'm just trying to get it all straight in my head.

Thomas,

I wasn't trying to be a wise ***, I was just sayin': What would you want to happen if the signal for one side went lean or rich? If it tried to dump more fuel because the 'average' AFR is lean, it would just be too much for the other side wouldn't it? I think it might lead to more problems than it would solve, and might even mask a problem that you'd otherwise see and easily fix.

If you do set it up with two narrow band O2s, please post a thread, that would be interesting to see.

Tampa 928s

I used one side for the WB the other for the NB for my S/c set-up.

hacker-pschorr

Three in mine:

1. narrow band
2. wide band
3. pressure gauge

PorKen

There's only one wire out of the LH for the injectors - they all fire at the same time, twice per revolution until ~4000 rpm/low load. At high rpm and load, the injectors are fired once per revolution, for a longer time, reducing the overall injector load (dwell time) somewhat. (It's not half.)

James Bailey

The injectors ALL fire at the same time same pulse width 1989> they pass through the "ignition moniotoring relay" which can shut off 4 injectors ,two on each bank ,which get their spark from the same coil. And running like that is NOT LIMP HOME MODE as the car should not be driven. Limp home is when the mass air sensor goes South and the engine will idle/ run slow on a stored default program just to get you off the freeway....

Mike Frye

AH! Thanks to both. Thanks for the clarification on 'limp home' mode. I got that part wrong (I should never comment on the S4 stuff, too many things I've never seen before). We now return you to your regularly scheduled O2 bung discussion.

tveltman

Mike, I didn't think you were being a wise-***. You are right that if there was somehow a problem with one bank, even the average A/F ratio would be problematic, however I think it would be less catastrophic than one side running normally and the *entire* fault going into one side of the engine. The factory has things configured to take an "average" of the two sides, and that was what I was interested in trying to emulate. You could still monitor both sides independently, but you would need to average them anyhow for the LH to function. Also I gather that the LH won't work off of a WBO2, so I could either drop a WBO2 in one side and the NB in the other (as suggested), or run dual NBs and average them, or plug one and forget it. I think it would be interesting to monitor the A/F mixture independently, as it might be an early warning sign of something going south, but certainly it can run without two.

Mike Frye

I see what you're saying and you're right it does kind of ASSUME that the other bank matches what's being monitored by the system.

Another option would be to add a bung like Hacker did and I did where the x comes together. He's using the third for a pressure gauge. I left the third one unused (but where the cross comes together) for use at the dyno since I have the stock O2 and a WBO2 for my Innovate logging setup.

Most of the WBO2 monitoring setups have a NB output, you could monitor dual WBs yourself and then use your averaging setup to average the NB output to give the computer an input or just add a third bung for the car and use the existing ones for independent WBO2 monitoring.

dprantl

I have been running my car off the NB simulation of my WBO2 for a year now (when the NB sensor crapped out) with no problems.

Dan
'91 928GT S/C 475hp/460lb.ft

IcemanG17

I also have three in mine....one for the stock narrowband O2 sensor to the LH....one for the wideband O2 to the techedge and one further down stream that is used for tuning and is plugged the rest of the time...