j.kenzie@sbcglobal.net

Please see post #9
I thought I had a bad O2 sensor, but my passenger side engine bank is running much leaner than the drivers side.

Hi guys,
On my 1984 US Auto 928S, I have a wide band O2 sensor that I use to set my idle mixture. With my old NB Bosch O2 sensor I was running very rich in the 11-13 AFR range, and I could not do any better with my AFM mixture screw.
I checked the voltage on my Bosch signal wire, and was getting <0.1V. I decided to try running my car's ECU with the simulated NB signal from my WB. It is set to 0-1.-V output. When I connect the SIM signal to my ECU I can easily tune my idle mixture to the 14.2-14.7 range. It idles well with slight oscillation that seems to go with the AFR variation. All is pretty good.
I thought maybe I'd get a new Bosch NB O2 sensor and maybe get a more pure signal. (I have two sensor ports in my Y-pipe.) Well my new Bosch still only puts out 0.0-0.1 volts. Nothing really. Maybe a bad sensor. I get another one and same thing. So two new sensors and one or two old ones all saying no signal. That is measured between the signal wire and a good ground.
What is going on? I think I must be doing something wrong. The sensors are all warmed up. With my car running on the SIM signal of the WB, at an AFR of 14.5, I should be seeing 0.5 volts or so, but I see 0.05 or so.

Thanks for reading,
Dave

Ducman82

Nb don't have a heater. So they do a "best guess". Stick with the wb output

dr bob

Man with more than one watch never knows what time it is...

So you have two NB sensors telling you one thing, and a single WB telling you something different. My faith might go with the two NB sensors.

The NB in my '89 has a heater.

j.kenzie@sbcglobal.net

Thanks Dr. Bob. I actually have two wide band sensors, and two or more heated narrow band sensors acting just as I described.
Dave

Hold On

Unplug the stock NB O2 sensor from your system. Plug is in fuse panel area. I think it was green. The car will run so much better. The NB will only fight to keep car as lean as possible. That`s what the sensor/ECU does in that model yr. That's a problem if you are supercharged. Plug the WB into a WB meter and use it from now on to monitor what is going on. Also you will find the idle mixture screw can be useless with the supercharger. There is enough air being pushed thru the AFM to push the door open past idle position. Pull off the intake pipe somewhere in line and feel the force of the air moving thru at idle speed. You will be amazed.

j.kenzie@sbcglobal.net

Thanks. I actually have a 3 position switch installed to feed my Ljet brain either WB SIM, NB, or no signal. For the NB and no signal, my WB reads AFR's in the 11-13 range. Car runs fine but 11 is pretty rich. When I run off my WB SIM signal I get fairly normal AFR's of 14.5 at idle going to 12 to 13 or so at full throttle.
Car runs fine either way. Would you still run open loop?
Thanks again,
Dave

hacker-pschorr

Do any of these connections have solder on the signal wire? O2 sensor wires should be crimped only, per Bosch.

We've tried many times to run a stock brain off the NB signal from a WB. Always something wonky with it. Stick to stock NB to stock brain and use the WB for tuning & monitoring.

If the NB is working and installed correctly, and the mixture is not right per the WB, fix the problem (AFM, temp sensor, wiring etc...happy hunting)

Also how is the WB powered & grounded? The ground wire should go directly to the block, nothing in-between. To power the unit I would run straight to the jumper post. These things are extremely sensitive to voltage.

I also added a heated NB to my 81 just to rule out any issues with a non-heated unit.

j.kenzie@sbcglobal.net

Thanks, Hacker.
No solder on signal wires. I get 0.0 volts on two different NB sensors on my PS Y-pipe arm, while I'm reading AFR of 14.5 on my WB on the DS Y-pipe arm. My WB SIM output is 0.4-0.6 volts. I have another WB that I am going to install on the PS y-pipe arm tomorrow, just for fun.
Thanks again.
Dave

j.kenzie@sbcglobal.net

Hi guys,
Looks like nothing wrong with my sensor. One bank of cylinders runs much leaner than the other.
I had an extra WB sensor so I added a second one to the passenger side. The car's ECU is running closed loop off the DS of my Y-pipe from its WB sensor.
The two WB sensors agreed when used on the DS before, so I have no real reason to doubt their results.
The drivers side of the Y-pipe is showing an AFR of 14.5
The passenger side Y-pipe is showing and AFR of 17.5.

I hear injectors clicking normally at all eight cylinders. The car seems to run fine. The injectors are pretty much original.
What do you think would cause this side to side discrepency?
Thanks,
Dave

Ducman82

you are correct Bob. i was just to use to seeing single wire NB, vs the WB multi wire...

j.kenzie@sbcglobal.net

Please see post #9 and new title of thread. All my sensors probably OK. Half of my engine running lean.
Sorry, and thanks for reading,
Dave

Speedtoys

That makes no sense, unless you have a bad injector(s) on the pass side leaning it out.

The 928 batch fires, so every injector is fired at the same time..always..all 8 in unison..once per RPM. (I think).


Swap WB sensors, does the lean reading move too?

j.kenzie@sbcglobal.net

Both WB sensors read the same on the drivers side. I bought the second one thinking the first was wrong, but they agreed perfectly. I can swap them, but it seems real. I used the passenger side for my NB and since it gave such a low voltage, I thought the NB sensors were bad. However they do seem to agree with the WB's.
I thinking about a vacuum leak somewhere on the lean side?
Thanks,
Dave

hacker-pschorr

Yup, bad injector(s) - agree with the above, swap O2's just to be sure.

This happened to my 81 & Scirocco. Simple test, while the engine is idling unplug / plug back in each spark plug wire. The "bad" cylinder will offer little to no change at idle.

It could be bad spark plug since a non firing plug will also offer a lean condition since raw fuel being pushed out of the cylinder is not metered by the O2. The O2 is simply picking up the non combusted air.
This would result is a soggy spark plug.

My scirocco with one dead injector was idling at 17-20:1 on the WB.

j.kenzie@sbcglobal.net

That makes sense. I measured exhaust temps on both sides of my Y-pipe. Lean side (PS) was 260 F., while the normal side (DS) was 400 F.
I will swap the WB to confirm AFR measurement.
Thanks,
Dave