Oxygen Sensor Wiring

[Mike B.]

Well, I ran the bypass for fuse #11 (fuel pump) as Jason suggested with no change in O2 heater relay functionality. I still get no voltage at startup when idling and no load on the engine, but I get 12v if I run the car, pull over and check the relay while idling. I am beginning to think this is how the relay is supposed to work.

So, now I need to find why I have a stumble/hesitation around 2000 to 4000 rpm when the engine is warmed up and I accelerate with partial throttle. When I hit 4K it almost seems like a turbo coming on boost. I think I need to test the VANOS and the coil packs.

[Rocla]

The green/yellow wire is power from fuse #9 that is intended to go to the o2 heater - maybe to the fuel pump relay too. The big difference with the e36 harness is that battery voltage goes directly to it.

I've done some 50 e30 engine swaps, and most certainly that green/yellow wire doesn't feed fuelpump realy or o2 heating relay on any euro e30 engine I've seen.

In e30 engines fuelpump relay is also fed from battery current via engine main power relay.

[Rev Engineer]

I could be guilty of poor memory here, or be just plain wrong.. I don't want to spread disinformation. If my spreadsheet is wrong, I'd like to correct it. I spent a fair amount of time tracing out my car as well as reviewing every schematic I could get my hands on.

This schematic shows power from the o2 heater coming from fuse #9 on a green/white wire. I believe I found my m3 to have the same circuit but used a green/yellow wire. According to this schematic, this wire is o2 heater relay only and has nothing to do with the fuel pump relay.

http://www.autolib.diakom.ru/CAR/BMW/1989/325i/WIRING%20DIAGRAMS/fig02.pdf

[Rocla]

I could be guilty of poor memory here, or be just plain wrong.. I don't want to spread disinformation. If my spreadsheet is wrong, I'd like to correct it. I spent a fair amount of time tracing out my car as well as reviewing every schematic I could get my hands on.

This schematic shows power from the o2 heater coming from fuse #9 on a green/white wire. I believe I found my m3 to have the same circuit but used a green/yellow wire. According to this schematic, this wire is o2 heater relay only and has nothing to do with the fuel pump relay.

http://www.autolib.diakom.ru/CAR/BMW...RAMS/fig02.pdf

There might be differences between euro-us engines.

But for fuel pump relay, green/yellow 100% no.

[tjhartge]

There might be differences between euro-us engines.

But for fuel pump relay, green/yellow 100% no.

i concur with rocla on the wiring differences between euro and us versions, some euro didn't even have oxygen sensor wirings

i had to refer to at least a dozen different wiing diagrams, plus the fact i practically traced some wires just to confirm the colour codes on it, its the E30 that is abit weird somehow, but the m50 are all standardised ,but i could be wrong.....

but since R3V is a US based site, i think most if not all will post findings based on US e30s, just the people on the other side of the pond may have to look alittle deeper.....

[Rocla]

For cross referencing purposes: M20 late modell harness plug:

http://doni.eniten.com/BMW/M20_C101_wiring.jpg

[Mike B.]

Well, I ran the bypass for fuse #11 (fuel pump) as Jason suggested with no change in O2 heater relay functionality. I still get no voltage at startup when idling and no load on the engine, but I get 12v if I run the car, pull over and check the relay while idling. I am beginning to think this is how the relay is supposed to work.

So, now I need to find why I have a stumble/hesitation around 2000 to 4000 rpm when the engine is warmed up and I accelerate with partial throttle. When I hit 4K it almost seems like a turbo coming on boost. I think I need to test the VANOS and the coil packs.

UPDATE: Upon further review and driving time, the bypass for fuse #11 seems to have elimated my hestitation. Don't know why or how, but the engine is running significantly better now. Very strange indeed!

[Jason89i]

UPDATE: Upon further review and driving time, the bypass for fuse #11 seems to have elimated my hestitation. Don't know why or how, but the engine is running significantly better now. Very strange indeed!

ecu takes time to relearn / slowly calibrate to major adjustments.

ok, now yu have experienced what ive been talking about. ive had the same good results on ...well...a number of the swaps. check your brn/grn wire coming from the o2 relay. you should not be getting voltage now (as you probabily were before.)

i spent months on my first swap (2-3 yrs ago) to figure this out. got the fix, but never figured out the source of the back feed. lets figure this out.

ps. i have a peake scanner, would be bennificial to check for any codes.

cheeers, jason

[Rev Engineer]

I'm baffled here. I would really like to know what's going too. When I opened up my fuse box, I could visually trace that wire from fuse #11 out to the c101 connector. Unless it splices within the short bundle or at the c101 connector itself, I don't see how jumpering it could make any difference.

Could you guys describe the driveability issues in more detail? Also, someone with a stock e36 obd i could potentially put this issue to rest by letting us know how their o2 heater behaves.

[Mike B.]

When the car was cold, smooth pedal input would result in smooth power delivery. However, once the car was warmed up, that same pedal input would lead to hesitation and jerky power delivery. This occurred between 2000 and 4000 rpm. If I would stand on it, and go wide open with the throttle there were no issues. I assume this is because at full throttle the engine functions in open loop.

Here is an interesting thread from BimmerForum that basically describes my symptoms - http://forums.bimmerforums.com/forum...=increase+idle - symptoms which have now disappeared with the wiring bypass.

Is there possibly some cross-talk at the C114 connector coming out of the power dist. box?

[Rev Engineer]

Interesting stuff! I do not have those symptoms. Mine's running smooth at all throttle and load positions. Just poor gas milage.

Any chance it's related to the knock sensors? I recall that it could be fairly easy to get the two banks plugged in backwards.

[Mike B.]

The knock sensors were already wired when I got my engine (harness attached). So I don't think they are reversed.

However, I now have some time to take a deeper look at the wiring as the car is out of commission for the forseeable future. I had a rude introduction to a tire wall at the Autobahn Country Club - http://www.autobahncountryclub.net/. All of the drivers side panels need to be replaced.

One lap before the 'incident'...

[m_dudey]

I'd like to bump this thread as I am getting ready to put in my wiring harness. Seems Jason89i, Rev Engineer, and MikeB have put a lot hard work and effort into this.

I have noted Jason's fix by taking power from fuse 11 directly to the e36 harness through a fusable link to power the fuel pump directly.

But after reading this whole thread, which ended back in 2006, I can't help but wonder if you guys ever found anything more after almost 3 years have passed. Anyone ever chase down the root cause or the source of the problem?

[Lof8]

bump again, someone with the knowledge come forth. :)

[Yage30]

I doubt I'll get many answers on this old thread, but how many of you guys who have the CEL coming on are running cats before the O2 sensor?