O2 sensor heater...what can affect it?

[Beej '86 325es]

I'm absolutely stumped. I've rechecked most of my sensors and wiring and I can't figure out why my car idles so rough.

I know my O2 sensor is not getting heated, and the engine idles lean.

What other components does the engine interface with that would tell the heater not to click on?

[328ijunkie]

coolant temp sensor.

[Sagaris]

I am sure nando would be the man to ask, but I do not believe the O2 heater circuit is anything more than wiring from the 12V source, a relay, then wiring to the O2 sensor. Within the sensor I suppose that the heater element could be damaged/broken.

I believe the O2 heater receives a constant 12V supply anytime the car is running, this is based off of people using the O2 heater wiring for wideband sensors and gauges.

[Beej '86 325es]

You're right about the widebands, that's how mine works. I'm not sure about OEM though, I haven't found any real conclusive info on when to O2 sensor gets its heat.

Here is what I've checked and replaced so far:
New O2 sensor
Checked O2 relay
Checked continuity on all O2 sensor and relay wiring
Done the wiring mod to address the Fuel pump relay backfeeding the O2 relay
New coolant temp sensor
New air temp sensor
Checked resistance/continuity on coolant & air temp sensors
New MAF
Checked TPS resistance/continuity
Checked ICV resistance/continuity

I've hit a wall...I just don't know what else to check. It's a custom engine build with custom software, but I doubt the tuning has too much to do with it at idle.

[butters]

What do you mean by rough?

My S50 was recently fully rebuilt, and I too have struggled with rough idle problems. Not bouncing revs or hunting, just vibrational that I can feel through my seat. Mounts are new and rubber, not poly. It idles pretty decent on cold start, but as it warms up the idle revs climb to 850-900 and the car gets more shaky at idle. I also get a CEL for TPS if the car idles for what seems like more than 20-30 seconds. I plan on replacing my coolant temp sensor, seeing as the startup routine is somehow backwards, as well as getting an intake smoke / pressure test among other things.

[328ijunkie]

Your TPS is prob dead and your car thinks your foot is on the gas. Try pulling on the throttle linkage shut while its idling and see what happens...

[Jason89i]

search: its been discussed and solutions provided many moons ago......

hope this helps. cheers, jason

http://www.r3vlimited.com/board/showthread.php?t=76548&highlight=o2+heater

http://www.r3vlimited.com/board/showthread.php?t=74958&highlight=o2+heater

[Beej '86 325es]

search: its been discussed and solutions provided many moons ago......

hope this helps. cheers, jason

http://www.r3vlimited.com/board/showthread.php?t=76548&highlight=o2+heater

http://www.r3vlimited.com/board/show...ight=o2+heater

I did this wire mod a few months back, hoping it would solve the problem, but it didn't change anything, unfortunately.

Is there a way to tell if a wire is being backfed with a meter or something?

[butters]

Your TPS is prob dead and your car thinks your foot is on the gas. Try pulling on the throttle linkage shut while its idling and see what happens...

funny you should say that... the story goes that at first when I finished the swap, it idled at like 1,100rpm. ICV was seized, open. I had actually not touched the idle screw, but my old TB didn't ever close on its own to rest on the throttle stop. I could (barefoot) pull the pedal and bring the rpms down. I tried playing with the throttle screw, and I thought I had a nice spot of not-too-much-vibration and not too high revs where the throttle did come back to the stop, but that got me where I am now, and it does the weird warm up sequence. I am swapping a used TB/TPS tomorrow (I hope) and will see what happens. I'm not sure if my O2 sensor is damaged, but I do know that the preheat works. When I initially got the car running, without exhaust, I was a dumbass and had the sensor hooked up leaving the plastic protector cap on the sensing end... and the cap melted. It came off the sensing end cleanly, but I'm now questioning if harm was done.

[Beej '86 325es]

Anyone know WHEN the O2 sensor would kick on? I would assume on a cold engine at idle it would be on, right?

[aplinweiss_is]

The o2 sensor signals are used once dme goes into closed loop. On cold starts the dme is in open loop until certain temp is reached.

I'm going through similar issues right now. The jump wire did not work for me either.
1991 318is M50 swap.

So to answer your question it's not used until operating temp.

Btw, did u live in metro east st louis?

[Beej '86 325es]

I did actually. I've been in Indy for a couple of years now. Did we meet up?

I've got my laptop open at the car now rechecking my whole C101 - x20 adapter. I'm thinking this adapter is crap.

[Beej '86 325es]

I've had some interesting finds today...

1) My harness adapter had the O2 relay wire (22 on x20) spliced with the the ignition wires. Fixed that, (6 on C101 to 22 on x20).

2) I have continuity between fuel pump and o2 relays pins 87 on both relays. This seems odd to me...I've already run the bypassed the E30 connector and run the fuel pump relay wire (GRN/VIO pin 21 on x20) directly to fuse 11.
EDIT: I'm thinking this isn't a concern. Even with the DME disconnected, I get some sort of continuity (weak or strong) between some of the fuel and O2 relays to half of the wires on the C101.

3) The O2 relay is clicking on as soon as I turn on ignition. I put a jumper wire to check continuity and it's sending power out of the relay...it clicks off a few seconds after the key is turned off.

But for some reason I'm still not getting 12V at the O2 sensor.

[aplinweiss_is]

I could be wrong but I still don't think continuity between 87 on fuel pump relay and the o2 relay is right. 87 is the energized output 12v to the o2 sensor. It doesn't make sense that the fuel pump 87 wire should come in contact with it?

Someone correct me if I'm wrong

[328ijunkie]

Ive done plenty of these swaps and never had this issue :dunno ;)