O2 sensor heater...what can affect it?

[nando]

coolant temp sensor.

not unless it's bad enough to dump raw fuel through the exhaust...

the O2 heater circuit is always on. closed loop is enabled as soon as the *sensor* reaches operating temp - it has nothing to do with engine temp, really.

it only takes a couple seconds for the sensor to reach operating temp - that is it's purpose, to enable closed loop operation ASAP, even if the engine is still warming up.

anyway, are you getting voltage at pin 30 of the relay? if you are, and the relay isn't bad, the next suspect would be O2 sensor grounds.

the relay staying energized for a moment after you shut off the ignition is normal. there is a capacitor in the relay circuit of the ECU that keeps it powered for a moment. this is to keep the relay circuit from switching on/off due to noisy voltage inputs (voltage drop on the "start" pin to the ECU would de-energize the relay circuit).

tying pin 87 together sounds like they were trying to bypass the O2 relay altogether. not really a good idea because each relay is only rated for so much current, and you'd have both the FP and O2 sensor(s) running through one relay.

[Beej '86 325es]

not unless it's bad enough to dump raw fuel through the exhaust...

the O2 heater circuit is always on. closed loop is enabled as soon as the *sensor* reaches operating temp - it has nothing to do with engine temp, really.

it only takes a couple seconds for the sensor to reach operating temp - that is it's purpose, to enable closed loop operation ASAP, even if the engine is still warming up.

anyway, are you getting voltage at pin 30 of the relay? if you are, and the relay isn't bad, the next suspect would be O2 sensor grounds.

the relay staying energized for a moment after you shut off the ignition is normal. there is a capacitor in the relay circuit of the ECU that keeps it powered for a moment. this is to keep the relay circuit from switching on/off due to noisy voltage inputs (voltage drop on the "start" pin to the ECU would de-energize the relay circuit).

tying pin 87 together sounds like they were trying to bypass the O2 relay altogether. not really a good idea because each relay is only rated for so much current, and you'd have both the FP and O2 sensor(s) running through one relay.

Thanks for the good feedback, nando! That definitely gives me a few things to check out.

So if I understand correctly, the O2 sensor is always heated, but the DME chooses when to take readings from it or go into a closed loop?

...If that's the case, and I can't figure this wiring issue out, I wonder what would happen if I just wired 12V directly to it and bypassed the relay.

As far as I know, my pins 87 aren't wired together...at least they shouldn't be. I've swapped the two relays around and run the car, so I'm 99% sure that the relay is ok.

I'll check pin 30 on the relay tonight.

[nando]

there'd be no real point in bypassing the relay. you're going to have to use switched 12v either way. the relay is the most convenient source, and it's pretty simple. +12v to the energizing side (86), ECU provides a ground to switch it on (85), +12v to the switched side (30), +12v output to the O2 heater (87).

so either:
-the signal from the ECU to pin 85 of the relay is not working (it's a ground, check for continuity to any ground plane with the car running)
-there's no voltage at pin 86 of the relay (test with ignition turned on)
-there's no voltage at pin 30 of the relay (test with ignition turned on)
-there's no voltage at pin 87 when the relay is energized (test with car running)
-the ground to the O2 heater itself is open (check for continuity to ground at sensor harness)
-the O2 heater is shorted somehow (check for continuity to +12v at sensor harness, ignition on)

[Beej '86 325es]

Awesome, thanks. It should be pretty easy to figure out where the problem is when you break it down like that. I'm digging back into it tomorrow night.

[Beej '86 325es]

so either:
-the signal from the ECU to pin 85 of the relay is not working (it's a ground, check for continuity to any ground plane with the car running)

Continuity!

-there's no voltage at pin 86 of the relay (test with ignition turned on)

Got voltage!

-there's no voltage at pin 30 of the relay (test with ignition turned on)

Got voltage!

-there's no voltage at pin 87 when the relay is energized (test with car running)

:( No voltage here. I had the relay installed with a jumper so I could check.
I do have continuity from pin 87 to the sensor and I do have continuity from the BRN O2 sensor ground wire to chassis ground. I swapped it with the fuel pump relay and the car ran the same, so the relay should be ok, right?

Any thoughts are much appreciated!

[nando]

sounds like the relay is bad.

what happens if you jumper from pin 30 to 87? that should force the O2 heater to function. then check for 12v at the sensor. or just replace the relay..

[Beej '86 325es]

sounds like the relay is bad.

what happens if you jumper from pin 30 to 87? that should force the O2 heater to function. then check for 12v at the sensor. or just replace the relay..

Nandooooooooo!!!!

Jumpered 30 to 87 gives me 12V at the sensor. My wideband sensor is showing more respectable A/F ratios immediately! Still a little leaner than I'd expect, but much improved.

It's got to be just a bad O2 relay...which means my fuel pump relay may be bad also. I'm going to replace both just in case.

When I blip the throttle and it's cold it wants to die, but once I get it idling again, it's rock solid. I'm not sure if a bad fuel pump relay would have anything to do with that though, maybe just the tuning.

Many thanks! Auto wiring is not my strong-suit.

[nando]

nice!

yes, at this point - any original relays (be they E30 or E36) are suspect. I chased my tail for 2 years, trying to solve what I thought was crankshaft sensor synch loss/ground issues, fuel pump, signal noise, etc. etc. the whole time it was a $20 main relay. I'd replace all 3 if you don't know how old they are.. it's just not worth the headache!

I'm actually finding I like the wiring more and more. since I can do it by thinking instead of crawling around on the floor under a dirty, greasy car...

[Beej '86 325es]

Got all 3 on order, due in Friday. :)

Out of curiousity, what are the symptoms of a bad Control Unit Relay?

[nando]

the engine will shut down randomly, or not start at all.

[Beej '86 325es]

Well, I put in the new relays.

Good news and bad news...
Good news: the relay is clicking on
Bad news: not until after 8.00 minutes flat

I'm wondering if that has anything to do with the custom chip. I guess I'll call the tuner tomorrow. I'm dumbfounded.

[lolcantturn]

Beej can you explain throughly and in layman's terms how you did the 12V backfeed that was unsucessful for you? From my understanding, you just run a direct wire from the green/violet wire coming from the E36 harness to the fuse 11? I'm getting code 1264- O2 sensor heater.

[Beej '86 325es]

I did it exactly per that thread explains. I bought a blade insert from Autozone for about $5. It didn't really seem to change anything on my car though. But then again my 02 heat relay isn't working properly anyway. I've got an '86 325e chassis.

[nando]

8 minutes? yeah, something's wrong. it should turn on immediately.

[lolcantturn]

I did it exactly per that thread explains. I bought a blade insert from Autozone for about $5. It didn't really seem to change anything on my car though. But then again my 02 heat relay isn't working properly anyway. I've got an '86 325e chassis.

When I disconnect the green/violet wire from the E36 harness and the E30 harness and connect a direct wire from the E36 green/violet to the fuse 11 my car doesn't start anymore..am i doing something wrong?