O2 sensor heater...what can affect it?

[328ijunkie]

ECU temp sensor. /thread
;)

[lolcantturn]

gonna place my bet on the Temp sensor too.

[328ijunkie]

You should run pig rich on cold start. Not lean. Unless your ECU doesnt know what temp it is then its like whaaaaa and doesnt engage the cold start enrichment cycle.
It doesnt give 2 shits what the O2 sensor has to say at cold start.

[Beej '86 325es]

I agree with you, all signs seem to point to a bad coolant temp sensor. How prone are the coolant temp sensors to failure?

The reason I ask is because when I built the engine, I installed a new M/S50 sensor. I just did a continuity check on the wires and a resistance check at the sensor and all looked good. Plus I've never thrown a coolant temp sensor code.

The symptoms kind of sound like a vacuum leak, but since the engine runs vastly better when it's warm, and my mechanic did a "smoke test" and addressed any leaks, I'm ruling that out.

[nando]

a coolant temp sensor probably wouldn't throw a code unless it was failed totally open or shorted.

[lolcantturn]

I am monitoring this thread closely, please get that sensor and tell us how it goes!

[Beej '86 325es]

I'll give it a shot and report back.
Thanks for the feedback guys.

[lolcantturn]

I'm having just about the SAME problem. whenever I start back up the car, whether it was already at operating temperature or not, it will act very strangly, lack of power and bogs down and the idle is TERRIBLE. I cant move in any gear because the engine has no power to do so, if I add gas it will just want to make it die. I can play around with the throttle to get the RPMs up to like 3k and then bring it back down to idle and that will sometimes do the trick, or I can wait I believe it seems like 5 minutes and it will fix itself and the idle will improve dramatically and i'll have power again


I'm gonna wait for beej to solve this though as it seems he has so much more patience then me for this :D

One thing i've noticed though
I have an E36 harness. I never had this problem with my old M50NV car with an E34 harness.
Trackjunkie21 who seems to have the same problem as us has an E36 harness as well
And you do too right?
To check, if your ECU wires inside of your glovebox seem way too short, its E34. If it's long enough to have slack when inside the glovebox, its an E36.

[Beej '86 325es]

Sorry my friends, no dice. I swapped the coolant temp sensor and that made no change. I tested the one I pulled out and it tested great...held it in my hand and watched the value slowly drop as it should from my body heat.

I honestly have no clue what harness I have. I have to unplug the harness before I remove the ECU (I don't have enough slack to pull it out of the mounting brackets with it connected), but it's not terribly tight either. My O2 sensor harness came routed more towards the driver's side of the engine though. I had to run the harness backwards to get over to the O2 sensor, so I'm leaning towards E34.

I had a nice talk this afternoon up at Zionsville Autosport...just a couple of miles from my house. The owner is one of the pioneers of this swap and is very knowledgable of these engines...
He mentioned that the E34 harness tends to burn up O2 sensor wires from the ECU. He also said the coolant temp sensors rarely fail.

I think the next step is to try and fabricate some test harnesses for the coolant temp sensor and oxygen sensor and run them in place of the factory harness.

Thoughts?

[lolcantturn]

Burnt wires..like this?




I dont know which wires those are but...yeah..Tell me if yours are like that too. Check inside the harness cover that rests ontop of the engine

[328ijunkie]

looks like a main engine ground...

[lolcantturn]

Do you think that would result in the hesitation I have then? It is brown which is a ground

It isn't disconnected though, there is continuity but I bet its poor since its burnt

[Beej '86 325es]

Bad grounds can cause a million issues that are hard to track down. It seems like 50% of engine swap problems I read about are bad ground related. That burnt wire looks bad dude! :) I'd remove that wire and re-run it...maybe using a slightly thicker gauge wire. Continuity doesn't always mean it's good. Logically, it might seem like it is ok, but it could be a weak connection....which is bad for grounds.

I'm pulling off my harness connector at the ECU tomorrow to inspect.

[lolcantturn]

Let us know how looking through the ECU wires go..

[lolcantturn]

Ok so I've been looking through an E36 ETM at the 88pinout diagram..
I'm not an expert on wiring AT ALL but

It seems the wire that are burnt in that photo are the exact brown and green wires that go to the O2 sensor. They come off the O2 sensor in that four wire pack (Yellow, Black, Brown, Green, the four colors of the O2 sensor), and almost go to the ECU, but get rerouted back to the relay (which I think is weird). However the yellow and black go to the DME as pin 70 and 71- O2 heater
BUT, there is one strange thick clear wire that also comes off that four wire pack, and splits into the camshaft position sensor Pin 16 and 44 on the ECU

http://www.bmwtechinfo.com/etm/data/e36/e36_92.pdf

Thats the ETM

I'm not trying to hijack your thread, but it seems like we are having the same issues after all.