O2 sensor heater...what can affect it?

[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

[328ijunkie]

looks like a main engine ground...

[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

[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]

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]

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

[lolcantturn]

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

[nando]

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

[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.

[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.

[lolcantturn]

gonna place my bet on the Temp sensor too.

[328ijunkie]

ECU temp sensor. /thread
;)

[nando]

no - the heater must work right away! the O2 sensor doesn't give appropriate readings until it's warm. that's why they have heaters. for emissions reasons, they're basically always active, even if the O2 input isn't being used.

your lean condition could be caused by something else. vac leaks? MAF cars are sensitive to those..

[Beej '86 325es]

Jumped relay installed, check out my relay now! (below) The O2 sensor has voltage as soon as I start it now.

...But guess what...

It still runs very lean when the engine is cold. I wonder if the O2 isn't meant to turn on until after that long of a period. I'm going to evaluate some more, as I didn't time it tonight. But it behaved exactly as it did before...lean for 5-10 minutes then suddenly the A/F ratio clicks down to a normal level and idle improves. It appears the O2 heat isn't what's causing the issue.

[M-technik-3]

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.

OFF Topic: Having two different discussions will make this thread convoluted. You have a thread relating to your idle issue correct? Maybe It needs a bump.