O2 sensor heater wiring 12V backfeed DIY

[boyd_dave]

The information used to come up with this DIY was derived from the following R3V’ers input:
Jason89i
Mike B.
Lof8
Rev Engineer
OrganicMechanic

They are the masterminds. the only reason I’m writing this up is because this mod was tremendously helpful for me but I had some trouble visualizing what needed to be done.

My car: 88 325is with 92 m50NV motor (lightened flywheel, dinan chip, e30 intake, custom exhaust)

If you are throwing a random o2 heater code (EGO heater) and/or have a shutter/lumpy idle after the car has warmed up and/or have some ease-on throttle hesitation at some rpm, this may be helpful to you. I got a great m50-m20 adapter from Gregslow318i and made this mod to it.

The pictures show it rigged up pretty ghetto, but I was skeptical so I just did a hack job. To be cleaned up later...
my e30 fusebox had a 15A fuse on the #11 fuse (fuel pump) but i had trouble finding a blade insert fusible link that was rated for 15A. all the ones and the auto parts stores are 10A. WTF! Anyway, I used a 10A fuse for testing and its been fine ever since.


After doing this mod, much like Mike B. stated, it didnt relieve my CEL coming on and off randomly. But after awhile and the long term trims had been set in the ECU, it stayed off for good. This is an awesome mod. Car idles really smooth and the acceleration is smoother.
hope this helps

Dave

[hoveringuy]

This seems to be a recurring problem with the DOHC swaps, I've had it occasionally and it went away on it's own.

I'd like to see a poll, of all DOHC swaps, who has had this problem?

[boyd_dave]

for the past month it had been coming on and off. sometimes off for 20 minutes, on for 5 minutes. sometimes off for hours, on for an hour. usually when cruising at a constant speed mid-rpm range or at idle.

always threw the 1264 EGO Heater code.

I figured a month was long enough to set the ecu, so i dont think it was going away for me. this helped.

[dirty30]

Whats this? A solution? HOLY SHIT!

Thank you so much for posting this!!! I'm trying it right away!!

[monkeytaco]

A. this is awesome.

B. I haven't had the problem yet, but only 350 miles on my swap. not sure if it is a problem on the 318...

[Fusion]

Whoa, that's the wire I recently found melted.
What is the shutter idle symptom? When the rpm falls nicely from ie. 3000 to 1000 and then rapidly from 1000 to 600, then stutters up to 750ish?

[trackjunkie21]

Can you explain this problem in more detail? This may just be the solution to my problem, I have the idle problem you speak of, but it feels gutless in certain rpm's

[MattM]

mine sometimes has a bit of throttle hesitation when cold... it always goes away after a few minutes..... i wonder.....

[Mako18]

I have had this issue for sometime now I finally decided it was time to do something about it.

I clipped the yellow signal wire from my factory o2. I did this at the ecu after tracing it with a voltmeter. I am using a 413 red label it was pin 13 (fyi all the o2 wires are in there own casing) I am now using the extra analog out from my lc-1 wide-band as a reference or signal for the ecu.

The reading before the signal swap was all over 10.5-21 depending on its mood, it was never consistent. Now the car runs between 14.2-14.8 nice and solid pulls allot smoother through the whole rpm range and it doesn't hunt for a idle when going into neutral at a light.

[trackjunkie21]

Will be doing this for sure then, may have found my problem

[Fusion]

Could someone explain this in layman terms?
Is the problem in the O2 relay and this mod feeds a reliable 12V? And can the green/purple wire be clipped a couple inches from the relay, thus being much closer and easier to connect to the fuse box? And why is the fuel pump fuse being used, not a different one?

[trackjunkie21]

Could someone explain this in layman terms?
Is the problem in the O2 relay and this mod feeds a reliable 12V? And can the green/purple wire be clipped a couple inches from the relay, thus being much closer and easier to connect to the fuse box? And why is the fuel pump fuse being used, not a different one?

[trackjunkie21]

The green purple wire seems to be the fuel pump wire, are the harnesses different between years? I know the vanos ones uave knock sensors and all but would those wires be different?

[Randomy]

I came upon this thread as a potential solution for what sounds like the same problem in my E36. But I am not exactly certain what has been done in the phootso, or neccesarrily what the result is of linking that purple\green wire to a 12v source at the fuse-box. Can some one elaborate, I would really appreciate it? Thanks.

[Jason89i]

this is somewhat like walking down memory lane.... its been at least 5-6 years. Its been fun to see some folks come and go. anyways, here is the original thread. the fix is seen in post 7 and 14.

http://www.r3vlimited.com/board/showthread.php?t=55208

some more interesting reading.

http://www.r3vlimited.com/board/showthread.php?t=76548

since i am feeling nostalgic...... go get a wiring diagram a do your own c101 adapter. this would end 60% of posts here on this forum and leave space for helpful posts..... like it was in the "good ol days."

off soap box. :)

continue on.



cheers, jason