Thread: Regrounding the O2 Sensor

nothing a few swipes with a steel brush wouldnt remove then re solder. but screw that idea. here a better idea.


ere is my idea. stainless steel sucks to ground with...ok doesn't meen we need to ground directly from the sensor to the block.

ground the following:
1. primary to secondary, flange to block.
2. secondary to cat, flange to chassis.
3. cat to mid pipe, flange to chassis.
4. mid pipe to axle back, flange to chassis.

personaly, i think doing that would give the exhaust system very little resistance to ground.

since we are doing this because we are concerned about the o2 sensor grounding might as well toss 2 grounding straps on area #1 in my list.

None... well at least at the very minimal. If you don't believe me, ask Calum, the ECU guy.

Solder is not used in the engine bay because everything kinda moves around when you drive. Solder breaks off in time, so almost everything is crimped inside the engine bay. All the wires at least.

You should see the crimps that they use, some good stuff, you have to pay some good $$$ to get a crimper that will crimp wires like that.

You guys has been busy tonight.. But so have I...

Okay.. to your suggestions..
I was thinking that anywhere on the O2 sensor would ground the thing.. Wrong!! Attaching grounds to anywhere but the screw threads only gave about a 2% improvement. But, grounds to the threads makes anywhere from 30-34% improvement. So, attaching a ground to anywhere but between the header and the washers was useless...
Now, the strap is to thick to fit without causing a leak. So, you could rig-up something with a thin ring an attach that someway to the strap. But, with the heat and vibrations, Im not sure that would last very long. So, looked at my original plan again.

Grounding the header. Attached one end of the Grounding strap to a chassis bolt and the other end to the header. Testing at different locations on the header: Under the header bolt, under the AIV bung, clamped to the front surface, and clamped wedged between the pipes. All gave me only a 9-10% improvement with the bung giving the 10% and believe it or not, the header bolt being the worst. I was really surprised by those results; especially the header bolts.

Making the Header Connection. Next, I cut the grounding strap in half and also split the cut end about 3 inches in the middle. Now, the cable can be split and placed between the Header/Downpipe joint. For this test, I decided not to break the seal and cause an exhaust leak... So, I put a hole in each of ribbon ends for the bolts and bolted it down between the washer and flange on both sides. The test result was a respectable 26% improvement.

Making the Cat Connection. Then, I took the other half of the grounding strap and did the exact same thing at the Cat by attaching between the bolt head and cat flange on both sides. The test results gave me a total improvement of 38% which is great!! . Although its not in the 40% range, I think its close enough...

I took the car for a short ride with the Datascan hooked up.. The O2 sensor is performing much better at low rpms.

Tomorrow, I will drive this car to work with the Datascan connected and see if rush-traffic bogging still exists or have improved. My idle still sucks but Im too tired tonight to put in timing mode and make the necessary idle adjustments & timing checks.

So, it appears that the first round of testing has been a success thusfar..
Im going to pickup another strap tomorrow for more testing.

Cautious jubilation!!

your a ****in trip.

Good stuff DC Scotty, how do you check the for the ground rate? With a voltage tester?

I'm considering on getting the 4 wire O2 sensor and just saving the headache...

Maybe Something Like this?

i dont find it nessecary to do this. just get it tuned and BAM ! but it doesnt hurt to try and see how it is. my 2 cents. thing is though will it have any effect on the ecu as in frying it?

how would adding ground straps to the exhaust fry the ecu? the only thing that would fry the ecu would be a short and that would only happen if you grounded one of the o2 sensor wires.

dcscotty: what type of grounding strap are you using? i just looked at summit and they only have stainless steel straps, which i was under the impression that they were poor sources of ground compared to copper, gold, etc. I was thinking that a couple of these and some copper wire would be better but that might be overkill

i dont know. just cautious. anything thats electrical gives me shakes

Tuning is good, but this will be a bottle neck for any performance or MPG's. You know how if you have a bad MAF ground your car will barely run? Will this is pretty much the same...




Wiring the ground to the black or the white wires will fry the ECU, but not to the ground haha...

Good idea on keeping away from SS straps... once again we are doing this because our SS headers are not doing a good enough job of receiving a ground... so that just says that SS is not as conductive as the OEM header (iron?)

I am using a Digital Volt meter (DVM). And I test two ways: Measuring Resistance Return with the DVM set on the 200 OHM scale
and then by Measuring Voltage Drop using the 2 volt scale.

Im not sure if you can just use any O2 sensor for accurate AFM readings. So, using a 4-wire sensor may not work. I have sent an email to Bosch support but havent received a response yet. We need verification on 2 things with the 4-wire sensor: the AFM measurement is the same @14.7:1 and the voltage signal is in the same range (so the ECU can recognize the signal).



Yep, I know. I purchased a 18" Napa Strap (pn#711884) for $10.. Its a silver braided grounding strap and dont provide the material composition. But, it works... Looks exactly like the strap on my Q45 but longer.. Heres a picture of a shorter one on Napa website: http://www.napaonline.com/MasterPages/NOLMaster.aspx?PageId=470&LineCode=PHI&PartNumber=9150&Description=Battery+Cable+Grounding+Strap
I think the one in your link is probably overkill and alot more work.

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Update,
I drove the NX today in rush-hour traffic. After getting to operating temps, the datascan O2 sensor readings are quicker. The bogging is still there but much improved (may need to adjust the idle/Timing tonight). The RPM drop when stopped has disappeared completely . Thats a good thing!! And overall operation has improved as the car seems peppy and throttle response is quicker.

During lunch, I drove to Napa (12 highway miles each way). Same as morning drive. Overall the throttle response is quicker.

ClassicAddict: I only said "Cautious jubilation" b/c as we all know, sometimes the improvements only last for a short period and the old problem retuns.. Especially with the Bogging issue.. So, Im not getting too excited about my results until I clock some serious miles after this mod.