Primary O2 Problems after Euro Header Install

[ATB88]

I kept getting SES due to my O2 wires touching headers (it also didn't exhibit issues right away.. it became an issue at a trackday). Apparently, they are routed differently on EU cars so I had my shop reroute them via the same way they did.

This is an encouraging data point. Thanks! Did your O2 sensors die permanently like mine? It would be great if this were the solution, as it sure seems to be the simplest.

Does anyone have any info/pics on how the O2 sensors are routed on a Euro car? Otherwise I'll probably just route mine like Cubieman's. I can't imagine it matters at all as long as the wires aren't touching anything hot.

[zivagolee]

This is an encouraging data point. Thanks! Did your O2 sensors die permanently like mine? It would be great if this were the solution, as it sure seems to be the simplest.

Does anyone have any info/pics on how the O2 sensors are routed on a Euro car? Otherwise I'll probably just route mine like Cubieman's. I can't imagine it matters at all as long as the wires aren't touching anything hot.

I believe I caught it in time and my shop was able re-route it via the drivers side (?) and plug it back in w/o having to get new O2 sensors. So far after a couple of more trackdays.. no issues.

[Cubieman]

Thats right, all 02 sensors/EGT are routed drivers side of the engine on Euro cars. I routed my post o2's for the euro cat setup driver's side but left my pre-cat sensors passanger side but "zip tie re-routed", I have never seen an actual picture of how the pre-cats are routed under/around the back of the engine from underneath on a Euro setup. I know how they route the post cat sensors though.

[zivagolee]

Thats right, all 02 sensors/EGT are routed drivers side of the engine on Euro cars. I routed my post o2's for the euro cat setup driver's side but left my pre-cat sensors passanger side but "zip tie re-routed", I have never seen an actual picture of how the pre-cats are routed under/around the back of the engine from underneath on a Euro setup. I know how they route the post cat sensors though.

Great.. my memory is still intact! :-P

[ATB88]

Update: I forgot that I still have a set of post-cat O2 sensors (the ones that came on the car when I bought it, had been on it for 73k miles and 18 years until I pulled the catted headers out on Thurs) that haven't yet been exposed to whatever has been happening that killed all the other ones, and therefore should still be functional despite having a lot of mileage on them. I pulled them out of my old catted headers, shaved down the connectors so they'd fit into the pre-cat harness connectors, screwed them into the cats, and sheathed both set of cables in heavy duty heat shielding I got from Autozone. As always after putting in "new" (in the context of this problem) sensors, the primary O2 voltages came right back to life and work perfectly again. Secured the wires with zipties to ensure they won't go near the headers, and went for a long, hard drive. So far, so good. Can't say it's definitely fixed yet, though, because I thought the third set of O2s that I threw in fixed it Saturday night just to have them conk out Sunday morning. But these sensors have lasted longer (in driving/run-time) than any others so far, so it definitely feels like a step in the right direction. Would be funny if in the end all it took was a set of 18 year old O2s to fix the problem Felt great to drive my newly airbox'd and header'd car again after 5 days of misery.

Let's see what tomorrow brings!

P.S. It's not even just the wires touching the headers that you have to worry about. My car has the MK20 DSC in the drug bin, so I've got ABS/DSC lines routed by the headers. I ziptied the cables of the third set of O2s that I installed to the DSC lines to keep them away from the headers. Turns out these lines pick up a ton of heat from the headers and themselves get very hot. Seemingly enough to kill the O2s again. That is, if heat on the wires is indeed the problem, which is what seems to be the case at this point.

[Icecream]

Update: I forgot that I still have a set of post-cat O2 sensors (the ones that came on the car when I bought it, had been on it for 73k miles and 18 years until I pulled the catted headers out on Thurs) that haven't yet been exposed to whatever has been happening that killed all the other ones, and therefore should still be functional despite having a lot of mileage on them. I pulled them out of my old catted headers, shaved down the connectors so they'd fit into the pre-cat harness connectors, screwed them into the cats, and sheathed both set of cables in heavy duty heat shielding I got from Autozone. As always after putting in "new" (in the context of this problem) sensors, the primary O2 voltages came right back to life and work perfectly again. Secured the wires with zipties to ensure they won't go near the headers, and went for a long, hard drive. So far, so good. Can't say it's definitely fixed yet, though, because I thought the third set of O2s that I threw in fixed it Saturday night just to have them conk out Sunday morning. But these sensors have lasted longer (in driving/run-time) than any others so far, so it definitely feels like a step in the right direction. Would be funny if in the end all it took was a set of 18 year old O2s to fix the problem Felt great to drive my newly airbox'd and header'd car again after 5 days of misery.

Let's see what tomorrow brings!

P.S. It's not even just the wires touching the headers that you have to worry about. My car has the MK20 DSC in the drug bin, so I've got ABS/DSC lines routed by the headers. I ziptied the cables of the third set of O2s that I installed to the DSC lines to keep them away from the headers. Turns out these lines pick up a ton of heat from the headers and themselves get very hot. Seemingly enough to kill the O2s again. That is, if heat on the wires is indeed the problem, which is what seems to be the case at this point.

I hope that fixes it for your sanity. Would be odd. When I did mine the routing I choose left them very close to the headers and they are still good. Also, don't you mean precat as those are the ones the car needs to run properly? The post cat O2's are the ones that you don't need.
Also, for another sanity check, websites list o2's as front and rear and pre and post. Front and rear is referring to header position only, not o2 location. Obvious I know but your issues you are having are unusual.

[ATB88]

I hope that fixes it for your sanity. Would be odd. When I did mine the routing I choose left them very close to the headers and they are still good. Also, don't you mean precat as those are the ones the car needs to run properly? The post cat O2's are the ones that you don't need.
Also, for another sanity check, websites list o2's as front and rear and pre and post. Front and rear is referring to header position only, not o2 location. Obvious I know but your issues you are having are unusual.

Yeah, honestly, the change in my mood and general life outlook in the last 3 hours has been huge. If it breaks again idk, man, car might end up in the ocean. If this really is a tune problem, figuring it out could get ugly.

I do agree that it's kind of odd if this was the problem and solution. Short of the wire sitting directly against the cat for a prolonged period of time, I can't see heat from being near the headers killing the wire. And if that did happen, I'd at least expect to see some sign of melting/burning on the sheathing. But the sheathing actually looks totally clean on all 6 "ruined" sensors. Moreover, if this were the problem, I would expect that if I continuity test the signal wires on the "ruined" sensors, I should get open circuit and a large resistance. But I took some of the "ruined" sensors and continuity tested the signal wires end to end with a multimeter, and always got continuity with a 2 ohm resistance. The sensors *seem* totally fine until you plug them into the harness and they give signals on the order of 10mV. Doesn't quite sit well with me, but, I also can't argue with the results so far with my extra heatshielded cables.

And I do actually mean post-cat O2s. I re-purposed my old post-cat O2s for use as pre-cat O2s. All four O2 sensors are actually completely identical regardless of their position. Only differences are in the shapes of the connectors, so that you don't confuse the wires and plug, say, pre-cat bank 1 into post-cat bank 2's harness connector. So, that means if you take a post-cat O2 sensor and shave the shape of the plug down, you can plug it into whichever bank you want and it'll work perfectly (provided you orient it correctly when you plug it in so that the signal wires go on the signal pins etc). I did this because these 18 year old post-cats are effectively worthless, and I was so anxious about this and generally impatient that I wanted to try and validate my latest hypothesis before the new pre-cat sensors arrive tomorrow. This has the added benefit that if these sensors still took a dump, I'd have time to re-evaluate my gameplan before installing the new fresh sensors that arrive tomorrow and ruining those too.

For the record, of the 6 O2s that I've burned through so far, 4 were "officially" pre-cat O2s installed in the correct banks. 2 were brand new post-cat O2s whose connectors I shaved down for the purpose of hypothesis testing. The current two sensors installed and functioning beautifully are 18 year old post-cat O2 sensors.

[zivagolee]

You got genuine bmw or bosch sensors, right? not some other brand or anything?

[ATB88]

You got genuine bmw or bosch sensors, right? not some other brand or anything?

Yes sir. Every single one of them, either Bosch from FCP euro or original BMW (Bosch) that came on the car from the factory. Quadruple checked all of the part numbers too. Of the 6 failed, 4 were FCP Bosch and 2 were original BMW Bosch. The two currently functioning are original BMW Bosch.

If the cable-routing fix lasts long enough to really seem like it worked, I think I might run a test where I move the cables closer to the headers, monitor the voltage signals, and see how long it takes them to fail. This would prove it beyond any shadow of doubt. But I want to get the car running reliably first.

[zivagolee]

Yes sir. Every single one of them, either Bosch from FCP euro or original BMW (Bosch) that came on the car from the factory. Quadruple checked all of the part numbers too. Of the 6 failed, 4 were FCP Bosch and 2 were original BMW Bosch. The two currently functioning are original BMW Bosch.

If I the cable-routing fix lasts long enough to really seem like it worked, I think I might run a test where I move the cables closer to the headers, monitor the voltage signals, and see how long it takes them to fail. This would prove it beyond any shadow of doubt. But I want to get the car running reliably first.

Cool, just making sure. Let's hope that's the issue and get your car running reliably!

[ATB88]

Drove some more today and it continues to stay fixed! So I went ahead and installed proper new fresh pre-cat O2 sensors, gave the cables some extra gratuitous heat protection, and routed them the same way cubieman did.

Thank god, was on the verge of a nervous breakdown.

[zivagolee]

LOL these cars does do this to us.. yet we love them