THSCC Forums

Does anybody know if you are allowed to swap in a heated O2 sensor for a non-heated one in the touring classes? Normally I'm capable of interpreting the rulebook myself but this seems to be a grey area. The exhaust is essentially free with the exception of the cat but does that extend to the O2 sensor as well?

The reason I ask is I think it will help my car run better under no/low load conditions. After installing a DC Sports header a couple of months ago (in the never ending quest to catch Ryan and Vincent! ), I've noticed that my gas mileage has gone down a bit and my idle has become a bit wonky (technical term!). The stock manifold had the O2 sensor about 6 inches downstream from the exhaust ports while the DC Sports header moved it to under the car ~2 feet from the exhaust ports. My current theory is that the sensor is cooling too much at idle and cruising which is giving the stock ECU a hard time. Does that seem reasonable?

Anyway, given that the O2 sensor has no impact on peak performance (it is completely out of the loop at WOT), it seems like it would be allowed but I wanted to make sure first. Note that I will be attending some national events with the car so I don't want to do anything that would make me protest bait. I've thought of having 2 sensors (one heated and one not) that I could switch back and forth for national events but that would be a big pain in the rear.

Any thoughts before I go harass somebody official?

Thanks,

Jim

My take on this. I do not think a heated O2 sensor will help. If your existing sensor is running too cold then you should be getting a check engine light on an OBDII (96-) car. You might want to check out the idle air controller if the car is so equipped. It might be getting dirty and sticking. You also might want to check and make sure there are no leaks at your header. It could throw the mixture off as seen by the O2 sensor.

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George Bright Member # 141
One of the youngest of the old farts.
Yes I voted against you joining the club.

Jim,

This isn't an official source (despite the site name) but chances are you can get somebody like Andy Hollis to chime in with a pretty darn useful answer. http://sccaforums.com/forums/default.aspx

Dick

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Dick Rasmussen

FS 50 2018 Mustang GT

Fixed that one for ya!

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02 Focus SVT
STF 9

George, the car is an '88 CRX which is OBD0. I'm sure I don't have any exhaust leaks as I've already thoroughly checked for that. The reason I think the O2 sensor is the problem has to do with what I observed when I first bought the car.

It had a bad O2 sensor (in the stock location) and I could easily tell when the ecu would try to go into closed-loop mode as the check engine light would come on and the car would hesitate for a second or 2. After the hesitation, I'm guessing the ecu gave up on the sensor and decided to run open-loop. If I let the car idle up to temperature, the idle would go wonky as soon as the ecu tried to go into closed-loop mode. As soon as I replaced the sensor, everything was cool and the idle was rock steady.

I guess I should define "wonky" a bit better. It's not like the idle goes crazy or anything. I'm just talking about a ~200 rpm fluctuation which some people may not even notice. The reason I think the sensor is cooling too much is the fact that I can easily tell exactly when the car goes into closed-loop mode again and as soon as it does, the idle starts moving around a hair. I don't think the sensor is suddenly running cold or anything but I think it cools just enough to give a slightly suspect output.

I tried swapping back to the stock manifold for a day and it everything went back to normal. I tried searching on honda-tech to see if anybody else observed what I have but no luck so far. Maybe I'm completely off base but I can't think of anything else it could be that I haven't already checked.

Thanks for the link Dick. I am aware of scca forums (and read them now and then) but I was hoping some of our ST* vets might know the quick answer. Buckley, you out there? I would ask Kevin Allen but he thinks everything is legal!

Anyway, I will contact the appropriate people and see if it is legal. I may pick up a heated sensor this week either way just to test my theory.

Jim

My CRX does almost the same thing, I just ignore it My idle has NEVER been right. I cant compare to stock either, I have always had my bling header.

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02 Focus SVT
STF 9

My guess is that it's not legal by the letter of the rules, for nowhere it states you can change an o2 sensor. I'm surprised none of the other CRX/Civic guys have complained about this, but I bet a lot has to do with that they're running a different ECU chip and have tuned around it. - AB

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'14 Toyota Sequoia Platinum 4WD
Super Westerfield Bros - '93 Integra - LeChump Du Jour
STX 93 - Scion FR-S

Where is your O2 sensor on your header? I was asking Scott Sawyer about it over the weekend but he has a different header than mine. His sensor is pretty close to the stock location and his idle is pretty darn steady FWIW.



That's what I'm thinking as well but I figured I'd ask anyway. I do know that DC Sports used to have the O2 bung much closer to the stock location but it was only reading off 2 cylinders (maybe even 1) at that point. The collector joining the header tubes is further downstream (right before the new sensor location) and while I don't know the true reason for the change, I'm guessing it had something to do with CARB and making it 50-state legal. But that is pure speculation...

I'm probably just picking nits but with gas prices where they are right now, it would be nice to have my 2-3mpg back!

If I get really bored, I may hook up a data logger to the O2 sensor in both locations and see if the output is truly different. That would certainly solve the mystery but I'm too lazy to do that at the moment and it is *way* too hot out there.

Thanks for the input guys.

Jim

If anybody actually cares (not likely), I did get final word that O2 sensors are essentially free in ST*. So much so in fact, there is a rule in the rulebook for it.

Jim