I've been dealing with this problem for quite a while now. I have a '95 Si stock engine. The O2 sensor keeps going out. The wiring has been replaced and even a small oil leak in the area. The dealer is stumped too.

The longer I go the worse it gets. Starts out with an occasional check engine light (CEL) ... usually at high speeds. Then the engine starts running a little rough even when at idle. As it progresses, the CEL will come as I'm going down the interstate but as I get off and the engine idles down ... the engine will die. The emissions go extremely high (won't pass inspection) and the MPG drops.

I can replace the O2 sensor and it runs great for about a week and starts the cycle all over again.

Obviously the O2 sensor isn't the root cause ... any ideas?

Thanks,

Larry
Memphis
'95 Si

 

Are you running extremely rich when its running good? are you burning oil?

 

As far as I can tell, I'm not burning oil. The mechanic said there was a small oil leak in the area of the sensor that he thought might be the root cause of the problem. It was fixed but the problem repeated afterwards.

Is it running rich when running well? I'm not sure. I suspect it is. But I don't know how to verify it is.

It's the chicken or the egg ... is the O2 sensor going out because it's running rich and fouling the sensor or is the sensor failing and thus causing it to run rich?

Thanks,

Larry
'95 Si

 

Do you really care about the O2 sensor?.......If not, then just take the thing off.

I say replace the cat - and then put a new o2 sensor in........what kind are you using by the way?

If you're still having problems after that - get ghetto on 'em and put a resistor there. j/k

 

[
It's the chicken or the egg ... is the O2 sensor going out because it's running rich and fouling the sensor or is the sensor failing and thus causing it to run rich?

Thanks,

Larry
'95 Si[/QUOTE]I'd say the O2 sensor is getting fouled by the rich run. Vacuum leaks are the #1 cause of rich running engines.

 

Do I care about the O2 sensor? All I can say is that the MPG is down, emissions are up, and it isn't as zippy as it normally is. I can't get my plates renewed with the emissions so high ... unless AMCKEE in Collierville lets me use his address for my plates since cars in Collierville (a suburb of Memphis) aren't required to go thru inspection.

I have already asked about a vacucum leak as a possible reason for running rich. The mechanic reminded me that I have electronic fuel injection. If you have another source for a possible vacuum leak, I'll be glad to bring it up.

I wonder if Honda keeps a database for their mechanics to research. I can't be the first one with this problem but the Honda mechs seem to be going in circles. The good thing is that I had a talk with the service rep and they aren't charging me for new O2 sensors and labor every time.

Keep the suggestions coming. I'm going to take them to mechs since they seem to have run out of ideas.

Thanks,

Larry
'95 Si

 

Try cleaning your egr.

Sometimes other problems can trigger your o2 sensor cel to come on.

 

If that was your mechanics response to your inquiry about vacuum leaks, then he is an idiot. Vacuum leaks cause unmonitored air to enter the combustion chamber. Although we don't have mass airflow sensors on these cars, The O2 sensor will see this extra air, look at the Throttle Position, and since it is more closed than this much air would normally allow, will think the mixture is too lean and will richen it to compensate. This vacuum leak will also change the reference vacuum to the MAP sensor which controls fuel and ignition. It's also a good bet that your EGR ports are clogged. Any mechanic who doesn't think fuel injected cars are effected by vacuum leaks doesn't need to be working at Honda. Which dealer are you going to? I could take a look at it after work one afternoon and maybe pinpoint your problem for them. amckee@allabs.com Give me an email and I'll let you know how to get in touch with me.

 

Naturally I go thru the service rep. I've brought this up a couple of times. But still, the mech should know. I'd like to think that they have real mechanics there who can think past a diagnostic machine.

A clogged EGR valve would definitely explain the rough idling and it dying ... but shouldn't that happen consistently? It doesn't reach that point until the CEL starts coming on frequently.

When the O2 sensor is replaced, it runs great for about a week. Then it all goes bad. I start to notice a little less zip, a slightly rough idle ... then in a day or two, at high speeds, the CEL comes on. It continues to get rougher and less zippy. The CEL comes on more frequently and at continuously lower speeds. At that point, it usually will die when it idles down if I don't keep my foot on the gas and the RPMs up a bit.

Replace the O2 sensor and it's fine again. I believe something is causing it to run rich and foul the O2 sensor. The O2 sensor is a symptom and not the root cause. I can't seem to get the mechanics to look beyond it. Could be a bad EGR valve or vaccum leak that is starting the process? I don't know.

Thanks,

Larry
'95 Si
Memphis

 

A clogged EGR will not effect performance unless it is stuck open and your ports are not clogged. It is more an emmissions and economy issue. I gained back 5 MPG two weeks ago by thoroughly cleaning out my EGR ports and fixing one vacuum leak (boost valve). Any air that enters your motor through any place other than the throttle plate will dilute your post combustion gasses and will be read by the O2 sensor as a lean condition. It will then increase the pulse width to the fuel injectors to richen the mixture. This causes the build up of carbon on the O2 sensor which makes it think it's even leaner and so on. You answered your own question about the mechanic with one of your last statements. "I can't seem to get the mechanics to look beyond it." Just because a guy works for the dealer does not make him a good troubleshooter. Your problem does not seem that complicated. Just curious, how old is your mechanic, or should I say how young?

 

i do have the same problem but i'm no mechanic to know what's what...the problem on here is that everybody thinks they know it all but sometimes don't....your mechanic could be wrong but also the other people here too....what ecu are you using...?

 

amckee, your really seem know what your doing. I have almost the same problem. Idle surges from 1500 to 1800 when the engine is at right temperature and im sitting at a light. And i got a code for Engine coolant circuit high input? And I think my engine is running rich, a way to reduce that is cleaning and checkin the EGR, vacuum leaks, and throttle body, right? Hope you can help. Car and motor in signature.

Jay

 

Let me check on that code and see if thats a high resistance value. You know, the ECT sensor controls fuel mixture too. I'll get back to you.

 

Hi all -- Been reading this forum for some time now. Great resource. I too have an issue with my integra type r .. here is a postr from another forum. Any help appreciated!!

Error Code 41 - O2 Sensor

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Hey all -- Glad I can finally make a thread lol

I have a dc2r that is running incredibly rich at the moment - about 250km's to a full tank driving 'normally'.

My mechanic hooked up his diagnostic computer to see where the problem was, (i.e. if it were a failed o2 sensor, or other problems making the o2 sensor trip out). Essentially the o2 sensor seems to be giving readings throughout the rev range, and they seem to be right. I previously that day thought I saw a Code 5 (MAP Sensor) come up, but may have mistaken for Code 41 (i.e. still five engine light flashes).

The light came on after a 'showoff session' with a friend recently, the engine was operating above 6500rpm for the majority of the time and bouncing off rev limiter between gears.

The engine is also idling at about 1100rpm most of the time and sometimes drops to 900rpm.

I am running a full mugen exhaust and trust intake - Is it possible the Mugen headers have cooked the o2 sensor? Has anyone else experienced this?

I have tried to provide as much info as possible -- Your help is appreciated.

My mechanic also brought up the prospect of a vacuum leak.. Any common places? How do I detect?

 

Thanks man. I appreicate the help. Hope to here from you.

 

The cEL is for you O2 sensor correct i assume they checked?? and your car is not running right when the o2 goes bad because the computer uses the o2 to adjust the fuel to the car if it cant read the a/f level then it cant properly adjust adventually causing it to malfunction how many o2's have they gone through? it sounds like alot I highly doubt oil dripping on it would screw it up ( unless it got in the sensor part) but just look at your oil filter/ oil pressure sender is there any major leaks?check at the back of your valve cover to and see if there are any major leaks that are running down on to that area. I doubt this could be the situation but here goes anotehr possible problem, in the honda prelude for a bad ecu it throws a CEL 0 which means no flash but your Check engine light will come on and not report anything back. Unless they have a bad batch of O2 sensors something might be screwd up with your ECU(just another thought but i highly doubt it cause you say it goes to running fine). Check your ground wires, then check the wires to the O2 sensor. a bad ground can cause funky problems. Check your exhaust manifold before it gets to the o2 sensor to and make sure there are no major leaks ( major leak = less exhaust getting to the o2 sensor the computer starts playing with fuel) You should notice if there is a vacuum leak though your car will idle higher than it should (stock around 800? id start mine up and check but the damn thing will just shoot oil out the front crank seal hehe, might want to listen for a sucking sound) and might possibly idle surge every now and then, but a vacuum leak, yes it will make your car run richer beacuse the rpms will be higher but will not create a problem the ecu will compensate for the extra vacuum with fuel if your o2 is working properly and or ecu. As for replace the cat no need cat comes after o2 sensor that will do nothing. Thats all i can really tell u with out being there ill ask a person i know tomorrow what he thinks its pretty sad he knows practically nothing about hondas ( doesnt matter though once u been around cars as long as he has automotive technology becomes very similar) but i bet he will know he is one awsome asa mechanic/ builder. Also, 6E Lude and i know this doesnt pretain to much but i figure u would look back in this post i live next to camp lejune and drive a 93 prelude vtec boosted maybe we can ride together sometime i probably just confused you more than helped heeh but maybe that will clear some stuff up

 

quote: And i got a code for Engine coolant circuit high input? And I think my engine is running rich, a way to reduce that is cleaning and checkin the EGR, vacuum leaks, and throttle body, right? Hope you can help. Car and motor in signature. 6e lude ill look up the engine coolant circuit stuff tomorrow to late right now about to go to bed sorry hehe but is your motor tuned via computer software or do you have a FMU manully boosting fuel? if you are manually boosting fuel chances are you are running rich but it wont hurt anything. maybe gas mileage a tad emails hifivelocity@hotmail.com btw so you can get up with me since i live in jacksonville.

 

I think I'm on my 4th O2 sensor. The first time they just replaced the O2 sensor. The next time they spotted a small oil leak they said was dripping onto the O2 sensor. The wiring has been replaced twice.

I should have a little time this weekend to take a look at the EGR.

Thanks,

Larry
'95 Si

 

Vacuum leaks don't always cause a sucking sound. The MAP sensor, EGR diaphram, boost valve, IAB diaphram, cruise control, and brake booster are just a few examples of potential vacuum leaks that will be too muffled to hear. The IAC valve is also capable of dropping the idle back down in the event of a vacuum leak. If the leak is too great, the IAC can't handle it and the idle will begin to surge. the vacuum leak doesn't just effect idle. That same extra air is entering the combustion at all throttle plate positions and will always appear as a lean condition to the O2. A vacuum guage/pump is an invaluable diagnostic tool, and this mans problem won't be found without one.

 

Of course the problem wasn't major. It was the Engine Coolant Circuit Sensor. The reason why it was having a High Input was because it was unplugged. I went to take out the sensor and check it but when I went to unplug it, it was unplugged already *sigh* So I plugged it back in and now it purs like a kitten. No more rich air/fuel mixture and no more surging idle, idles at about 800 rpm's.

 

Sorry I was too busy to get back to you. Glad you found the problem.

 

I have a '91 Accord that have had 3 o2 sensors put in since probably May or June. Every time they have been replaced, the car runs great for about 2 weeks if I'm lucky. The last one most recently, end of August, was actually was from Honda. It ran beautifully after that one was put in, until Nov. 1 when the cel came on again. Started noticing the less zippiness, rougher idle, just feels less powerful. I check the engine light code and it's the same every time; 43, which per the Haynes manual is fuel supply system. When Honda checked it last time they said it for sure was the o2 sensor. I just took my car back to the shop today since the sensor is under warranty still, they said that something else has to be causing it, but I have to leave my car again. This is getting really frustrating being without my car. Any suggestions before I take it back and have to leave it again

 

Honestly, given that info, the first thing I would do is pull another ecu from the junkyard.

 

I have a 93 Accord EX that's on its 4th O2 sensor this year- very similar failure. Replacing the sensor causes the car to run beautifully for about a month or so, then one day the car will instantly begin chugging/bogging down when you try to accelerate (although it always idles fine). About the time you're forced to the roadside, the car sets the CEL and begins running fine. I've replaced the plugs, wires, rotor, distributor cap, recently had the head gasket, timing belt & water pump replaced, had the EGR passages cleaned, and checked my compression myself- which was on the low end of good, but for a car with 292,000 miles, I was happy. Also cleaned the IAC & fast idle valves. It uses a bit of oil, drips a bit of oil, but doesn't seem to lose coolant (since the head gasket was replaced). I'm at my wits-end. I love my Honda, but I swear I'm about ready to set fire to it.

Okay, I vented all that to ask why you pegged the ECU as a possible culprit, given that doing nothing but replacing the O2 sensor will bring things back into line for a while? (And in hopes a lightbulb will go-on for you and you'll be able to offer me some bit of sage advice) *fingers crossed*

BTW: O2 sensors have been BOSCH x2, then DENSO, then NGK......

 

Sometimes I think the cel should just stay on just so it would continue to run good without all the stupid intermittent issues which makes it so hard to diagnose.....Yes, why the ecu?