Hey all, I've done the search and it seems to most likely be the o2 sensor. Had a question about this thread I found: http://www.hondacivicforum.com/forum...de-43-a-83475/.
In one of the post he said that he fixed timing and pulled the "backup" fuse after replacing the o2 sensor. Why did he do that? I also just replaced my blow backup fuse right before this CEL code came up. Any help is appreciated! Need to get this fixed to get smogged.

 

BTW I have a 94 Civic EX bone stock with 180,xxx on it. The CEL came on after a few miles of driving also, just like the others in the searches I've done.

 

the o2 sensor does not make a "huge" difference on fuel economy didn't look in the book at the code but the drive for a few and then come on is usually a 02 seonsor. I had bad gas mileage and it was caused by the thermostat being stuck open. my ended up would go up to normal and cool back down into warm up mode = bad mileage hard to tell on the gauge that the needle was even moving much

 

The thermostat wouldn't throw a CEL, would it? I think my thermostat is messed up also. It stays open sometimes, causing engine to be cool at times. I didn't think that would contribute to bad gas mileage though. Well, I'll be doing a radiator flush and thermostat change. But yeah, about the CEL... Anyone else have an idea?

 

change your thermostat that is surely the reason for your horrible mileage, and if you have never changed your 02 sensor before then it is a great idea to do so regardless if its your check engine or not.

 

Yeah, I will be doing some tuneup on it. Changing the fuel filter, thermostat with flush, o2 sensor, oil change, oil pan gasket (looks to be leaking a little). I just bought this car. Need to get it ready to smog legitly.

 

fail!!

 

Bad fuel will also throw code 43

 

Excuse me ? you better know your **** cause its not fail and it does happen chump ill own you in knowledge.

 

Never heard of such tripe.

 

Please keep the discussion here civil and on topic.

 

Can you give us more information about that theory? My point of view is when the engine is finishing warming up, even if the car cool down a little, the revolution won't go up forever to compensate for the heat loss. I understand that the coolant is always cooled because of a bad thermostat during warm-up but will it cause such a bad gas mileage only because of that? Sorry to put your knowledge in doubt. I'm looking for more information.

Can you also elaborate on the fact that the O2 sensor is not playing a huge role on gas mileage. Also what would be then... the other role, if there is any, the O2 sensor should playing?

Thanks

 

The primary O2 sensor (in conjunction with multiple other sensors) plays a key role in allowing the ECU to determine the most optimal air/fuel ratio for both fuel efficiency and performance. So yes, it can affect gas mileage.

If the thermostat is stuck open, the engine will either take a very long time to reach full operating temp or never will. This can reduce gas mileage because until the engine reaches full operating temp the ECU remains in open loop where a predefined rich air/fuel ratio is used.

 

I never experienced a bad thermostat before... Can you tell me... If it's really hot outside making the engine to heat up very quick under a normal thermostat operation. Does an bad open thermostat will prevent the engine of reaching normal operating temperature under hot weather condition? Assuming that of course it will take more time to reach it? (I know I am going into detail )

 

Yes, yes, yes.

 

+1

 

The thermostat should be completely closed or almost that way if the car is at ambient temperature when you take it out. If it is wide open, it is almost certainly bad. (I have seen ones that have fallen apart.)

The only way I know to actually test one is to put it in a pot of cold water. It should be closed at this point. (If you have a thermometer, take readings as you warm things up and especially the temperature that it opens up. (It is possible to have one that opens and closes, but not at the correct temperatures.)

The in the dash temperature gauge supposedly should be somewhere between a third and half way up as the normal operating temperature is reached.

I guess I should take mine out as I am having the poor fuel economy problem as well. Considering the price of a replacement thermostat, it makes sense to just replace it rather than reinstall the old one, but it is still good to test things to find where the problem lies.

 

The idiot that I bought the car from never did any tune up. The thermostat was pretty much rotted away. Only the outer ring piece was left. The coolant ports to the IACV and FTIV was clogged with ****. But yeah, after replacing my thermostat, doing radiator flush, and replacing the o2 sensor, my car runs like a champ. Also replaced the spark plugs, air filter, and fuel filter too.