I need help my civic is running really rich. its a 98' civic ex with 4cyl 1.6l soch vtec D16Y8 all it has done to it is CAI, welded on can, no cat, header, wires, new plugs, new coolant temp sensor and im pritty sure the 1st o2 sensor is good. im probably missing stuff but give me some advice i only get about 25mpg and after idleing for a few min it suts out the exhaust. help me out thanks

 

How do you know it is running rich? Bad gas mileage doesn't always mean running rich. Ok first question is do you have a check engine light? Second question is how do you know the O2 sensor is good? Third question is what do you mean by thie "after idleing for a few min it suts out the exhaust"? Have you done all the proper maintenance? Have you replaced fuel filter, replaced air filter, checked your tire pressure, checked the plug gap before installing the new ones, replaced cap and rotor, cleaned out your throttle body, maybe even run some seafoam through the engine, cleaned your injectors? All of the things I mentioned, and much more, will contribute to bad gas mileage. The only real way you can tell if you're running rich is with a wideband O2 sensor. We need more information on your set up, what you've done and so on.

 

ive dont all maintanance the o2 sensor is good i just replaced it. the sut is when it idles for a few min in my drive way or whare ever it blows black sut out and leaves it all over the ground expecally if you rev it alittle just after sitting which sut is from to much gas and its not burning it all i have checked the gap have replaced the fuel filter 5000 miles ago air filter was new k&n mid summer tire pressure is at about 43 all the way around i have never replaced cap and rotor but it was new when i bought the car like 1 years ago i think we cleaned the throttle body at that time to but i will do it again tonight and i will run sea foam threw it today when i fill it up with gas. all i have done is whats on the first post. thanks for the help 97civicex thats great info please help me out some more if anyone can.

 

ok black sut,.. if I'm understanding you correctly is probably carbon deposits, not excess gas. If it was excess gas there would be a constant black smoke out of the tail pipe, or black smoke when you stepped on it. I would get a good cleaning through the entire system and see how that works for you. I would get a bottle of seafoam and put half in through the PCV or brake booster hose, and the other half in the gas tank. If you are going to do that put the old plugs back in for the cleaning and that 1 tank of gas. then put the new plugs back in once everything has been cleaned. If you don't have the old plugs anymore make sure you at least clean the new plugs after the seafoam treatment. get yourself a aerosol spray type of seafoam and clean the throttle body really good. Pay close attention to the area around the butterfly inside. I would also look into getting your injectors cleaned and balanced after the sea foam treatment. All of this should get your air delivery and fuel delivery back up to par.

Keep in mind that without the cat your exhaust fumes will be much stronger and there will always be unburned fuel out of the tail pipe, so you cannot go by odor either on the running rich thing.

 

Sounds good ill do that tonight i also realize that the fuems and that there will be a little stuff comming out but this is excessive. i will probably just put new plugs in the car when im done with it. thanks if there is anyother stuff i can do let me know

 

Oh yeah and how did the spark plugs look when you replaced them? This is the best way to tell how your engine is doing. How many miles do you have on it now? have you replaced your PCV valve lately? Keep an eye out for engine oil slug through the return line of the PCV system(from valve cover to intake tube) as that will also add to the sut in your combustion chamber.

 

couldnt it also be low octain? i think if you were to put 93, that would stop.

 

I wouldn’t think higher octane would eliminate this. Octane is the measure of gasoline’s resistance to spontaneously igniting. That is what we call engine knock or ping, which is due to pre-detonation. Unless his car is pinging, then that is a totally different situation and the black sut in the tail pipe would be the last thing we should be worried about.

 

i always thought when you mod your car you have to use better gas. if you dont you will run rich. thats just what i was told.

 

"better" gas is over rated.

Unless your car is knocking, run the lowest octaine you can.

Also "rich" is your friend..........

"lean" makes things go BOOM!