Ok, I have searched for hours and haven't found the real answer I'm looking for. My friend said my car was smoking the other day, so I let him drive and got behind him. Sure enough, in the higher rpm range, it's blowing out black smoke very noticeably. Seems not to when driving normal. My car has Bosch Platinum (I guess)plugs with the 2 electrodes on the end. Would putting in regular NGK's possibly stop this? If the gap isn't perfect would it cause this? If not, what other suggestions do you have? By the way, my exhaust is a Greddy "Street Performance" cat back system. Don't know if this makes a difference with the smoke or not. Thanks everyone for any help you can give me.

 

I would try the plugs first. I had some Bosch Platinums in my car and it ran crappy, I put new NGKs in and it ran fine. :dunno:

If it doesn't work, let me know. I have another idea too.

 

cool. Let me know any other ideas you have. Oh, my car has a test pipe instead of a cat. Would that make it smoke at high rpm?

 

my 94 civic does the same thing when i punch it......but for me i changed the plugs, used fuel injection cleaner, and even tried going back to a lower octane gas...but it still smokes...any ideas on whats wrong or what to check?

 

Black smoke at WOT (wide open throttle) means that your car is running to rich. This is due to either too much fuel pressure, flooring the throttle at low RPMs (this is how the computer compensates so the engine doesn't ping or detonate), or just excess carbon being blown out of the exhaust that accumulates during normal driving. Fresh plugs aren't going to fix a rich running engine, but as far as recommendations go, the NGKs or Nippondensos are the plug of choice. I like the bosch platinum 4419s myself in my 93 si, but I had bad luck with regular or dual platinum bosch's. I recommend checking your fuel pressure (should be between 35 to 40 psi at idle with vacuum line attached to regulator on a 92-95 D16Z6). I assume your car is a stick and not an auto. Usually you will get bad gas mileage with an overly rich running engine. A lot of aftermarket computer chips will make the engine run way too rich... they are typically made for heavily modified engines. I've seen it more common to see black smoke from cars without a cat, since converters tend to light of any extra unburned fuel that comes from the engine. Under normal driving after about 500 or so miles with correct plugs in your car you will see a light tan to slight grey discoloration on the ceramic part of the plugs. If the're black and sooty, there's a problem. Also check your ignition timing. If I'm not mistaken, you should be running premium gas in your EX (D16Z6 ?). Let me know if you need more info.

 

You sound like you know a lot about what you are talking about, but I've been seeing lots of people say that any civic just needs regular unleaded. Anyone know the real answer? I'm not sure. Since I'm not spraying I run regular gas.

 

I agree with doctorshoc. He sounds like he's got a good bit of knowledge. I'm guessing from your setup, that's what's happening. The one point I will argue him on is that spark plugs could cause a rich like condition. If the plugs are carboned up, they will make the engine miss and act like it's running rich because it's not burning the fuel completely. New plugs could help this condition. Also, make sure your plugs are the right heat range. If they are too cold of a plug, they will foul easily, if they are too hot, they will burn up. You may want to stick the recommeded stock plug size in to see if it makes a difference.

As far as fuel goes. I don't see any reason you can't run regular. What octane is it? I wouldn't go less than 87 octane on your car.

 

I agree that if you have black plugs, you possibly might not get a good enough spark at the electrodes of the plugs and therefor not burn all the fuel-air mix in the combustion chamber, but this will leed to an overall poorly running engine even under normal driving conditions. Fresh plugs always make a difference - I've seen up to more than 4 horses gained on a dynojet with fresh plugs in an engine. As far as the fuel requirements for your EX (it would have a single cam VTEC engine), I'm pretty sure it needs 91 or better octane fuel (my D16Z6 in my 93 si needs premium according to the owners manual) When I first got the car I mistakenly put regular in it and it pinged like crazy, even though the timing was set properly. One thing I always notice in most honda motors is that they carbon up pretty heavily when I pull the heads off of them, especially when they're driven hard, or mostly in stop and go traffic.

 

I didn't think they put VTEC's in the 93 EXs. Maybe I'm wrong.:dunno: What year did the VTEC first come out? (obviously if he has a swap, then it's my bad)

But anyway, yes, if it does have VTEC, I would recommend >90 octane depending on where your timing is set at as well. If it's set at stock, I think >90 is just a waste of money. Other's will disagree or agree to this point. I havn't been persuaded either way as of yet.

 

honda put single cam vtecs in all 92 and up civic EXs and Sis, as well as Del Sol Sis. You can tell this by looking for the VTEC solenoid on the left rear corner of the head, and on 94 and up models having "VTEC" written on the valve cover. 92 and 93 models don't have the indication on the valve cover, they look like plain D16s.