D16Z6_owner

so i go out to warm my car up for 10 mins because its cold and when i get ready to leave i notice a pretty nice black spot on the driveway where exhaust is coming out. the car has 211000 miles on it. would that be poor compression or a bad cat. i already know its unburnt something or another but any imput would be great

gearbox

iTrader: (95)

might just be old cat that had some of the catalyst fall off, and they need to be hot to work properly. even new cars the cat wont work for the first few mins, and the ecu dumps alot of fuel to make it warm up faster. if you let the car warm up full temp, and then let it idle and theres no black stuff, its a bad cat.

skipbarber

iTrader: (34)

wait, it's actually leaving residue on your driveway? or a black smoke cloud?

D16Z6_owner

actual soot on the driveway. and my exhaust tip has a nice layer or the stuff caked on it too. and i barely passed emmissions

skipbarber

iTrader: (34)

something is causing your car to run way rich, and your cat is most likely dead. do you have any CEL's?

D16Z6_owner

no cel gas mileage is mid 20's in the city. pretty sluggish but i contribute part of that to it beaing an automatic. also when i look in my rearview when i get into vtec i see a cloud of black smoke......

skipbarber

iTrader: (34)

does it have a really smooth idle? if so, youve definately got a high fuel trim problem. something is making your car think it's getting too much air, so it fattens up the AFR with more fuel to compensate. but the problem could be an endless list of things. im surprised you dont have a CEL on, then again, what is your model year?

FGCOUPE

if the cat was plugged youd end up with a hot floor board and an engine that couldnt or barely run.
If its leaving black soot on your drive way it could be that its running rich or a sign of a near dead engine as it is a high mileage engine?
No CEL is definetly interesting to me however as the ECU/PCM should have picked up on something?? odd??

D16Z6_owner

idle is actually pretty good. sometimes when im at a stoplight i put my hand where the ebrake comes out and inside the space the air is a little warm. its a '93 civic ex sedan auto. (d16z6) i cleaned the vtec solenoid and IACV. apparently i have no EGR as i found as my honda savvy friend and i discovered..... acceleration is crappy. thats about all i can think of....

skipbarber

iTrader: (34)

yea, obd1 cars arent very sensitive to excessively rich conditions. but you probably have a bad sensor somewhere like your MAP or primary o2, high fuel pressure, leaky injectors, leaking injector seals, leaky exhaust, a small vacuum leak, and the list goes on. Something is making the ECU think youve got more air coming in than you really do, so it's throwing in more fuel to compensate. this is a likely case assuming all your sensors and wiring are in good condition, or something is 'forcing' the car to run rich, like an injector hanging open or high fuel pressure from a bad pressure regulator. Id get a shop to hook up a scan tool and make sure all the sensor readings make sense. otherwise, check all your vac hoses for cracks or pinholes. wiggle your injectors too, if they are really loose, chances are air is getting in. sorry i cant provide you a straight answer.

FGCOUPE

just wondering?

wouldnt a vacuum leak be the cause of a LEAN mixture??

skipbarber

iTrader: (34)

exactly, and the computer compensates to a lean mixture by throwing in more fuel. if the leak is small, the computer could be compensating enough that the motor wouldnt appear to have a vac. leak. if the leak is too big, the car will want to shut off, but we're talking brake booster hose sized leak. if it's small, like an injector seal, the computer could compensate enough for the smaller volume of air. and now that i think about it, this probably wouldnt drive the trims up far enough to make black spots on the driveway.

D16Z6_owner

thats interesting. what about faulty grounds? my interior and exterior lights pulse and sometimes the battery light flashes.

skipbarber

iTrader: (34)

your alternator belt might be a bit loose, or you might have a poor grounding issue, but i doubt it would cause the rich fuel condition.

FGCOUPE

id take it in if you dont have the tools such as:

Pull each plug out one by one checking the condition of the plug!
If one has excessive oil on it, dont assume its the cylinder gone bad right off the bat....it could be a dead plugwire?

Do a Compression test on all cylinders

slap a voltmeter on the battery with the car running, does it hold at 14.4v?
then hit the headlights, signals etc... does the battery go down but come back up compensating the losses? if not....Altenators shoty!
Otherwise maybe a new battery is in order?

Make sure connections, vacuum lines, etc are in good condition and installed right.

look for things, cracked, broken, leaky, etc...

Clean the TB out with throttlebody cleaner thats o2 safe.
Clean MAS sensor with it, this sometimes gets fouled after mileage and/or pre-oiled filters.

list goes on!

skipbarber

iTrader: (34)

honda doesnt use MAF..

D16Z6_owner

well how about the voltage regulator. the voltage is apparently going up and down causing the wierd light pulsing. could this variance of voltage be throwing the sensors off?

skipbarber

iTrader: (34)

The ECU regulates voltage to the sensors, but if it's REALLY bad it could still be causing some problems.

FGCOUPE

there is a sensor on my CAI pipe right before the TB, i believe thats a MAS.

skipbarber

iTrader: (34)

^ok sorry, i suppose i need to specify for some people. up until recently honda only use MANIFOLD ABSOLUTE PRESSURE SENSORS (MAP), but the introduction of the new FG/FA civic and the RDX brought in MASS AIR FLOW (MAF, not MAS btw) to the line up. but because the orginal poster has a pre obd2 car, i didnt think id have to be specific about this.

D16Z6_owner

so im leaning toward tps or map sensor. im pretty sure the alternator is getting ready to die and i was planning on a new cat sometime soon anyways to try to fix the emissions problem. is there any other sensor that could throw something off like this?

skipbarber

iTrader: (34)

yea, the primary o2 sensor could be fouled out, it most likely is if the cat is dead.

D16Z6_owner

so do you think its the o2 sensor (my car only has 1) and what should i do about the cat go to autozone and buy the one for 200 bucks or get a high flow for 100 *****i found a cat at autozone for 70 bucks. it says its CARB legal so would it be ok?