94 vette with 47000miles. car runs rich and has a slight miss through the exhaust. new opti spark, plugs, wires just installed. gets about 15mpg around town. exhaust tips are full of carbon. mechanic says no codes and vehicle is fine. says vehicle needs to be driven. vehicle runs fine except for this. im not convinced all is well. steve
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Re: 94 vette running rich andslight miss
Check intake manifold for leaks and also inspect all vacuum hoses also may be good idea to replace opti spark ignition module its located on the coil mounting bracket at front of right cylinder head if its been exposed to water , antifreeze, or moisture it can effect ur cars timing
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Very hard to say what is wrong, do you have any kind of car history like if the waterpump was leaking or replaced? If so like my 1994 vette the pump is in the front of opti-spark 99.9 percent of the time the water will ruin the opti. I have replacement mine many times, mainly because of the waterpump. if you replace pump you Must change opti-spark, its right there in open after you take out pump.it will save you 4 hours labor time.
You don't have to pull the fenders off. The passenger side is fairly easy. On the Drivers side it is more of a challenge. First, remove the serpentine belt. Then remove the belt tensioner which is held on with one bolt. From here you can get to the wires on the drivers side of the opti spark. On the plug end you may need to remove a couple of bolts or the ASR mounts but if you work at it, you can fish them through. Don't do them one at a time under the Alternator. Put them in the clip and run them to the Opti-Spark. It is not fun but with patience you can get the plug end take care of without busting too many knuckles.
You have a fuel injected car. Things that can cause too rich would be a bad altitude sensor like the map or mass air flow depending on which one you have.
Anything that would cause excess air to go into the exhaust system like a cracked exhaust pipe before the 02 sensor, or low compression, or a stuck open pcv valve, intake gaskets, throttle body base gasket.
Or a Throttle position sensor which is telling the computer you foot is on the gas when it is not.
Its possible you have a bad PCM,, or coolant temp sensor saying the motor is still cold as its warming up.
Its possible you have a vacuum hose somewhere on the engine with a big crack in it or its just inplugged and you dont see it.
But my first guess would be possibly a bad computer.
Try creating a big vacuum leak when its loading up. It should run better.
Also if you have an egr valve it could be stuck open a little causing excess air or an idle air control valve stuck open.
Does it clean up if you rev it up or does it blow black smoke reved and at idle. This could point towards the altitude sensor.
Make sure the spark plug wires are on right (propper firing order), and check the TPS sensor. Are there any exhaust leaks or vacuum leaks? Did you use the original intake manifolds and Holley throttle body? If not you need to replace the PROM chip with the one from the donor car.
ya its running very rich that why it makes that black smoke,this carbon is made because the sparks plugs does not make a good and sufficient spark,so i advice u to change the 4 spark plugs,also renew the air filter
I have seen on manyengines that using high performance plugs can cause problems like your's. If you used split-fire's or platinum 4 plugs change them back to OEM sytle plugs and your problem should be solved. If you used OEM plugs check that none are loose or cross threaded as this can cause a loss of compression.
Let me know what type of plugs you iinstalled and I can try to assit further.