So about a week ago I came home with a '94 Z28. I picked it up in a part of Ohio that does not have emission testing. I need to test it where I live and it failed because the Hydrocarbons and Carbon Monoxide levels were too high. Both of these are related to unburned fuel in the exhaust. The car has a tune from PCMforless because it has Kooks longtube headers and y pipe with a Flowmaster muffler and a K&N cold air intake. I believe my tune is too rich because I can smell a bit of fuel in the exhaust. I cant afford to send the PCM off to get it tuned again, and I dont feel comfortable doing myself yet. Is there another way I can reduce these numbers, or get around the car being rich, ie hotter plugs or something? Even something temporary that will work long enough to get it tested and pass. I was thinking about unplugging a couple injectors. This way the cylinders without injectors pulsing will have air moving through them still and that will add more air to the exhaust making seem less rich. Any thoughts?

 

Make sure all the plugs are firing. Pick up a PCM for your particular car at a junk yard and swap it in. Hopefully it will still have the factory tune. Or, you could go to GM dealer and have the PCM reflashed, 15 minute job. Or, fill the tank 1/2 with gasoline and 1/2 with straight ethanol or methanol, car will lose power but will burn leaner. Good luck.

 

im sure its not good to run a cylinder dry. do you have a adjustable fpr, if so you could drop the fuel pressure.

 

No adjustable pressure regulator, and I had a stock PCM but I sold it already. Wouldnt a stock tune make it run richer anyway?

Where can I get straight ethanol? Will it burn too lean if I do that? I will be pulling the plugs to look at them in the next day or so. What is the best type of plug out there for these engines?

 

You can get 90% ethanol (rubbing alcohol) ar most drug stores. Methanol is sold by Home Depot, they call it methyl alcohol. They both work about the same.

 

I dont know if I want to put pure alcohol in with the gas. What if I mix a little E85 in with some 87?

 

Update:

Plugs and O2s look very good, but I did find 2 places in the exhaust that are leaking around clamps, and two header bolts were loose around the number 7 cylinder. Both of those could cause the O2s to read too much air and richen the mixture. Also, the MAF looked pretty dirty. My race car is speed density so this is my first encounter with MAF sensors, but this doesnt look good:





I tried to get a good picture of the little wires inside, but I had trouble getting my phone to focus on them. Two of them look pitch black and there is a light film of oil on the inside of the housing and inside the intake tube leading to the MAF (most likely from the K&N filter). I am going to clean the MAF tomorrow, and look for a universal filter roughly the same size as the K&N but without oil.

I am also going to pick up some band clamps to seal up the exhaust leaks, and hopefully it will pass next time around.

Im going out of town this weekend, but I will update you guys when I get results from the next test.

 

so long as the k&n filter is allowed to drain overnight after cleaning and oiling your ok. it can ruin the maf if the oil gets on it. some guys have been able to clean them and get away with it.