tonyp6392

Need some help here . I just took my 94 in for mandatory emissions testing and it failed because of high hc levels, it registered a 5.84 .80 is passing. so i cleaned the air filters and the new plugs i just installed at the beginning of summer cleaned the throttle body and installed a new maf sensor. dumped a can of seafoam in the tank and got the engine nice and hot and returned for another test. Failed again but better this time 2.04 hc level. any help with something else i can do will be great. thanks.....

GKK

High HC levels indicate an uneven Air/Fuel mixture.

Replace O2 Sensors, check the fuel pressure and check the fuel injector resistance. Also, change the oil and filter.

Could be a weak fuel pump or worn out/leaking fuel injectors resulting in a lean or rich misfire?...

tonyp6392

i replaced the o2 sensor on the drivers side i couldnt get the passanger side off im going to have to try again. i had a buddy of mine test the injectors they all had the same reading so i think they could be good. as for the fuel pressure it checked ok i'm thinking the cats can be going out but not sure. as for the oil i changed it around a month ago. however on occasion i have been getting a misfire after warm-up under driving conditions i started thinking its a fuel pressure reg but again i just dont want to start dumping parts into it.

hooked073

High hc is more or less raw fuel. You may think ok look at the fuel system but that is not the case if you had high co look at fuel. You need to look at things mechanical that would case this. Timing burt valves. plugs or wires a lean fuel mixture this causing a lean misfire. cats or air induction after the cyl has fired (air pump, and related parts). Make sure you have a good tune and you cats are up to par. You have some pretty high numbers so really concintrate on timing and engine tune and the engine is in good shape. with a engine in good shpe and tune it will usally pass hc with out a cat so check tune and engine shape

yd328

If your cats were going out you would have a high NOx reading. Changing the oil will drop the HC. How old are the plug wire and how many miles are on the car?

Gary

hooked073

cats do not cause high nox at least that I have ever seen the only thing that causes high nox is egr

wydopnthrtl

You can add 2.5oz of acetone for every 10gal of gas to the fuel tank.
This will help to atomize the fuel better.. but its not a permenate fix and it won't fix a wrong signal being sent to the ECM (possibly making it overly rich). Should get you to pass though if your sitting at 2

yd328

You are correct about egr but the cats can also cause high NOx
Gary

tonyp6392

I heard denatured alcohol works good i might try it.

tonyp6392

the vacuum on the egr seems good and i know if the cats are going they wont burn off all the fuel. any affordable cats that are reliable ? i heard the exact fit cats from some of the sites dont actually dont fit well

GKK

Is the engine all stock?...

hooked073

tony i know your worried about the cats but like I said eailer if these things are tuned right and mechanicly sound they will pass with out cats. Your numbers are really high esp with cats on. I would to a major tune plugs wires caps rotors. timing set ect. i have never seen a egr problem cause high hc not saying cause i have not seen it does not mean it cannot happen what I can promise is you egr is messed up you would fail for nox. i know you just replaced the plugs but in all honestly the plug wires will break down before the plugs now days. I would do a major tune set to factory settings and see where you stand at that point. I would avoid cats untill I covered all other bases

yd328

As stated above I wouldn't worry about the cats. The high hc problems that I have come across were related to plugs, wires, timing, o2 sensors, injectors and fuel in the oil. Its a good idea to change your oil just before going for an e test. Also check PVC
High mileage cars the oil change and old O2 sensors come into play.

Gary

zr1fred

A 94 vette will not pass without cats. Neither will any C4 for that matter. I would check everything else first though.

yd328

I missed the no cats part, it will not pass without the cats. With only a high hc reading I don't believe the cats are the problem so I would not worry about them until the other items are attended to or investigated.

Gary

desertmike1

Are you sure your not talking about Co%. because the PPM for Hc would be a much larger Value: say 30-60 PPM.. having said this Hc could play into the Co% out put value.. just need to look in the right place!

tonyp6392

heres my exact numbers from the indiana emissions sheet hc/ standards 0.080 are passing mine were 5.84 first test second test 2.06 fail

co standards 15.00 my numbers 4.80 pass

nox 2.50 standards 1.55 my numbers pass

what i have changed or repaired new plugs, and wires new water pump as everyone knows much better to change when doing a tune-up new l/s o2 sensor new valve cover gaskets new maf sensor oil one month ago cleaned throttle body and air filters ( slp air box) its getting close but still a little off. i did not change the opti. should i?

GKK

What's the Timing, Fuel Pressure set to?...

tonyp6392

not sure what there set at. or how to check on an opti system i'm learning on the fly. I bought the car in october and just started working on it and fixing anything i can fix. did a lot of interior work and basic body work replaced all the missing plastic inside repaired the engine code which was for a left o2 sensor. other than the that the car runs good and strong for a 20yr old with 115,000 on it. thats why i spend a lot of time reserching as much as i can from corvette forum its been a huge help.

zr1fred

You can't set the timing or fuel pressure on an LT1, its preset. Change the fuel filter if you haven't, and get a gauge and check the fuel pressure and make sure the regulator is working. Get the car warmed up, and make sure both cats are hot. Unless you have an obvious misfire, I would not change the opti for this problem. Take the car out for a long drive, the things you have done may have fixed your problems, but they (the problems) may have loaded up your cats.