Need some good help with this thing and it's really starting to **** me off! Have a 95 z28 with the lt1 t56, cannot seem to pass emissions for the life of me. What i have replaced, injectors, Opti, installed new cat, fuel filter, replaced long tubes with shorty headers. Numbers last time were hc: 1.19, limit 0.80. Co: 12.94, limit 12.00. Nox: 1.56, limit 2.00. Only one passable was nox. Replaced the k&n with the factory air box in between testing. Numbers today, hc: 1.37, limit 0.80. Co: 5.99, limit 12.00. Nox: 2.20, limit 2.00. I even ran i think 87 octane for a better burn of the fuel. What the heck is happening here and why? I may not have got the cat hot enough, but how did the co go way down and others cane slightly back up? I'm in mesa az, so if anybody has a guy at one of these places that would be cool lmao. Any info regarding this or how to help it out would be great guys. The other site I'm on has one person that actually answers questions, but i need serious help. Thanks in advance!!!

 

You ran 87 octane for better burn of the fuel? Who told you this? You are gonna have preignition and I imagine that won't help your emissions any better!

From the very top, how stock is your engine? You mention reinstalling the factory air box in place of the K&N but does that also include the air filter? If so, the oil based K&N filters have been reported to mess up mass airflow sensors by sending fine oil particulates to the heater wire of the MAF sensor thus fouling it and sending the computer erroneous data. This is why I now strictly use O.E. AC Delco brand paper filters on my car. I was suckered too by the K&N filter marketing until I had my MAF go bad on me and after some decent research I discovered the problem with using oil based cotton gauze air filters on cars. I felt like a moron but I was young and I learned a valuable lesson. As one person made a great point, the Corvette does absolutely fine with paper air filters and is that extra few ponies of horsepower really that worth it? You may need to check your MAF sensor and get the thing cleaned with MAF cleaner.

I would also advise you start using "Top Tier" 91 octane gasoline along with a treatment or two of fuel system cleaner that uses PEA to clean out any deposits in your system that may be hurting overall engine performance and increasing emissions.

I don't know how modified your engine was from reading your post but I hope you didn't tinker with the computer program as well. You may need to go through a dealership and get the PCM flashed to the stock program in order to get the car's emissions back on track. You seem to have gone out of your way to get her stock parts back on and replaced parts that don't play too much of a role in emissions, I would check out the PCM program.

If the car still does not pass emissions after everything mentioned here, you need to check all of your emissions equipment to ensure they are functioning properly. Do you still have a smog pump on the engine? Is your EGR valve in good shape, no punctured diaphragm or fouled valve stuck in position? These are just some thoughts that come to mind...

 

I'm not sure how different connecticut emissions are but I just did my 95 for the last time and I am running full bolt ons and no egr or smog long tube headers straight pipe exhaust and a tune from f body tech which I opted to delete egr and smog from the tune and selected all the "performance" options. I did have to weld in a cat after the y pipe. But other than that my car passed no problem. I was sitting there with my fingers crossed the whole time! They had sniffers in the tailpipe and a bunch of stuff in the engine bay. Guy didnt attach sensor on the spark plug wires cause he didnt wanna get scorched by my headers lol.

 

First thing, do you have a stock tune

 

I have read numerous times that 87 octane burns more complete, not entirely sure how true it is though. Anyway, the egr valve is new along the pcv valve. The motor has about 15k on it since it was rebuilt, only had a stock rebuild done. The only thing i can really think of is the opti is missing causing the high hc count and slightly higher nox now. The ecm as far as i know of is at factory form, I've never messed with it anyway. It's never thrown a code for the maf or shown signs of it being bad either. I think I'm going to swap out the Opti with one i warrantied and go from there. I really don't want to have to use alcohol or anything to pass, but i only have so many more options here lol.

 

Well, you can't get gasoline to burn any more complete than the laws of physics and thermal dynamics will allow within the combustion chamber of an internal combustion engine! The ONLY THING the octane does is prevent the gasoline from igniting too soon which will cause pinging and throw off the entire cranking process and if not corrected soon enough can damage the internal parts of the engine because you have the piston being forced up during that crank stroke and the gasoline ignition trying to push down and expand on the piston at the same time! This is why it is critical to use the correct octane rating for the engine, 91!

Now, with regards to the opti, do you feel pulsation from the engine or irregular combustion? Sometimes the opti may not throw a code but you can feel the engine is not operating smoothly as it should. (I noticed this for like a year and maybe half before my opti took a crap on me after years of collecting oil due to a bad water pump seal.) This would indicate something is amiss with the ignition system but I would refrain from throwing parts at this problem until you are absolutely certain that the opti is the problem! A dirty MAF may never trigger a check engine light! It merely will give your PCM bad readings and in turn the PCM will send more or less fuel which will increase emissions. However, this may or may not be the problem you are experiencing.

One last thing and this is a long shot, are you using an oil catch can for the PCV system? Now that I am running one I am amazed at the moisture contamination I am seeing in the PCV system that my catch can is collecting! This would surely increase emissions if thrown back into the combustion chamber! It is worth noting.

 

It definitely has a miss to it right now which I'm almost certain is from the cheap Opti on it, was hoping it would get me by for awhile. I'll switch back to the 91 octane in it as well, I was only trying to help it pass this stupid test lol. I have no catch can or anything like that, I'm not trying to do anything fancy with it, don't even really want to race it, just drive it lol.

 

Okay. I can recommend you purchase an opti from a vendor on this site, Pantera EFI.
http://panteraefi.com/
Phone number: 949.250.1797
2824 S. Willis Street
Santa Ana, CA 92705


I decided to go through a non-LS1 tech contributor vendor who swears by their workmanship, offers new vacuum tubing with metal filter, and who offers a two-tone red/black cap which looks awesome by the way. I have no codes especially the notorious bad sensor code the car throws off the bat when you buy a bogus opti, and the car has a smooth crisp idle now. I strongly recommend you look at your timing cover seal for the water pump shaft just in case for preventative maintenance it needs to be replaced. The last thing you want is an oil leak down the road that will screw up a brand new optispark that took hours to install. I should know!

One last thing, you can pick up a cheap Jegs oil/air separator unit kit which is another name for the catch can! You simply connect one end of the vacuum hose to your PCV valve and the other end to the intake manifold, you cut the hose in half where you can best mount the oil/air separator and hook those hose ends to the nipples on the barb connectors. I mounted mine where the factory air box goes and where an LT1 SLP cold air intake would slide into the metal track that exists, and zip-tied the catch can to that mounting place! Yeah, it is an inconvenience to have to check on and empty the thing seemingly each week, especially in the winter, but the foamy moisture/oil mix that it catches is not something I want to have pumped into the combustion chamber to be burned off. My mileage does seem to have gone back to factory new EPA standard despite knowing that my engine has possible problems being a Jasper remanufactured engine. So, I recommend the catch can, even for a daily driver! Sure, you would think that only race cars would benefit from it but my daily driving experience supports the seeming necessity for oil/air separators on every street car! It is your choice!

 

This question needs an answer. I suggest you listen to anything this member has to say.

As for octane discussions and snake oil additives, etc. it's way simpler than that. Lower octane = less knock resistance. More knock = more knock retard commanded by PCM = less spark advance. Less spark advance = more unburnt fuel out the exhaust valve = higher emissions. These cars (10.5:1 SCR from the factory) were designed to run minimum 91 and preferably 93 if available so they can run all the timing they were programmed to, which is still pretty conservative and borderline emissions compliant. upset that balance and you're chasing gremlins.

Factory tune = safe timing, probably more conservative than it needs to be. A mail order tune for a stock or near factory setup can give great benefit in terms of improved spark tables which can reduce emissions, and slightly improve performance with additional timing with a sensible approach. And to change the oxygen sensor timings when they're moved around. There is a delay expected by the PCM from the (small) delay of an exhaust pulse exiting the head to arriving at the sensor. Long tube headers means increasing that delay. Mids changes it a bit less than that.

If you're up for learning how to capture (datalog) what's going on, members here can probably help pinpoint your issues. A number of them are highly respected tuners in the LTx community. They can help keep the parts-throwing and mental masturbation to a minimum. And save you some cash in the process.

 

I got a CC306, LE2 headed car with long tubes to pass emissions in Missouri and here is how: I had a custom y-pipe fabricated that had a 93-95 OBD1 catalytic converter (from AutoZone) right after each collector. Yep, I ran double the cats and it pumped out daisy fresh emissions. Then it ran into an old 3 inch cat back that I had lying around. After I was done with emissions, I swapped back in the true duals. I'm not sure if you have to pass visual at the same time where you're at, but it might be a solution.

Second: Be sure to drive around for at least 30 minutes to get the cats nice and hot before getting emissions tested. They don't work well cold.

Third: The cat you have on there now might not be the best quality? Try a different brand or a high performance converter to see if it works better. Although that is just a shot in the dark.

 

Ok, as far as i know the tune is from the factory, I've never touched it, and the guy i bought it from said he never touched it. Right now the opti is being swapped out, again. The one i installed today is missing due to no spark coming from cylinder 3 from the opti end. I replaced it in the first place due to the car idling up and down at a certain temp, then slightly missing after. The motor itself has maybe 15k on it since it was rebuilt. The cat is a walker one and is a pretty good one. Hopefully once i take care of the opti everything else will be ok, that's my crazy hope though haha.

 

a dead miss will absolutely send HC up. I'd make sure once the opti is changed you have no more miss, get a can of MAF cleaner from the parts store and shoot your sensor and clean it up in case of any oil or filter contamination. Drive it and get some higher octane fuel in it, get it up to temp romp on it a bit to get the cats lit and working and I bet you'll be good to go.

 

One last thing that dawned on me though it is not very likely, it may be the catalytic converter if, by chance, it is a performance cat with less filter material. I also read that such aftermarket cats will throw off the oxygen sensors as the sensors are designed to work within factory specs for catalytic converters and using one with less filter material than a factory cat would certainly bump up emissions. This is also on the basis that you do not, in fact, have a "Walker brand" EPA/Federal compliant catalytic converter, OR, the EPA/Federal standard still lacks the right amount of filter material. I live in New York state and by choice now have CARB compliant cats on my 1997 Trans Am. Even though my car is of the age where I don't need to meet the CARB standard in New York, I prefered to ensure that my emissions equipment was working by having the extra level of certification that my cats have all the filter material needed for proper emissions measuring from my oxygen sensors.

That is my two cents...