i have a 95 obd2 lt1. i purchased the car with a 355 ,comp cc305 stock injectors and it is tuned via lt1 edit. i have never tuned a car using lt1 edit so i am in the dark here. The car failed the LOW idle emissions test which i knew it would. How can i lean out the LOW idle to get this car to pass emissions. Any help would be appreciated.

 

Cam overlap causes false lean conditions (O2s seeing fresh bursts of air from the valve overlap). I have the same problem with my cam and had ot dick around with it to pass emissions myself. Ultimately what i do is setup an open loop tune before running through emissions. Then after i pass i set it back.

BTW, if your car is stock it is OBD1 - not OBD2. GM put an OBD2 style port ont he '95 cars, even though they still ran an OBD1 computer.

 

What did it fail for? If its HC and/or CO, it may need to be leaned out. If it failed for NOx, it may be running too lean already.

 

That cam is supposed to pass emissions standards relatively easily.. relative to say hotcam. I bet if you blew too high on hydrocarbons then you have an exhaust leak or bad oxygen sensor.

Do you have a cat on the car?

 

The car failed the Low idle hydro carbons (hc). The limit was 220 ppm and the car delivered a whopping 1424 ppm. ( idle was 874 rpm according to the test). It definately seems alittle fat at idle but that shocked me. The cat was hollowed out prior to me getting the car.

 

Wow, i have a bigger cam with more overlap and i only put down around 420 idle hydrocarbons. 1424 is ridiculous - like turbo_z said you might have a bad O2(s) or exhaust leak causing issues on top of the came. cc305 should pass emissions.

 

Thanks for the insight guys, i will go over the car to see what looks a miss. Would o2 Sims be a good idea or should i just keep the sensors?

 

That is not the purpose of O2 sims. They serve to simulate REAR O2 sensors only found on OBD2 cars(96+). Youre car doesnt have rear O2 sensors.. only front. The front are there to measure the A/F ratio via oxygen content of the exhaust stream. Without those O2 sensors the computer cant adjust fueling so youll want to keep those intact. Like I said they measure OXYGEN so if you have an exhaust leak, it will pull in extra oxygen which tricks the O2 sensors into believing the motor is running lean and compensate by adding fuel. That is just 1 explaination of why you didnt pass.

The other and probably the biggest factor is that fact you have NO CAT.