Car wont pass smog

[Stang9663]

Hi everyone so I'm having an issue with my 1996 mustang v6 not passing smog. The shop I have taken it to told me that the sensors are not resetting. I've driven the car over 100 miles, and also have been given a step by step on how you are supposed to drive to reset the sensors and they still haven't reset.

All the sensors are not registering (told by smog technician), the smog mechanic said he has not seen a car do this or has ever heard of this issue. Can anyone tell me if they have had this issue and or how to fix this.

The car is modded with some basic bolt-ons, it has a cold air intake, shorty headers, true duel exhaust, and the vehicle is not tuned. All the mods are California compliant. Thank you for any help/advice

 

[95 Cobra Tim]

What sensors are you and the mechanics referring too? I'm guessing that you both are referring to your O2 sensors. Without knowing exactly what you are talking about, I would say disconnect your battery for about 5-10 minutes in an attempt to allow those sensors and your computer to "reset". Then see what happens. Also, you may want to look into some type of way to monitor your car's engine and electronics. I don't have one on my 95 Cobra but I do use the TORQUE app on my 99 F250. You will need to purchase a OBDII bluetooth plug ($20-$25) and download the app (cost $5) to your smartphone or tablet. This will give you the ability to run diagnostics and monitor several different perameters yourself and save a few dollars by not going to a mechanic for small issues. Hope all or some of this helps.

 

[01yellercobra]

Like Tim said you need to figure out which monitors aren't setting. Once you know that we can help.

 

[Stang9663]

Yes the o2 sensors are not setting for sure I do know that. I will go pick up an obd II reader and try to monitor what it reads. The car also isnt putting out a check engine light (it works) and no codes came up when I asked about them. I dont know if that means anything but just a little more information I can give to everyone. Thank you for your help it is greatly appreciated.

 

[Jakespeeds]

I just went through this with my 98 GT. I have Torque on my phone and a handheld unit. Neither could find a problem even doing data logging. I have access to a professional unit and immediately found the problem. Both O2 sensors on the passenger side were running .02 under voltage. My simple units just didn't have the resolution to show that. Replaced them both and it smogged no problem. You might be better of just looking around for someone that will put a high end unit on it for an acceptable price.

Jake

 

[MyLittlePony]

The only way I could get my 94 to pass was by adding a switch that would turn off one of the STI.
https://www.stangnet.com/mustang-forums/threads/emissions-problem-very-high-hc.891415/
I don’t know if it will help a 96

They started testing for emissions in my county in 2004. In 2008, the car was upgraded to a v8, with different heads, SCT chip, and the smog pump didn’t do anything but act as a belt tensioner. Bought a used H pipe, which the owner didn’t mention the cats were GUTTED. (Not sure why you’d do that as it’s much cheaper to buy them without) also bought some Ford Racing header exhausts that were “seconds.” This meant it leaked. Ran Guaranteed to Pass in it. Everything I did, including parts replacement helped, but still didn’t pass. I drive it less enough to qualify for a mileage exemption. I also paid enough in parts that proved to help to qualify for an exemption for the year, but the DoT inspector claimed these were all “safety” parts, not “emissions.” So I ran it illegally for a year with a sticker off another car of mine until I got a notice in the mail stating that I would not be allowed to reregister. That’s when I got my switch that would disconnect the STI. I would drive up to the station, flip the switch, pass, then flip the switch again.

Last year, they did not test emissions. Vehicles 24yo and older are exempt. So this year, now being a classic mustang, I don’t have to fiddle with the switch any more. You take it to the station, request a safety inspection only. They stick a sniffer in the tail pipe, and you start arguing about how they’re not supposed to test it! Apparently all Kwik Kars are the same, because I once brought a 1967 Triumph GT6 in for a safety inspection at a different location, and they tried to test it for emissions! No idea how without the computer data. Anyway, both techs did it, while both office clerks agreed that it shouldn’t be tested.

Maybe you can buy yourself enough time to get a classic car exemption.

 

[95 Cobra Tim]

What is this STI switch that you speak of and do you have a link to where I could get one?

The only way I could get my 94 to pass was by adding a switch that would turn off one of the STI.
https://www.stangnet.com/mustang-forums/threads/emissions-problem-very-high-hc.891415/
I don’t know if it will help a 96

They started testing for emissions in my county in 2004. In 2008, the car was upgraded to a v8, with different heads, SCT chip, and the smog pump didn’t do anything but act as a belt tensioner. Bought a used H pipe, which the owner didn’t mention the cats were GUTTED. (Not sure why you’d do that as it’s much cheaper to buy them without) also bought some Ford Racing header exhausts that were “seconds.” This meant it leaked. Ran Guaranteed to Pass in it. Everything I did, including parts replacement helped, but still didn’t pass. I drive it less enough to qualify for a mileage exemption. I also paid enough in parts that proved to help to qualify for an exemption for the year, but the DoT inspector claimed these were all “safety” parts, not “emissions.” So I ran it illegally for a year with a sticker off another car of mine until I got a notice in the mail stating that I would not be allowed to reregister. That’s when I got my switch that would disconnect the STI. I would drive up to the station, flip the switch, pass, then flip the switch again.

Last year, they did not test emissions. Vehicles 24yo and older are exempt. So this year, now being a classic mustang, I don’t have to fiddle with the switch any more. You take it to the station, request a safety inspection only. They stick a sniffer in the tail pipe, and you start arguing about how they’re not supposed to test it! Apparently all Kwik Kars are the same, because I once brought a 1967 Triumph GT6 in for a safety inspection at a different location, and they tried to test it for emissions! No idea how without the computer data. Anyway, both techs did it, while both office clerks agreed that it shouldn’t be tested.

Maybe you can buy yourself enough time to get a classic car exemption.

 

[Stang9663]

Alright so I have taken the car to another shop where they were able to reset the monitors, both the o2 and the egr were not setting. While they got them to reset they went to give it a smog test and within the 45 minutes of the vehicle waiting in line to get smogged the monitors reset themselves. Now what the shop had told me is they have never had a vehicle do this but have heard of something like this happening before in basic terms the computer is desetting the monitors as if the battery is being disconnected so they told me they want to keep the car to test some things to see if it indeed is my computer desetting the monitors or if it is something else that happens to be wrong. I want to thank all of you taking the time to help me out.

 

[01yellercobra]

I did read somewhere that a bad battery could cause that issue. Like what the mechanic said as far as the computer resetting itself. How old is the battery?

 

[MyLittlePony]

What is this STI switch that you speak of and do you have a link to where I could get one?

Forgive the lateness of my reply but post #2 here explains a lot:
https://www.stangnet.com/mustang-forums/threads/emissions-problem-very-high-hc.891415/

“The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.”

For cleanliness of the engine bay, my wiring was hidden under the fender, and removing the wheel well was the only way to access this gray connector, so an after market switch was wired in order to disconnect it, hidden under the headlight cover.