HELP!!! Failed Emissions Beyond Belief


Jan 22, 2007
So I just took the mustang over to get it smogged for the first time since buying it a little while back. Anyways the car failed horribly. Failed every portion of the test except for all the visual crap. Car threw a P0420 code 2 weeks ago and it got cleared, and never came back. Looking under the car its obvious that the cats were replaced and welded in after the precats. Sounds like there may be an exhaust leak but I don't even know. This is all shocking to me since there is no code showing up for anything. Please give your opinion on how to fix this issue.

Smog Reading

15 MPH: MAX - 51 MEAS - 171
25 MPH: Max - 35 MEAS - 90

15 MPH: MAX - 0.48 MEAS - 0.56
25 MPH: MAX - 0.46 MEAS - 0.70

15 MPH: MAX - 419 MEAS - 748
25 MPH: MAX - 706 MEAS - 1541

As you can see I bombed the test on a monumental scale. The guys says the car needs a lot of work just based on the test results. I'm hoping its not something terrible since I do not have the money to be fixing problems like this.

Thanks for the help in advance
  • Sponsors (?)

couple things u might want to try. When doing emissions tests make sure to run your car for a good 30 min b4 you head over to the testing center. What happens is carbon deposits will settle inside your motor and other debris and you want to get them out or at least as much as you can. Sea foam is a good thing to use and as well a solution not sure if its placed in your gas tank or what at the local auto stores that will guarantee that you pass or they will pay for the test.
hc is uburned fuel out tail pipes,it is misfiring,you may or may not notice,the co and hc readings are consistent with advanced you have a timing adj on car? if so retard a couple of degrees
Yeah I'm going to pick a stock h pipe soon. How exactly to you adjust timing on a car with coil packs? I'm used to just rotating the disty. Thanks for the help so far guys.
You have to have a hand held tuner or a chip. Or steeda sells one that bolts on to the crank pully. Your timing probably isnt the problem unless theres a chip in the car. I would sea foam it and look for smoke coming from under the car. Its probably an exhaust leak.
im assuming this was done on a BAR 97 machine, doing a 15/50 25/25 loaded mode test. and im assuming you are in CA.

based on what i see, the elevated CO and HC levels indicate a rich condition. what were the O2 CO2 readings. they are not a prt of the test, but are used for diagnosis. high HC and O2 would be a lean condition. what is your fuel pressure? also, the increased NOx is indicative of a inoperative EGR. the lines are known to get blocked fairly easy on our cars. EGR valves are cake to replace. what is the mileage on the vehicle currently. also what is your STFT and LTFT? are your O2 sensors pulsing at proper voltage and interval?

i took most of the classes to get a CA smog license btw.
Well lets see..

Are you in the right section?

don't you have an 84 GT??

you have a inline 5 cyl engine?

wait, isn't it a datsun?

Get the point? you need to specify what you have done or think you have done on your car so we can help out better, if not then you are wasting peoples' time trying to figure out what is wrong :)
on par with what tom said, it helps a lot ith diagnosis if you put you year/trim package and mods in the sig. just because you passed a visual does nto mean that a complete visual inspection was done. also some recent service history, or in some cases lack thereof helps with diagnosis.
Well lets see. Bought the car 2 weeks ago so I don't know exactly what has been done to the car recently. As of right now the car is bone stock from what the owner says. The only thing that looks sketchy is welded in cats after the pre cats and possibly some weld in muffler (based on another mustang owners opinion of sound). Judging by a stock h pipe pic on ebay the welded in cats look shorter than the stockers. The car is a 2000 mustang gt with 55k miles. Don;t have any service records since the car was salvaged, bought 2 years back and then sold to me.

CO2 reading: 14.1 for both 15 and 25 mph
O2 reading: 1.0 for both 15 and 25 mph

The guy at the shop said I'm running overly rich and that the gas isn't burning up. Also during accelration or revving I hear possibly an exhaust leak coming from the cat location (sounds slightly like a ping but more behind the motor) maybe hollowed cats after the precat but I dunno. I'm picking up a stock h pipe tomorrow locally so a bad cat/hollow cat will get resolved. Don't know what you mean by STFT and LTFT. O2 sensors have not been checked in terms of voltages or checking pulses. Like I said before it did throw the bank 1 catalyst efficiency code few weeks back. Any more info needed?

Sorry I didn't post this info prior. I was a little jumpy since I just failed so badly on a car I purchased no more than 3 weeks ago.

When I install the stock h pipe this week I will look for an indication of leaks and post up my findings.
Well lets see..

Are you in the right section?

don't you have an 84 GT??

you have a inline 5 cyl engine?

wait, isn't it a datsun?

Get the point? you need to specify what you have done or think you have done on your car so we can help out better, if not then you are wasting peoples' time trying to figure out what is wrong :)

i thought the fact his username is 00pearlGT was pretty self-explanatory :shrug:

to 00pearlGT, i think we already have a thread about your issues, you should add to that thread instead of making a new one. like i suggested, it sounded like the cats were replaced with high-flow units and thusly they are not doing the job (high-flow units are merely there so you cant get fined for running catless, they suck at actually doing the job stock cats do though) like they should. id definately stick a stock h-pipe on there and see what happens.
Have you checked to see if the welded in cats are actually cats (ie. have substrate)?

Around here inspections are just visual and they check for codes. Alot of guys just have their cats gutted and rewelded. Just an idea. Goodluck with it.
thomas - do you know what the regualtions are for passing smog? My dad tells me that if you fail twice the car can't be registered. I thought that was for test only stations.

I can get some pics of the engine bay tomorrow and I'll shoot some of the cats. I have a guy here in Fremont that used to have a 99 gt. He;s actually the one I'm buying the h pipe from.

Haven't taken a detailed look at the cats in terms of coding. I did tap the right one to see if it was breaking up and all I got was a hollow sound. Should a full cat have any kind of hollow sound?

Sorry for making a new post guys. Just another newb to the forums.
no they give you a temp registration i believe, and a sticker that goes on your window that states when you need to fix it by. at least, thats how i think it works. if you cant get it to pass then you can take it to litigations i believe, or you can go through the process of rescinding the contract, since its basically illegal for someone to sell a car that doesnt pass smog in commiefornia, unless you bought the car out-of-state from a state that doesnt need smog testing to transfer title, in which case its up to you to get it smoggable.

id usually recommend a "hookup" shop, but usually thats for cars that can pass sniffer but fail visual, but they really cant do much if the car flat-out fails horribly.

my advice is you need the stock H-Pipe on there, and you need to check to make sure all smog equipment is working.