StevoX1

Alright so i just took the stang in for the 3rd time for a smog check and it still didn't pass...
It's HC and NoX readings are higher than a kite.

So far i re-charged my air filter, new spark plugs, new oxygen sensors, cleaned out my EGR and reset the computer.

1st attempt: NOx = 1160 on a max of 695 @ 15mph
717 on a max of 717 @ 25mph

HC = 52 max of 85 @ 15mph
22 max of 50 @ 25mph

2nd attempt: Nox = 1203 max of 695 @ 15mph
840 max of 717 @ 25mph

HC = 88 max 85 @ 15mph
39 max 50 @ 25mph

3rd attempt: Nox = 878 max of 695 @ 15mph
958 max of 695 @ 25mph

HC = 117 on max 85 @ 15mph
83 on max 85 @ 25mph

I dont know what the hell else to do, the technician says its the cats but i just got new ones put on barely 2 years ago..any suggestions?

dreamer1uk

Hi,

High HC readings usually mean its running rich.
High NoX is based on high cylinder temps as well as high cylinder pressures.

I would start looking for vacuum leaks.

Do you have any way of testing the voltage coming from the o2 sensors? They should fluctuate between 0.2 and 1.0v. If there stuck on a low volt reading, its running lean, high reading its running rich.

Any signs of cracks in the exhaust manifolds before the o2 sensors?

Hope this helps alittle.

luckythirteen13

clean the maf and set base timing to 8*

how long are you driving the car before the test? are you shutting it down when you get there? you want to run it for 20min before the test and when you get there, leave the motor running and dont shut it down till the test is over. make sure you have a 195* thermostat in as well

mjr46

WELL FOR ONE IF YOU RESET THE ECM AND WHEN STRAIGHT THERE, OF COURSE THE CAR WILL SPEW WORSE NUMBERS, YOU NEED TO DRIVE THE CAR for a good while, I'd give it a day or two so the adaptive strategy can be learned.

Styg

Like lucky said, set your timing low and let the car's computer learn to run with new plugs and O2 sensors. Did you replace the cats on your car with reputable ones ? If no, than maybe they did in fact go bad on you.

I checked my last smog check numbers and my car passed it with original cats, mushroom shaped spark plugs, and open thermostat.

HC 107/112 72/86
CO 002/072 002/060
NO 274/778 366/717

Joel5.0

High HC's = unburned fuel. O2's do not detect HC levels.
High NOx = EGR not working, too much spark timing.

Did you run a set of DIY KOEO/KOER self tests to check if it shows any failure codes? LUK

jackskid

My 89 was running rich. Tailpipes and bumper were black. A new Ford fuel pressure regulator did the trick. I would also look into some of the other things posted here. Clean mass air, correct thermostat 195deg, base timing set to 10 deg, new plugs. Do all of the above, reset the computer, then drive 50 miles or so before retesting. LUK

loping5.0

try all of the above but also run some alcohol in you tank, make sure you have about 1/4 tank of gas or so (so that the alcohol is not deluted) this will give you a hotter cleaner burn. you should be able to pick some up at autozone or any other parts store. i have had to do it in the past on other cars worked every time

stanks347

Maybe try SEA FOAM. I've heard this works. It eats all of the carbon build up on your pistons. If you have been dumping too much fuel through your exaust your cats could be goobered up but I doubt it.