how to figure out what causes a truck to fail emissions?

[hnm3355]

i have a 1985 2.4 pickup and it recently failed emissions, first thing i did was check timing with a light, found it at 20 over tdc when warm in drive. so i retarded it back down to a 5* over tdc like the book said, imidiattly noticed the smell of gas dissapeared. and ran a bit slower. i went ahead and replaced the following thinking it would solve the problem, CAT,plugs wires , dizzy cap and rotor, air filter as well as the muffler. after replacing all these the CO reading was reading 20 grams higher than the first time it tested, 160 over 40allowed , alot. i did managed to improve the HC levels from 6.0 over 4 to 4.7 over 4 almost there to pass on the HC.


Big question is what else is needed i have spent a little over 150.00$ on all new parts and need help to see if any one has ideas or knows what causes the high lvls of C.O.


note one thing i think needs replacing is the dizzy's vacuum advance the year prior to failing the truck passed perfectly and all of a sudden it failed and was advanced 20 degreees, any one else think its bad. plz if any one can help me out, im in dire need of assistance. im past my 30 day permit that i al allowed and time is running out.

[PapaSmurf2k3]

Was the cat you replaced brand new or used? I would think if it were new, you'd be looking at over $150.

Do they test NOx emissions? If not, you can try advancing your timing a bit (from 5 to say around 10) and seeing what that does. Usually it cuts down on your HC and CO a bit, but increases NOx.
Also make sure the car is good and hot when they test it. Cats work best when they are hot. If your exhaust is custom, you can move your cat closer to your engine to improve it's efficiency.

[hnm3355]

its a brand new cat it was a universal weld on one from boral ran me 43 bux with my discount.they do test for nox my nox levels were .6 of 5.5 allowed. also tested the egr by hand and it seems to be working since it stalls the engine like the test said it would, vacuum advance is indeed working from 5 to 20 degrees. but i just started to look at this thread and looks like some of my lines are not in the right place everything is connected wrong. so know i will be redoing the lines one by one to match this up and see if that makes a diffrence.


cat is in the stock place aswell as the muffler and stock size tubing




http://www.nicoclub.com/archives/nissan ... guide.html

[hnm3355]

well as soon as i fixed the vacuum lines the cars time retarded about 20 degrees, and ran like s***, with my timing light i advanced it back to a 5 degree warm in drive. and the truck is now running a bit smoother and it doesnt have much of a smell out the tail pipe after driving it a bit. im going to hope this was all it needed and will be taking it to emisions the 5th of july, some of the vacuum lines that wernt hooked up right didnt have vacuum because they wer conected wrong .

[PapaSmurf2k3]

ah, that can do it. The only other thing I could think of is if your O2 sensor is getting old.

[hnm3355]

well the truck runs better it is the 4 of july so testing will have to wait till tomorrow i will be replacing the o2 sensor for the heck of it since it only rings me up 15 bux or so. and i hope for the best.

[Critiko21]

How did it go? I'm also having smog problems. High CO and HC levels