So i've been working with my 98 montero sport ls, and i've got to say that it's been a handful.. I've been through 3 pre-tests so far and failed the first 2, passed the 3rd one by 2 MEAS in the HC, BUT.. immediately after the 3rd pre-test pass, they ran the actual test and it failed by 6 MEAS in the HC.

Now on the first pre-test they also ran a diagnostic and noted the cat was below efficiency and that the rear o2 sensor was mimicking the front.

First pre-test fail : 15 mph |HC| MAX,50 - MEAS,105

Instead of doing the repairs suggested, I had the spark plugs, wires, 10w30 mobil1 oil change, oil filter, valve cover gaskets (there was an oil leak, though I hadnt changed the plenum gaskets because lack of funds >.<) and new air filter. Ran some seafoam through the vacuum lines and fuel tank with about 13 gallons.
Took it in for second pre-test..

Second pre-test fail : 15 mph |HC| MAX,50 - MEAS,58

So close! but not enough. After that I decided to finish off the 13 gallons of gas which was actually about 4-5 months old hehe, and put 10 gallons in it. Changed out the pcv valve too, hoping that I could beat the 8 measures.
Third test.

Third pre-test, pass : 15 mp |HC| MAX,50 - MEAS,48

Since it passed they proceeded to run the real test.. Only to find out that somehow it failed!!

Final test : 15 mph |HC| MAX,50 - MEAS,56 NOOOOOOOOO

Luckily he told me to fix or replace other things like the oxygen sensors and to come back, and he'll give me a free test. Now i'm just wondering what other things could I possibly replace? and would oxygen sensors even help the HC come down.. EGR valve maybe? Any help would be much appreciated. This is the first vehicle i've ever purchased and trying to get her up to rock and roll!

~Thanks

 

use HEAT, its a little bottle sold thru O'Riellys for 1.99 its a fuel additive to remove moisture from old gasoline. Made my truck pass with flying colors after having failed miserably the first time. One bottle to a quarter tank.

 

Is your check engine light on?