jduawa

Hello...I have a 99 2wd 4Runner SR5. Took it in for emissions test last week and it failed because the NOx GPM was 2.12 and the limit is 2.0000.
So i took it to a repair shop and he said the vacuum was ok and he cleaned the MAF sensor. I also replaced the air filter with a FRAM tough Guard CA7626. Took the 4R back to emissions today and it failed again. This time the NOx was 4.0419.
So now what...The vehicles has 198500 miles. The tech at the repair shop said next step would be to replace the catalytic convertor. But after reading on these forums it seems like replacing the O2 sensor might be the answer. Any thoughts?
Thanks

mt_goat

Try running some alcohol in your fuel for the test. I've heard a bottle of rubbing alcohol works. I might look for an e85 pump and put in a gal or 2 for the test then fill up with regular fuel to dilute it down after the test because alcohol is hard on parts unless the vehicle is designed for flex fuel (FF). Nox is caused by high combustion temps. Running lean makes for higher combustion temps so I'm not surprised it was worse with the new air filter.

jduawa

What exactly does running lean mean? does that mean that the air to fuel ratio is more air than fuel?
Also the mechanic where i brought this in for the first fix said that the engine has blow by, because there was some oil on the air filter? is this the beginning of the end of this truck
Thanks

jduawa

should i put the old airfilter back in???

mt_goat

Right, lean is too much air for the amount of fuel. Could be from fuel delivery problems, ie... clogged fuel filter, low fuel pressure for some reason, weak fuel pump, clogged fuel injectors,...etc. You freed up the air supply and just made it worse IMHO. Put the dirty filter back in? I don't think I'd do that, I MIGHT consider covering the air filter slightly with a plastic bag or something like that (if I was desperate to pass) First, I'd try the alcohol in the fuel myself.

Yeah blow by is not a good sign, but you have to expect some engine wear at nearly 200K miles.

4Crawler

iTrader: (3)

NOx is typically controlled by the EGR system, I assume that engine has an EGR valve. Might want to check that out first, common for those valves to clog up and not pass enough exhaust gas back to cut the NOx readings. My '85 failed NOx and cleaning/tweaking the EGR system dropped my NOx readings by a factor of 3.

jduawa

I havent actually looked for an EGR but after reading a different post on these forums someone else with the same year did not have one.

mt_goat

Yeah Roger they did away with the EGR on the 5VZFE in about 96 or 97.

Here's some more ideas: https://www.yotatech.com/forums/f2/f...-check-106293/

4Crawler

iTrader: (3)

OK, did not state what engine he was referring to in the post. I also found that retarding timing a few degrees helped with NOx along with running some premium gas, not sure if you can do that on the newer engines either.

904_runner

Nope.. Do not believe you can adjust the timing on these.

mt_goat

Yeah he didn't did he, I was assuming again. I don't know about the 2RZ or 3RZ.

jduawa

The engine is a V6

mt_goat

Over sized tires?
Old front O2 sensor?

jduawa

Tires are standard size. I really am not sure if the o2 sensors(either of them) have ever been replaced. If they werent replaced as part of scheduled maintenance, then they are originals.

mt_goat

That's probably the problem, anything over 100,000 miles is just bonus for an O2 sensor.

I quote from that link I posted earlier:

jduawa

Just an update...had catalytic converter replaced, they said it wasnt getting hot enough, and the front O2 sensor and the NOx reading was 0.914 GPM. Thanks everyone