Smog question

look 171 · 09-03-2020, 06:13 PM

My kid's 4 runner fail smog for the second time today.

98 4 runner, runs strong and smooth. Failed first time (barely) and tech told me its per-ignition from the carbon deposit and suggest the typical Italian tune up. This car sat for a year. I burned off the bad gas, installed new plugs and wires. I even use Seafoam to scare all the neighbors before I drove off on my Italian tune up. Failed again. He now thinks its the car or O2 sensor but there's no code. Now I am started to not trust him. What do you think?

Tobra · Tobra's Garage

There is a drive cycle that you can put most OBD 2 cars through that resets all the sensors and clears the readiness codes. That is probably all you have to do to get the readiness codes cleared. A few things give high NOx, one of which is the cat, but you would be getting a code if that was the case, I would think. Bad EGR or running lean/hot are more likely. I guess carbon deposits on the pistons could raise compression and make it do that.

The Italian tuneup is more for high HC I thought. Did it improve the numbers at all doing that?

ninelevenick · 08:35 PM

I think Tobra is steering you in the right direction suggesting driving your vehicle more through its cycles to clear all the readiness codes. In my experience the catalyst is the last one and most time consuming to clear. There are certain inexpensive OBDII readers that have a very easy smog sensor readiness display function. For reference, mine is made by Autel. Anyway, my question for you is how long ago did you disconnect or reconnect the battery? How many miles has the truck been driven since?

Pazuzu · 09-03-2020, 08:35 PM

The evap system is at LEAST 100 miles, maybe more. You can't just do an Italian tuneup that morning and hope for the best anymore. I had a reoccurring EVAP code ("minor pending issue") which would crop up once a week. I'd wipe the code, and it would come back. Turns out, the code triggered at the end of the entire Evap cycle, because it wasn't really a leak, just a "minor pending issue". Still couldn't get it smogged with the Evap cycle incomplete.

look 171 · 09-03-2020, 08:45 PM

Ahh, got it. Drive cycle means get out and drive the thing. What is the estimated miles needed? It will clear itself? Thanks for explaining this to me. Smog puzzles me.

Truck sat for over a year plus, maybe two?

Battery completely dead.

Drove truck home, 10 miles

After new battery, it wad disconnected at least 5-6 times while we worked on the truck over a period of two months.

Yesterday was the first drive after work was done to smog station, 7 miles. Failed test.

Same night, seafoam, drove almost 50 miles doing Italian tune up.

Drove 20 miles today, 10 on street, 10 on fwy back to retest. That's all the miles on it so far.

ninelevenick · 09-03-2020, 08:57 PM

If the correct driving conditions are met, 60 miles would be adequate. However, more miles could rack up if those conditions are not met. From my experience the catalyst sensor needs the vehicle to be driven about 25mph in low rpm for about 3 minutes followed by a steady cruising speed, say 55mph, for about 10 minutes. This is a very generic scenario, but you get the idea. I would Google your specific vehicle to glean the correct driving procedure to ready the catalyst monitor.

Pazuzu · 09-03-2020, 09:14 PM

The best way I found to make sure that I wasn't wasting my time was to use the bluetooth OBD sensor that I already had

Get any generic $15 bluetooth sensor. Plug it in, Test car using the Torque app. You can test for, look at and cancel check engine lights, but you can also see the status of the various long term cycles. Some will be grey, that means you don't have/need it. The others will be red, until enough miles to trigger the cycle, then they're green. Once all of the live checks are green, you can go get tested. They're basically giving you the exact same info the smog testing sight looks at.