Zebra

I tried to get my newly repaired '93 4Runner 3.0 V6 inspected the other day and it failed due to high HC and CO. The limits were about 150ppm for HC and I was doing like 250ppm and 1.5% for CO and I was putting out about 1.9%. Pretty much the same story at the high and low speed tests. Just a little bit off the mark. NOx was fine at about 90ppm with a limit of 1000ppm. Dilition was 15.4. I will admit I only drove it a few blocks to the inspection station at lunch after a 4 hour cool down, but these engines appear to get hot pretty quickly, so I don't know if that was a factor. Also, the oil is fresh.

The results indicated that the truck is running a bit rich. I checked the O2 sensor and it appears to be functioning normally. After it warms up, it fluctuates in the upper 0.9v range which indicates a constant rich condition. I pulled a vacuum cap to introduce a lean condition and the O2 sensor responded immediately and fluctuated around 0.1v trying to respond to the lean condition. Cap back on and it goes back up to 0.9v. Revving the engine quickly also creates fast voltage shifts as it tries to compensate for the varying air introduced into the system. If I pull a plug wire from any of the cylinders, the value oddly lowers. I would think the opposite would occure due to the raw fuel coming from the non firing cylinder.

I checked the cold start valve for leakage and found none. With the valve removed and the hole plugged, it still responded the same. DO NOT underestimate the vacuum force through the hole! My first stopper was sucked into the hole and I had to fish it out through the throttle body.

The spark plugs looks fine with the only notable deposits on one plug being what appears to be burnt reminants of rubber from when the stopper was ingested into the plentum and some of it mush have been scraped off. I am not sure how old the plugs are, but they are OEM NGKs and the electrode edges are fairly sharp. The #3 cylinder that I repaired in the past looks fine as well.
I have not checked the ECT or any of the other control systems. Comression is good. Lifting the airbox lid up to allow nothing but fresh air instead of through the admittedly slightly dirty air filter had no effect. I thought about tweaking the AFM, since it does respond to increased (unmetered) airflow and calling it a day, but this is a stock engine as far as I can tell and all I have read recommended not adjusting it on a stock engine. On the other hand, after 150k miles, a well used engine does not exactly operate under the same parameters like as new.

One of the only other things I can think of is the gas is quite old, although I am not sure how long it has been in there. The dealer I bought it from had parked it some time ago when they thought the engine was bad which turned out to be out of adjustment valves. The only clues I have are the original inspection sticker expired on 01/05 and there was an oil change sticker on it that stated it was originally changed in 11/03 at 148k. It now has 150k mile on it. It also had a battery in it with a production date of 04/04, but that could have been put in after it was parked to move it of something. Based on that, I am thinking it was parked anywhere from January to April of this year, but more likely the earlier time frame based on the oil change sticker. This puts the gas at anywhere from 5 to 9 months old. I also put a little seafoam in the tank when I did the upper intake treatment recently. Perhaps older gas that has obviously not increased in volativity does not combust as well as fresh fuel. Plausible? Unfortunately it still has 2/3rds of a tank left and I don't exactly like cruising around with a long expired sticker to burn it up. If the fuel is the culprit, that would explain why the reading are only a little out of spec.

If I need to, I am certainly willing to start replacing things, but I just want to rule out the simle things. The truck appears to have been well maintained with a recent dealer timing belf change sticker on it and an entry on the AFM about a coolant change in 2003. Thanks for any help in advance!

-Chris

Zebra

I put it in diagnostic mode and there was a stored code 41 for the TPS. The check engine light has never actively been on though. I fool a little with the AFM for the hell of it and it did change the O2 sensor readings, but I would like to find the real cause.

Zebra

I went to check the TPS today and it appears that when I put the intake back on, after adjusting the valves, I failed to plug the TPS back in. DOH! After plugging it in the O2 readings are great now, quickly alternating between the .3v to .6v range like it should. I put the AFM settings back to stock and adjusted the timing, as it was set to about 15 degrees instead of 10. Hopefully that should have fixed the problem. : )
I am really surprised it ran relatively fine and did not have a constant check engine light while driving.

Yoda

We used to do emmisions at a shop I worked at (adjustments, not testing). When a customer failed a test we would ask what station the had been to. It was usually the one 5 minutes from their house...NOT long enough to get totally warmed up (engine and exhaust system). We would tell them to go to "X" test station (that would involve about 15 minutes of freeway driving) because it was easier to pass there. They would usually pass.

SlimJim248@earthlink

next time you go to smog it, drive it really hard to get your cat hot, this way it burns all the unburned stuff away. I did it with my 4runner and it was good enough to pass the second time, the numbers were about split in half.

MTL_4runner

Having the converter hot can make all the difference in the world when it comes to emissions readings. When I used to do inspections I would ask people how long they had been driving the car for before they arrived. Anything less than 15 min and I would make them take it out on the freeway for another 10 min before I would test it for them.

Zebra

Well, I passed on the retry! Along with hooking up the TPS, I did drive it around a bit before going and left it running while I went inside. Woohoo!