4RUN-GT

I took my '96 4Runner 3.4 V-6 in for the state mandated smog test. After all is said and done, the tech tells me it did not pass due to "high emissions". It passed the visual and functional test but failed the emissions test. I guess they test at a simulated low speed(15 MPH) and higher speed(25 MPH). It mysteriously passed the low speed test and failed the high speed test.

All scheduled maintenance has been performed, so maintenance is not an issue.

When I got back in my truck, the overdrive light was activated, meaning the test(s) were conducted with the overdrive off. I concluded the engine was revving higher and was possibly putting out more pollutants.

The tech said it was probably a bad sensor and offered to do a diagnostic test for $60.00 but I refused and paid the test fee and was on my way. I should also point out, that the check engine light was not triggered and there has been no performance problems issues with my vehicle. If a sensor were bad, wouldn't that alone trigger the "check engine" light? Could running this test with the overdrive off cause excessive emissions at 25 MPH?

If anyone is knowledgable in this area, especially Jay, I would appreciate any feedback.

Mannnnn! I feel better already.

Thanks for letting me vent.

Tony

DH6twinotter

Hey,
I don't really see how having the O/D off would make any difference at that low of speed. On my 2nd gen, O/D kicks in around 45mph or so.

That's about the only thing I could answer. I dunno about the sensor thing. Hope you get it all worked out.

Have fun.
DH6twinotter

BTW, that's a sweet looking rig you got there. I'm thinking about painting my bushwacker (when I get them) and valance silver too. Me thinks it would look good with my light blue truck and white outs (when I get them) on the front.

L33T35T 4Runner

i would suggest getting a second test... with a completely different company

PhxTRDRunner

I would also get a second test. Make sure you have the cat good and hot before you go, run good gas, and try not to idle forever while you are waiting..those seem to help a car pass when it has troubles....just my couple pennies


~ I'm sure Jay or Dr. Z will have an exact diagnosis.

Mohamed

Another reason why to get rid of the stupid requirement. God, everytime I go for a test, I am paranoid it won't pass and always praying for passing marks. Good luck man, I eventually broke down and went to the dealership to have them fix my problem which turned out to be the Throttle Position Sensor.

Might I suggest cleaning the intake (plus add a new air filter)before the next test, use definitly good gas (California is loaded with bad gas at a lot of stations), trying running injector cleaner for a tank load (maybe your EGR valves are clogged and that cleaner will help very minimal though, but that would give a "Check Engine" light if that was the problem), could definitly be a bad cat sensor try replacing that (cheap part, but usually stuck on there). Good luck.

4RUN-GT

Appreciate all the great ideas. I'm going to another shop to have it tested next week, probably on Monday. But in the mean time, I'm going to clean out my intake and run some injector cleaner through the fuel system. I'll post the results.

Thanks again.

Tony

Jay

Sorry for the late reply.

I get the impression where your from dealerships and independents can certify your vehicle? They were wanting to diagnose it on the spot? Thats seems odd.

If so.... definitally get a second opinion.

And make sure to have the vehicle good and warm. Drive to the place with overdrive off. You want your catalytic converter (yes, i had to use spell check) at its peak performance.

Here in Oregon you go to a state operated facility to have them inspect your vehicle. If you dont pass you then take it to get fixed. But I do remember in Florida, the dealership I was employeed had the certification equiptment.

Did they give you a print out of the inspection results. Id be interested in a look.

High HC | Normal CO | High NOx = Lean misfire
High HC | High CO | Normal NOx = Rich misfire

HC = Incomplete combustion
CO = Rich
Nox = High combustion temperature

4RUN-GT

I do have a printout of the results, but unfortunately I don't have a digital camera. One thing I didn't do was let my car warm up as everyone is suggesting. The shop is a short distance away and after arriving, I let the motor idle for several minutes before taking the test. So now I know. Jay, I compared what's on the printout to what you wrote about. And I stand corrected. It failed the low speed(15MPH) test. Any additional info about my results would be appreciated. Here's what's on my printout:

MAX=MAXIMUM
AVE=AVERAGE
MEAS=MEASURED

__________________________________________________
HC(PPM)

___________MAX______AVE_______MEAS
15MPH______50________8__________3

25MPH______34________6__________2
__________________________________________________
CO(%)
____________MAX_____AVE_______MEAS
15MPH_______0.64____0.02_______0.00

25MPH_______0.78____0.02_______0.00

__________________________________________________
NO(PPM)
____________MAX_____AVE_______MEAS
15MPH_______508_____82________647
25MPH_______761_____74________630

__________________________________________________
Sorry for the long post... I just want to get as much info as possible. Thanks again to everyone.

paddlenbike

iTrader: (1)

Usually low HC and high NO means your engine is running lean. Are you supercharged by any chance?

4RUN-GT

Well fella's. I'm back in business and happily registered . I took my baby to another smog test station, thinking the tech was a little too eager to offer a repair to fix my 3.4 liter 4Runner after it initially failed. After several diagnostic tests, turns out my upstream 02 sensor was bad. After all was said and done, it was repaired and passed with no problem.

Also while investigating possible causes, along with the great advice from members here at YotaTech, I went ahead and cleaned my throttle body and changed my PCV valve for good measure.

Anyway, thanks again to all who gave input to help me solve my situation.

Tony

paddlenbike

iTrader: (1)

Glad you passed.

I find it a little scary that the bad O2 sensor made the engine run lean. That could damage a forced induction (supercharged) motor in a hurry. When the O2 plug on my turbo Supra got disconnected, the ECU went into full rich mode to protect the engine from leaning out and blowing a hole in a piston. I can't understand why yours didn't do the same. Maybe your O2 sensor was just mis-reporting the oxygen content in the exhaust...?

4RUN-GT

You might be right. I don't believe the 02 sensor was completely malfunctioning. Somehow, my 3.4 was still able to adjust to the lean condition. There was no audible pinging, but that doesn't mean it wasn't running lean. So maybe, just maybe, there is such a system installed on the 4Runner too. But this is mere speculation on my part though.

On a diferent subject, with all the supposed benefits of an EGR valve, and lowering NOx emssions, along with stringent California rules, I was really surprised to find that my '96 California 4Runner has a dual catalyst system. Maybe a dual catalyst system lowers emissions more than an EGR equipped system.