Update: Passed - 99 3.4 Smog Fail HC and NO California

Just took my car to get smogged. In cali my 99 needs to go on a dyno. It failed with a high HC and high NO at 15mph. Car was sitting for a week and I drove it for 15 min on the freeway to get here. No CELs coming up, decent mpg, and I’d rather not take it to a mechanic as I do all the work myself. Any ideas before I start throwing more money at it?

 

I would honestly recommend leaving California...

My uncle lives in Monterey and has two Volkswagen buses, a 1971 and a 1977. The 1977 won't pass smog, and California doesn't do antique tags for vehicles older than 25 years, so he cheats the system and registers it at his brother's house in Texas; California is seriously the most unfriendly state in the country to automotive enthusiasts!

Seriously though, I read an article from about ten years ago (2013) about a couple stuck in smog check hell because their car (2007 model) wouldn't pass despite being in excellent mechanical condition and not having a CEL. If I'm reading it correctly, it looks like your truck fails smog at 15 MPH but does fine at 25 MPH...? I'm shocked that they do a dyno test on a 1999 vehicle, because I thought that OBD2 vehicles didn't require this?

 

The discrepancy is surprising.

When have you last serviced or replaced the usual suspects? Clean MAF, O2 Sensors, Injectors, etc? What grade gas was in the tank and was it fresh?

I'd run a can of sea foam (1/2 in the gas tank, 1/2 into the intake). Clean the MAF, etc.. Once you're through that tank fill up with 91, get it good and warmed up (WOT getting on the freeway) and try again.

 

Great questions. Cleaned the MAF maybe 3 months ago, don’t know the last time the injectors got cleaned or the O2 sensors replaced. Replaced the engine last year with a lower mileage engine with 140k on the clock. Shop that did the swap said they checked over everything.

Pulled up to the test center/gas station with the gas light barely on, filled up with low grade fuel then pulled around back for the test. Definitely didn’t do any WOT pulls on the way over, I drive like an old person for the MPGs. I’ll give those a try and see what happens.

 

Haha I live so close to the Nevada border, wish I lived 5 miles east so I wouldn’t have to deal. They do dyno on cars older than 2000 which is ridiculous because a 95.5 taco and a 04 taco should in theory have the same everything.

 

There are one or two counties in California that don't require smog testing for any vehicles due to being so sparsely populated. Also, weren't the earliest Tacos OBD1?

 

Dont throw money at it… there are things you can do in your driveway with minimal tools like pulling a spark plug and looking at it, if the gaps are too big that could be an issue. The passenger side is easy, the D/S not so easy, not difficult at all, just not as easy as the other side.

Check the PCV valve. Take the oil fill cap off and see if there is any blowby. Rev the motor to see if the blowby increases with RPM, if it does you could be fighting a loosing battle. The convertor(s) can only do so much clean up. If there is no or not much blowby then depending on your experience and tools in your tool box, i.e. scan tool, there are things that you can check, if you dont then you are at the mercy of what ever tech gets you truck and attempts to figure it out.

Everyone just might say your cat(s) are bad… all I can say is maybe, maybe not, 99% of diagnosing is proving what is right and not what is wrong.

 

Nope, all tacoma are obd2. Toyota switched to obd2 at the end of 1994 and all 1995 and up are obd2.

 

Denature alcohol. Google it.

 

So 1995 pickups, T4Rs, and Camrys are OBD2?!?!

 

Maybe… you HAVE to check the under-hood sticker. I should have taken a picture of the OBD1 tacomas sticker I had many years ago. It wouldnt pass smog either as the smog techs kept entering the wrong data, MY 96. I had to get the referee involved and show him the OBD1 sticker of a 95.5 Tacoma. We entered it as a 95 MY and it passed. For this transition period, 95 to 96, just because it has a 16 pin connector under the dash does not mean it is OBDII. On the CA BAR smog site there are LOTS of exceptions to the rules even for current vehicles… some vehicles just wont run some smog monitors, some vehicles have mid year emissions changes.

 

That's banned for sale in CA too now. That actually really pissed me off when that happened so I had to stock up.

 

Does that truck have EGR? If it does make sure it’s working, maybe clean the passage.
Hook up a scan tool and see what the fuel trim is in that window.

 

My 95 5vz t100 emission label under the hood is listed as obd2...

 

Just guessing here...but I would check the EGR valve first. It seems to be vacuum related, so maybe vacuum hoses (that'll be fun), maybe the lines to the EGR valve, or the valve itself, which is like $50 on Amazon.

 

I did notice a little bit of oil in the air box. I bet the Pcv valve is shot. That will be a good place to start

 

How many miles was the trip there? You need to have your truck nice and hot right before it gets on the roller. Leave it idling while you wait next time.

 

Probably only drove 7 miles or so after it sat for a week. Then parked it at the shop and waited for maybe 30 min before I got tested

 

Let your truck get really really hot before the next test. Drive it hard on the highway, push it to its limit. They pass easier when the catalyst is hot.

High NOX is usually catalyst related I think?

 

The mityvac vacuum pump might be a good tool to have to see if you’re getting vacuum at various rpm on the egr. You can also use it to see if your egr is working properly.