Car is an '86 IROC with the 305 TPI with 86.300 miles. It had previously sat for 11 years.

While waking it from its slumber, I replaced all 8 injectors with Bosch IIIs and the EGR valve with an Autozone replacement. The original EGR valve did not hold vacuum.

1st Smog attempt


After the original failure, I only replaced the catalytic converter. I waited a week before attempting to smog it again

2nd attempt


I'm wondering if the Autozone EGR could be at fault here.

 

I would double check and make sure you don't have any vacuum leaks, especially since you just pulled the plenum to get to the EGR valve. Did you get new runner gaskets or did you reuse your old ones? Check the vacuum lines as well while you are at it. If they are all in good order, then I would take a look at your EGR solenoid.

 

Weird that your NO went up after the cat replacement. Did you drive the car around for 30 minutes to get it nice and hot before the test?

 

Weird. I thought the EGR was supposed to reduce NOx.

Lean Fuel Mixture - Lean fuel mixtures cause high NOx. ... Combustion temperatures increase causing high nitric oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors.

 

After the new EGR valve and cat, the NOx went down at 15 mph by a significant amount. But the NOx at 25 mph was way high. I would think that the EGR solenoid is not operating correctly.

 

I'm curious why there was a 500 RPM difference recorded between the first test, and the second test.

 

Did you replace your O2 sensor as well? When I bought my L98 a few years ago (and living in CA) it had readings similar to what you posted. Thought it was a EGR issue but after testing the system I found it was functional. Some thread searching on here persuaded me to get a new O2 sensor which I did and it passed just fine. I used an Autozone replacement ($20).

 

Should mention this worked AFTER I replaced all the vacuum lines, and hoses and such. This was the last thing I replaced that actually made it pass.

 

I just noticed the rpm difference. Did the tech leave it in first gear on the second test? A 500 rpm difference does make a difference during the test. Maybe hes trying to scam for more money. Did you take it back to the same place?

 

Yeah, I noticed that also.

 

Agreed. Hard to compare test results when the engine is under a totally different type of load. Depending on the vacuum difference at 1100 and 1600 rpm, this will greatly effect EGR operation. I wouldnt change a thing, take it back, point out the rpm difference and have the test redone, then go from there.

 

Looking at my own pass/fail emission test results over the years, they show varying degrees of engine speeds. No real trends with regards to pass/fail results; Some pass at higher rpm, some fail at higher rpm and vice-versa.

I think it's more a function of the tech trying to get the car to pass. What matters is the road speed at which the numbers are recorded, not the engine speed. I'm thinking that when they see borderline fails for either HC or NOx, they run the car in a lower gear (?) to try and keep the converter hot.

Like someone else said, I'd try a new O2 sensor. An NTK or Denso direct fit and retest. I'd also look for vacuum leaks.

Hint: If there was a way for him to cut back the ignition timing, I guarantee it'll pass. The catch is doing this so it's undetected.

 

Problem solved.


Jk bud. Hope you get this handled. Cant wait to check out the car....

 

On todays test screens there is no real time data showing emissions during the test only the mph. Good theory but they changed the system so you cant manipulate it.

 

Good theory but they changed the system so you cant manipulate it.

Volkswagon begs to differ. Seriously, that was brilliant, maybe wrong, but still brilliant.

 

Lol that was good. Kind of different how they did it though. Once the smog tech plugged into the cars obd2 port it triggered the cars computer to change the tune to pass smog. Pretty genius but they are paying for it now

 

The tests were performed at two different smog shops, fortunately both times I wasn't charged.

I'll report back once I have time to accomplish some work on the car.

Thanks for all of your help!

 

maybe that EGR isn't getting activated properly. There is a combo of temp sensor, and vacuum line to control the valve, plus some EGR valves are very sensitive to backpressure.
One other thing with TPI is the EGR passages like to clog, especially in the little runner tubes. It may be cutting down the flow