Failed CA smog test

[kc15842]

Failed CA smog test, High NO only at low speed
The last test 2 years ago all other results are basically unchanged. The only difference is at 15MPH NO went from 453PPM to 2183 PPM at 2500 MPH unchanged from the last test.
I checked all vacuum lines from the temp switch to the module and egr. All fine.
Checked the modulator and egr and they also seem to be operating fine.
I'll check the timing. It does appear it was a bit more retarded in 2023.

Any other things to check, thanks for your help!

 

[Hungryhawk]

I would start with least expensive thing. Clean the MAF sensor. Looking for vacuum leak is good.
Do you have a OBD2 reader? If yes it might give readings on your O2 sensors which can directly affect the Cat converter (expensive thing).
Hope attachments help.

 

[Twisted Sid]

I would start with least expensive thing. Clean the MAF sensor. Looking for vacuum leak is good.
Do you have a OBD2 reader? If yes it might give readings on your O2 sensors which can directly affect the Cat converter (expensive thing).
Hope attachments help.

Nothing to clean in a AFM of this generation and where exactly would an obd2 reader get plugged in on these trucks?
I'd start by setting the timing to 5°. It will probably be down on power but then bump it back up to where it is now. I'd also check that your sparkplugs are gapped correctly and in good shape then re-test it.

 

[kc15842]

Thanks, I did exactly that, retarded the timing to 5. It was closer to 7 or 8. I removed the egr modulator and just cleaned and checked function. Removed the egr and same thing cleaned and checked function. Both seemed to operate correctly. I removed the intake hose between the air cleaner and the TB and found the rubber boot had a gapping rip in one of the ribs. So, I'll replace, button it up and go for a retest. I'll also fil it with higher octane gas.

 

[fourwd1]

Nothing to clean in a AFM of this generation and where exactly would an obd2 reader get plugged in on these trucks?
...

It wouldn't, it's pre-ODB2.

There is a procedure you can perform to get the MIL/CEL to flash and interpret the flashes into a code you can look up. It's very basic but better than nothing.

 

[fourwd1]

Some of the errors it can detect are a Rich or Lean air-fuel ratio and the Air Fuel Meter (AFM) circuit.
Those can point to injector related problems, fuel pressure problems, and AFM problems.
Also the EGR and Cat Conv have a lot to do with NOx issues.

 

[kc15842]

Agreed EGR is a main player in reducing NO. So, I ended up:

Replacing the intake hose between the TB and the cold air intake pipe, due to open tear in a rib, very clear leak.

Cleaned the TB special attention on the vacuum ports that connect to the modulator, cleaned and replaced the gasket.

Cleaned the EGR valve- check operation of the diagram- checked good, checked the EGR would open and close. Checked while engine running by applying vacuum- engine stumbled almost dying. - GOOD

Cleaned the EGR modulator, checked while engine running inserted a vacuum gauge between the Q port verifying vacuum.

Checked proper routing and vacuum lines

Found EGR pipe gasket (at Plenum) installed incorrectly partially blocking the port. Replaced gasket and installed correctly.

Reset timing from 7 to 5 degrees at 750 RPM.

Passed with outstanding results.

 

[fourwd1]

Passed with outstanding results.

:cheers:

:cheers:

:thumb3: