1FZ NOx Fail - Emissions

[WalterGreen93]

Hello Folks,

Need your help. My 93 1FZ failed emissions again today with too high NOx levels. Prior to this I’ve replaced the O2 sensors, plugs, wires, cap and rotor. Cleaned the throttle body, replaced the fuel filter, air filter, PCV valve. I’ve been running premium since the last fail a month ago, and put a bottle of CATAClean in the tank this morning on the way to the test station.

I assume the catalytic converter is the next thing to replace, but I’m also wondering if the EGR valve has anything to do with these results. Any help or suggestions would be much appreciated.

 

[audi2nr]

Make sure the egr system is working properly. The egr system is specifically there to combat nox, check egr vac lines/ egr temp sensor and egr valve, and the egr vsv and wiring. Could also have clogged egr gas port too.

 

[BILT4ME]

Also look at IAC Valve operation and tubing.

Have you cleaned the ports in the intake manifold that get clogged by the EGR?

Is the CATAKleen an isopropyl alcohol based product?

I have read about many others that add about 4 bottles of HEET to their fuel tank and run the truck hard for about 30 minutes and keep it hot while in line to keep it in closed loop and running well.

 

[OSS]

NOx is formed when the combustion temperature is too high. That’s specifically what the EGR system is for —reducing NOx.
Other things that can reduce NOx is retarding the timing a bit and alcohol added to the gasoline. It’s perfectly legal to put some E85 gasoline in the tank prior to a test. It has ethanol in it which effectively acts like reducing the timing.

 

[WalterGreen93]

Make sure the egr system is working properly. The egr system is specifically there to combat nox, check egr vac lines/ egr temp sensor and egr valve, and the egr vsv and wiring. Could also have clogged egr gas port too.

I didn’t think of the vac or gas ports being clogged. I think I’ll just replace all of it to eliminate going back and forth. Thanks for your help!

 

[WalterGreen93]

NOx is formed when the combustion temperature is too high. That’s specifically what the EGR system is for —reducing NOx.
Other things that can reduce NOx is retarding the timing a bit and alcohol added to the gasoline. It’s perfectly legal to put some E85 gasoline in the tank prior to a test. It has ethanol in it which effectively acts like reducing the timing.

Sounds like the EGR system needs an overhaul. 30 years and 270K miles and it makes sense. Thank you for the information!

 

[WalterGreen93]

Also look at IAC Valve operation and tubing.

Have you cleaned the ports in the intake manifold that get clogged by the EGR?

Is the CATAKleen an isopropyl alcohol based product?

I have read about many others that add about 4 bottles of HEET to their fuel tank and run the truck hard for about 30 minutes and keep it hot while in line to keep it in closed loop and running well.

I thought I cleaned the intake pretty darn good but maybe I inadvertently clogged them by doing so. I also couldn’t find HEET at the local AutoZone but Ill give it a try. Thank you for the information!

 

[BILT4ME]

I thought I cleaned the intake pretty darn good but maybe I inadvertently clogged them by doing so. I also couldn’t find HEET at the local AutoZone but Ill give it a try. Thank you for the information!

There is one in particular just behind the throttle body that fairly sizeable, but it's a long port and is frequently the issue. it's on the top (internal) side of the intake manifold.

 

[WalterGreen93]

There is one in particular just behind the throttle body that fairly sizeable, but it's a long port and is frequently the issue. it's on the top (internal) side of the intake manifold.

I took a look at them this evening and they are all dried up and brittle. I’m going to replace all of them tomorrow. Thanks again for your help!

 

[BTLSHP]

I am trying to assess our '94's ability to pass CO Frontrange emissions standards/test prior to shipping the car out there where it will reside with the owner's granddaughter. In Maryland, it is exempt from emissions testing and the local dealer and mechanic lack tailpipe test systems, the State will not help because the car is exempt. I am looking for a garage that has the gear..... I understand the Frontrange requires CARB compliance and this is a not a California car.

As of right now:

EGR system is functioning per the FSM and ports in the IM thoroughly cleaned. The VSV seems fine in terms of testing th solenoid operation with a battery and resistance. Vacuum lines are all new. The EGR valve now moves freely but I do not have actual vacuum gauge pressures.

Pair system is ok.

The bank 1 O2 sensor is new (CEL 21 cleared), the bank 2 is five years old. Both seem to ticking nicely between rich and lean on a Toyobd1 device.

I have no information about the CATs as this is an OBD1 car, but I have no reason to believe they are deficient at this point.

Plugs, wires and distributor are less than 20k miles old.

I am a bit concerned about CARB vs EPA standards, does this put passing out of reach?