pishta

First time it failed smog. Had it for 6 years (3 tests ) and all passed except one with a cracked intake hose, passed visual after that. So now I have 129 HC (73 is limit) and 531 ppm NO (487 limit). Strange that the HC failed on the 15mph @ 1452 RPM and the NO failed on the 25mph @1410 RPM. We did the plugs 2 years ago (170K) and now it has 214K. WE have never touched the 4 O2 sensors so we are replacing all 4 (Amazon has a great deal both upstreams for $42/pr and both downstreams for $46/pr. The cats are not great as one (or both) have the catalyst bricks coming apart as it sounds like some rocks in the mufflers, but it has been like that since the last smog test and it passed with great numbers. So I took the EGR apart and the bearing is perfect, spotless in the top section. I pushed a 1/4 extension through the top EGR passage in the intake and It was a little scaled but I hit something at 4" in the hole. This seems to be right where the plenum turns to the throttle body section but nowhere close to the throttle blades. Am I hitting an obstruction? Bad NO usually means EGR is not working creating higher cylinder tempos and that creates NOx. I also made the mistake of testing it on regular gas when it says it needs premium. Would that F my test results? I don think I used premium for any of the last tests.

KahnBB6

iTrader: (5)

It is entirely possible that you need to clean out the upper intake manifold's Y-plenum. It can get clogged after 20-25 years of use. Hilariously, Toyota/Lexus published NO official procedure for doing this in their TSRM.

Did you get a CEL Code 71 for "Obstructed EGR passage or malfunctioning EGR circuit"?

In 2016 I had to do this myself and made two DIY threads with a step by step picture guide detailing how to do it. I will add that for the MOST thorough cleaning you would want to take apart all the exterior aluminum manifold parts, then remove all the factory freeze plugs (but hold onto them for later reassembly) and then send it to a shop that will give it a thorough sonic cleaning bath.

Then you would want to spray the aluminum in new 500F VHT Clearcoat in order to re-seal the porous aluminum to protect it from getting oil and smudge stains.

Doing this helped me pass smog in 2016 when everything else still failed. I hope it helps!

https://www.clublexus.com/forums/per...-cleaning.html

https://www.clublexus.com/forums/per...manifolds.html

pishta

This 92 is <OBD2 so there are no codes to read with a traditional OBD2 scanner. My intake is a 1UZFE so the EGR is a stepper motor and the port looks more accessible a its on the driver side and just goes straight in unless it hits a cast T somewhere in the plenum at 4". I supposed I could open the butterflys and shoot some compressed air in there to see if I have good flow? Taking the manifold off is not out of the question. I do want to investigate your 2 EGR sensors. I do see a thermo sensor in the bottom of the EGR passage. I dont have a Vacuum sourced EGR, it is electric.

t2d2

iTrader: (8)

Here's a few pictures that may help from when I ported the upper and lower intake manifolds on my '94 SC400, along with an EGR delete.

Looking through the TB opening, at the upper EGR tube (and cold start injector):



Cleaned up, EGR pipe removed from manifold and opening blocked off:



Bottom side, for layout and plumbing reference; that horizontal groove between the CSI and PCV is the remnant of the EGR channel that I fully removed:



DIY block-off plate, maintaining the PCV barb:

KahnBB6

iTrader: (5)

My 1993 SC300 is pre-ODB2 as well and I drove and maintained it in California for years. It has OBD1 and that system does register codes if something is off... but it doesn't remember those codes in the ECU's memory so as soon as you fix something that was off... the CEL code goes away almost instantly (or comes back and goes away and comes back, etc. if the issue is intermittent).

OBD1 cars don't use a code scanner the way OBD2's use (although technically there is an old vintage Snap-On scanning tool that will work... but there is no real advantage to that function with it on an OBD1).

You read the OBD1 CEL codes in flash sequences of the in-cluster CEL light. You take a paperclip and bend it to bridge pins TE1 & E1 on the diagnostic port on the lower left side of the driver's side below and to the left of the steering wheel to engage the CEL code reading mode. As for the counting you just have to count the flash sequences manually with your eyes. If you get a bunch of codes you write them down. There's a first number determined by the number of flashes, then a short pause, then a second number determined by another number of flashes... and that represents one CEL code. If there is more than one CEL code then all of that is followed by a longer pause and then another of the same number sequence, a short pause and then more flashes... and so forth. How many long pauses totally depends on how many different CEL codes the ECU is registering at that time.

There is a key chart available of common Toyota/Lexus OBD1 CEL codes.

.....

And since I somehow missed this and I apologize. I thought you had an SC300. Yes, the SC400's EGR uses an electric stepper motor unlike the SC300's mechanical/vacuum diaphragm EGR valve.

This means the cleaning guide threads I posted above do not apply to your car, sorry.

However the basic principles involved in cleaning out clogged EGR passages by accessing parts of it through factory intake freeze plugs would still apply... if such EGR passage freeze plugs exist on the 1UZ-FE.