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Emissions failing

I have a 1992 Toyota Land Cruiser that I am having a very hard time passing emissions. I have new o2 sensors, new catalytic convertors, it has been timed to spec and I just placed a new MAF sensor on it. I am failing emissions because it is still running way too rich with the CO reading in the 80s while the passing range needs to be less than 20. I have been to several mechanics who don’t seem to know the answer because no codes are being displayed. I have spent several thousand dollars on it (including an engine swap) and can’t seem to get it running right and now I have an emissions waiver because I met the requirement. I can’t sell the truck where I am at while not having passed. Any advice?
Thank you.
Bryce Carter in Denver, CO

Sell it someplace else? I live an area without emissions testing and often do see people from other areas post around me for this reason. Sounds like it’s time to cut your losses and run.

As for telling you why it runs rich, common reasons include things like faulty coolant temperature sensor or thermostat, leaky fuel injectors, fuel pressure regulator, bad spark plugs, wires etc. It’s hard to comment in any specific way because all you listed a few things that are new and then just left the rest under: “I have spent several thousand dollars on it (including an engine swap) and can’t seem to get it running right and now” That leaves only questions open.

Why was the engine swapped? Has the compression been checked? Does it burn/lose a lot of oil?

If a fuel injector is hung up with dirt or deposits, try some fuel system cleaner like Berryman B-12, Star-Tron or Sea foam. If you have throttle body injection you may have to change the injector because it’s just plain worn out. If the exhaust leaves a black spot on the ground when idling you should consider changing the injector without trying the fuel treatment.

For multi point fuel injection, try pulling the spark plugs and change the injector to the cylinder with the black deposit on the plug. High HC is a fuel system problem or poor ignition. Be sure that you have the correct rotor in the distributor and a good ignition coil or igniter. Usually if the engine starts well, the igniter is OK.

As you have discovered, trying to keep 20+ year old vehicles on the road in emissions control areas can be almost impossible…The emissions control systems installed on your vehicle are 3 or 4 generations behind the times…Mechanics skills and diagnostic equipment have moved on and they have little interest in working on vehicles like yours…

So list it for sale as a parts vehicle as it can’t be registered in the emissions control area…Mention that those living outside the Front Range emissions control area can register the truck if they wish… But for you it has turned into a money-pit and it’s time to move on…

Maybe the engine you installed is not in the best of shape. The first thing I’d want to know is compression results.

Did those code-readers masquerading as mechanics even pull the plugs? That will tell you a lot about running rich. Did you buy universal cats at McParts? Sometimes they are of questionable quality.

The ODB-1 system on these trucks are not very sophisticated. Unlike '96 and newer ODB-II systems, there is no misfire detector, catalytic converter back check, vacuum monitor, or sensor back-checks. Problems with these cars need to be diagnosed the old-fashioned way. The engine must be checked for mechanical soundness. The injectors and sensors need to be checked for proper operation. Many of the younger mechanics don’t know how to do this and are trained to read the scanner and follow a technical flow chart.

Who advised you to replace those parts? Did you know the coolant temp sensor can also affect fuel mix? So can a leaky or stuck injector. Any of those items you replaced can easily be checked before paying out the dollars to change them.