Hey everyone, my first time posting here.

I have a problem with my 92 ranger passing smog. (California)
I took it in for the first test and it passed all the tests except the NOx levels at both 15 and 25mph. The other readings were great, way below the limit.

I know this year model is not equipped with a EGR. I fixed a couple small vacuum lines that connect to the air filter box and some small lone canister up near the firewall. I ran an entire bottle of this "Guaranteed to Pass" solution in a full tank of gas. Got the truck warmed up and took it for a 2nd test. Failed again with almost identical results.

I started to suspect the catalytic converter. I took the converter out and inspected it, none of the meshes/screens are broken and nothing is loose inside. Im pretty sure its the original CAT that came with the truck in 92. Im a little lost of what to try next, i'd buy the CAT but worried ill just waste the money being that it might not be the problem. No check engine codes either. Truck has 140,xxx miles.

An issue i ran into 4-5 months back, when starting the engine in the morning when its cold out i can easily take off without warming up (even tho i still do). However, during the day if the engine is cold and i try to take off without warming up, it would bog and even died on me before. When it died i had to wait 10 minutes before i could get it to start again. Oddly enough it seems to have stopped. However, it still drives very sluggish. I can floor it sometimes and get very little response. Can the CAT still be defective even if it visually looks okay? No sign of blockage and i can see light come through.

Test Results

15mph
CO2: 14.30
O2: 0.00
HX Max: 124, Ave: 37, Meas: 12
CO: Max: 0.75, Ave: 0.14, Meas: 0.18
NO: Max: 1020, Ave: 290, Meas: 1424

25mph
CO2: 14.19
O2: 0.00
HX Max: 104, Ave: 28, Meas: 0
CO: Max: 0.95, Ave: 0.13, Meas: 0.06
NO: Max: 880, Ave: 243, Meas: 1480

 

High NOX is a function of either lean operation (fuel pressure too low, fuel filter plugged, fuel pump not functioning correctly:these can be addressed by measuring the fuel pressure under various conditions), ignition timing incorrect (too much advance), compression too high (carbon build up in cylinders artificially raised compression and creates hot spots, multi-probe plugs can raise compression, incorrect reach can also raise compression), major intake/vacuum leaks can also cause lean operation, which will cause high NOX. A faulty MAF sensor give the computer incorrect information, which can cause rich or lean operation.

140,000 miles is nothing to the cat. They do not wear out or fail over time. They contain no moving parts are are not affected by how much they are used. However, subjecting it to conditions it was never meant to handle (too rich or too lean for extended time periods, misfires, incomplete combustion, oil contamination, antifreeze contamination, overheating) can damage it and cause it to stop working. In any of those causes, you still have to address the reason it failed. In your case, the high NOX is caused by an engine problem, and it is likely related either to a need for a tune up, incorrect settings, or age causing seals and gaskets to deteriorate, causing a lean mixture. Most high NOX situations are caused by lean operation, especially since your other numbers look good.

A faulty cat would likely give you high readings on the other gases as well.

Replacing the cat might reduce your NOX readings, but it would be a temporary fix, next year the symptoms would likely return.

Hopefully this is helpful to you. The 3.0L in your year has a distributor, it is not just possible, it is likely that the timing could have drifted or been adjusted incorrectly. And the upper and lower intake gaskets are made of rubber. Rubber hardens and shrinks and cracks with age, which causes leaks. Leaks cause unmetered air to get into the engine, which means its leaner than the computer thinks it is. It is not uncommon for engines with your mileage to have this issue, and especially with the age on top of it.

Injectors wear out, and the spray pattern is less precise, which can create lean pockets due to poor atomization, which will cause high NOX. Run a good injector cleaner, and decarbon your intake. Getting that crud out usually makes the engine run better, and emissions often improve as well.