92 Ranger 3.0L failed NOx

[frdrks]

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. My exhaust tailpipe and muffler did rust/rot off a while back about 4 feet from the cat.

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

 

[alwaysFlOoReD]

I just did some reading on this but I'm no expert. Experts please feel free to correct me.
The egr puts in exhaust gas in order to reduce the temp. of the cylinder. This reduces NOx. So maybe other things are causing higher than normal temp. Such as timing being too advanced or an injector being slightly plugged up making the engine run lean. Try using some injector cleaner and check your timing, making sure the spout* is disconnected.
*the spout is what looks like a fuse, and when pulled makes the computer run the timing at initial with no advance.
Good luck,

Richard

 

[RonD]

Running too lean sounds like your issue, with sluggishness as well

If possible I would check the fuel pressure at the rail, below 30psi at idle will give you a leaner mix. The computer expects a certain pressure and opens injector based on that pressure, if pressure is too low then lean mix is the result.

O2 sensor helps computer(PCM) to set lean/rich levels
You can test the O2 sensors with a voltmeter, they don't start working until they get to 650deg so engine needs to be warmed up.
You should have .1v-1.1v if O2 sensor is working, sweet spot .4v-.7v, below .4v means lean condition so PCM should open injectors longer, above .7v means rich condition so PCM won't open injectors as long.
.0v or above 1.1v means bad O2 sensor.
If O2 sensor is off even by a little it can cause PCM to run engine leaner than it should.
If O2 sensor is at .8v all the time then PCM will run lean all the time.
O2 sensors wear out just like a spark plug does, some say 60,000 miles others 100,000 miles is replacement time, but they do wear out.

MAF sensor also helps control fuel/air so needs to be clean and working.