Emissions issue w/ '93 B2200 (Carbed)

Hello all,

Sorry my first post is a trouble post, but I recently picked up a '93 B2200 to daily (my other car is a Speed3 which, of course, I couldn't leave alone and now can't rely on for daily purposes), and it has now failed VA state emissions twice for high NOx readings. Here are the results:

At 15mph (1763 RPM)
HC ppm: 14 (state limit 162)
CO %: .02 (state limit 1.32)
NO ppm: 1500 (state limit 1000)

And the figures are fairly similar at 25mph so no need to post those as well.

Here are some things that I've done to the truck since buying it that may be relevant:

1.) I've replaced the spark plugs, wires, cleaned the EGR valve, and installed a new cat.

2.) It was having a high idle problem which I traced to an intermittently functional choke thermostat. Having no success finding another choke thermostat anywhere, I remedied this by removing the choke plate and zip tying the fast idle cam down. Not the most robust fix, but workable in the meantime.

Also of note - the coolant gauge doesn't seem to work very well; it will intermittently read, but most of the time it remains pegged on the 'C'. I'm not sure if that sender also communicates with whatever fuel mixture control system the truck has.

Based on the extremely low HC and CO figures, I'm guessing it's either overtimed, running lean, or both. Google did not yield great results finding B series owners with this issue, so I was wondering if anyone here has had any similar experiences. Your thoughts?


Thanks,

CJ

Retard your ignition timing to around 2 degrees BTDC as a work around to the high NOX numbers, then reset it to 6 BTDC after the test. The emission testing stations have training mode set ups that they can check your truck before they actually test it.

http://www.mazdatrucking.com/forum/showthread.php/11089-Smog-Problems-And-How-To-Correct-Them

"Also of note - the coolant gauge doesn't seem to work very well; it will intermittently read, but most of the time it remains pegged on the 'C'. I'm not sure if that sender also communicates with whatever fuel mixture control system the truck has."

Check for a good ground at the front of the head. It is a single wire that may have a loose connection.

"Also of note - the coolant gauge doesn't seem to work very well; it will intermittently read, but most of the time it remains pegged on the 'C'. I'm not sure if that sender also communicates with whatever fuel mixture control system the truck has."

On these trucks, all the air must be purged out of the cooling system, and not so easy to do on these. I jack up the front end, take off radiator cap, and run engine 20 minutes, adding 50/50 coolant as necessary.

How far are you on this? I Have a 89 b22 carbed as well. It passed smog but the tech failed me because of exhaust leaks.

Well after i fixed the leaks it began running like cr@p. Well i changed almost everything you can think of, worth changing, and it doesn't pass still. It runs really rich and I've had the brand new carburetor tuned twice now.

Are you running a stock Mikuni carb? They are designed to run rich until they go into closed loop operation. The o2 sensor has to be working. The EGR valve has a wire on it that feeds a signal to the ECU. There is a heater under the carb that is designed to get the carb off the choke sooner. Check to see it your choke heater wire is plugged into the back of the alternator and that the choke is opening all the way. Just some things to check.

Ok sorry for taking your thread hostage. Stock carb, yes. Mikuni, idk.
So i followed the o2 sensor at the connector and on the truck side of the connection the wiring is frayed a bit. Idk if this is supposed to be grounded to something or wrapped. Thanks tweak

Heres a picture. Theres exposed wiring threading off in the area around the black tape. Does anybody know the deal with that?