1992 Ford Bronco Failed California Smog Test

Tiny
K6PNG
  • MEMBER
  • 1992 FORD BRONCO
  • V8
  • 4WD
  • AUTOMATIC
  • 174,000 MILES
My 1992 Bronco just failed the California smog test. I had it tested at a "test only station" and they would not give me any advice what might be wrong. The Visual and Functunal tests passed, the emissions test numbers that failed are the CO (%) the numbers are:
at 15 mph
max allowed=.60 average=.12 measured=1.57
at 25 mph
max allowed=.79 average=.09 measured=1.85


thanks for helping,
Ray
Do you
have the same problem?
Yes
No
Wednesday, May 27th, 2009 AT 6:18 PM

7 Replies

Tiny
RASMATAZ
  • MEMBER
Carbon monoxide failures indicate an overly rich fuel mixture. On older carbureted engines without electronic feedback controls, look for things like a stuck choke, misadjusted or fuel saturated float or a rich idle mixture adjustment. On newer vehicles with electronic carburetors or fuel injection, the system may not be going into closed loop because of a bad coolant or oxygen sensor.

Dirty air filter. A restricted air filter will choke off the engines air supply, causing higher than normal CO readings.

Dirty oil. The oil in the crankcase can become badly contaminated with gasoline if a vehicle has been subject to a lot of short trip driving, especially during cold weather. These vapors can siphon back through the PCV system and cause elevated CO readings.
Was this
answer
helpful?
Yes
No
Wednesday, May 27th, 2009 AT 8:11 PM
Tiny
K6PNG
  • MEMBER
Prior to having this vehicle tested I did the following.
Changed the oil (mobile 1 full synthetic oil and filter)
Cleaned the air filter (K&N Filter)
installed new spark plugs (Bosch Platnum)
installed new O2 Sensor (bosch)
and inpected the rotor and cap (they look perfect)

when I did my pre-test maintenance I dis-connected the battery. Is it possible that the computer reset itself and since I only drove it from my house to the test location that it did not re-configure itself? It is only about 1 mile to the smog station.

Thank you for your help and fast response,
Ray
Was this
answer
helpful?
Yes
No
Wednesday, May 27th, 2009 AT 8:59 PM
Tiny
RASMATAZ
  • MEMBER
Could be possible that the computer is going thru relearning process.

Did you check the coolant temperature sensor might not be switching over to closed loop and dumping fuel when not needed due to an out of range signal
Was this
answer
helpful?
Yes
No
Wednesday, May 27th, 2009 AT 10:36 PM
Tiny
K6PNG
  • MEMBER
I only know of one coolant temp. Sensor and the gauge on the dash seems to be working correctly. I will change this part out since it is not expensive. How long/far does it take for the computer to re-learn everything that it needs to?
Again thank you for all your help,
Ray
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 12:00 AM
Tiny
RASMATAZ
  • MEMBER
Could be 40/50 engne cycles before it picks it up-Could also be a leaky injector/s
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 4:00 PM
Tiny
K6PNG
  • MEMBER
I replaced the Coolant temperature sensor, the coolant temperature switch, Air Temperature sensor, Dist. Cap and rotor and cleaned the egr valve. Had it tested again and it still failed.
I purchased a code reader since I found it difficult to read the code by the flashing light. The system passes the key on engine off tests but I get codes during the key on engine on test. The codes are:
312 thermactor air system/fault during engine run self-test
313 thermactor air system/air not bypassed during self test
213 spout circuit open

thanks for your help/ideas
Ray
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 8:56 PM
Tiny
RASMATAZ
  • MEMBER
Check the air injection system

EMISSIONS PERFORMANCE CHECKS

There are four things you should always check on every vehicle that has a computerized engine control system:

1. Scan for fault codes. Any codes that are found need to be dealt with before anything else.

2. Make sure the system is going into closed loop. No change in loop status often indicates a coolant sensor problem.

3. Confirm that the system is alternating the fuel mixture between rich and lean. This is absolutely essential for the converter to function efficiently. You can do this by observing the O2 sensors output with a scan tool, or directly with a digital storage oscilloscope or voltmeter. If everything is okay, the sensor should be producing an oscillating voltage that flip-flops from near minimum (0.1 to 0.2v) to near maximum (0.8 to 0.9v). O2 sensors in feedback carburetor applications have the slowest flip-flop rate (about once per second at 2500 rpm), those in throttle body injection systems are somewhat faster (2 to 3 times per second at 2500 rpm), while multiport injected applications are the fastest (5 to 7 times per second at 2500 rpm).

4. Confirm that the system responds normally to changes in the air/fuel mixture. To test the system response, pull off a vacuum hose to create an air leak (not too large or the engine will die). You should see an immediate voltage drop in the O2 sensor output, and a corresponding increase in injector dwell or mixture control dwell from the computer. Making the fuel mixture artificially rich by injecting some propane into the intake manifold should cause the O2 sensor output to rise and the computer to lean out the fuel mixture.
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 11:05 PM

Please login or register to post a reply.

Recommended Guides