Help, failed MD state emissions test

[thom]

Happy New Year

My 86 failed 2 exhaust emission test, listed below are the test readings, and some results a friend and I discovery from a "SCAN" tool test.

Hydrocarbons Carbon Monoxide Oxides of nitrogen
HC CO NOx
standards 1.8000 GPM 30.0000 GPM 2.8000 GPM
tested 2.4400 GPM 66.0517 GPM 1.0944 GPM
results FAILED FAILED PASSED

I was a bit surprised because its running great, no codes, no driveability problems, good throttle response...etc

Results from "SCAN" tool diagnostic procedure, tested with engine at 'NORMAL" operating temperature (of course).

Coolant temp reading above 90C

Oxygen sensor reading 400-500mv (when first checked showed above 600mv, but after monitoring it dropped into the 400-500mv range.

OPEN or CLOSED loop: indicated it was always in 'OPEN LOOP'
never went to 'CLOSED LOOP'

Were do I go from here??? Thanking you in advance, for all your help!
Thom

 

[Hib Halverson]

How many miles are on this vehicle? Has the cat ever been replaced? If so, how many miles are on it?

Additionally, you say the scan tester showed the engine controls *never* went into closed loop. Is that correct?

Also, this scan test you did...was it only with the engine at idle or did you road test the car with the scan underway?

 

[thom]

Ken & Hib

Thanks,

Answer to your questions.

Before the test, it was driven several miles (10-12), and waited in line with the motor running, temp was up around 200.

Hib,

I have over 95k miles, and the cats have never been replaced, when conducting scan test it was at idle and with variable RPM'S.
As mentioned, performance is great, question is, if it was a cat problem, would'nt I notice very poor performance.

Right, the scan tester and the 'SERVICE ENGINE SOON' light indicated it never went into closed loop.

Could it be a bad, or problem with the ECM ????
Thom

 

[rrubel]

12 miles is not enough time for the engine to warm up and enter its proper cycle. I drive my cars at least 30 miles beforehand. In fact, I think our little booklets say to drive 20 miles.

Alternately, you could try a different testing station and ask for an exemption based on height. A number of us MD Vette owners have been able to get renewable exemptions (myself, Sothpaw, I think Mad Mic, and some co-workers of mine at the least). We've had good luck at the Glen Burnie station and at the Mt. Airy station.

Also, you can buy a can of stuff at Pep Boys or AutoZone that guarantees a pass. They'll know the name of it there - it's popular!

Now if there IS something wrong with the car, get it fixed... but if you need more time than the state wants to give you, try the above solutions.

[RICHR]

 

[vettenick]

High CO is because it's running rich. Since the O2 sensor is not registering above 800 millivolts, it may need replacement. The ECM looks at the O2 senor switching (that's above and below 450 mv) before it goes into closed loop. You'll never pass unless it goes into closed loop. Try spraying a little carb cleaner into a vacuum nipple while looking at the O2 senor voltage. If the voltage doesn't go to at least 800 millivolts, it's dead.
When the ECM sees low voltage it thinks it's running lean, so it enriches the mixture to try and compensate.

Good luck.

 

[bradfordsvettes]

my guess is a lazy o2 sensor or not working at all . how is the coolant temp the ecm along with o2 sensor readings also checks engine temp and run time steve

 

[grapeknutz]

A shot in the dark, but the injectors could be the culprit!

 

[XJ6GUY]

if it was me i'd replace the o2 senser and change the oil,
just my 2 cents

 

[vetteguy]

Thom, we must be neighbors. I hate the MD Emmis. Test. I would try changing the 02 sensor. I replaced one in my 85 and it was only like $20. It probably needs it anyway. Good Luck, Guy

 

[Rich96c4ce]

Happy New Year

My 86 failed 2 exhaust emission test, listed below are the test readings, and some results a friend and I discovery from a "SCAN" tool test.

Hydrocarbons Carbon Monoxide Oxides of nitrogen
HC CO NOx
standards 1.8000 GPM 30.0000 GPM 2.8000 GPM
tested 2.4400 GPM 66.0517 GPM 1.0944 GPM
results FAILED FAILED PASSED

I was a bit surprised because its running great, no codes, no driveability problems, good throttle response...etc

Results from "SCAN" tool diagnostic procedure, tested with engine at 'NORMAL" operating temperature (of course).

Coolant temp reading above 90C

Oxygen sensor reading 400-500mv (when first checked showed above 600mv, but after monitoring it dropped into the 400-500mv range.

OPEN or CLOSED loop: indicated it was always in 'OPEN LOOP'
never went to 'CLOSED LOOP'

Were do I go from here??? Thanking you in advance, for all your help!
Thom

Gotta be closed loop mode in order for the system to work properly. The closed loop mode uses all the sensors and constantly modified the A/F ratio, spark, and etc. to minimize emissions. The open loop mode is typically used during warm-up and for limp home operation. Sound to me like you have some sensor that is not working or the computer is not thinking correctly, or you have some burned-out tell-tale bulbs.

Good luck. I just got my '88 Caravan passed an hour ago, with it running way too cool, about 120F . Thought it would fail!

 

[RedRagTop]

What the hell is an emissions test???:t

Lovin' the clean air of Canada!
Even if it was -43F here this morning...

 

[grapeknutz]

How many miles on the engine? The O2 sensor readind seem ok, I still think it might be the injectors are the problem. ( bad spray or dripping)

 

[Robertwav1]

I would think all the basics should be performed, like a tune up. Plugs cap rotor if it has one, air filter. I would change the O2 sensor absolutely. A tuned car should pass emmission tests anywhere. Also there is an emmission cleaner which was mentioned here, I would have that done also. Good Luck!