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  #1  
Old 04-17-2003, 09:08 PM
Harpman
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Angry Smog test Failed on my '86 420SEL????

Here's the background:
107K on the Odo.
New Copper core plugs, 91 Octane gas, 4 year old cat-back Time Valve Exhaust system.
Had the plugs changed to the coppers back in December, since that time the Tuna Boat has has a slight lope to the idle (800rpm+/-).
Two weeks ago I had a Lambda test done, just checking to see if any error messages came up.....shop owner tells me that on my year 420 the Lambda won't show any error messages????
He said, "I checked the "sweep" and it appears to be in the proper range. O2 sensor checks out OK!"....hmmmmmmm?????

Here's the real issue: Went to have the smog test done today, passed the idle, but failed the high speed(rpm) side of the test!

Looked under the hood, saw that the hose from the vacuum control valve to the throttle assembly was NOT connected!!!

On the test, the Tailpipe HC ppm reading @ 2500+/- 300rpm was 258. (No smoke!) And the CO% reading was 5.24. Yet, when he did the 4 gas test it passed?

Did a second test...the readings were 222 & 5.44 respectfully!

Is the hose disconnect the reason for the failure
p.s. - O2 sensor dash light is NOT lit.
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  #2  
Old 04-17-2003, 09:09 PM
Harpman
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P.S.-----

Connected the hose back to the throttle assembly........no more lope! Whatcha think?
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  #3  
Old 04-17-2003, 09:39 PM
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With 5 +_ % CO blowing out of the tailpipe ( after the catalytic converter ), your fuel mileage must be pretty disgusting.
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  #4  
Old 04-17-2003, 10:06 PM
Harpman
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15 mpg -city
24 mpg - highway
?????????????????
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  #5  
Old 04-17-2003, 11:09 PM
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I would do the following:

1. Have another look at the O2 sensor.
2. Check fuel pressure.
3. Possibly an injector "dripping".

Not sure about the vaccum hose you're talking about. Where else does it connect to besides the throttlebody?
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  #6  
Old 04-18-2003, 02:32 AM
Harpman
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Manny,

Thanks for the reply!

1. Would the O2 sensor create the failed test? Do I just R & R the sensor as apposed to testing for failure?

2. On page 14.0712-050/14 of the service manual, it shows the schematic for the Mixture Control Valve, Intake manifold, EGR valve, Vacuum Control Valve and Thermovalve 50 degree C.
The recirculation line or "hose"as I called it...."line" is a more apt term, was disconnected (line was pulled out from the rubber elbow connector) from the Throttle Assembly (that sits on top of the Intake manifold) to the Vacuum Control Valve.

3. Any "easy" way to check fuel pressure?

4. "Dripping"...????? Is there something obvious to the eye that I would look for on an injector?

5. Any help with my first post question? Wouldn't the Lambda test have caught any irregular rich/lean fuel mixtures via the sweep of voltage? The book says the lambda is not operational if the O2 sensor is defective! I didn't witness the actual test...had to take my mechanics (my first visit to this guy in Vegas, he came recommended?) word that the test was performed properly!
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  #7  
Old 04-18-2003, 07:17 PM
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1. O2 sensors, over time, get "lazy", i.e. rather than sweeping, say 5 times/second between rich & lean, they may slow down to 1 or 2 times/second.
This is called " cross-counts".
So, watching the sensor toggle rich/lean is one part, how fast this happens is another matter.
O2 sensors are considered part of a major tune-up. It is as simple to change, as changing a sparkplug on an engine.

A dripping injector would best be isolated by pulling the sparkplugs, and examaning them very carefully.
If one is noticeably different from all the others ( indicating too much fuel ), that would be the injector to suspect.

If you have a fuelpressure regulator with a vacuum line attached to it, pull it off with the engine idling.
Your fuelmixture should go extremely rich instantly, you would hear the enginespeed change quite drastically.
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  #8  
Old 04-18-2003, 09:29 PM
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Some theoretical stuff to add. What follows is taken directly from "Bosch Fuel Injection & Engine Management" by Charles Probst.

Rich mixtures increase fuel consumption and emissions of hydrocarbons(HC) and carbon monoxide(CO) - the products of incompletely burned gasoline.

Lean mixtures reduce power, elevate engine temperature, and increase emissions of oxides of nitrogen(NOx) - a product of combustion at excessively high temperature. They also tend to cause driveability problems.
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  #9  
Old 05-21-2003, 11:26 PM
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Manny..... lazy -OO

Thanks Manny for the "lazy oxygen sensor" tip.

That was my problem with the 300SE (127K miles)
Refer to: 'Exhaust Emissions Test' posted by johnwallace.
I recorded all my data there.

My failure was due to rich fuel mix.
failed the HC and CO portion.

Archives are good education.

Denis
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1989 300SE 148 K miles *SOLD
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  #10  
Old 05-25-2003, 09:40 PM
Harpman
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Manny,

Thanks from me , too!

Indeed, it was the "lazy" O2 sensor on my 420SEL!
Replaced it and it runs like a scalded dog, now!

Keep up the good work !
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  #11  
Old 05-25-2003, 09:54 PM
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Harpman

Next time I'm in " Sin City ", maybe we'll have a beer(s) together.
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  #12  
Old 05-26-2003, 02:58 AM
Harpman
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Absolutely! Would be a privilege!
Email me when your coming!
Love to chat MB's and teach ya "How Not to Get Cheated At A Tittie Bar In Five Easy Lessons"!
Drinks on me and the lessons are free!
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