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Failed Smog Test - Making Adjustments
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EZ Gruv
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PostPosted: Fri Jan 22, 2010 3:01 pm    Post subject: Failed Smog Test - Making Adjustments Reply with quote

So, for the first time since I bought my bus 8 years ago, it failed emissions testing.

My idle speed CO was 3.28% (bus idles at 910 rpm), when the limit is 2.50%. It was within specs at 2800 rpm.

I read in Bentley to adjust the CO by turning the adjusting screw on the AFM. I guess I need to turn it counter-clockwise to lean it out some.

My question is (searching hasn't found an answer yet) without having it hooked up to an analyzer, how far do you turn it to go down 0.78%ish? Any ideas?

2.0L Type IV FI
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PostPosted: Fri Jan 22, 2010 3:15 pm    Post subject: Reply with quote

No good answer from me but just a shot in the dark... why not lean it until it sputters and then richen it a bit while keeping track of where you started from?
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PostPosted: Fri Jan 22, 2010 3:40 pm    Post subject: Reply with quote

Quote:
why not lean it until it sputters


Coming from carbed cars I would have said the same but with the Bosch FI - no - don't do that. First it won't even get you close. And, if you are running at over 3% CO that is really rich. You need to find out why if it has drastically changed as to CO. A Federal 2.0 runs at 1.1%- 1.5% CO typically. What was it last test?

Hi CO means too much fuel is being pumped into the engine. If you haven't tampered with the mixture it should not have changed on its own. Several things can cause that. A bad TSII that is telling the engine it is colder than it really is can fool it into a rich mixture. A leaking injector can cause it. A failing pressure regulator that kicks up the fuel pressure can cause it - so can it if the small vacuum line to the fuel pressure regulator is bad. A sticking AFM door or a dirty air filter.

If you change it without determining why, you may be trading one issue for another. Example - you will make it lean at RPM if you adjust it at idle because unlike a carb, on FI the bypass always bypasses air even at RPM and it affects the mixture across the board.

I would replace the TSII sensor and the air cleaner then test again. Also check the timing and dwell. The base signal for FI comes from the distributor pulse. The ECU then adds or subtracts fuel for temperature and load. The TSII controls what temperature the engine thinks it is at.
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EZ Gruv
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PostPosted: Fri Jan 22, 2010 3:54 pm    Post subject: Reply with quote

I've never touched the mixture setting before.

I replaced the TSII back in August when I was having starting issues. It wasn't the issue, but it got replaced regardless.
At the same time I replaced the fuel pressure regulator (which was the issue), I am now getting the proper amount of pressure when I hook up the gauge.
The AFM door swings smoothly. The air filter could be dirty, don't remember when I changed it last.

Unfortunately I have no idea what the CO tesed at last year, since we only get a detailed printout if it fails.

For the record, I adjusted the valves, changed the oil, checked the points, dwell, and timing last week before my road trip. The spark plugs are 5 months old.
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PostPosted: Fri Jan 22, 2010 4:02 pm    Post subject: Reply with quote

Like SG said about the fuel pressure regulator. If the vacuum hose is off or bad it will cause high fuel pressure. That's easy enough to check. Also, as far as the temp sensor 2. i believe you can check it easily with an ohm meter to see if it's within limits. They are only about $20 as I remember. You might also check as see if there is corrosion around the threads where is screws into the head.
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PostPosted: Fri Jan 22, 2010 4:06 pm    Post subject: Reply with quote

Eric,

Humor me and check the resistance in the spark plug wires to see if any of them are off the scale.

I would likely invest in some new spark plugs since it is cheap to do.

Was the engine well warmed up prior to the test? Oil freshly changed? Charcoal canister correctly hooked up?
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PostPosted: Fri Jan 22, 2010 4:09 pm    Post subject: Reply with quote

Randy in Maine wrote:
Eric,

Humor me and check the resistance in the spark plug wires to see if any of them are off the scale.

I would likely invest in some new spark plugs since it is cheap to do.

Was the engine well warmed up prior to the test? Oil freshly changed? Charcoal canister correctly hooked up?


Will check those wires. The engine was warmed up; I drove about 30 minutes (home from work) and the flaps were completely open. I'll do a long freeway run before the next test.
I changed the oil just last week, and the charcoal canister is properly connected.
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PostPosted: Fri Jan 22, 2010 4:20 pm    Post subject: Reply with quote

if the CO is high it implies low oxygen. The low Oxygen is robbed by either too much EGR leaking back in or too much fuel burning. If the plug wires are bad then the unburned HC's are high but CO is low and O2 is high. We don't have his other numbers so we don't know what they are. If this is a dual bed cat bus then CO high can be caused by a failing cat but I don't think that is the issue here.
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PostPosted: Fri Jan 22, 2010 4:31 pm    Post subject: Reply with quote

Non-Catalyst.
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PostPosted: Fri Jan 22, 2010 4:47 pm    Post subject: Reply with quote

Was last years test with the old AAR installed by any chance? the mixture may have been set to compensate for it's issues. You really need to get it on an analyzer to set that screw right, there's a fine line between just right and high Hc's from a lean misfire.
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PostPosted: Fri Jan 22, 2010 4:48 pm    Post subject: Reply with quote

busdaddy wrote:
Was last years test with the old AAR installed by any chance?


Indeed it was.
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PostPosted: Fri Jan 22, 2010 7:28 pm    Post subject: Reply with quote

Quote:
Was last years test with the old AAR installed by any chance?


BusDaddy - you know this bus? No where in this thread is AAR or AUX mentioned as having been replaced.
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PostPosted: Fri Jan 22, 2010 8:10 pm    Post subject: Reply with quote

Yes, the aux air regulator was replaced a couple months ago. My old one stopped functioning and my bus wouldn't start when cold.
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PostPosted: Sat Jan 23, 2010 1:08 pm    Post subject: Reply with quote

So after looking at the valves again (all at spec), air filter (clean), dwell, timing, and idle...everything ok.
I went ahead and tried the mixture adjustment. The smog tech was cool and let me do it while connected to the machine. Still couldn't get it down enough.

I went ahead and took it to the one mechanic in town that I know really KNOWS FI VWs. He made the same adjustment until the adjustment screw came out completely. Shocked After putting it back in and positioning it about halfway within its home, he popped open the AFM itself. He made an adjustment to the spring tension. He said this adjustment will tell the system to use less gas.

Passed the test on the first try. I went from 3.28% CO to 0.72% CO.

Plus, my engine should be happier after the adjustment.
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PostPosted: Sat Jan 23, 2010 2:29 pm    Post subject: Reply with quote

Keep an eye on your plugs for the next while, fiddling with the spring in the AFM alters the mixture profile over the entire RPM range, maybe it was off, or maybe your TS2 was lying to the computer.
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PostPosted: Sat Jan 23, 2010 2:32 pm    Post subject: Reply with quote

Yep, I made a note to check everything over in 30 days.
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PostPosted: Sat Jan 23, 2010 2:35 pm    Post subject: Reply with quote

For the benefit of the esteemed readership here:

Now you need to know (because this is important for the exhaust valves) the high rpm mixture. The spring adjustment was one of two possible adjustments and he chose the one that has a greater effect upon the upper rpm range. Had I been there, I would have moved the wiper clockwise to lean the idle right there, and then I would have relaxed the spring as necessary to bring the high rpm back to where it needs to be.

You said your high rpm CO was within specs, what we need to know is if it leaned out with the spring adjustment. This could enter valve burning territory. An idle of .72% is lean, but it doesn't have too much effect on exhaust valve tempereratures. Too lean at high rpm or under load, however, is trouble.
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PostPosted: Sat Jan 23, 2010 3:43 pm    Post subject: Reply with quote

yeah yeah yeah!
what was the 15mph/ 25mph co% reading on your passing test?
do they do the dyno test in vegas?

maybe the mech adj the wiper too???did he say?

good thread. im in this smog world too!
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PostPosted: Sat Jan 23, 2010 4:57 pm    Post subject: Reply with quote

Eric let me know where this Tech is cos i may need to use him!!
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PostPosted: Sun Jan 24, 2010 2:01 am    Post subject: Reply with quote

pkrboo wrote:
Eric let me know where this Tech is cos i may need to use him!!


Youll know soon if his motor burns up, then you may not want to use this guy.
Get a wideband on this thing asap. Smile
Eric we talked by PM.
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