HC a little high - why?

Hi all.

81 Scirocco has 255K+ miles on original motor. Wife drove it less than 3400 miles during the last 2 years. It seemed to be running good, so I just drove it to the smog tester without any interim hard driving. It failed. HC was 90/110ppm at 15/25mph 2 years ago but is now 190/150 (max is 162/132). CO has risen slightly, NO has dropped slightly, but both less than 50% max.

CATC and Oxy switch about 4 years old. Air filter old but well within mileage limit. The engine uses about 1.5qt oil per 500mi (almost all short trips) and is due for oil change. Wonder which of the following might bring HC into spec.

  1. switching from the usual Castrol GTX 20-50W to a full synth 20-50W, then taking a long drive
  2. new air filter
  3. new spark plugs
  4. new CATC (only 10K mi but I'm told high oil consumption ruins catalysts. Is it possible to clean a CATC subjected to excess oil?)

Thanks.

nf

Reply to
nutso fasst
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I would guess that the engine has deposits on the inside of the cylinder head and combustion areas. I like #s 1-3 but instead of #4 try some SeaFoam in the gas tank before your long drive. Oh and add a new BOSCH cap & BOSCH rotor and some good spark plug wires. Cleaners along with a good long drive can work wonders cleaning up the combustion chamber IMHO.

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can find it at some auto parts stores and even Menards Make sure that the frequency valve near the fuel distributor is buzzing after the engine has been warmed up.

later, One out of many daves

Reply to
dave AKA vwdoc1

Yep, I pulled a couple of plugs. The electrodes looked good but the rim is carboned up.

Last smog check I added Techron and drove 200 miles after car flunked HC. Next test, HC, CO and NO were all high. Problem turned out to be a vacuum leak in the rubber boot, so maybe Techron was useful but no way to compare. This time I bought some WalMart FI cleaner that promises not to harm Oxy sensor or CATC. Also putting in Mobil 1 'old car' 10W40 oil ( $5/qt, yikes!) and Bosch Platinum Plus plugs. Then, a long drive. Hope this works!

Anyway, thanks for the comments & suggestion.

nf

Reply to
nutso fasst

I would prefer you use the less expensive copper in that engine or the triple side electrodes. I have seen some issues with the platinum plugs so I don't use them in the

1.6l or 1.7l engines.

I would have thought that the CO would have been lower with a vacuum leak.

BTW Your CO can be adjusted with a Dwell meter.

let us know what happens! ;-)

Reply to
dave AKA vwdoc1

The reason platinum appealed to me was that it supposedly oxidizes HC, which, if true, means that it's a lousy electrode for anything but smog checks, where it might have a positive effect. But I took your advice and went for the 'Super Plus' copper instead. Initially I felt no difference, but on a 26 mile ride today, I was very pleased. I don't recall when the car has run so smoothly. Engine seems to approve of that 'high mileage' Mobil 1, too, as water and oil temps stayed well within range, in spite of high RPMs.

I know nothing of "triple side electrodes." I had a hard time finding copper 'Super Plus' as opposed to the readily-available platinum.

Dunno about that. I never got a detailed receipt for work done.

There is a CO adjuster screw in the fuel distributor. How would a dwell meter help?

Will do. Thanks again for advice.

nf

Reply to
nutso fasst

read some info here

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(page 103) or better yet read here
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I think the triple side electrode spark plugs are: Bosch WR7DTC or W7TDC. Sold at stores that handle VW parts, or the dealer.

Those Super W7DC should last 6,000 miles maybe. ;-)

Hmmm I need to research platinum and HC reduction! thanks!

Reply to
dave AKA vwdoc1

"dave AKA vwdoc1" wrote

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Excellent suggestions. Thanks.

The old W7DCs lasted a lot longer than that.

The 'Super Plus' part number is 7200, but in small type on the box: WR7DC+. Super Plus have a "Yttrium-enhanced copper core". I called a couple of VW parts stores and was told that WR7DTC is discontinued. WR7DC+ is the recommended replacement. I did find one store that still had four WR7DTCs - at $4.50 each.

Engine has a repeatable 'rough cold start' symptom that I wasn't really paying attention to. Listening when someone else starts the car, it's clear it's running on 3 cylinders for the first 4 seconds or so.

nf

Reply to
nutso fasst

Dwell meter basically measures duty cycle, you hook it up to your frequency valve and use that to tune the mixture. you want basically a

50% duty cycle which means a 45 degree dwell reading on the 4-cylinder setting (did I get that right? it's been a while since I've done that)

nate

Reply to
Nate Nagel

you da man nate! ;-)

Reply to
dave AKA vwdoc1

Thanks. After asking I read all the way through the web page that Dave linked to (beyond the "not recommended" section) and saw that the question was answered. I wonder how many mechanics know about this. Wish I'd seen that article a few years ago.

nf

Reply to
nutso fasst

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