'81 240 failed emissions test--barely...

The max CO is 1.5, I think PPM. My 240 went to 1.96 at idle, burned clean at
2500 rpm.

The emissions sheet said that a rich idle mixture causes this. Could a vacuum
leak make it rich? I thought a leak would make it a little leaner, if the leak
was after the throttle plate.

Maybe I should just set my idle a little higher. I can't get my idle
adjustment screw to slow the idle down below 1000 rpm or so, and maybe that
means there is a vacuum leak somewhere. What are the common vacuum leak
points?
KennyH

Horsepower is cheaper than therapy.

 

I did some searching at brickboard.com and found that there's a mixture
adjustment on the injection system, just like the one my '79 Audi 5000 had.
I'll be tweaking it in the morning and revisiting the emissions shop.
KennyH

Horsepower is cheaper than therapy.

 

It would help to know where you are, as that may affect the type of
fuel system you have, and the allowable emissions levels.

In the UK you should be allowed something like 3.5% CO on an engine of
that age (and 1200 ppm HC).

A vacuum leak on its own won't make the mixture richer - what else to
look for partly depends upon what fuel system you have, but make sure
that the ignition system is OK, plugs are good, air filter clean, etc.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

OK. If it is Bosch K-Jet, or one of its varients, then take it slowly
(a quarter turn or less at a time), and *count* the turns so that you
can restore it to the start point.

It is possible to adjust the mixture reasonably accurately by ear, but
if you are not experienced at doing it, an exhaust gas analyser would
help a great deal.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

This morning before I took it to get retested, I checked the timing, then I
turned the mixture adjustment leaner, which decreases idle speed, which I then
increases with the idle adjustment knob. I went as lean as I could with the
engine still running smoothly.

Presto, it passed with flying colors. CO was 1.94, now it's .54. Big
difference. Thanks for the advice!
KennyH

Horsepower is cheaper than therapy.

 

You may have to go back a bit the other way if you have problems with
stalling right after a cold start.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

You may have to go back a bit the other way if you have problems with

None of my cold-start stuff is working, so you may be right. I know the air
bypass valve is closed all the time, and I assume the enrichment circuit is
also bad, as it's hard to keep running for a minute or two.

I still can't believe the thing idles so well with 282K on it. Next project:
Rear bushings.
KennyH

Horsepower is cheaper than therapy.