[DML] Re: New parts don't ALWAYS make your car run better...

["content22207" <brobertson@xxxxxxxxxxxx>]

Slow down and take a deep breath. You're going to be very glad you did
this tuneup. You just aren't finished yet.

Because of the various preceding vacuum leaks, your fuel mixture screw
is set way too rich. That was the only way to meter any fuel at all.
Every ounce of air, except for PCV, must pass over the air sensor
plate. You were sucking air everywhere else. A PO compensated by
dialing the fuel mixture WAY up. What little movement the air sensor
plate then gave the metering piston at least delivered enough fuel for
the engine to run.

Now that the leaks are closed -- EXCEPT FOR THE ACCESS HOLE FOR THE
FUEL MIXTURE SCREW! COVER THAT BAD BOY! -- the air sensor plate is
moving farther and the metering piston is delivering too much fuel.
You're downing your engine.

The proper way to set the fuel mixture screw, also known as the CO2
adjustment screw, is with an exhaust gas analyzer measuring CO2 in the
exhaust stream (there are two access ports in the exhaust crossover
pipe). In its absence you can monitor the condition of your spark
plugs and adjust it until they burn a caramel brown color. It the
plugs are clean and white, your mixture is too lean. If they're black
and sooty (dry), your mixture is too rich. Note that your plugs may
also be in other conditions (oily, melted, bent, etc) which indicate
other problems with the engine.

Your brass screws may be open to compensate for malfunctioning CIS. In
a properly functioning system they should indeed be closed. In a
system that does not move the idle speed motor correctly, they are one
of only two other means to idle the engine (cracking open the throttle
plates is the other). If you're going to idle with the screws, you
need to understand what each one does and how to set them. Contact me
off list (brobertson(at)carolina.net) and I'll walk you through them.
If it makes you feel any better, I have no vestiges of CIS on my car
anywhere. Even removed the ECU. Engine idles just fine on the manual
circuit.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "supermattthehero" <supermatty@xxxx>
wrote:
> Dear DMC Troubleshooting Experts,
> 
> Recently I purchased a bunch of parts from the various vendors to do 
> a BIG tune-up.  This involved replacing all of the vacuum hoses, new 
> ported vacuum switch, cleaning the fuel injectors (ultrasonically), 
> new injectors seals, installing the auto-coolant bleeder, pulling 
> the intake manifold to clean up the 'valley', install new spark 
> plugs, new heater pipe, new MSD Blaster2 ignition coil, new intake 
> manifold o-rings, calibrating the throttle and idle speed switch, 
> and general overall cleaning.  Whew!  So, all of the above has 
> already been done.  
> 
> Let me take a step back for a moment, prior to this, my car was 
> running very well, or so I thought.  Then I started to read the DML 
> more, and started to find little things.  Namely, the three brass 
> screws were all turned open, there was no tamper-plug or plug of any 
> kind on my fuel distributor, and there was some sputtering 
> when 'revving' the engine.  Many of the vacuum hoses were dry and 
> cracked.  So, I installed all of the above parts, and closed all 
> three brass screws.  This leads me to where I am today...
> 
> Now that all of these vacuum leaks are taken care of, (or atleast I 
> think they are) my car starts, runs for about 10 seconds, and then 
> when the RPMS begin to settle down it either idles VERY rough or 
> stalls.  The exhaust is awfully foul smelling.  Now I won't lie to 
> you, the gas in the tank is probably 6 months old, and 93 (yes, I 
> know now that it's wrong and I should be using 87) octane.  But 
> anyway, the last interesting tidbit is that, if I take some tape or 
> whatever and put it in where the 'tamper-proof plug' should go, the 
> car will behave the way I just mentioned above, however it will be 
> accompanied by visible black smoke.  Removing the plug makes the 
> black smoke go away.  
> 
> Now, I also have a new oxygen sensor waiting to be installed, but I 
> wanted to wait until I got some fresh gas in the car first, in fear 
> of ruining it.  Call me dumb, but could this be a case where I need 
> to adjust the mixture screw?  
> 
> thanks,
> 
> Matt
> #1604




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