[W126 Coupe] 89 560 sec with engine miss and rich, poor idle

[Tim Graney]

If the car is running rich the first thing you need to do is isolate the
problem. Remove the spark plugs and keep them numbered so you know what
hole they came from. Look for the plug or plugs that have carbon
deposits on them. Those are the holes that are running rich. Secondly
remove the injector or injectors in the suspect holes and see if they
are operating properly. The spray pattern should be nice and even. The
next item is the fuel controller...that's where this gets expensive. If
that is defective you can buy them reman for around 500.00 bucks. The
other culprit might be the Lambda device or system. A faulty O2 sensor
or bad frequency valve can make the car run rich at idle. 

You can also adjust the fuel mixture yourself at the controller...it is
very sensitive and you need either a vacuum gauge or a exhaust gas
analyzer to do it properly. A vacuum gauge works best and is
inexpensive. Just hook it up to a vacuum source like the advance on the
distributor and read your vacuum...it should be around 20 bar nice and
even no fluctuation. Adjust the mixture by inserting a hex head wrench
and pushing down on the spring loaded adjustment screw until it makes
contact then turn counter-clockwise to lean and clockwise to richen.
Watch your vacuum gauge and watch the needle to see if it moves towards
more vacuum. More is better, when it drops you are either too rich or
too lean. Make sure the car is good and warm when you do this and check
it after each adjustment by clearing the throttle. Turn the screw in
small increments like 1/8 turn and watch the needle on the vacuum gauge.
There are more things to check but start with these.  

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com
[mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Rick Granlund
Sent: Thursday, July 19, 2007 10:28 AM
To: mbcoupes at mbcoupes.com
Subject: [W126 Coupe] 89 560 sec with engine miss and rich, poor idle


HI-
	I don't mean to bother the list, but I have qa rather sever
problem 
with my '89 SEC.  I tried earlier but did't get any takers in trying to 
diagnose the problem.  Hoping someone will chime in with the solution to

my problem.
thanks in advance.
Here is the problem:
    The car
does not appear to have any enrichment when first started, but acts like
more than one injector is running wide open.  When it is first started,
cold, it will stall unless you give it enough gas (1000rpm or more.
After about 30 seconds you can let it try to find idle, but it hunts
between ~500rpm and ~800-900rpm or stalls.  The exhaust is VERY rich (it

stinks
with fuel). I bought the car with a broken ( front vacuum
tube nipple)fuel pressure regulator and the idle was erratic and had 
bumped up to
1000 - to 1400 rpm isong the throttle linkage (the one link down under 
the front of
the throttle body, just behind the cruise linkage. It would still stall
and hunt up to 1400rpm. I replaced the fuel pressure regulator.....no
change!  So I replaced the Idle control valve....no change! I seems to
have a severe miss....running on seven, but it does that well above idle

too.
   The miss is it running very 'rich'.  I replaced the distributor cap
and rotor and the plug wires thinking it was an electrical miss.....no
change. It appears just to be a very rich condition....all the time.  It
will not idle, just hunts 400 to ~900 rpm and stalls.  After stopping, 
it is very hard to start...like leaking injectors.
     I am thinking this rich condition is controlled by some
electronics, rather than a faulty injector....it just runs too rich.
     Could someone guide me through the logical troubleshooting steps to
get to the bottom of this problem? How do I check if the cold start
injector 
is 'open' all the time.  Removing the electrical leads to it does
nothing.
	I think if I can find the reason for the ery rich idle and run 
condition, it will solve the idle and 'miss' the car has at idle and in 
running.
Rick
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