[DML] Re: Engine running half rich half lean.

["content22207" <brobertson@xxxxxxxxxxxx>]

Sounds to me like a common vacuum leak at the driver's intake rail
(crosses over to passenger cylinders), especially if plugs 1-3 all
look the same. I'm assuming they are either clean & white, or even
worse are melting.

Vacuum leaks cause a lean mixture (and severely elevate combustion
temperatures). People compensate at idle by over enriching. As the
throttle plates open, this then translates into a too rich mixture,
which is what massacres fuel economy -- one of the symptoms of a
vacuum leak is terrible MPG. That would account for the condition of
plugs 4-6 (they should be caramel colored, not charcoal).

Another symptom of a vacuum leak is erratic idling. The engine will
nearly die, then catch itself and rev back up. Lambda and CIS add
their own variables to this possibility, but can easily be disabled to
isolate the problem.

I've re-uploaded a pic of my spark plugs to #5939's photo album so you
can see what a vacuum leak in my HVAC supply line (yet another hard
plastic DeLo line. Warning -- is every bit as worth replacing as the
clutch line) did during a several hundred mile road trip. Note that
plugs 4-6 are all damaged equally. I'm just lucky I didn't warp a
valve or melt a piston! HVAC is supplied from passenger intake rail BTW.

Stock DeLo has a vacuum nipple in the driver's intake rail that feeds
spark advance and full throttle CPR enrichment. Since neither is
needed at idle, unplug that line and cap with a vacuum plug. Test the
loose hose with a hand vacuum pump to ensure those lines and
diaphragms are still intact. Then start the engine and test the nipple
threads, the plug right below it, U pipe mating surfaces, and the plug
by the A/C compressor with an aerosol of some sort. If any are
leaking, the engine will suck it in and bog down. Also check the
throttle plate shaft where it rotates in the aluminum housing and the
middle brass balancing screw.

Because your plugs are behaving differently on either side of the
engine, I wouldn't worry about the idle speed motor, charcoal
canister, or anything else supplied by the cold start tube (is
centrally located). 

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, Enid/Jeremiah
<hispanicangeleyes@xxxx> wrote:
> This is a unique problem.  When I start my car now, the engine will
run half lean and half rich.  The driver's side (4,5,6) all run rich
(spark plugs are charcoal colored), and the passenger side (1,2,3) are
lean.  The mixture screw has been adjusted properly, and these
sparkplugs have been replaced recently.  I assume the fuel distributor
sends fuel out equally, so I'm pretty sure the problem doesn't lie
there.  Could it be dirty/faulty fuel injectors?  I'm kind of lost on
this one.  
>  
>    The car does something else unusual.  The engine will idle fine
when cold, but as the car warms up, the idling becomes very erradic. 
It will "jump" around when in drive or park.  Don't get this confused
with high idling or idling up and down in a cyclic motion - this
idling goes fast then slow and repeats this pattern very rapidly. 
It's very uneven and just all over the place.  It almost sounds like
the car will literally die when sitting at a stop light or a traffic
light.  When this idling problem occurs, I get alot of "spitting and
sputtering" when going from a dead stop to acceleration.  After it
spits and sputters for about 3 seconds, I get a sudden burst of
acceleration (almost as if one of the cylinders isn't opening, and
then WHAM! it opens all of a sudden)  The car will do this generally
around the time the cooling fans on for the first time, and then after
about 10 minutes the idling is perfectly normal.  When the idling is
normal, there is no more "spit and sputter"
>  either; the car runs completely normally.  Any ideas anyone?




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