From: dje@sword.bellcore.com (Don Eilenberger)
Subject: Re: Carbon Buildup in engines ( valves ? ).....
Reply-To: dje@sword.bellcore.com (Don Eilenberger)
Organization: Bellcore, Livingston, NJ
Distribution: na
Date: Fri, 24 Jul 92 14:00:32 GMT

In article <4902@gold.gvg.tek.com>, jimd@pequod.gvg.tek.com (Jim Delwiche) writes:
|> I saw a blurb on Motorweek a while back where a non-invasive
|> technique for removing carbon buildup was described.
|> 
|> Basically, the idea is to scrub the insides of the cylinder and head
|> with coarsely ground walnut shells.  There is some kind of gizmo which
|> I guess pumps these walnut shells down the intake side, and swirls
|> them around with sufficient energy to remove carbon deposits.  The
|> advantage, obviously, is you don't have to take the head off.  I don't
|> know--it might be necessary to remove the intake manifold or
|> something...
|> 
|> Jim


This technique is called an "Intake Blast" by BMW. Beemer's, I've
found out after purchasing a used one.. love to carbon up the
intake valves unless they're driven hard with a high detergent
(meeting BMW standards - note how many gases now have tried to
qualify for this) gasoline. The problem is usually caused by
lots of around town driving, and using the automatic in the
"E" (economy) mode. The typical symptom is a loss of power
and they don't idle worth sh*t.

When I bought my used 535i.. it was badly carboned (driven formerly
by a proverbial mom - doing around town errands).  BMW wants about
$500 to do the intake blast, since it involves removing all the
intake plumbing (manifold, etc), and the fuel injectors. The process
is then done with a sandblasting gun loaded with ground walnut
shells... (and it is sorta important that the intake valve you're
working on is closed at the time..). This technique does NOT
do the inside of the cylinder head or piston top (how would you
get all the walnut shells out?).

Anyway.. to avoid this expense.. my own mechanic - who is very
experienced in BMW's (used to be service manager at a dealership)
suggested I use several doses of full strength Techron(tm) [which
is the same stuff BMW sells as their gasoline additive].. and
run the piss out of the engine.

First step I took was to disconnect the automatic solenoid that
switched the transmission into Economy every time you start the
engine (BMW owners: easy to do - pop off the panel the E-S-123
switch is on, and unplug the bottom two wire connector on the
switch).

Next step was sorta fun.. run the piss out of a few tanks of
fuel dosed with Techron. 

The idle has now almost entirely cleared up.. idles great for
several minutes after running hard, and just gets a little
rough after sitting idling. I suspect continuing to run it
hard should clear out the rest of the carbon.  Power is now
where it should be, and at crusing speeds (80mph in the
Garden State Parkway Commuter AM Grand Prix).. the engine is
very smooth and powerful.

I guess the lesson here is: try non-invasive techniques first
- there are ones that can work, given a little time.

I would be very cautious about the water technique - although
I know this is an old method (remember hearing about it when
I was a kid - many decades ago..).

Another technique my mechanic suggested - sorta as a last
ditch non-invasive (cheap) technique, was to use some carbon
remover (forget the brand.. but might be something called 40-40),
and get it down the intake so it soaks the valves (he pointed
out that this was much easier on a carburated car than fuel
injection) - and let it sit overnight.. he claimed that
when you started the car in the morning the carbon would be
loose enough to be banged loose by the action of the valves.


Don Eilenberger (dje@sword.bellcore.com)
Newsgroups: rec.autos.tech