| ChrisBennet |
01-06-2003 06:03 AM |
Here is a post from 1996 on the Porschefans/Rennlist on the subject:
Quote:
From: "Tony Staples" <tstaples@piedmont.net>
To: porschefans-911@ioio.com, porschefans-914@ioio.com,
Subject: Re: fuel injectors (Warning: LONG)
Anyone who knows me from the old P'Philes days, has seen my postings
on fuel injection issues before. I am a Sr. Design Engineer for a
major automotive fuel injection OEM. I absolutely had to respond to
this thread.
> > From: tmarlow <sesame@pacbell.net>
> > Does anyone know of a specification for how many miles you should put on
> > fuel injectors before replacing them? Are there any tricks to getting
> > them in and out? Aside from the o-rings, are there any other parts that
> > should be replaced while you're doing the job?
> >
> > I've got a 1983 SC with close to 100K miles that sometimes run a little
> > rough when cold. I've got this wild hair that tells me it might be time
> > to replace the injectors. Any concensus on this?
> >
> From: rgrayson@atlanta.com
> There's no hard and fast rule for injector replacement. The typical
> failure mode is clogging or restriction due to debris and fuel
> breakdown. This can happen in as little as 60,000 miles if you use
> cheap gas. If you use good gas, regular use of additives like
> Techron or BG44, and change your fuel filter every 15,000 miles,
Most fuel additives are much better at making the vehicle owner feel
better than for providing any actual benefit. Replacing the fuel
filter every 15-30k is good idea, however. High quality fuel is alo
a good idea.
> they'll last a lot longer. Once they get over 100,000 though, many
> can usually benefit from reconditioning.
What do you do to the injectors specifically? Since they are not
designed for any type of disassembly, short of cutting the welds open,
it's almost impossible for anyone to rebuild an injector. There is
one company that I am aware of that does this, but they have millions
of dollars tied up in specialized equipment, and the rebuilt injectors
that I have tested of theirs, were inconsistent performers, part to
part.
We design our injectors for over a billion cycles of operation. This
would equate to over 300k miles of typical street driving. Mileage
is not really a factor in the demise of an injector. Fuel quality is
far more important.
Debris can be a problem in mechanical systems, like CIS, but the
electronic injectors have a inlet filter that prevents particles
larger than 30-40 microns from entering the valve. Anything smaller
than this can be easily flushed through the valve.
>
> There's a good article on this subject by Allan Caldwell in the July
> 1996 Panorama.
>
> Replacement injectors for the SC are relatively inexpensive --
> Imparts has them for $27 each. Bosch injectors for other Pcars can be
> considerably more expensive as in over $100 each.
That's because they are very different animals. CIS injectors are
mechancal orifice tubes, whereas most other Porsche's (non MFI) use
electronic fuel injectors (solenoid valves).
>
> There aren't any tricks to replacing them, at least on my '85. Not
> sure if an SC is very different...I doubt it. You'll want to disconnect
The 78-83 SC's use CIS injection (see above), which is very different that the
Bosch Motronic system used on the 84-on 911's.
> your battery to avoid fireworks while you're working on the fuel
> lines. Remove various paraphernalia like the air cleaner and blower
> fan to get better access to everything. Remove the A/C compressor and
> pivot it up, leaving the A/C lines connected of course. Relieve the
> fuel pressure by opening the test connection at the end
> of the fuel rail. (Put an absorbent rag under the connector before
> you open it.) Disconnect all the rail plumbing and mounting brackets. Disconn
ect the
> electrical connectors. The rail should then pull out with moderate pressue
> along with the injectors.
>
Obviously, this is not the procedure for a CIS equipped car, as the
mechanical injection has hard lines running from the distribution
pumpt to each orifice tube.
> When you install the new ones, lubricate the O-rings with automatic
> transmission fluid so they seat properly. Keep everything clean,
Warning: We have tested some of the new Dexron III transmission
fluids and found them to contain compounds which can contaminate O2
sensors. I do not recommend lubricating any fuel system components
with transmission fluid, or any synthetic oils. The best o-ring lube
that we have found is a light mineral oil, or just plain motor oil.
> especially the rail fuel connectors or else you'll have leaks. After
> you button everything back up, run the engine and check closely for
> any possible leaks. Shut it off and check again. Fuel leaks are bad
> things and can really ruin your day.
>
I can second that!
> By the way, in September I plan to open my shop -- INJECTOR CLINIC --
> and will offer injector cleaning services with discounts to list
> members. I'm getting the ASNU cleaning machine shown on page 44 of that same
> Pano. I'll post a note when I open my doors.
>
> Hope this helps.
>
> -----------------------------------------------------
> Richard Grayson, rgrayson@atlanta.com
> INJECTOR CLINIC - Fuel Injector Service & Repair
> '85 Porsche 911, '73 Datsun 240Z (slow restoration)
> PCA member, IZCC#309
> -----------------------------------------------------
Warning #2: We have tested some of these "injector cleaning
systems". We have found that on certain types of injectors,
specifically the older pintle types typically found on Porsche's,
these systems can have some very limited benefit, and a whole lot of
drawbacks. Newer injector designs, especially non-pintle designs,
derive no known benefit from "injector cleaning", but still suffer
from the drawbacks.
Here's the bottom line:
Pintle type injector clogging is due to varnish build up on the
orifice edges, and thepintle O.D., at the end of the injector. As
this varnish builds up, the effective metering orifce diameter is
reduced. The results in a drop in flow rate, and a deterioration of
proper spray pattern.
The varnish is a resultant of two factors, the presence of very long
chain hydrocarbons (called olefins) in your fuel, coupled with heat.
When you shut off your engine, there is a residue of fuel that remains
on the tips of the injectors. As your engine heat soaks, the oelifins
in this residue get converted, by the surplus heat, to varnish. Here
is an analogy. Margarine contains a very high percentage of olefins.
If you put some in a pan, and heat it on your stove, what forms on the
bottom of your pan? Right, Varnish. Is that burnt of crud easy to
remove? Not without some serious elbow grease or a really nasty
solvent.
Here's the dilemma: In order to effectively remove this
crud from the ends of the injectors, you need to "scrub" the orifice
metering area clean. Mechanical contact with this part of the
injector will damage it, dramatically altering the flow rate. Most
solvents won't remove this crud from the end of the injectors in any
reasonable amount of time. Acetone can take days to dissolve a few
microns of the stuff. The only solvents that we have found to remove
this varnish are so aggressive, they typically cause other problems
with the injectors They attack the rubber and plastic materials
commonly used in the manufacture of electronic fuel injectors. They
are also extremely harmful to humans.
We have seen some field returns from our customers that have been
internally damaged by some of these witches brew solvents used in
"Injector Cleaning". We had one case of a fuel leak, caused by an
o-ring that had disintegrated due to some "cleaning" solution. This
fuel leak resulted in an engine bay fire, which resulted in a very
unhappy vehicle owner. We contacted the vehicle owner directly, and
found that he had just had his injectors cleaned about a week
previously, at a local garage. We supplied him with all of the
evidence of the damage done, and he filed suit against the garage, and
against the manufacturer of the cleaning system. He won a nice
settlement.
Mr. Grayson, if you choose to enter into a fuel injection cleaning
business, please be sure to get some very good liability insurance.
Here's my advice: The next time that the pimply
faced kid at Jiffy Lube suggests that the injectors in your wife's
Honda need "cleaning", Just politely say no thanks and keep that $50
in your pocket. It will probably save you another visit to your
mechanic, and it might even save your life.
Cheers,
Tony Staples
tstaples@piedmont.net
'88 Carrera Cabrio
'87 944S Track Car
"Nothing like a little horsepower to brighten your day!"
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