[T3] Engine Backfire

[Dave Hall]

I replaced one injector with a NOS Bosch one, and got spectacular backfires
- a visible flame at night - for a few days, then it just stopped happening.
I assumed that was maybe due to internal O-rings or something causing some
fuel leak, but it may not have been.  

Dave
UK VW Type 3&4 Club
===================



-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim Adney
Sent: 16 July 2012 22:41
To: type3 at vwtype3.org
Subject: Re: [T3] Engine Backfire

On 16 Jul 2012 at 16:48, BilDylJ at aol.com wrote:

> Can anyone out there tell me how to change the fuel injectors on a  
> 1972 type 3  engine.

I would not suspect injector problems as the source of engine backfire,
unless you have some non-Bosch injectors there. Non-Bosch injectors can
usually be easily identified by the fact that they don't have the nicely
rounded corners around the electrical connector.

If you're having problems not related to leaking gas, I suggest you go to
the bottom of this message and check the tightness of all 2 push on
electrical connectors.

There is very seldom any need to replace all 4 injectors, unless you're
talking about an engine that has not run in decades. If the problem is gas
leaking from failed original hoses crimped onto the injectors, the crimp can
be cut off and that short piece of hose replaced. However, you still have to
remove the injectors to do this.

Removing the injectors is a mid level job, neither easy nor really hard, but
it is cramped, especially working on the LHS.

Start on the right. Remove the air cleaner.

Unplug the electrical connectors from the injectors. Don't pull on the
wires, pull on the connector body. (You can feel the body thru the rubber
boot.)

Loosen the clamps that attach the multiple port "Tee" to the 2 injectors.

Rock the Tee back and forth while pulling it out of the injectors. 
When it comes out gas will spill. Do this outside or with good ventilation.
No smoking.

Find a combination of 10 mm socket and short extension that will let you get
to the nuts in the center of the injector mount. Remove both nuts and
washers.

Pull both injectors outwards, along with the mounting hardware. Each
injector will have a large and small rubber ring. The small ring may stay in
the socket when you pull the injector out. The small rings are still okay as
long as they are plyable and not broken all the way thru. The large rings
are okay as long as they will still fit in the phenolic retainer.

Note that there should be a small metal sleeve surrounding each mounting
stud. They may stick inside the phenolic mounting plate. 
They are necessary to keep from breaking the plate.

The phenolic plate may be broken if the injector has been leaking. If this
is the case, you will also need to replace that rubber ring, because it will
be swollen too large to fit back in the plate. I just swap these and let the
gas slowly evaporate from the rubber and use them again in a few months.

Installation is the reverse of removal. Repeat on the LHS.

I have all the parts and I can replace the hose ends on the injectors if
that's a problem for you.

I have had poor results with non-Bosch injectors. That's about the only time
I ever replace an injector. I have new Bosch injectors, too, but I never
recommend replacing injectors unless there's some good reason to. They do
NOT seem to wear out, but they sometimes develop leaks that can't be fixed.
Small thru leaks can be ignored.

If you are having injector problems, you should also check that the
electrical connectors are tight on the injectors. Bosch made a major mistake
at some point in their production: They reduced the thickness of the
material used to make the injector pins. This causes huge problems with poor
connectons there. To fix this, you must remove each pin from it's connector
body and very carefully squeeze it down until it is snug on the injector
pin. Then snap it back into the connector body. This is actually more work
than removing the injectors.

--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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