[T3] Engine Backfire

[Jim Adney]

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
*******************************