Fuel injectors play a critical role
in delivering the high performance standards to the engines of these cars.
Unfortunately they have a history of failing. The good news is that you
can quickly do a few simple tests to identify a faulty injector. The
Left or Right "Check Engine Light" is usually your first indication that
something is wrong. The tests here then will help you identify the
If a fuel injector is stuck open or close (this
has been seen many times on 6.0L Diablo cars) the following will happen.
Stuck open will cause raw fuel to dump into cats causing a rich
condition and overheat cats and shut down power. The "Check catalyst"
light will come on. If instead the injectors are stuck closed this
will cause no burn (power loss) situation and excessive oxygen will
get into the cat and cause a lean cat to overheat. Again the "Check
catalyst" light will come on. In both situations there is a
dramatic loss of power as the LIE computer is trying to correct the
situation. It there is a closed injector the temperature on the
exhaust manifold will be low. On a car where the cylinders are fine the
manifold temperature will typically 400-450 F immediately external to the
Fortunately there is a simple way to measure these
temperatures. There are a number of IR/heat sensing guns available these days. Figure 1 shows one example.
These guns contain an IR detector that measures radiant heat. A
laser beam points to the pot being measured. The LED display gives the
reading within a few seconds. To use first point the gun on your
hand and take a reading to check the gun is working correctly. It should
read 98.6F Then point the gun's laser spot on the cast iron
surface of the exhaust manifold of each cylinder as shown in Figure 2.
When the engine is warm. All cylinders should be the same (+/-) 30
degrees. Typical readings are 450 degrees F. A blocked injector will
give a reading of 200 to 250 degrees F. while an open one will give
temperatures of 600 degrees or more.
There is an even simpler method to diagnose fuel
injector problems. Most auto stores these days supply engine steascopes.
One example of one is shown in figure 3. To check each injector
position the tip of the scope on each injector as shown in figure 4.
A good injector should emit a distinct clicking sound. If you do not
hear this or hear a purring sound chances are the injector is faulty.
Removing a Fuel
Removing a fuel injector is not difficult but
does require time and care. On the Diablo all the injectors are
fed from a left and right fuel rail, as shown in Fig 5. This rail contains gas
at constant pressure, so the amount of fuel delivered to a cylinder is
completely dependent on how long the fuel injector stays open.
To remove and examine a fuel injector: First loosen and remove the 5 retaining screws
that hold each fuel rail to the engine. See Figure 6 below.
Do not disconnect the fuel injectors from the rail or the connecting
wires at this time. When all the screws are removed simply raise the
whole rail vertically from the engine. Rock or twist each fuel injector
if they are tight. The whole assembly comes up as one piece
as shown in figure 7 below. To remove an individual injector from
the fuel rail you must then slide out the metal clip that holds the
injector against the rail. They slide out on a grove as shown in figure
8 below. Fuel will gush out of the fuel rail at this point. It
will stop after about 1 minute so take extreme care -- no smoking!
Figure 9 shows how to remove the electrical connection to the injector.
Each injector has a wire spring clip that holds the electrical
connection socket in place. Use a sharp point need to get under this
spring to pry it off. Figure 10 shows an isolated injector.
Recently I had an injector the failed the tests above. It was for
cylinder 12 of my 6L Diablo. I switched injectors 1 and 12 and found to
my surprise that I still did not get the correct sounds out of injector
12. I then examined the plug socket for this injector. Instead of
seeing two silver contacts as shown in Fig 11. I sow only one as
shown in Fig 12. What had happened is that the connection was
pushed (or pulled) back up into the socket making no contact with the
injector. The solution was to simply peal back the rubber hose covering
the outside of the connector wire and push the wire back into the socket
until it "clicked." The simple tests above identified this
problem. It gave a check engine light warning and check catalyst signal.
Inserting a Fuel
Care also needs to be exercised in reassembly. First reinsert
the metal clip that retains the injector to the fuel rail. It is
absolutely essential that the injector is seated correctly back into the
fuel rail socket. This rail has gasoline under pressure. You must hear a
distinct "click" or "snapping" sound as you press the injector upwards
into the fuel rail. If in doubt, try and remove it without removing the
clip. It should not come off. use a mirror to see around the back
of each injector.
Next the whole rail is held over the engine so each injector is
directly over its appropriate air intake hole as shown in figure 15.
Gently press them all evenly into place taking care not to pinch any of
the rubber rings in the process. Tighten down the retaining bolts and
you are all done!