|
|
|
The Balloon Test
A 6.0L equipped 2005 E350 with about 1500 miles on the odometer rolls into the dealer with complaints of a
lack of power and running rough. A road test confirms the concern and you also observe that the MIL is
illuminated. A review of the vehicle history reveals several repair attempts by another dealer for an
intermittent miss and lack of power. The engine is still misbehaving and the customer states that this
recently started happening but clears up for a few days and comes back. Normal diagnostics show misfire and
cylinder balance codes on one bank but you are unable to pinpoint a cause With all of the wiring and injector
issues that have come to light you start to think injector. But which one? There have been reports of
combustion leaks into the fuel system which can cause random misfiring of multiple injectors.
Combustion gas in an injector can cause a random misfire in one or many cylinders. Combustion gas may leak
past the injector's needle and seat, or the copper combustion seal. Once the combustion gas enters the
fuel rail in the cylinder head, it then distributes to other injectors, typically on the same bank. In this
case it turned out that an injector was intermittently causing combustion gasses to enter the fuel system.
While watching the WDS power balance screen you could see one cylinder was running at -30% which fell to -60%
when the RPM's were raised. When a load was put on the engine the rest of the cylinders were being
affected by the gasses in the fuel rail and would begin randomly dropping as well. Surprisingly, all of the
misfiring cylinders began running properly and the engine smoothed out. Running OASIS symptom codes brought
up several things to check for, one being combustion leaks affecting the fuel system and the Balloon Test is
how you can check for this condition.
After identifying the cylinder, removal and inspection of the injector and the injector bore revealed the
failure. The injector hold down clamp bolt was fully seated and the copper seal at the bottom of the injector
was missing indicating that it may have been missing when the injector was installed. (A-below) Without the
copper seal combustion gasses traveled into the injector bore and past the lower fuel rail o-ring on the
injector.(B-below) Once this seal failed, combustion gasses were able enter the fuel rail and affect all of
the injectors in that cylinder head. The repair involved cleaning the injector bore, sleeve and seat, then a
new injector was installed.
If you haven't heard of the "Balloon Test" or have never performed it, the term certainly
sounds silly but the results are undeniable. All kidding aside, this is a great method for detecting a
seemingly unlikely cause and it works. This engine was diagnosed using this procedure and this is how it was
done. The image below is the actual test being performed on this vehicle. Hats off to the guy that thought
this one up!
|
Disable the fuel pump and FICM relays to prevent engine firing and spilling fuel.
|
|
|
Access the primary fuel filter, remove the cap and the filter. Look for a low fuel level in the housing
for your first clue. Cranking the engine at this time might also produce fuel bubbles at the standpipe
inlet, clue number two.
|
|
|
Next, remove the fuel outlet lines from the fuel filter housing and install a balloon over each fuel
line and secure with a zip tie making sure to seal the balloon to the fuel line.
|
|
|
Crank the engine and observe if either balloon begins to fill. Compression pulses will likely fill the
balloon quickly if the leak is big enough. Allowing time between cranking to cool the starter, you may
need to crank for some time to allow a small leak to become evident.
|
|
|
Once a cylinder bank has been identified, remove all of the glow plugs from that cylinder head except
for one and repeat the cranking procedure. Remove the glow plug from that cylinder and move it to the
next once again performing the cranking procedure. Repeat two more times until you have checked the
entire bank.
|
|
|
Any cylinder(s) that show compression leaks by filling the balloon need to be serviced. Remove the
injector(s) and observe the injector hold down clamp for looseness. Inspect the copper gasket, lower
O-ring and the injector for damage, replace if necessary. If the copper gasket and O-ring are OK
replace injector for leaking combustion past the delivery valve.
|
 FDDTS
|
|
