Featured Articles
Injector O-Rings
by Kim Lux
Copyright© 2000, 2001 Diesel Research Inc. - all rights reserved
Lately I've seen/read or been emailed a number of questions about
Powerstroke HEUI injector O-Rings. As we've become involved in troubleshooting injector O Ring problems as part of
our cackle kit research, I thought I would share a bit of information on the subject that will
hopefully help some of you. There seem to be a lot of misconceptions floating around and hopefully this information will clear up a few things.
Background
(It may be useful to find a picture of a HEUI injector and reference it while reading this.)
The Powerstroke HEUI injector seals in the engine head with 3 "sets" of
O-Rings, that I will term the top, middle and bottom O Ring "sets", viewed when the injector is held in the upright position. I say "sets" because the
stock top O Ring set consists of multiple rings, but the stock middle and bottom set consist of only one ring, so they are not really a "set" per se.
For those not familiar with a HEUI injector, it is supplied by two fluids
from cavities or "rails" built/cast right into the engine head:
a) High pressure injection activation oil (500 to 2500
PSI)
b) Diesel fuel (nominally 50 PSI)
The "injector O-Rings" that people keep talking about serve to seal the
injector into its bore in the head, thus preventing the leaking or contamination of the
aforementioned fluids. When the injector is inserted into its bore, the O-Rings
on the injector provide a seal to isolate the
fuel rail from the high pressure oil rail. The fluid between the upper and
middle O Ring sets is the high pressure oil and between the middle and the
bottom O Ring is the diesel fuel.
Top O Ring Set Description
The top O Ring set prevents the high pressure (500 to 2500 PSI) HEUI injector activation oil from escaping out of the injector cavity and into
the valve cover area.
There have been a couple of upgrades to the top O Ring set over the years.
The current stock top O Ring set consists of (from top to bottom) a steel backup ring, a square cushion ring and an O Ring.
For those not familiar with seal design, the purpose of a backup ring is to
provide backing (thus the name) for the sealing element (usually an O Ring)
between the bore and the inside part. The backup ring in the upper O Ring
set on a HEUI injector is quite a bit like an upper piston ring. The cushion ring serves to prevent the sealing O Ring from rubbing on the
backup ring.
Middle Injector O Ring "Set"
The middle injector O Ring "set" serves to seal the high pressure injector
actuation oil from mixing with the injector fuel supply.
The stock middle O Ring "set" is a simple O Ring, with no backup.
Bottom Injector O Ring "Set"
The bottom injector O Ring "set" serves to seal the diesel fuel from entering a space at the bottom of the injector, right over the combustion
chamber.
The stock bottom O Ring "set" is a simple O Ring, with no backup.
Scope
Although leaks and O Ring deterioration have and can occur with any of the 3
injector O-Rings, I am going to limit this discussion to the HP Oil O-Rings,
the upper and middle O-Rings on the injectors. It is entirely possible to
have the lower O Ring fail as well, but that has a different set of symptoms, causes and troubleshooting
procedures.
Symptoms and Troubleshooting Injector O Ring Problems:
HP Oil O-Rings (Top and Middle
O-Rings)
The amount of fuel and the quality of the injection from a HEUI injector is
highly dependent upon the injector actuation oil pressure. The high pressure oil pump on a Powerstroke has finite delivery volume and is sized
to have just the right amount of oil delivery when the injectors are operating at their maximum delivery. (A "cushion" volume has been designed
in, but it isn't much.) Thus, if there is a leak in the high pressure injector oil supply system,
i.e.: oil leaking past leaking injector O-Rings, there can be a significant effect on engine performance.
Sources of Leaks
There are 5 sources of oil leaks within the HP Oil Rail/Injector system:
a) Upper Injector O Ring
The stock backup ring on the upper injector O Ring is much like an upper
piston ring, including the fact that it has a gap where the two ends of the
ring meet. On several trucks we have observed the cushion ring being pushed
into the gap between the backup ring and causing significant damage to the
cushion ring. Typically, this allows the cushion ring to push upwards, allowing the O Ring, which it supports, to bow upwards in the injector bore.
This bowing action decreases the ability of the O Ring to seal and can allow
oil past the injector/bore interface and into the valve cover volume.
Oil leaking from the injector cavity to the valve cover volume does not harm
anything, but if the leakage volume is significant, there can be insufficient pressure or volume to properly activate the injectors. (See
Symptoms below.)
b) Middle Injector O Ring
The stock middle injector O Ring is a single O Ring. Should this O Ring
leak, typically high pressure injection activation oil will leak into the
injector fuel rail.
c) HP Oil Rail drain plugs
Inside the valve cover volume, on the periphery of the HP oil rail are two
drain plugs. The purpose of these drain plugs is to drain the oil from the
HP oil rail when removing/installing injectors.
Typically these plugs are trouble free, but they could, theoretically, be a
source of a leak.
d) HP Oil Rail end caps
On the end of each HP oil rail is an
end cap. These caps are typically 2 inches or so in diameter and have a 1/2" square drive "hole" in them. The
purpose of the end caps is to allow access to the inside of the oil rail,
and of course, to seal the ends of the rail.
The caps seal to the rail by an O Ring/Backup ring set. I have witnessed O
Ring wear/failure on these caps. When that occurs, oil typically leaks out
the ends of the rails, dirtying the ends of the heads.
e) Injector oil solenoid
The upper portion of a HEUI injector is an elaborate, precise hydraulic
system that provides the "power" to pressurize the fuel to inject into the
combustion chamber. A critical element of that system is a solenoid valve
that controls the flow of the HP Oil to the intensifier piston.
It is possible for the solenoid valve to leak and we have witnessed such an
occurrence more than once.
There are two causes of injector solenoid oil leaks:
a) dDbris caught in the poppet valve
b) Wear between the poppet valve seat and the valve itself
I have not witnessed any occurrences
of b, but I have seen debris caught in the poppet valve of injectors cause them to leak.
f) Cracked HP Oil Rail
It is possible under certain conditions to crack the HP oil rail walls.
This is a very unlikely occurrence
and it takes special troubleshooting methods (maybe head removal) to isolate such a leak.
Symptoms
Here are common signs that you might have a HP oil rail leak. Note that these conditions are not conclusive, as other engine ailments may cause
similar symptoms
a) Hard start/ no start when hot
b) Hard start/ no start when cold
c) A large difference between starting times hot and cold, specifically
quick cold start and long hot starting
d) Loss of power when hot/ low power/ high fuel consumption
e) Oil consumption
f) Blue exhaust smoke, especially on startup
Troubleshooting HP Oil Rail Leaks
Troubleshooting HP oil rail leaks can be tricky. Here are some of the procedures we use at, from simplest to hardest:
a) Exterior visual inspection
b) Fll load HP oil pressure
-
Build a HP oil gauge assembly consisting of a damped 3,000 PSI oil gauge,
a piece of 1/4" hydraulic hose and a #5 ORB connector.
-
Plumb the oil gauge assembly into the HP oil rail via one of the 5/8" (ORB
#5) oil rail plugs.
-
Secure the gauge such that it can be (safely) seen while operating the
vehicle
-
Place the vehicle under load. Under full load, the gauge should read 2500+
PSI. At idle, the gauge should ready a steady 500 PSI
NOTE: A reading of less than 2500 PSI does not isolate the problem to the HP
Oil Rail as there could be a problem with the HP oil supply system: pump,
reservoir, IPR, ICP, etc.
c) Cranking oil pressure
-
Install the HP oil gauge assembly described in b) above
-
Remove the IDM relay from the power box near the master cylinder
-
While cranking the engine, observe the maximum developed pressure. The
gauge should rapidly climb to 2000 PSI or more. (At least 1500 PSI.)
What this test does is disable the injectors from operating while allowing
the HP oil system to develop significant pressure.
NOTE: The IPR and the relief valve in the HP oil pump will prevent the HP oil system from over
pressuring.
NOTE: A low reading does not isolate the problem to the HP Oil Rail as there
could be a problem with the HP oil supply system. It is useful to perform this test with the engine both hot and cold.
There should be little or no difference in the readings.
-
If the truck blows blue smoke when it is started after performing this
test, the middle injector seals were probably leaking.
-
In our opinion, this is the first test to perform anytime a Powerstroke
won't start. A Powerstroke needs at least 500 PSI of oil pressure to start.
d) Individual HP Oil rail manual pressure test
- build a hand rail pressure pump consisting of a high quality lever (not
pistol) type grease gun as the pump, a high pressure shutoff valve, a high
pressure (3000 PSI) hydraulic gauge, a length of 1/4" hydraulic hose and a
#5 ORB connector.
-
Fill the hand pump with a good diesel engine oil
-
Disconnect the HP oil supply line to one head, at the head by removing the
fitting from the head
-
Connect the hand oil pressure pump to the rail where the supply hose was
connected
-
Pressurize the rail to 3,000 PSI by pumping the pump. (It is pretty easy
to do this with a good pump.)
-
Close the hand valve and watch the pressure reading on the gauge. The HP
oil system should maintain the pressure. (In a bench top environment, the
HP oil system will hold 3,000 PSI for days.)
-
Repeat for the other head/rail.
-
It is useful to compare hot engine and cold engine results. They should
be the same.
e) Internal oil leak inspection
-
Remove the valve covers on one or both heads
-
Pressurize the oil
rail's with the hand pump as described above
- inspect the interface between the injectors and their bores for oil leakage
- inspect the injector oil exhaust ports for oil leakage
If oil pressure does not maintain and no oil leakage is found at the
injector bore or exhaust, one might remove the fuel line connection to the
head and observe if fuel is being pushed out of the head by oil from leakage
past the middle O ring.
Note: This test can also be performed by removing the IDM relay and cranking
the engine in the absence of a hand pump. (Obviously, one cannot disconnect
the fuel line when cranking the engine, unless one also removes the fuse for
the fuel pump.) However, the pump will NOT maintain oil rail pressure when
the engine isn't cranking.
Injector Oil Leaks
Injectors leaking oil do not always do so in a predictable way. For example, we have observed injectors that will hold 2500 PSI of oil pressure
when stationary, but after firing a time or two will leak and not reseal until the oil pressure is significantly reduced. This is typical of an
injector with debris in the poppet valve. Thus it may be that an engine may
have a perfectly good static oil test (as outlined above) but still suffer
from low oil pressure under full load.
Furthermore, the typical source of debris in the injector poppet valves is
the O-Rings themselves. It is quite common when O-Rings fail that they extrude bits of O Ring material from the ring itself into the oil supply.
We have witnessed such extrusion on upper, middle and end cap O-Rings. Once
such extrusion has occurred, it is almost assured that the O Ring debris will
end up in the injector solenoid, where it may interfere with proper injector
operation. It is therefore our *opinion* that anytime O Ring extrusion failure is observed on a Powerstroke HP oil O ring, including the end caps,
the engine be tested for sufficient high pressure oil pressure under full load.
SES Light
It takes a significant HP oil pressure deficiency to illuminate the Service
Engine Soon light, especially under non loaded conditions. Actually, it is
not the pressure level itself that will ultimately illuminate the SES light,
but rather the engines inability to attain sufficient HP oil pressure for a
given IPR duty cycle.
Cackle Kits
I have no public comment on the status of the cackle kits at this time.
Please do not email me asking for further information. Yes, we have trucks
running kits. Yes, we are still working on and testing solutions. No, the
kits are not ready yet. I'll let everyone know when they are.
Further Questions
I do not have the time to answer individual questions about troubleshooting
Powerstroke engines. I *may* answer a group of questions pertaining to the
topic of injector O-Rings as a follow up posting to this discussion group.
