Fuel System Explained.

[DMCVegas@xxxx]

Over the past couple of days the subject of the fuel system has been 
a sizeable topic. Even if you have th workshop manual, it can be 
difficult to understand the componets involved due to the authors 
wording, and the mechanical/electronic aspects of the system. So 
hopefully this will help everyone understand thier cars better.

Background:
The system is called the BOSCH K-Jetronic fuel injection system. 
Commonly known as a CIS, or Continuous Injection System because the 
fuel injectors never close when the system is active. It is also 
known as a Mechanical System because it can operate independant of 
any electronic components. The system is driven by fuel pressure. The 
System was designed in the early to mid 70's. A good reliable system, 
but when it hit the market strict emissions regulations appeared. So 
the LAMBDA System was created to enable the system pass EPA testing 
via fine tuning.

Mechanical Components and their Functions.

Fuel Deliverly Section:

Baffle.
This is where fuel that will be pumped into the system collects. It 
resembles a large cup. To keep the baffle from collapsing, two 
sections of wire are installed. Located within the baffle is a filer 
screen to keep particles large enough to damage the fuel pump out of 
the system. The baffle itself also does this to a certain extent. 
Something else to note is that the rubber hose that connects to the 
return line is supposed to be clipped in place to pour directly into 
the baffle. That way when fuel in the tank is very low, it can still 
gather enough fuel to keep the intake submurged and keep the car 
running.

Fuel pump.
Pretty straight thru. It's job consists of two tasks: 1. Supply fuel 
to the fuel system. 2. Maintain the proper fuel pressure to keep all 
meachanical components working. It also has a check valve installed 
to prevent fuel from flowing backwards into the tank.

Accumulator.
It's purpose is to maintain the high pressure within the fuel system 
when the pump is turned off. The enables quick starting of the engine 
rather then waiting for the system to build up pressure. An emergency 
overflow hose is connected between the accumulator and the return 
line. This hose catches any overflow from within the accumulator 
incase it fails, and directs it into the gas tank rather then letting 
it spill onto the ground.

Fuel Filter.
Filters out anything that could possibly clog the fuel injectors, or 
any delicate parts of the fuel system from here back.


Fuel Management Section:

Fuel Distributor.
The purpose of the fuel distributor is to not only route gasoline to 
the injectors and the other components that help manage fuel. But it 
utilizes feed back from some of these components to measure out just 
how much fuel the injectors will supply into the engine. It is a 
simple method, but it does use small, delicate parts.

There are two chambers, and upper and a lower. Both are seperated by 
a diaphram. Fuel in the upper chamber will flow to the injectors. 
Some of the fuel in the lower chambers will flow to the upper 
chamber, but the remainder will be returned to the gas tank. In the 
upper chamber, there is an intake that opens against the diaphram. If 
pressure in the lower chamber is reduced, then the diaphram will bend 
down. When the diaphram moves down, more fuel is allowed into the 
intake, and thus the injectors. Pressure is reduced in the lower 
chamber by allowing more gasoline to return to the tank. There is one 
of these diaphram chambers for each injector.

Primary Pressure Regulator.
This item is located inside of the Fuel Distributor. It's job is to 
determine what the pressure of the fuel system will be when the 
system runs under normal conditions. Has the ability to increase or 
decrease pressure by determining how much fuel is allowed to return 
to the gas tank. Set by the factory and/or mechanic. Contains no 
movable parts, and is probably only adjusted when a new distributor 
is installed.

Air Flow Sensor.
Measures the amount of air that enters into the engine in order to 
keep the air/fuel mixture the same. The more that air enters the 
engine, the more the air will push down on the plate accordingly. The 
plate is connected to a lever that will push up on a plunger located 
in the center of the fuel distributor. When moved upwards, this 
plunger will in turn allow more fuel to flow from the lower chambers 
in to the upper ones, and some to the Primary Pressure Regulator and 
the Control Pressure Regulator. The Air Flow Sensor doesn't enrich 
the fuel system, it simply keeps the air/fuel mixture the same. The 
air/fuel mixture can be adjusted by way of a hex screw. Under normal 
conditions, adjustment should rarely, if ever be nessisary.


Fuel Enrichment Secion:

Control Pressure Regulator.
The Control Pressure Regulator can lower fuel pressure within the 
fuel distributor to enrich the fuel mixture. In other words it can 
change the air/fuel mixture by allowing more fuel then normal into 
the injectors automaticly, yet the amount of air that enters into the 
engine stays the same. Two important things to note about about the 
Control Pressure Regulator is that any enrichment it performs for the 
fuel system is only temporary. And the Control Pressure Regulator 
only lowers the presure for the fuel system, it does not raise it 
above what is set but the Primary Pressure Regulator. The way that 
the CPR works is simple. Think of the chambers in the fuel 
distributor. When the diapram moves down, more fuel flows thru. But 
this time the fuel comes from the distributor. And instead of fuel 
going off to the injectors, it goes to the Primary Pressure Regulator 
to be returned to the tank. The result is pressure is lowered in the 
lower chambers of the distributor to allow more fuel into the 
injectors. But now in the CPR there are 2 diaphrams with 4 chambers. 
The 1st diaphram has a bimetal armature attached to it. This diaphram 
divides the 1st and 2nd chambers. The 2nd chamber is open to the 
outside air. The two bottom chambers are connected to vaccums.

The CPR only enriches the fuel mixture for two reasons:
1. Cold Engine. It's a fact, when metal is hot, it expands. And when 
it is cold, it contracts. Your engine is no exception. And when the 
motor is cold, the cylinders will naturally constrict against the 
pistons. This causes more friction then normal inside the engine. So 
to be able to run properly with this extra friction involved, more 
fuel is needed to give the pistons a little more power. When below a 
specific temp, the bimetal arm will bend down pulling the diaphram 
with it. This will activate the Cold Pressure regulator. Once the 
engine has warmed up, the extra fuel is no longer needed, and the CPR 
will deactivate. There is no long term benefit from the extra fuel. 
The engine will just burn it off decreasing you gas milage. There is 
also an electric heater in the unit which will warm the bimetal arm 
with in a certain amount of time since the unit relys on radiant 
temperature of the engine.
2. If you need to acellerate quickly you hit the throttle. This 
increases the vaccum in the intake manifold. The lower 3rd & 4th 
chambers of the CPR are connected via a hose to the manifold by way 
of the Thermal Vacum Control Valve that is split by a "T" fitting. 
But the side which connects to the upper of the two chambers is 
fitted with a delay valve. When an increased vaccum is applied to the 
CPR, the pressure in the lower chamber decreases first pulling the 
diaphram down. A spring connects the lower diaphram to the upper one, 
and will increase the fuel flow. As this ocurrs the Delay Valve is 
slowly decreasing the pressure in the upper chamber. Once the 
pressures in both chambers are equal, the diaphrams will return to 
their normal positions. The purpose of the Thermal Vaccum Control 
Valve in this circuit is to only allow this enrichment to occur once 
the engine has reached a specific temperature.

Cold Start Valve.
Just as with the Control Pressure Regulator, your engine needs extra 
fuel to run properly when cold. But it also needs even more fuel to 
initaily start when cold. That's where the Cold Start Valve comes in. 
When the engine is below a certain temperature, the CSV will activate.

Thermo Time Switch.
A bimetal arm inside of the Thermo Time Switch will ground itself to 
complete the electrical circuit for the Cold Start Valve to open. But 
unlike the CPR, the Thermo Time Switch reads engine temperature 
directly from the engine coolant. Located in the TTS is a heater. So, 
if within a certain amount of time the engine does not start, the 
bimetal arm will heat up enough to bend and break the circuit to 
close the valve. If the valve stays open too long, it can pose a 
possible fire hazard. Which is why the use of a "Hot Start Relay" is 
not always reccomended except for in extreme situaions. It should 
also be noted that circuit is only active when the ignition key is in 
the Start position (marked as "III" on the ignition itself).


Fuel Injection Section:

Fuel Injectors.
The end of the line for fuel. From here it is sprayed into the engine 
to be burned. Here is the differance between EFI and CIS. In the K-
Jetronic application the fuel injectors will only open when the 
pressure behind them has reached a specific level. So, once this 
level is achieved, the injectors do not close. Hence they 
Continuously Inject. On a EFI system the injectors will only open 
when they have recieved an electrical signal to do so. more precise, 
but as a mechanic explained it to me, CIS is better in the long run 
because EFI injectors will wear out and eventually fail. But with the 
life span of most cars, that's why it isn't a concern.

Cold Start Valve.
It's purpose has already been explained above. But is is listed here 
as well since it does deliver fuel to the engine. An interesting not 
about it is that it recieves it's fuel before any gasoline goes to 
the fuel distributor.


Electronic Components:
As mentioned above, the K-Jetronic system is purely mechanical, and 
requires no solid state electronics of any kind for proper and 
reliable operation. BUT, on it's own it does NOT meet EPA standards. 
Volvo saw this, and thus the LAMBDA emissions system was born! The 
LAMBDA gives the K-Jetronic system more precise control over itself 
with out any major modifications. It is a "bolt-on" component, not an 
intergrated one. EPA emissions cover not only how much CO, H-C's, and 
other toxins are expelled out of the engine, but also gas milage.

LAMBDA Emission Control Unit (ECU).
The heart of the system. This computer monitors by way of a oxygen 
sensor how well fuel is being burned inside of the engine. It also 
can take over the all mechanical duties of the Control Pressure 
Regulator. The ECU executes it's functions be controlling the 
pressure of the fuel system. This is accomplished by allowing fuel to 
return to the gas tank.

Frequency Valve.
What the ECU uses in order to control the pressure in the fuel lines. 
The Frequency Valve functions by cycling on and off, or rather 
opening and closing. When open it allows more fuel to return to the 
gas tank, thus decreasing pressure in the lower chambers of the fuel 
distributor. The faster the cycle of the frequency valve, the more 
fuel it allows to flow thru. The cycle it self is determined by the 
ECU

LAMBDA Probe.
Also commonly known as the oxygen sensor. This little device reports 
back to the ECU how much oxygen is in the exhaust gases. The more 
oxygen it detects, the more fuel pressure is reduced, and vice-versa. 
For proper operation, the probe must reach a specific temperature 
first. If no signal from the probe is detected by the ECU, then will 
run in a preset mode if the thermal probe has not been tripped.

LAMBDA sensor.
A thermal switch that is tripped if the engine coolant is below a 
specific temperature. Will activate the ECU to run in a "Warm Up" 
mode.

Microswitch.
When the throtle is full open, a microswitch is tripped telling the 
ECU to run in a rich mode. Creates a fuel spike same as the CPR does.


I hope this helps everyone understand thier fuel system better as in 
how it works. I also hope this helps as a trouble shooting guide as 
in if something is not working properly, you'll be able to find the 
problem much quicker by way of detecting what isn't doing it's job.

You can also see that while I described the detail of how everything 
works, I did leave out specific data as to pressures, temperatures, 
etc... This is because this write up should not be used alone in 
trouble shooting. There is no substitute for the workshop manual, and 
there is certainly no reason that any DeLorean owner should not own a 
copy.

The reason I created this write up was to give a better understanding 
of the fuel system. The DeLorean workshop manual does a good job, but 
it uses more advanced terms then most folks are used to. Is has ok 
diagrams, but if you don't understand the wording, they don't always 
make sense. The Volvo 760 Haynes manual has some good pictures, but 
is way too vague in it's explinations. Plus it doesn't cover all 
aspects of the K-Jetronic system. It also has in my opinion a very 
poor trouble shooting guide. The DeLorean t.s. section is much more 
complete. The BOSCH handbook uses easy to understand terms, but lacks 
any good descriptions of the DeLorean application.

This write up combined with the workshop manual descriptions and 
diagrams should make things much easier to understand.

After reading this, hopefully everyone is more comfortable in dealing 
with their fuel system. Even if you yourself do not do the actual 
work on it, you can give your mechanic more direction as to what you 
want done.

One more thing. If you elect to perform any repairs on your fuel 
system, particuarly the injectors and the distributor, make sure of 
one thing:
NEVER, EVER UNDER ANY CIRCUMSTANCES REUSE ANY OF THE COPPER SEALS 
THAT CONNECT THE FUEL HOSES! ALWAYS USE NEW SEALS!!!!!!
The seals are "crush-fit". In otherwords, they seal themselves by the 
banjo fittings and bolts crushing down into the copper. If resued, 
leaks can develop and cause engine fires. If ever in doubt, take you 
car either to a DeLorean service center, to to an "early" Volvo 
specialist. They will know the car, and they will know better about 
it.

-Robert
vin 6585