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Some people call it CIS, continuous injection
system. Others call it K-Jetronic. The K comes from
konstant—German for constant. But when things go
wrong, you call it things we can't print! Always apply
the same preliminaries to K-Jetronic that you apply to
L-Jet: a basic engine/ignition analysis and fuel system
pressure tests. And fuel pump pressure/volume tests
are extremely important during K-Jet analysis.
Anytime you have a fuel delivery problem, check
for a bad fuel pump or fuel pump pickup. With prac
tice, you'll learn how a bad pump sounds.
Because the K-Jet injectors are hydraulically
operated, they need a steady diet of clean, bubble-free
fuel or they won't open. Therefore, fuel pressure and
fuel quality are critical on all K-Jet and K-Jet derivative
systems.
Special thanks to the people who helped us
research these fuel injection articles: Mark Blair,
Dre Brungardt, Tom Caterina, Ben Davis, James
Demas, Andy Demrovsky, Merry Ann Edwards, Eric
Von Gunten,
Jeff Hislop,
Steve
Louden,
Jeff
Melchiorre, Dick Mitchell, Fred Muder, Doug
Paquin, Andy Pfcgues, John Savarda, John Sayword,
John Spaminato, John Steiner, and Gary Strnad.
—By Dan Marinucci
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It doesn't take much dirt or rust to clog up or partially
clog the fine metering ports inside the fuel distributor.
When a dirty fuel distributor weakens a cylinder,
swapping injectors from cylinder ta cylinder won't im
prove the weak one.
Don't be afraid to slice open a fuel filter and show
evidence of fuel contamination to the customer. Often,
the only permanent cure for fuel contamination is a
new fuel tank, tank pickup, and/or more-frequent filter
changes. If you use fuel-cleaning additives, use
alcohol-free ones.
This is the result of too much blow-by and too little
maintenance. During cold weather, crankcase conden
sation and/or outside moisture can freeze on and jam
up the air flow sensor plate. Spray off the plate with
spray cleaner. Then check that the intake air preheat
system is working properly.
If you try to diagnose a K-Jet system without hooking
up a pressure gauge and three-way valve, you're crazy.
Unless you test the system's pressures—control pres
sure, primary pressure, and rest pressure, you are lost,
lost, lost! However, some people still try!
Whenever you repair or service a K-Jet system, be
super-conscious of dirt, particularly around the fuel
distributor. Always flush away dirt with a spray cleaner
before you crack open any fuel distributor fittings. And
take extra care when you're changing fuel filters or fuel
tank pickups too!
A partially clogged control circuit causes a rich con
dition. Did the fuel pump test good? Is the fuel filter
fresh? If so, then route a hose from the centermost
distributor fitting into a container. Run the pump for
one minute. A clean control circuit will flow at least
5.3 ounces of fuel.
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To isolate a bad injector from a bad fuel distributor,
check injector volume—or engine performance. Then
swap the suspect injector to an adjacent fuel line.
Repeat the volume or performance test. If the problem
follows the injector to the adjacent fuel line or engine
Suppose you swap injectors from strong cylinder to
weak cylinder and there's no improvement. Some guys
prefer to remove these outlet screens from the fuel
distributor ports and then retest the weak cylinder.
Sometimes, cleaning or discarding the screen will cor
cylinder, the injector's bad.
rect the problem.
To do a quickie opening-pressure test, let all the in
jectors hang free. Install your pressure gauge in place
If you've found rust elsewhere in the system, take a
moment to inspect these ports in the warm-up
of one injector. Energize the fuel pump and move the
air flow sensor plate. The moment the injectors squirt,
note the gauge reading. Injector with the lowest open
ing pressure will spray first.
regulator (control pressure regulator). If you find rust
in here, at least notify the customer. That contaminated
control pressure regulator may live for some time—or
it may fail next week.
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Tiny o-ring on the inner end of the primary pressure
regulator may be out of sight and out of mind. But a
damaged o-ring will leak off rest pressure and cause
hard hot starts. If you service this regulator, don't lose
those tiny shims that sit inside the regulator fitting.
Wondering where the rest pressure went? When this
type of accumulator leaks rest pressure, the fuel drains
back into the tank. Remove this hose. If fuel runs out
of this nipple, replace the accumulator. Sometimes,
a bad accumulator will suddenly make the pump
begin moaning a low-pitched moan.
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On K-Jet, many hard hot starts are caused by a bad fuel
pump check valve. Valve's available separately. But
watch out for alcohol-laden fuel too! When alcohol is
causing a hot no start or hard start, a short cool-down
will often make the car start right up. When in doubt,
This is NOT the idle speed screw, it's the throttle stop
screw! It's often factory-painted so you can tell if it's
been disturbed. If you pinch off the auxiliary air hose
and the engine still won't idle down, then some joker
probably tried to set the idle by cranking in this screw.
sample the fuel.
Shining a light through a suspect auxiliary air valve
can be impractical and inconclusive. When in doubt,
disconnect the suction side air valve-to-engine hose
and squeeze it. If you can regulate the air flow well
enough with your fingers to restore fast idle, the aux
iliary air valve's bad.
Many shops don't wait for vacuum leaks to occur at
the injector o-rings and/or insulators. They replace the
entire set as part of the car's maintenance program!
Some techs lube these parts with anti-seize because
it holds up better than grease does. No sense fighting
the same injector twice.
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If the engine backfires violently enough to blow this
boot off the air flow sensor, the engine won't start. You
guessed it—no air flow through the sensor, no fuel to
the injectors! To prevent a replay of the no start, find
and fix the cause of the backfire before you return the
car.
K-Jetronic responds to air leaks between the air flow
sensor and intake manifold the same way its cousin
L-Jetronic does. It hesitates, stumbles, and misfires!
Wratch for small cracks on these air flow sensor
boots—especially on the older, high-mileage systems.