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IMi
K-Jetronic can look deceptively simple. Some of us
remember the days when we looked at this system and
thought " Servicing this will be a breeze—the system's
almost entirely mechanical!"
But we didn't anticipate the ravages of fuel con
tamination. We also didn't know that the system would
evolve into electronically controlled versions such as
K-Lambda and KE. But electronically controlled or
not, fuel contamination is the number one prob
lem-starter in any K-Jet/CIS system. (Most of the tips
described here apply to all versions.)
Never attempt to separate the two halves of a fuel
distributor for cleaning. However, you may be able to
save a fuel distributor by cleaning the control circuit
and control plunger bore. When you opt to remove a
control plunger, always catch it in a clean shop towel.
Note which end of it pointed up.
When you spray out the plunger bore and its
dampening restrictor with carb cleaner, blow out the
cleaner residue with compressed air. Then dip the
plunger in clean fuel and slide it back into its bore.
When you tilt the fuel distributor, the plunger should
slide up and down on its own weight. If it doesn't,
replace the fuel distributor.
If you use baby bottles to measure injector flow,
respect and heed the fire potential here. After all,
you're spraying and collecting raw fuel.
—By Dan Marinucci
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The most cost-effective tools for K-Jet injector volume
tests are plain old baby bottles. Use one bottle per in
jector. Turn on the fuel pump, move the air flow sen
sor plate, and collect a few ounces of fuel. Line the
bottles up on a level surface. The lowest fuel level pin
points the leanest cylinder.
Deteriorated injector lines aren't commonplace. But
the inside of the line can "flake" and restrict fuel flow.
If you've got misfiring and low injector volume in one
cylinder, try swapping the line for a line from a
known-good cylinder. If swapping lines corrects the
miss, replace the bad line.
Would you replace just one bad spark plug instead of
replacing the entire set? No? Then apply the same
reasoning to injectors. Explain to customers that
replacing just one injector—especially on highermileage engines—is false economy. Replacing all the
injectors is cheap insurance.
In order to run the fuel pump during your K-Jet tests,
you can by-pass the fuel pump relay. See how the mid
dle two terminals (30 and 87) form an inverted T? After
you pull out the relay, just remember to connect your
jumper wire across the two female terminals that form
theT
Checking injector flow/volume on a problem car?
Remember to take three separate readings at three dif
ferent sensor plate positions. Check it with the sen
sor plate barely open, with it halfway open, and with
it wide open. At each of these plate positions, the in
jector's volumes should be equal.
During testing, some guys prefer to run the fuel pump
directly off the battery. To make a good jumper, splice
a fuseholder and 10-amp fuse onto some 12-gauge
wire. Be sure you have an alligator clip that fits the
fuel pump terminal and another one that fits the bat
tery terminal.
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When the fuel pump fuse keeps blowing or the pump
sounds draggy or noisy, check the pump's current
draw. A typical K-Jet pump draws about 8 amps.
Remember that the brown wire connected to the
thicker-diameter terminal is the ground wire.
When you're troubleshooting a low power and/or fuel
starvation complaint, don't overlook a cracked fuel
pump inlet hose. Symptoms? Listen for a howling
pump. Look for bubbly fuel when you do the fuel
pump volume test. A collapsed in-tank fuel strainer
can also make the fuel pump sound noisy.
It's bitter cold, the car won't start, and you notice the
pump fuse is blown. Maybe there's water in the fuel
and the pump froze. Replace the fuse and gently warm
the pump with a hair dryer or a dryer-like electric heat
gun such as this one. Don't use an open flame here!
Whatever you do, never dump that fluid out of a new
or remanufactured pump. Remember that fuel cools
the pump. That funny fluid you find inside the pump
both keeps the pump primed and keeps it cool dur
ing start-up. Running the pump dry can kill the pump
Most of the problems you encounter on K-Jet fuel
systems are originally caused by damp and/or dirty
fuel. You really can't change fuel filters too often on
this system—but try convincing the customer of that!
When you replace a filter, it can't hurt to log the
mileage right on the filter can.
Blazing dipsticks? This is an old trick—but an effec
tive one. If the customer balks at your suggestion to
change the fuel-diluted oil and filter, pull the dipstick
and put a match to it for him. If the crankcase is fuel-
or shorten the life of the pump.
diluted, there's no way you'll get an accurate CO ad
justment on the system!
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One sensitivity K-Jet shares with its cousin L-Jet is oil
temperature. Preferred temperature for an accurate
mixture adjustment is about 80 degrees C (175 degrees
F). If the oil temperature isn't right or the oil's diluted
with fuel, that CO adjustment will come back to haunt
you!
When you have to remove a K-Jet mixture concealment
plug, carefully—and very gently—center punch the
plug. Then slowly drill the plug without drilling
through it. Thread a self-tapping screw into the plug
and use a dent puller or locking pliers to pull the
screw and the plug out.
If you're removing this anti-tampering plug, we recom
mend using a drill bit no larger than about 9/64 (0.140
inch/3.5 mm). To be safe, drill the plug no deeper than
about 3/16 (0.187 inch/4.7 mm). To keep dirt out of the
air flow housing, install a new plug after you've ad
justed the CO.
The K-Jet mixture adjustment is so sensitive that it'll
See how fine the threads on the mixture adjustment
screw are? If someone forgot to reinstall the conceal
ment plug, these threads may be badly rusted. If the
adjustment screw won't budge, soak it with penetrat
ing oil for as long as practically possible. Don't force
this screw!
change when you put your 3 mm wrench into the ad
juster screw! Because it's so sensitive, we prefer a
lighter-weight tool for this job. Remember that chang
ing the idle CO on this system automatically changes
mixture at all engine speeds!
Suppose you have to service the primary pressure
regulator but the regulator won't cooperate. Grab a
clean, untorn shop towel and hold it over the regulator
opening. Have your assistant turn on the fuel pump
for just a second or two. Fuel pressure will pop the
regulator valve out of its bore.
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This is a typical later-model K-Jet primary pressure
regulator assembly. Be careful with it, because there're
lots more little parts here than there are in the earlier
regulator. Changing that washer-like shim changes the
primary system pressure. A thicker shim increases the
The injection system seems to be flooding the engine?
Shut the engine off and pull the injectors. If the in
jectors are spraying fuel when the air flow sensor plate
is at rest, then the control circuit is restricted or the
control plunger's sticking in its bore.
pressure.
When you slowly move the sensor plate up to full
travel, you should feel steady, even resistance. If you
feel uneven resistance, move it to full travel again and
release it. If the plate doesn't freely drop down to rest
position, its lever is binding inside the air flow sen
If you feel uneven resistance when you move the air
flow sensor plate but the plate drops freely to its rest
position, then the control plunger is sticking. A blast
of compressed air may free the plunger. You can also
sor housing.
dislodge it by rapping the fuel distributor against a
pair of wood blocks.
Contributor Dre Brungardt uses his cutaway to show
the restrictor above the control plunger. If this clogs
up, the engine will flood out. To clean it out, remove
the fuel distributor, remove the control plunger, and
blow carb cleaner and shop air into the centermost fuel
distributor fitting.
Violent engine backfiring can bend this air flow sen
sor plate. If that engine's got a whole list of driveability
problems at the same time, check for a bent or
uncentered sensor plate. Don't invite a comeback. Pin
point and correct the cause of the backfiring before
you return the car.