Volkswagen Cabriolet DIY Guide

K-Jetronic: Measuring Duty Cycle, Adjusting Air-Fuel Mixture, & Setting Idle
Overview

Before doing anything, let's discuss what CIS, K-Jetronic, lambda, and duty cycle are so that you get a very basic understanding of
how the system works and what it is you'll be testing.

K-Jetronic is a mechanical fuel injection system developed by Bosch in the 1970s and is used in a wide variety of vehicles around the
world. K-Jetronic is a continuous injection system (CIS), which means that the fuel injectors receive and produce a constant flow of
fuel, provided there is proper pressure, whenever the engine is running. CIS is a mechanical injection system because fuel is
metered by the mechanical link between the fuel distributor and airflow sensor plate, which are linked together in one housing. In
other words, fuel is metered in proportion to the incoming air flow.

In order to adhere to stricter emissions requirements in North America, Bosch enhanced K-Jetronic by adding lambda control. With
the addition of an oxygen sensor (aka lambda probe) feedback system, K-Jetronic's air-fuel mixture can be more precisely controlled
while the engine is running under various conditions (cold, warm, full-throttle). K-lambda (as it's often referred to) has better
emissions, in theory, than its basic predecessor. It is called lambda because Bosch uses the Greek letter lambda (λ) to represent the
stoichiometric ratio (14.7:1) of the air-fuel mixture the system strives to achieve for peak operating performance.

When the engine is warmed up, the oxygen sensor

produces an electrical signal based on the oxygen
content in the exhaust that is sent to the Jetronic
control unit under the dash. This control unit takes the
oxygen sensor's voltage, converts it to a square wave
signal (a pulsed 100 Hz on/off ground signal), and sends
that signal to the frequency valve (aka lambda valve, an
injector of sorts), which determines the amount of time
the valve is open. That pulsed ground signal is the
lambda system's duty cycle. The valve's on/off behavior Photos by Myndex (l.) and Walt Fricke (r.) from benzworld.org forum.
is what creates the audible buzzing (reminder: if the
frequency valve does not buzz/vibrate, there is something wrong). Note: The frequency valve does not meter fuel, but, rather,
controls the fuel distributor's lower chamber fuel pressure, which, in turn, changes upper chamber pressure to vary fuel enrichment.
The photos above show two lambda system duty cycles as produced by oscilloscopes. The left photo depicts a system that is being
enriched while the vehicle is being driven; the right photo shows a system at approximately 50%.

While it is often called an electronic control unit, the Jetronic controller is not a computer
and should never be referred to as such. Because this control unit is analog and merely
processes and reroutes voltage signals, it is very wrong to refer to K-lambda as an
electronic fuel system… it is not an electronic fuel system! While the frequency valve
operates based on an electronic voltage signal, the air-fuel mixture still takes place
mechanically inside the fuel distributor as described above. The K-Jetronic lambda
controller installed in Volkswagen Cabriolets (and Rabbits, Golfs, Sciroccos, and a host of
other vehicles) consists of nothing more than a circuit board with a bunch of capacitors,
inductors, resistors, transistors, and diodes. As you can see from the photo at left, the
Photo by Myndex from benzworld.org forum.
controller is really nothing more than a relay (of sorts) on steroids.

The basic stages of the lambda system:

1. Open loop - cold: Engine is cold-started, thus providing cold-running enrichment during warm-up period.
2. Open loop - warm: Cold enrichment has ended; system is at 50% duty cycle, waiting for oxygen sensor activity; also known as
limp-home mode.
3. Closed loop: Oxygen sensor is sufficiently heated and is now sending voltage signals to control unit during the engine's warm
running period.
4. Open loop - WOT: Full-throttle (aka wide-open throttle) switch has been activated, providing fuel enrichment override.

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While the pulsed ground signal sent from the oxygen sensor control unit to the frequency valve is a square wave valued on a 100
Hertz (Hz) frequency scale (with spikes up to 12,000), this voltage signal is measured in duty cycle (0-100%), or in dwell (0-90°). This
information is used to adjust, if need be, the air-fuel mixture on a K-lambda car.

Here's how the system works (provided everything is functioning as it should):

1. If you start the car when the engine temperature is cold, the oxygen sensor thermoswitch closes and sends a signal to the
control unit.
2. The control unit, in turn, sends a fixed 80% duty cycle (65% for 1988+) signal to the frequency valve. That fixed cold-
running enrichment signal (80% or 65%) remains in place until the coolant reaches a specific temperature (25°C or 45°C,
depending on the thermoswitch installed in your car).
3. The thermoswitch then opens, cutting its signal to the control unit. If the oxygen sensor is not at its operating temperature
when the thermoswitch opens, the system reverts to warm open loop, or limp-home mode (50%).
4. Once the oxygen sensor is heated to its proper temperature, it sends a signal to the control unit and the system enters
closed loop, or its normal regulating function (50% ±8% duty cycle). Should the full-throttle switch be activated, closed-loop
is overridden for forced full-throttle enrichment (65% duty cycle).

Up through and including the 1987 model year, cold-running enrichment (80%) overrides full-throttle enrichment (65%). From the
1988 model year onward, cold-running enrichment does not override full-throttle enrichment because the two values are the same
(65%).

"Open loop will also happen when the car has been parked briefly, the oxygen sensor has cooled off, and the thermoswitch
hasn't closed; upon restarting, it takes a minute or more before the oxygen sensor heats enough to produce a signal and send
the system into closed loop. That's why oxygen sensors are now heated; they start working faster, systems go into closed-loop
sooner.

"There isn't always an open-loop stage during warm-up. If the engine is cold (real cold, like winter in Montana cold), and the
oxygen sensor is in great shape, the oxygen sensor's heater and the exhaust heat may get the oxygen sensor up to operating
temperature before the thermoswitch warms enough from from the coolant to open. In that sort of circumstance, the system
will go straight from cold-running enrichment to closed-loop; no open-loop transition at all. Same car, same cold weather: The
oxygen sensor will cool quickly when the car is parked, while the coolant will retain heat much longer; on restart, there will be
no cold-running enrichment -- the system will be in open-loop until the oxygen sensor warms up enough to put the system into
closed-loop." ~tolusina of VWvortex.com

Likewise, if the car is in a warm climate (or during warm seasonal months), the system may revert to open loop upon initial start-up,
skipping cold-running enrichment due to the coolant already being at or above the thermoswitch's pre-set temperature.

The preceding is only a very brief overview of how K-lambda operates. For much more detail on the theory, application, component
descriptions, performance, modifications, and troubleshooting, please obtain Charles Probst's book, Bosch Fuel Injection & Engine
Management.

The Required Meter

In order to read your lambda system's duty cycle, you need a digital or analog meter that can read duty cycle (%) and/or dwell. A
simple volt-ohm meter will not do the job. This is also a case of "you get what you pay for". While you can visit Harbor Freight with
your 20% off coupon, the quality of meters they sell is substandard and there are numerous reports of inaccuracy. You don't need
the most expensive meter on the market, but you want quality. Additionally, while you can use a dwell meter, it has been reported
that using a dwell meter does not provide quite as accurate of a reading as a duty cycle meter, but it gets close enough. If you
already have a dwell meter, go ahead and use it; if you are new to the game, try to find a duty cycle meter (or better, a meter that
has both for additional automotive troubleshooting).

An oscilloscope, like those above, is actually the best and most accurate device for this job, but it is not a multifunction tool for your
toolbox. There is no need to buy this type of instrument just to read your car's duty cycle, unless you wish to have a neat toy to play
with.

So, what do you look for? Example meters are on the following page. Remember, these are merely examples highlighting what
setting your perspective meter should have in order to read your lambda system's duty cycle. I.E. these meters are not necessarily
being recommended (for the record I, personally, use a Craftsman duty cycle meter that is, ironically, not shown in the examples).

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Meter Examples

If buying a duty cycle meter, the meter MUST have the ability to switch to %/duty. Otherwise, you will be measuring Hertz (Hz),
which is not included in these instructions.

The above is a modern digital, portable

oscilloscope that not only graphs the
signal, but provides the actual duty cycle
number on the screen, which is very
handy when needing to make fine
adjustments of the air-fuel mix. An
oscilloscope is a neat tool to play with,
Be sure to read your analog meter's
especially for visual, scientific-types, but
manual. Some meters require you to
it's a tool that will go largely unused for
double the 8-cylinder reading, others
most DIY home mechanics. Fun device
require you to divide by 2, if they do not
that is the most accurate, but it's
have a separate 4-cylinder gauge.
certainly not necessary to have.
Your digital dwell meter must have a 4
cylinder setting.

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Before Checking Duty Cycle & Making Adjustments

Requirements:
 Car should be otherwise well-tuned (see below for further information)
 No, and I mean zero, vacuum leaks
 Distributor advance mechanism(s) should be operating correctly
 Timing should be correctly set with a closed throttle plate
 Air-fuel mixture plug removed and mixture screw free of gunk
 Frequency valve should be buzzing/vibrating whenever the fuel pumps are running; if it is not buzzing, please test it.

Start with a complete tune up (if not recently conducted):

 Replace ignition components: spark plugs, cap, rotor, wires (use Bosch ignition parts and use NGK plugs)
 Replace air and fuel filters
 Replace injector seals and idle screw O-ring
 Tighten the injector holders; replace the injector holders, if needed
 Check for vacuum leaks using carburetor cleaner (spray around hoses, gaskets, injector O-rings); if idle goes up, leak found
(replace faulty part -- use a bit of RTV when replacing gaskets)
 Check your K-Jetronic grounds at the cold-start valve: they should be clean, fully connected, and intact
 Test your oxygen sensor (pages 9-10) and replace, if need be
 Check your full-throttle switch and idle boost valve(s)
 Check your CIS system and control pressures
 Check your distributor's centrifugal and vacuum advance mechanisms
 Set your timing, if need be

Do NOT, under any circumstances, disassemble the fuel distributor and/or airflow sensor unless you know for
certain what you're doing! Taking this piece of precision equipment apart on a whim because your CIS fuel injection
system is not running right is a disaster waiting to happen, and usually ends with you having to buy a new (actually
used/rebuilt) fuel distributor!

If you feel that you and your car are prepared for testing, proceed to the next section.

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Checking Duty Cycle & Making Adjustments

Tools needed:
 Volt-ohm meter that measures duty cycle (dwell meter can also be used, but duty cycle is a bit more accurate)
 3mm Allen wrench (T-handle version advised)
 7mm crescent wrench

Duty cycle = 0-100%

Dwell = 0-90° scale (45° dwell = 50% duty cycle).

Step 1 ~ Connect meter Step 1 ~ Notes

 Connect the red positive (+) meter wire to the blue/white *If you have installed spade terminal disconnects in place of the
wire's terminal in the two-pin test connector by the cold-start OEM connector, simply attach the red (+) probe’s alligator clip to
valve. Connect the black negative (-) DVOM wire to any the blue/white wire terminal and the black (-) probe’s alligator
convenient ground*. clip to the brown wires’ terminal.
 If using the dwell setting, set meter to "4 cyl";
 If using the duty cycle setting, set meter to "frequency %" ** **If using duty cycle, be aware that Cabriolets produce a
negative slope reading. Many meters read only in positive slope.
Read your meter's instructions; some meters require an Easy test: Connect the test leads as described. With the engine
additional step, such as pressing a button such as “range”. running, actuate the full-throttle switch. If the reading is 35%,
reverse the test leads: red (+) to brown wire, black (-) to
blue/white wire. Actuate the full-throttle switch once more; the
reading should be 65%.
Step 2 ~ Warm the engine Step 3 ~ Read your meter

Target reading:
 50% duty cycle (±8%)
Run the engine up to operating temperature (oil at 80°C); the  45° dwell (±7°)
cooling fan should cycle on/off at least once. Keep all
accessories off. If it is not within this range, continue to step 4. If it is within this
range, skip to Step 5.
Make note of where the air-fuel adjustment screw is on the
airflow sensor (do not put the Allen wrench in the hole until you Note: If the needle bounce/swing is higher than a range of 10
adjust the mixture!!). Note: The factory anti-tamper plug must (ex. 55-74), there are issues that need resolving before
be removed first! Please click here for details on removal. continuing.

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Step 4 ~ High reading Step 4 ~ Low reading

Lean setting, rich correction Rich setting, lean correction

Your air-fuel mixture setting is too lean and the control unit is Your air-fuel mixture setting is too rich and the control unit is
making a rich correction. making a lean correction.

Check for vacuum/air leaks; fix any that are found. Check cold-start valve to verify that it is not leaking.

Insert your 3mm Allen wrench into the adjustment hole and turn Insert your 3mm Allen wrench into the adjustment hole and turn
the wrench clockwise. You are richening up a lean condition. the wrench counterclockwise. You are leaning out a rich
condition.
NOTE: The weight of the wrench will affect the mixture! Turn the wrench a little, just enough to feel it move, then lift the wrench
out of the adjustment screw hole. Repeat this process until 45° ±7° dwell / 50% ±8% duty cycle is achieved.

Step 5 ~ Idle adjustment

Have your 7mm open-end wrench handy; you may have to tweak the idle bypass screw (backside of the throttle body) if the idle
changes too much after adjusting the mixture. You need to stay below about 900 RPM while adjusting the idle. Use the tach on the
dash and your ears, you know what sounds right and normal. If you go over 900 RPM, the centrifugal advance starts to kick in,
changing the timing and confusing all your readings. Set the idle RPM at 900±, but above the threshold of the idle boost valve.

If the idle boost valve kicks in while you are adjusting, you've dropped too low on idle RPM. You can unplug the idle boost valve
electrical connector, or better, pinch off either of the hoses going to it. When the idle boost valve (or hose) is reconnected, idle
should not change if you've adjusted the idle correctly.

Switch on the A/C (if installed) to make sure that the A/C idle boost valve works; idle should stay about the same with the A/C
compressor running.

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Notes ~ 1988-1989 with cold-running enrichment system
"I had the fuel pump go on me and replaced it with a Bosch original OEM that has the threaded Check Valve screwed into the top of
it. While I was there I replaced the Accumulator as well seeing as it was all rusty and original and more than likely due soon for
replacement.

Upon replacing these 2 parts the engine would run great and start fine cold. So well in-fact that I equipped the car with a Remote
Starter unit. The problem was that when the car was hot (Oil temperature between 80ºC - 100ºC) and had been sitting for 10, 15 or
20 minutes the car would be almost impossible to start or would start and studder like crazy and require you to step on the
accelerator to clear it up.

My dad (mechanic of 35 years) and I spent days trying to remedy this problem and drove ourselves nuts. We checked fuel pressures,
we checked the warm up regulator, the cold start valve (also used in hot-restart). The relays and control modules, the thermo time
switch and the list goes on and on.

We found out that the Dwell of 45º that is listed on this site and others my not apply to all models. What we did was rev the engine
to 2,000rpm and set the idle-mixture screw until the dwell fell to 45º at this RPM. Then it would naturally enrichen the mixture when
the idle was allowed to fall to the 925 ±25 rpm as indicated on the hood sticker. It was only then that the car would start/restart
properly under hot conditions.

I wanted to share this information with you to help anyone else banging their head against the wall like we did trying to get it to
start properly when hot with this Hot-Pulse Start system.

Please note that we checked all cold/hot fuel pressures and residual pressures on shut-down both cold/hot and they were within
spec. The car also has brand new injectors, thermo-time switch, fuel pump, accumulator, filter, air-filter, cap/rotor, spark-plugs,
spark-plug wires, vacuum enrichment switch, Oxygen Sensor, idle-stabilizer relay, fuel pump relay, Hot-Pulse Start Relay. As we
replaced all this trying to remedy this problem. So we know that this is the setting that it should be at."
~ Steve C.
Notes ~ Questionable readings
Should you find questionable meter operation while measuring frequency valve duty cycle (ex., the reading never changes):
 Connect your test lead to the Hall sender green/white wire and test your meter. It should read a very steady 36-37° on the 4
cylinder dwell scale, 40.5-40.6% duty cycle.
 If the meter proves to be good:
 Conduct the tests in the lambda system testing section starting on page 8.
 The test port connector itself could be faulty. Refer to the Test Port section on page 12.

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Lambda System Testing

Tools needed:
 Volt-ohm meter that measures duty cycle (dwell meter can also be used)
 Hose pinchers
 New D-cell battery
 Jumper wire using two male spade connectors
 Test tables on page 11 and a pen

Step 1 ~ Connect Meter Test 1 ~ Cold Running Enrichment 1980-1987

Open Loop - cold

1. Disconnect the leads from the oxygen sensor thermoswitch
Connect your meter according to the Step 1 instructions on page and bridge the terminals using a jumper wire with male
5. spade terminals.
2. Start and run the engine.

Target reading:
 80% duty cycle with little fluctuation
 72° dwell with little fluctuation
Test 1 ~ Cold Running Enrichment 1988+ Test 2 ~ Limp-home Mode all

Open Loop - cold Open Loop - warm

1. Disconnect the leads from the oxygen sensor thermoswitch 1. Leave the engine running.
and bridge the terminals using a jumper wire with male spade 2. Disconnect your jumper wire from Test 1 and leave the
terminals. thermoswitch disconnected.
2. Start and run the engine. 3. If the engine is at operating temperature by now, disconnect
oxygen sensor.
Target reading:
 65% duty cycle with little fluctuation Target reading:
 58° dwell with little fluctuation  50% duty cycle with little fluctuation
 45° dwell with little fluctuation
Disconnect the oxygen sensor after doing the above test. Your
meter should read 65% duty cycle (or 58° dwell) with very little
fluctuation. If the meter reads 50% (or 45°), check the cold-
running enrichment vacuum switch. Reconnect the oxygen
sensor before continuing.

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Test 3 ~ Full-throttle enrichment 1.8L Test 4 ~ Warm Running all

Open Loop - WOT Closed Loop

1. Leave the engine running. 1. Leave the engine running and ensure it is at operating
2. Leave the oxygen sensor thermoswitch disconnected and temperature.
unbridged. 2. Reconnect oxygen sensor and the oxygen sensor
3. Actuate the full-throttle switch. thermoswitch while keeping an eye on your meter.

Target reading: Target reading:

 65% duty cycle ±2%  50% steady duty cycle to ±8% fluctuation
 58.5° dwell ±2°  45° steady dwell to a ±7° fluctuation

You should see the reading change from constant to fluctuating.

If the meter is already fluctuating when you connect the
thermoswitch, turn the engine off, let it cool down for a bit and
retry this test.
Test 5 ~ Rich Correction all Test 6 ~ Lean Correction all

Lean Condition, Rich Correction Rich Condition, Lean Correction

1. Disconnect the leads from the oxygen sensor thermoswitch 1. Keep the engine running and the wires in Step 5
(do not bridge/jump them). disconnected.
2. Disconnect the black oxygen sensor wire from the green 2. Ground the negative end of the D-cell battery while
control unit wire. touching the oxygen sensor control unit’s green wire spade
3. Run the engine (if you've shut if off). terminal to the positive end of the D-cell battery.
4. Ground the green wire's spade terminal on bare metal (use a
jumper wire if need be). Target reading:
 20% and falling, engine may stall
Target reading:  18° and falling, engine may stall
 87% and rising
 78° and rising
Test 7 ~ Oxygen Sensor method 1
1. Start the engine and let it run until it reaches operating temperature (80°C or higher); if it's already warm, let it run for two
minutes.
2. Clamp off the hose from the idle speed boost valve (white valve, if your car has A/C).
3. Disconnect the crankcase ventilation hose.
4. Make note of the duty cycle reading.
5. Plug the crankcase ventilation hose. The duty cycle should drop, then rise and fluctuate.
6. If the duty cycle does not drop, then rise and fluctuate, the oxygen sensor is faulty.
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Test 7 ~ Oxygen Sensor method 2
1. Start the engine and let it run until it reaches operating temperature (80°C or higher); if it's already warm, let it run for two
minutes.
2. Disconnect the oxygen sensor wire (black) from the oxygen sensor control unit wire (green).
 If you have two DVOMs, you can connect the second one as shown in Step 1 to read the duty cycle/dwell at the same
time, but this is not necessary.
3. Connect the black DVOM lead to any convenient ground and connect the red DVOM lead to the oxygen sensor lead wire (black).
4. Set the DVOM dial to 2 DCV (or 4 DCV, if that's the lowest setting on your meter).
5. Ground the oxygen sensor control unit lead wire to bare metal to simulate a lean condition. The oxygen sensor's voltage should
go high: 0.8 to 1.0 DCV
 Duty cycle/dwell should go high, 85%/75° or higher.
6. Connect the D-cell battery's positive end to the green oxygen control unit lead wire and ground the negative end of the battery
against bare metal; this simulates a very rich condition. The oxygen sensor's voltage should go low: 0.15 DCV or lower
 Duty cycle/dwell should go very low, 10%/9°.
 Note: The system may go so lean that the engine stalls; this is normal.
7. Keep the engine running and leave the meter’s black lead connected to ground, but connect the meter's red lead to the green
ECU (aka Vref) wire. You should see a steady 0.45 DCV to 0.50 DCV. Flex the green ECU wire; if voltage drops to or near zero
there is most likely a short in the green ECU cable that needs to be repaired.

What you are measuring in Step 7 above is Vref, or reference voltage:

This Vref is pretty much the heart of this (or any, really) 'closed loop' mixture control system. The ECU sets a steady reference
voltage of 0.45 VDC to 0.50 VDC (this voltage is steady, varies slightly between different ECUs) on the green oxygen sensor wire, the
black O2 sensor lead connects to this wire.

The oxygen sensor, once at operating temperature, outputs a voltage between approximately 0.1 VDC (a lean signal), to
approximately 0.9 VDC (a rich signal).

When the ECU sees an oxygen sensor voltage higher than its Vref, it correctly interprets that to mean that the mixture is richer than
stoichiometric (i.e. 14.7:1 air-fuel ratio), the ECU then leans the mixture to compensate by lowering the duty cycle to the frequency
valve below 50%. Once below 50%, it is now too lean; oxygen sensor voltage is now below Vref, so duty cycle goes back up to
correct.

On and on goes this continuous correction, the ECU constantly trying and failing to get the oxygen sensor voltage to match Vref.
The system is actually designed to strive and fail. There are two reasons it strives and fails. One is built in response delays, the other
is that those response delays are built in so that the catalytic converter will always have a slightly fluctuating mixture, something the
cat converter requires for its chemical reaction to work properly.
above information provided by tolusina of VWvortex

Notes
 A sluggish oxygen sensor may cause a failed smog inspection while exhibiting absolutely no other drivability issues.

 Should you see an operating range at the oxygen sensor ranging from -0.5 DCV to 0 DCV (instead of the normal +0.1 DCV to +0.9
DCV), your sensor has been permanently damaged by chemical contamination and needs replacing. You may also experience a
constant, very high duty cycle reading, like 96% during duty cycle check.

 Cabriolets built from July 1987 through 1989 have heated (3-wire) oxygen sensors. Should you see 12 DCV (or charging voltage)
at the oxygen sensor wire, replace the oxygen sensor immediately -- the heater has shorted to the sensor.

 Should the oxygen sensor control unit happen to be faulty, it will fail to compensate for the simulated lean/rich conditions
described above. The oxygen sensor control unit rarely goes bad, but is does happen. Before condemning the control unit as
being faulty, verify that the control unit is receiving power (pin-out diagram on page 15) and that all ground wires/connections
are good. Additionally, if the duty cycle stays at 65% or 80%, disconnect the cold running enrichment switch (if installed) and the
full-throttle switch, one at a time, then both together if need be.

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Lambda System Condition Simulation Testing Tables

1980-1987 without cold-running enrichment system

Full-throttle Oxygen Sensor Reading Should Your
Test Oxygen Sensor Running Stage
Switch Thermoswitch Be… Reading
1 Disconnected, Cold-running 80% (±2%)
Connected Connected
Open Loop - cold leads bridged enrichment 72° (±2°)
2 Connected or Limp-home 50% (±2%)
Connected Disconnected
Open Loop - warm Disconnected mode 45° (±2°)
3 Connected & Full-throttle 65% (±2%)
Connected Disconnected
Open Loop - WOT Actuated enrichment 58.5° (±2°)
4 50% (±8%)
Connected Connected Connected Warm running
Closed Loop 45° (±7°)
Disconnected,
5 Lean condition, 87% (increasing)
ECU lead Connected Disconnected
Rich Correction rich correction 78.3° (increasing)
grounded
Disconnected,
6 +1.5V applied to Rich condition, 20% (decreasing)
Connected Disconnected
Lean Correction ECU lead, -1.5V lean correction 18° (decreasing)
grounded
Test 6 requires a These are Reminder:
D-cell battery; ECU Located on simulation tests; Readings are in
lead wire is green. Located at front underside of being at operating negative slope %…
Notes
Test 6 may lead to part of throttle body coolant hose flange temp is be sure your %
engine stall (this is on 1.8L unnecessary for all meter leads are
normal). tests except 4. connected properly

1988-1989 with cold-running enrichment system

Full-throttle Oxygen Sensor Reading Should Your
Test Oxygen Sensor Running Stage
Switch Thermoswitch Be… Reading
Disconnected,
1a Cold-running 65% (±2%)
Connected Connected brown/red wire
Open Loop - cold enrichment 58.5° (±2°)
grounded
1b Disconnected, Cold-running 65% (±2%)
Disconnected Connected
Open Loop - cold leads bridged enrichment 72° (±2°)
2 Connected or Limp-home 50% (±2%)
Connected Disconnected
Open Loop - warm Disconnected mode 45° (±2°)
3 Connected & Full-throttle 65% (±2%)
Connected Disconnected
Open Loop - WOT Actuated enrichment 58.5° (±2°)
4 50% (±8%)
Connected Connected Connected Warm running
Closed Loop 45° (±7°)
Disconnected,
5 Lean condition, 87% (increasing)
ECU lead Connected Disconnected
Rich Correction rich correction 78.3° (increasing)
grounded
Disconnected,
6 +1.5V applied to Rich condition, 20% (decreasing)
Connected Disconnected
Lean Correction ECU lead, -1.5V lean correction 18° (decreasing)
grounded
Test 6 requires a These are
Reminder: Readings
D-cell battery; ECU Located on simulation tests;
are in negative slope
lead wire is green. Located at front underside of being at operating
Notes %… be sure your %
Test 6 may lead to part of throttle body coolant hose flange temp is
meter leads are
engine stall (this is on 1.8L. unnecessary for
connected properly
normal). all tests except 4.

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Test Port & Whacky Readings

If your meter is giving you odd readings and you have verified that the meter is working properly, the test port may be faulty as
evidenced by my own experience:

The first two tables below contain readings on my 1986 CIS-lambda Cabriolet. The initial test readings in attempts 1 and 2 point to a
possible control unit issue and/or meter issue (one reason a new meter was bought). However, the tests prove that while the
readings are bizarre, the idle changed as did the meter readings, which indicates the control unit is good as well as the meters
(meters were double-checked using the green/white Hall generator wire). The thermoswitch was proven good after conducting a
resistance test. The frequency valve buzzes every time the engine runs and the engine purrs like a kitten. The components as well
as the meters all indicated that everything was A-Okay. So, in the name of science...

Hypothesis: Test port is faulty, which was suspected at the very start.

Attempt #1 (dwell meter)

Full-throttle Oxygen Sensor Reading Should My
Test Oxygen Sensor Running Stage
Switch Thermoswitch Be… Reading
84° w/
1 Disconnected, Cold-running
Connected Connected 72° (±2°) slight idle
Open Loop - cold leads bridged enrichment
drop
2 Connected or Limp-home
Connected Disconnected 45° (±2°) 84°
Open Loop - warm Disconnected mode
3 Connected & Full-throttle
Connected Disconnected 58.5° (±2°) 84°
Open Loop - WOT Actuated enrichment
4
Connected Connected Connected Warm running 45° (±7°) 84°
Closed Loop
Disconnected,
5 Lean condition, 65° &
ECU lead Connected Disconnected 78.3° (increasing)
Rich Correction rich correction decreasing
grounded
Disconnected, 42° &
6 +1.5V applied to Rich condition, decreasing
Connected Disconnected 18° (decreasing)
Lean Correction ECU lead, -1.5V lean correction w/ idle
grounded drop

Attempt #2 (new duty cycle meter)

Full-throttle Oxygen Sensor Reading Should My
Test Oxygen Sensor Running Stage
Switch Thermoswitch Be… Reading
1 Disconnected, Cold-running
Connected Connected 80% (±2%) 89-98%
Open Loop - cold leads bridged enrichment
2 Connected or Limp-home
Connected Disconnected 50% (±2%) 70-98%
Open Loop - warm Disconnected mode
3 Connected & Full-throttle
Connected Disconnected 65% (±2%) 90-98%
Open Loop - WOT Actuated enrichment
4
Connected Connected Connected Warm running 50% (±8%) 76-98%
Closed Loop
Disconnected, Rose to
5 Lean condition,
ECU lead Connected Disconnected 87% (increasing) 53.7% &
Rich Correction rich correction
grounded stopped
Disconnected,
Dropped to
6 +1.5V applied to Rich condition,
Connected Disconnected 20% (decreasing) 91.2% w/
Lean Correction ECU lead, -1.5V lean correction
idle drop
grounded

^Those are some pretty serious whacked-out readings!

© 2015 KamzKreationz Page 12 of 15 K-lambda Adjustments

Experiment: The factory probe harness was cut off and spade terminals were crimped onto the wires in order to provide a better
contact using alligator clip adapters on the meter probes. The tests were then conducted for a third time:

Attempt #3 (new spade test terminals)

Full-throttle Oxygen Sensor Reading Should My
Test Oxygen Sensor Running Stage
Switch Thermoswitch Be… Reading
1 Disconnected, Cold-running 80% (±2%) 80%
Connected Connected
Open Loop - cold leads bridged enrichment 72° (±2°) 67.8°
2 Connected or Limp-home 50% (±2%) 50%
Connected Disconnected
Open Loop - warm Disconnected mode 45° (±2°) 42°
3 Connected & Full-throttle 65% (±2%) 65%
Connected Disconnected
Open Loop - WOT Actuated enrichment 58.5° (±2°) 55°
85%
4 50% (±8%)
Connected Connected Connected Warm running (running
Closed Loop 45° (±7°)
lean)
Disconnected,
5 Lean condition, 87% (increasing) 80% +
ECU lead Connected Disconnected
Rich Correction rich correction 78.3° (increasing) 78.3°+
grounded
Disconnected,
6 +1.5V applied to Rich condition, 20% (decreasing)
Connected Disconnected Not tested
Lean Correction ECU lead, -1.5V lean correction 18° (decreasing)
grounded

Result & conclusion: As can be seen in the Attempt #3 table, the readings from both meters are within specifications (aside from #4,
which showed me the car had a too-lean mixture). The factory test port was indeed faulty by not providing good enough probe
contact, which can be seen in the photo below.

© 2015 KamzKreationz Page 13 of 15 K-lambda Adjustments

Callaway Turbo Kit

* * Remember, you are responsible for working on your car; Cabby-Info.com, KamzKreationz, VAG, VWoA, or anyone
else are not responsible if anything goes wrong while you are working on, in and under your car!
Use this information at your own risk!* *

© 2015 KamzKreationz Page 14 of 15 K-lambda Adjustments

K-Jetronic Lambda Controller Pin-outs

Wire colors based on Volkswagen diagrams;

colors and ground point locations may differ
depending on your model year. Oxygen sensor input

Pictured: ECU #035906263F; found in all

1980-1987 North American Cabriolets with
CIS-lambda.
Ground at cold start
valve

Full-throttle switch input

Power input from
lambda relay

Oxygen sensor
thermoswitch input

Output to frequency valve

Ground at cold start
valve
Output to test port

© 2015 KamzKreationz Page 15 of 15 K-lambda Adjustments