Service Solutions: The 'CKP' Script

Service Solutions: The ‘CKP’ Script

The signal of the position or rotation speed of the crankshaft position sensor (CKP) contains a lot of information about the engine. When the engine is operating, the engine cylinders push on the crankshaft journal. This is why the crankshaft briefly accelerates after top dead center (TDC) on the expansion (or combustion) stroke. If the fuel did not ignite in the cylinder there would no acceleration.

By Vladimir Postolovsky, Translated by Olle Gladso, instructor, Riverland Technical and Community College Albert Lea, MN

The signal of the position or rotation speed of the crankshaft position sensor (CKP) contains a lot of information about the engine. When the engine is operating, the engine cylinders push on the crankshaft journal.

This is why the crankshaft briefly accelerates after top dead center (TDC) on the expansion (or combustion) stroke. If the fuel did not ignite in the cylinder there would no acceleration.

The crankshaft would decelerate instead. Thus, the power contribution from each cylinder can be determined by observing crankshaft acceleration and deceleration.

Even if the engine control unit continuously adjusts the speed of the engine rpm at idle in order to maintain speed in a specified range, the acceleration and deceleration from the engine cylinders are present.

frame 1The signal from the CKP sensor taken together with the ignition signal from the timing cylinder (usually cylinder #1) contains information about a significant number of engine parameters.

Analysis of these signals allows us to:

• evaluate the static and dynamic compression for each cylinder;

• identify faults in the ignition system;

• evaluate the condition of the injectors;

• obtain information about the ignition timing;

• identify the rotational characteristics of the flywheel; and

• identify missing and bent teeth of the flywheel.

The signal from the CKP sensor together with the ignition timing signal can be recorded using the USB Autoscope (or an oscilloscope) and analyzed by using the script “CKP.”

The CKP script is able to analyze the signal from the speed/position sensor for the engine crankshaft, working together with flywheels having any number of teeth and with or without gaps such as 60-2, 36-1, 60-2-2, 36-2-2-2 and so on.

frame 2 A main requirement is that the flywheel or flex plate is rigidly attached to the crankshaft. Chain or belt-driven flywheel attachments will give poor results since, in this case, there is a considerable smoothing of the signal from the crankshaft.

The CKP script needs a minimum of information for analysis — the signal from the crankshaft sensor, the ignition signal from the timing cylinder, the number of cylinders in the engine, the firing order and the initial ignition timing. A detailed description of results of the analysis that are displayed in the tabs of report script “CSS” is shown below.

The “Report” Tab (Frame 1)
In first line of the given tab, the name and version of the script analyzer is given. This helps to ensure that the latest version of the software is being used.

The results of the analysis run by this script are then displayed:
• Number of teeth per rotation of the crankshaft:

• Formula of flywheel drive, that works together with rotation speed/CKP sensor.

For example, a “60-2” means that disk has 60 teeth, with two missing.

frame 3Note: Ford often uses flywheels with formula 36-1; new diesel Volkswagen – 60-2-2, Subaru – 36-2-2-2.
If the signal is recorded from a CKP using the flywheel ring gear, there will be no gaps and there will usually be 136 teeth.

• Deviation in determining number of teeth:
The deviation value of formula calculation of the flywheel.

• TDC of the first cylinder coincides with the tooth number: This is the number of teeth away from the marker tooth. This tooth may be located directly opposite the speed sensor/CKP when the piston of the timing cylinder is at TDC.

The TDC may also be given as the number of teeth away from a missing tooth (signal).

If a missing tooth is found on the crankshaft reluctor wheel, then the application calculates the number of teeth away from the missing tooth to TDC 0° of the timing cylinder.

frame 4If there are no teeth missing, then the first tooth will be the tooth that is situated 180° away from the CKP sensor when the piston of the first cylinder is at TDC.

It should be noted that the accuracy of the number of teeth on the passage of teeth before TDC depends on the accuracy of the user-specified initial ignition timing. Also in this tab are tips for the diagnostician as well as error messages that may be displayed.

The “Efficiency (Acceleration)” Tab
(Frames 2-6)
In our first set of frames (2-6), we see how the gray waveform shows the instantaneous frequency of crankshaft rotation.

The colored waveforms show the effectiveness of each engine cylinder. The higher the acceleration waveforms are, the more powerful the cylinder is. A cylinder that does not work at all creates a crankshaft slowdown, resulting in a waveform that is below the black horizontal axis.

frame 5Test Vehicle: Audi A6 1995 V6 2.6L:

Symptom: Alternate unplugging of the injector for cylinder #4 and cylinder #5.

During the recording, the engine initially was operating at idle. The electrical connector for the fourth cylinder injector was disconnected, and then reconnected. The same procedure was then followed for cylinder #5.

We noticed an interesting feature in the algorithm of the engine control unit. After disconnecting the injector, the engine began to shake.

As a result, the ECU immediately reacted to the decrease in the instantaneous frequency of crankshaft rotation, and to retain a given engine speed at idle, increased the efficiency of the next cylinder in the firing order by advancing the ignition timing. During the recording, the throttle was smoothly opened.

These graphs show that the power contribution from each cylinder increased as the throttle was opened. The throttle was then abruptly closed.

The power contribution from each cylinder dropped below the zero line. The engine then continued to run at idle speed.

The throttle was then abruptly opened. The graphs also show a significant increase in the power contribution from each cylinder. As soon as the engine speed reached 3,000 rpm, the ignition was turned off, but the throttle is held in a fully open position until the engine is completely stopped.

As soon as the ignition is turned off, the speed of the crankshaft starts to decrease.

At this point, the engine is operating as an air pump. The engine is taking in air, compressing it and then expelling it. (There is no ignition and usually no fuel, since the ignition is turned off.)

As a result, the compressed air in the cylinder (after the piston has passed TDC on the compression stroke) acts like a spring and pushes down on the crankshaft journal.

The greater the amount of air that was compressed in the cylinder, the more powerful the “push.” The calculated acceleration of the crankshaft at this stage depends only on the mechanical operation of the engine and does not depend on the state of the ignition system or the state of the fuel supply system.

frame 6Another example was recorded on a carbureted engine — VAZ 2109 1.5L.

The efficiency of cylinder #3 decreased because of leakage. The acceleration waveform of the third cylinder at idle is located below the black zero line (Frame 5).

This indicates a significant reduction in the efficiency of this cylinder. The engine has a misfire. In other words, the engine shakes.

It is interesting that when the throttle is opened, the efficiency of this cylinder increases. Compared to the other cylinders, however, it has reduced efficiency.

According to this graph of the acceleration phase (as the engine speed with full open throttle, and with the ignition off is slowing down), it is clear that as the engine speed goes down, the acceleration waveform of the third cylinder deviates more and more down from the acceleration waveform of all other cylinders.

This character of the deviation chart indicates the reduced running compression in the given cylinder.

Measurement of compression with a compression test gauge in the conventional manner by using the engine starter gave the following results: Cylinder 1 = 12 Bar, Cylinder 2 = 14 Bar, Cylinder 3 = 7 Bar and Cylinder 4 = 12 Bar (174, 203, 102, 174 psi respectively)

Note: The engine in this example is not equipped with a CKP sensor. In this case, the signal was recorded with the help of an inductive sensor (Lx sensor) installed near the teeth on the flywheel that is used to engage with the starter gear during engine start. Inductive-type sensors (often called variable reluctance or VRS) are often used as crankshaft, camshaft and wheel speed sensors.

(An optical type sensor can also be used.) We stated earlier that the script “CKP” is able to record and analyze the signal from almost any rotation sensor, as well as detect any speed of any flywheel, as long at it is rigidly mounted on the crankshaft of the engine being diagnosed.

frame 7In the last phase of the acceleration graphs (Frame 6)  addresses a drop in engine speed with full opened throttle, with ignition off. The contribution from some of the cylinders is less than from others during the entire range of engine speed. This indicates either a lack of filling the cylinder with air, or that the degree of compression in the cylinder is reduced (perhaps because of a bent rod).

Thus, the script “CKP” can accurately identify faults in the mechanical part of the engine. Since fuel and/or spark is removed from the equation, variations in ignition timing and fuel delivery do not affect the measurement.

Likewise, the script “CKP” can identify intermittent and difficult to diagnose mechanical problems such as valves that are intermittently sticking open or closed. A cylinder’s power contribution depends on the quality and quantity of the air/fuel mix, the quality of the ignition spark, the accuracy of the ignition timing, as well as mechanical conditions affecting engine compression (valves, bent rods).

Ignition system malfunctions can be effectively diagnosed because this type of malfunction will affect the cylinder contribution during certain conditions and not at all during other conditions.

frame 8Bad Ignition Coil
An acceleration waveform addressing a bad ignition coil would highlight the affected cylinders.
An ignition system failure will generally cause the affected cylinders to have no power contribution at all. A partial reduction in power contribution is generally not seen with ignition system failures.

There may be some possible exceptions to this, however (weak spark or the spark happening at the wrong time, for example). An ignition system malfunction may cause a reduction in compression if left unchecked for a period of time. (Ring sealing may be affected by the reduction in cylinder pressure caused by a lack of combustion.)

Diagnosing Dirty Injectors
When at idle, this engine has a distinct misfire. The last phase of the acceleration graphs (while the engine is slowing down because the ignition was turned off) indicates that the engine is mechanically sound. The cylinder fill and compression is normal and equal for all cylinders. 

The cylinder efficiency is not equal during deceleration, but no cylinder is completely misfiring. The most likely cause for this type of a problem with no particular mechanical problem evident is fuel delivery. Measuring the flow rate of the injectors on a test stand yielded the following results: 64 ml, 80 ml, 40 ml, 60 ml.

In conclusion, if the last phase of the graph (when the ignition is off) does not indicate a problem, and the graph during ignition does indicate a partial loss of cylinder contribution (but not completely), the most likely cause is a fuel delivery problem such as a bad or plugged injector. This method can detect a partially plugged injector before it has a significant effect on the engine’s efficiency. This spares the technician from having to remove the injectors to flow-test them without a valid reason.

It should be noted that if the engine is equipped with two spark plugs per cylinder and only one of the spark plugs has a spark, the power contribution from that cylinder could be reduced by 10% to 20%.

The “CKP” script can serve as a good tool to aid in the diagnosis of an intermittent misfire and/or a rough-running engine. The script cannot in and in itself identify whether it is an ignition or a fuel delivery problem that is the cause if a cylinder has no power contribution at all.

However, if we add fuel to the engine while it is running and the cylinder contribution increases on the faulty cylinder, the cause for the misfire is a lack of fuel from, for example, a plugged injector.

The “Ignition Timing to TDC1 (Relative Ignition Timing)” Tab (Frames 7 and 8)
When analyzing the signal from the CKP sensor together with the time-of spark signal from the timing cylinder, the “CKP” script can calculate the ignition timing angle and display the result in graphical form. Frames 7 and 8 address the result of the script analyzing ignition timing. The result shows the timing variations caused by engine rpm and load.

Test Vehicle: Renault Laguna:
The graphs show that the ignition timing advances more with medium load on the engine as the rpm is increased (green trace) than it does with heavy load.

The following example was recorded from the VAZ 2108 gasoline engine.

This engine uses a carburetor and a distributor with mechanical vacuum and centrifugal advance.

The graph shows that there is no ignition timing angle correction as engine rpm is increased.

The centrifugal timing advance mechanism is inoperative. The timing change as the throttle is manipulated shows that the vacuum advance works as intended, however. This script is, in some ways, similar to the “Px” script. The “Px” script calculates the absolute value of ignition timing, whereas the “CKP” script
calculates the relative value. This means that when the “Px” script calculates the ignition timing as being 10°, then the ignition timing is that number of degrees away from TDC. If the “CKP” script displays 10°, then the ignition timing is that number of degrees away from the initial timing that has been set.

frame 9For this reason, the “CKP” script cannot be used to set initial ignition timing. In the graph, the zero degree area is grayed out to show that this is not an absolute measurement.

Even if a graph or chart only gives relative values, timing advance problems caused by faulty timing control mechanisms (whether electronic or mechanical) can be easily viewed.

The “Toothed Disc to TDC1 (Flywheel)” Tab (Frames 9 and 10)
The “CKP” script automatically determines the number of teeth and gaps on the flywheel, and their location with respect to TDC of the timing cylinder, and generates charts that show the characteristics of the flywheel and the CKP sensor.

One example was recorded from a VAZ 2107 engine, equipped with fuel injection. The black chart (Frame 9) shows presence and/or absence of teeth. In this case there are two missing teeth in the 120° to TDC region.

The red chart shows the deviation between the teeth. If the distance between the teeth is varying (due to a bent or broken tooth, for example), the deviation will be shown.

Also, a bent or otherwise deformed flywheel will show here. If the variation is more than 2%, the red chart will be outside the pink area.

On some engines, the flywheel may be designed on purpose with one or more missing teeth. The purpose of the missing tooth or teeth is to create a reference for the engine control computer. TDC for the timing cylinder may be shown with a missing tooth, for example. In 1-, 2- and 4-cylinder engines, the red chart will have a cyclic, almost sinusoidal variation. This is because all the cylinders will be at their dead center simultaneously.

For example, in a 4-cylinder engine, when cylinder #1 and #4 are at TDC, cylinder #2 and #3 will be at BDC (bottom dead center).

frame 10At this moment in time, all kinetic energy is accumulated in the flywheel and crankshaft. Because of this, even without a load on the engine, the crankshaft rotation is not uniform and the change in speed is recognized by the “CKP” script as a small deviation of the position of the teeth.

For 3-, 5- and 6-cylinder engines and more, the nature of the crankshaft rotation is more uniform. The green chart shows the signal strength from the CKP sensor. The amplitude of the output signal of this sensor, among other things, depends on the speed of crankshaft rotation.

The algorithm for calculating the signal strength in this chart is designed so that the calculated signal strength does not depend on the speed of crankshaft rotation. Thus, the calculated signal strength depends on the sensor itself, the flywheel, and the distance between the sensor and the teeth on the flywheel.

If the green chart is situated below the light green color axis, the air gap between the sensor and flywheel may be too large. Also, the green chart clearly shows the speed variation of the flywheel.
The next frame shows a flywheel with more pronounced problems than the previous example.

This example was recorded from an Alfa Romeo 146 1.4L twinspark engine. The alignment accuracy of the teeth is low and the tooth pitch “walks” in the range of ±2%. The missing teeth are located closer to the TDC than in the previous example.

It should be noted that the charts in the “Flywheel” tab show only the permanent faults associated with the specific flywheel. If the signal from the CKP sensor is intermittently distorted, it will only affect the chart of instantaneous engine speed in the “Acceleration” tab in the form of distortions of this chart.

Distortions of signal from rotation speed/position sensor are due to unreliable electrical connections.USB Autoscope II, seen here, is designed to diagnose various electronic systems, ignition systems and fuel systems on gasoline engines.

Diagnosing a Diesel Engine
The “CKP” script is applicable for the diagnosis of a diesel engine, and is relevant because not all diesel engines control systems allow you to display information via the scanner about performance of each cylinder. And, those that do allow you to see this kind of information will, in most cases, only display data about values of the cylinder-by-cylinder fuel supply at idle or lower rpm. This is because the computer requires a relatively stable rpm to perform this type of test.

When working with a diesel engine, we must use other means of synchronizing to the timing cylinder, since there is no spark plug to obtain a synchronization signal from. If there is a pressure sensor on the injector rail, that sensor can be used for synchronization.

If the sensor is built into the third cylinder injector, for example, start with #3 cylinder in the firing order. So, for a four-cylinder engine with a firing order of 1-3-4-2, use 3-4-2-1. Start the firing order with the cylinder number that is used for synchronization.

For diesel fuel injection systems that use common rail and for systems with integral injectors, a current probe with a sensitivity of 100 mV/A can be used. Clamp the probe around the injector wire. It should be the wire used to control the electromagnetic or piezoelectric pintle of the injector.

The “CKP” script will automatically synchronize to the main injection signal, ignoring the pre- and eventual post-fuel injection events because the duration of the main fuel injection is much longer than the duration of the other injection events.

On a 2003 Renault Trafic 1.9 DCI engine, we found that the rod in cylinder #3 was bent because the engine has been hydro-locked (water or other incompressible liquid in the cylinder).

The bent rod caused the compression in that cylinder to be too low. If the diesel engine is equipped with mechanical fuel injection, a piezoelectric transducer (such as a knock sensor) can be used to generate the synchronization signal. Here, you would attach the sensor to the fuel line going to the timing cylinder to diagnose this issue.  

To learn more on diagnostics and repairs of fuel injection systems, ignition systems and vehicle electronics using the USB Oscillograph, visit

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