Script Px version 3

Purpose of script

Script Px uses a pressure transducer installed in place of the spark plug. The script allows for checking the characteristics of the cylinder, intake system, exhaust system, and the timing system in order to evaluate the relative impact of these systems on each other.

The script allows:

  • To evaluate cylinder leakage. Cylinder leakage is affected by piston ring wear and/or ring gap, cylinder wear, intake and/or exhaust valve damage or clearance, head gasket, cracks in the combustion chamber, in piston, in cylinder;
  • To measure compression ratio. Compression ratio is affected by presence of large amounts of carbon deposits on the piston top and in the combustion chamber, bent connecting rods due to hydrolock. The compression ratio can also be affected by the use of “non-native” crankshaft, piston, or piston rod.
  • Automatically measure the actual valve timing. (intake and exhaust valves opening and closing angles);
  • Using animations to show the real process of gas exchange that occurs in the cylinder during the measurement. This takes into account the effect of the measured valve timing and the characteristics of the intake and exhaust system etc.
  • To identify the insufficient filling of fresh mixture into the cylinder, and to determine their cause. (Non-optimal valve timing, or the geometry of the intake tract, insufficient air filter or throttle bandwidth, poor removing of exhaust gases from the cylinder due to the poor performance of the exhaust system);
  • To assess the effect of systems used to force extra air into the combustion chamber. (Turbocharger, supercharger, variable valve timing system (Vanos, VVT …), changing the height of timing valve lift (VTEC …), changes in the intake system geometry such as variable length intake runners, intake system resonators);
  • Evaluate the efficiency of the turbine. (Balance between extra resistance created by the turbine wheel of turbocharger and optional supercharged air produced by compressor wheel of turbocharger)
  • Identify excessive cylinder pressures due to malfunctioning of the mechanical or turbocharger, which can cause piston and cylinder damage.
  • To identify power loss from scavenging exhaust gases from the cylinder including the loss from the turbocharger. (Exhaust system flow limitations from, for example, clogged catalytic converter or muffler, the exhaust valve closing too early, insufficient exhaust valve lift, or an improper exhaust system installation.
  • Check the ignition timing advance angle and identify modes of engine operation, in which the measured timing advance angle is later or earlier than optimum. This takes into account the measured geometric compression ratio and cylinder fill.
  • Check whether the diagnostic test is performed correctly. To conduct this test it is sufficient to install pressure transducer in place of the spark plug, then connect a spark tester and synchronization transducer to high-voltage wire of this cylinder.

Report script

Report of Px script consists of multiple tabs with the measurement results shown in text, table, graphical and animated forms. In addition, the script analyzes the measurement results and independently identifies diagnosis, which can be found in the “Summary” of tab “Results of the analysis”.

This tab can be printed out and given to the customer or interested party.


Cylinder leakage

Consider report from Px script, obtained on Audi A6 equipped with engine 2.4 V6 AGA.

The amount of gas losses here is 66% and has gone far beyond the typical range of 15 … 20%. As a result, the script diagnosed “The cylinder is losing compression”.

In addition, the script can identify some causes of the leaks. Because exhaust valve clearance is too small:

And sticking timing valve:

Valve timing

The Px script measures and displays the actual valve timing by constructing and by automatic analysis of a diagram concerning the amount of gas in the cylinder. The diagram has an interactive animation that demonstrates the real process of gas exchange in the cylinder. During construction of the diagram variables such as the initial installation of the camshaft, stretch and slack of timing chain / timing belt, valve clearance, the shape and the wear of cam lobes, and variable valve timing system is automatically taken in to account.

During day to day usage of the script it is not necessary to examine the diagram manually because the script automatically calculates the valve opening and closing angles and assess their impact on the operation of the engine. Primarily the filling of fresh air-fuel mix into the cylinder (volumetric efficiency) is estimated, because this parameter limits the maximum power and torque of the engine.

For this engine script diagnosed “Insufficient filling of the cylinder…” and found the cause of this, “Detected atypical valve timing” – namely, the measured closing angle of the intake valve has gone beyond the typical range of 570… 600°.

This diagnosis often points to an incorrect intake camshaft installation. Too late closing of the intake valve results in a substantial part of the air/fuel mixture being pushed back from the cylinder into the intake manifold as the piston starts on the compression stroke. As a result, there is considerably less air and fuel in the cylinder after the closing of the intake valve than it could be. In practical terms, this causes a loss of effective compression ratio. Because of this, the engine power is significantly reduced.

Thus, only one tab “Results of analysis” shows that the engine efficiency throughout all of the RPM ranges is lowered, and immediately determined the cause of this – suboptimal valve timing.

If necessary, the results of filling the cylinder are available in table and graphical form. For example, for the engine discussed above report tabs data are as follows:

In the table it is clear that at all engine speeds the measured values of the cylinder filling are below typical range. At the same time on the filling diagram the red color graph (corresponding to snap throttle) is located below the limits of the standard areas:

Forced induction

Consider the example of the test results serviceable engine on Ford Focus II, equipped with a turbocharger:

According to the results it is clear that the turbo operates at engine speeds above 3000 RPM and increases drive torque by approximately 20% in the range of 4000 … 6000 RPM.

Exhaust system

The script is testing one more important engine system – exhaust. At the same time exhaust system restrictions are estimated.

Here from the script report it is seen that the blockage of the exhaust system not only led to an increase of power losses on the exhaust stroke, but also negatively affected the filling of the cylinder (volumetric efficiency) with fresh mixture. Due to insufficient cylinder scavenging there is less room for a fresh air/fuel mixture on the intake stroke. The cylinder is completely filled, but the density of the charge is reduced (inert gas takes up room allowing less air and fuel to enter). Loss of fill density in turn reduces the power of given cylinder. The result is that at engine speeds just above 3300 RPM all the power developed by the engine cylinder is spent on cleaning cylinder from the exhaust gases on the exhaust stroke and the engine speed cannot be increased more. The diagram shows this clearly.

Ignition timing

If the synchronization transducer is used during the measurements, then the ignition timing angles are also checked. This method of measurement is the most accurate, because the real ignition event as measured by the synchronization transducer is compared with the actual top dead center (TDC) (the peak pressure in the cylinder). The ignition timing advance angle is measured during different engine RPM and load modes.

This example shows incorrect initial ignition advance angle. This is a Mitsubishi Lancer IX 2007 equipped with an 1.6l 4G18 engine. Ignition timing is not adjustable on this engine because it does not have an adjustable distributor.

Diagnosis and tear down found the reluctor wheel for the crankshaft position sensor incorrectly installed.