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Engine Misfire Sensors

The LIE computer system in Diablo and later cars is a state of the art system for getting the maximum power out of the engine. It has a very sophisticated system of diagnostic tests that run in real time to check that the engine is running properly. Even minor out of specs changes in engine performance are flagged to the driver in the form of the Left or Right "Check Engine" light.

There are many questions and comments on the web as to the understanding of the "Check Engine" indicator. Some simple diagnostic tests for these lights are given in other sections of this web site. 

The LIE computer has a number of sensors to determine how your engine is running. One,  is a set of sensors called  "Engine Misfire" sensors. These sensors are located on the left and right sides of the engine (Fig 1). They should be checked periodically to make sure the hose connection to them is not leaking.

  Figure 1. Diablo Engine Misfire Sensor

First a few words about the engine Misfire Sensor.  The sensor itself is made by a company in California called Kavlico (fig 2).  In summary, the misfire detection sensor is capable of sensing a spark ignition misfire under all load conditions from idle speed to about 6000 rpm by monitoring each exhaust manifold separately. It is installed between the engine and catalytic converter. The sensor has the capability of detecting increasing resistance to flow through the catalytic converter, to initiate a warning to the engine operator. The sensor is used in conjunction with Kavlico's decision logic circuit which is based on the use of a Motorola MC68HC11 microcontroller. The output from this controller is sent to the Lamborghini LIE computer.

Fig 2.   Kavlico Engine Misfire Sensor Fig 3.   Sensor unclipped from engine   
Fig 3.   Sensor removed from car Fig 4. Sensor with hose clamp attached.  
The most common problem with this sensor is that the rubber hose connecting it to the metal pipe attached to the exhaust manifold is loose or broken. This will give "cylinder misfire" readings on the Check Engine light and OBDII system. It is absolutely essential that  this hose be in good condition and form a tight seal with the input hole (fig 2) of the sensor. As supplied by Lamborghini these sensors simply have the rubber hose pushed over the sensor inlet. I have placed a small hose clamp on mine to insure no leakage occurs (Fig 4).  

A less common problem is that the sensor becomes clogged up with soot from a badly tuned engine. Clearly this is the least of your problems in a situation like this!  If however, you take time to lookup the patent numbers (on each sensor, fig 3) and read the patents you will see they simply contain a thin membrane that flexes with pressure changes. This changes the electrical resistance of a Wheatstone bridge circuit on the membrane and this in turn sends a readable output signal. If the membrane becomes broken or rigid a faulty signal will be sent.  For the same reason don't  try measuring resistance readings etc. on the electrical contacts of the sensor (fig2),  they will not be meaningful unless setup as part of a circuit.


This page was last modified on 03/12/2014

This page was last modified on 09/06/2014