VP V8 Ignition

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Page created by T May 19th 2015:

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VS V8 Commodore Rotor Button, Reluctor and Hall Effect Sensor. Click to enlargen. Photo by Kinswood.

VP V8 Ignition:

Description:

This Ignition System is the same from VN - VT. It is a clever adaptation of the original Bosch Hall Effect Ignition System which was fitted ex-factory to Mercedes-Benz's, other brands of cars and also as an aftermarket retrofit to Bosch Breaker Point Ignition Systems.


Control Unit:

While the original Bosch Hall Effect Ignition System was entirely analogue, this system uses an analogue Control Unit that communicates with the digital ECU.


Coil:

This ignition system uses the Bosch MEC718 which is a medium energy coil.

VN-VT Module Operation:

I've had a scope on my car and it's definitely not multispark. How it works is the trigger signal from the dissy is fed to the module which then sends it to the ECU which then sends a delayed trigger signal back to the module. At cranking speeds and up to ~400rpm (and in limp home mode) the leading edge of the dissy trigger (10 deg BTDC) is used directly by the module as the firing signal. Above 400rpm the ECU tells the module to use an ECU-delayed version of the trailing edge of the previous dissy tooth, delayed from 70 deg BTDC trigger down to the operating value. The gap between the teeth on the dissy trigger wheel is 60 deg hence the 10 deg and 70 deg values. The extra circuitry on the board is to allow the ECU to select which signal to turn off the coil to make the spark, the 10 deg cranking or retarded-from-70 deg running. End of submission by Circlotron.


Waveform Analysis:

First pic is idling at 600 rpm. Blue (coil current) trace runs up to just over 7 amps in about 5.5 milliseconds dwell time. At the left the yellow trace pulls down as the ignition module switches on, and right near the centre of the pic the yellow kicks up a little to reduce the voltage fed to the coil so the amps levels off at required 7 amps (blue trace quits rising). Module switches off and (blue) amps drops suddenly to zero. Coil inductance says not on your Nellie so it chucks it's voltage to the moon in a vain attempt to keep the amps where it was a moment ago. Yellow voltage goes off the map (limited to ~350V on primary, 35,000V on secondary) and hopefully before it gets that high the plug fires and pulls the voltage down to 1500-2000 during the duration of the spark. This spark duration is where the yellow is horizontal for a whisker over 2 milliseconds (2 divisions). After that the coil energy runs out and the yellow flatlines at 14 volts waiting for signal to turn on for in preparation the next spark. Next pic shows primary amps at 3000 rpm. Dwell is 3.7 milliseconds and spark duration is 1.3 milliseconds. Next pic shows how much the voltage feed to the coil droops when the amps is running up before a spark. Cheap, nasty thin wiring in VP bombadore. End of submission by Circlotron.

VN-VT ignition module board.The 6 solder joints all in a row roughly in the centre of the pic, the ones that the connector pins go to, these joints often get a circular crack around the pin and with vibration or changes in temperature or when you are in a hurry to go somewhere they intermittently give trouble. Pull the board out of the box, resolder these and any others that look sus and maybe save yourself a buttload of money. Click to enlargen. Photo and info by Circlotron.
VN-VT ignition module board. Click to enlargen. Photo and info by Circlotron.
VN-VT ignition module board underside. Click to enlargen. Photo and info by Circlotron.
VN-VT ignition. First pic is idling at 600 rpm. Blue (coil current) trace runs up to just over 7 amps in about 5.5 milliseconds dwell time. At the left the yellow trace pulls down as the ignition module switches on, and right near the centre of the pic the yellow kicks up a little to reduce the voltage fed to the coil so the amps levels off at required 7 amps (blue trace quits rising). Click to enlargen. Photo and info by Circlotron.
VN-VT ignition. First pic - Module switches off and (blue) amps drops suddenly to zero. Coil inductance says not on your Nellie so it chucks it's voltage to the moon in a vain attempt to keep the amps where it was a moment ago. Click to enlargen. Photo and info by Circlotron.
VN-VT ignition. First pic - Yellow voltage goes off the map (limited to ~350V on primary, 35,000V on secondary) and hopefully before it gets that high the plug fires and pulls the voltage down to 1500-2000 during the duration of the spark. This spark duration is where the yellow is horizontal for a whisker over 2 milliseconds (2 divisions). After that the coil energy runs out and the yellow flatlines at 14 volts waiting for signal to turn on for in preparation the next spark. Click to enlargen. Photo and info by Circlotron.
 
VN-VT ignition. This pic shows primary amps at 3000 rpm. Dwell is 3.7 milliseconds and spark duration is 1.3 milliseconds. Click to enlargen. Photo and info by Circlotron.
 
VS V8 Commodore Rotor Button, Reluctor and Hall Effect Sensor showing the 10, 35 and 45 degrees of triggering used to calculate advance. Click to enlargen. Photo by Kinswood, markings by T.
 
VN-VT ignition. This pic shows how much the voltage feed to the coil droops when the amps is running up before a spark. Click to enlargen. Photo and info by Circlotron.
 

 

VS V8 Commodore Rotor Button. Click to enlargen. Photo by Kinswood.

 

Here is a pic of the reluctor of a VN-VS distributor. VT has an extra smaller reluctor with a single tooth, umbrella'd by the main one. The gap width is 14.77mm and tooth width is 8.46mm. Click to enlargen. Photo and info by Circlotron.
 
VN-VS Distributor. These are approximate measurements because of measuring a straight line across the chord, not around the curved circumference. This works out to 57.22 crank deg gap and 32.77 crank deg tooth. These figures will also be affected somewhat by the Hall effect sensor hysteresis so I will have a look on a scope soon and provide exact figures. Click to enlargen. Photo and info by Circlotron.

 

VN V8 Hall Effect Sensor.  Click to enlargen. Photo by Arsewipe.
   

 

Links:

See the Bosch Hall Effect Ignition Page

VN - VT V8 Ignition Thread 1

Terms:

Terms

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