Diagnostique de l'allumage de nos RV8

[e635815]

Si comme moi, vous avez des problèmes avec l'allumage de votre moteur, ceci va certainement vous intéresser au plus haut point.

TESTNG IGNITION COMPONENTS - BACK TO BASICS

The circuit represents BOTH the system where the amplifier is mounted in an aluminium housing behind the coil AND where it is mounted on the side of the distributor. The effective electrics are the same, just the physical locations of components differ.



Be sure the earths and the wiring from the ignition switch through to the coil, distibutor and amplifier module are pretty much the same as shown.

Getting Started

o Reasons for testing the ignition system are a proven loss of sparks at the spark plugs, or weak/intermittent sparks causing misfiring.

o To proceed, separate the Low and High Tension circuits to find out immediately which circuit is faulty, then persue the fault condition in either circuit according to the results of some logical tests.

o Remove the king lead from the distributor, connect it to a good spark plug and lay the plug on the engine somewhere.

o Switch on the ignition and crank the engine.

o Is there a fat spark at the spark plug.

o If Yes - then the problems are downstream and away from the king lead at the dizzy cap, rotor arm, plug leads, plugs, or ignition timing so that is where to look - see " Other Components" (later) for checking the usual suspects, inspect, clean, substitute and only replace if faulty.

o If No - change the king lead.

o If still No - then the problems are upstream from the king lead and towards the coil, amplifier, distributor innards or their local connections all the way back to the ignition switch.

Testing the Low Tension Side Voltage Feed

o Switch on the ignition and use a multimeter to verify there are 12 volts at coil positive.

o If No - find out why, by checking the circuit between coil positive and the ignition switch and beyond, all the way back to the battery if necessary, for corroded or loose/broken connections.

o If Yes - dont take it for granted, waggle local wiring and toggle the ignition switch a few time to ensure the voltage is reliable, even using a bright lamp to check the wiring can supply a load.

Test the coil independently

o Disconnect the wire from coil negative to the amplifier.

o Turn ignition on, and strike coil negative to earth with a flying lead to see how good is the king lead spark.

o If sparks are absent/poor/weak and +12 volts is still present at coil positive then the coil is prime suspect for inspection/replacement.

o If sparks are fat/healthy then coil must be OK, so look for amplifier/pickup coil problemss.

Test the Amplifier and Distributor Pickup Coil Together.

o Remove Distributor Cap.

o Disconnect ECU trigger wire from the 6.8k ohm resistor to prevent spurious signals getting to the ECU.

o Disconnect amplifier wire from coil negative.

o Connect a 12v 21W bulb from the same amplifier wire to coil positive (12 volt supply).

o The 21W bulb acts as a substitute coil load.

o Turn ignition on and rotate distributor rotor arm back and forward against the vacuum/mechanical advance springs.

o As the toothed reluctor wheel triggers the pickup coil, the amplifier should flash the bulb.

o If bulb flashing is positive and consistent the amplifier and pickup coil are working correctly together.

o If lamp does not flash or is inconsistent/weak either the amplifier or pickup coil is faulty.

Check the pickup coil independently

o Remove the amplifier connections to the pick-up coil and measure the resistance of the distributor pickup coil for a steady value between 500 ohms to 1500 ohms on the ohm-meter. Flex the wires at the same time to test their integrity.

o Outside the above range, short or open circuit indicates a croaky pickup coil.

o By process of elimination, if the pickup coil is OK, one might conclude the amplifier is faulty but nothing is ever that simple with electronic components, so to be sure:

Test the Amplifier independently

o What follows is an elegant but slightly complex test process.

o Use a 1.5 volt pen-cell battery connected in series with a (say} 2,700 ohm resistor and two flying leads to simulate the pickup coil.

o With the coil and amplifier connected normally and the distributor pickup coil disconnected from the amplifier, connect one flying lead to one of the amplifier input connectors and touch the other flying lead intermittantly across the second amplifier input connector.

o This emulates a pulsed input thereby activating the amplifier in sympathy to generate sparks from the coil?

o Polarity of this simulation is non-critical as neither flying lead is connected to earth, only to the amplifier input connectors, and the pulsing voltage from the pen-cell via the 2700 ohm resistor acts similar to the pickup coil input without causing stress or damage to the amplifier.

o The above test can be performed with the 21 watt bulb as the coil substitute as previously described, except in that circumstance, the pick-up coil simulation will flash the bulb.

Alternatively (for even more elegance), going one step further:

o Construct a small test box complete with switch, 21 watt bulb/holder, pen-cell battery, 2700 ohm resistor, 12 volt pos/neg power connections (from a car battery), spade connectors to the amplifier, etc.

o Connect up the 12 volts power and the amplifier to the test box and flick the switch repeatedly to emulate the pulsed input from a pickup coil and see the 21 watt bulb flash in sympathy to show the amplifier is working correctly.

Other Components

o Another possible component failure will be the suppressing condenser breaking down under the back-EMF from the coil.

o Remove condenser from circuit to see if the problem disappears.

o If yes, replace the condenser.

o Almost finally! For all the previous components check the LT wiring is not corroded, broken, dodgy or otherwise failing.

o Because all the components upstream of the king lead now check out OK, if fat sparks emerge from the king lead but not at the spark plugs its time to review the downstream components to see if they are dragging down, or failing to conduct, the Hi-Tension energy.

o Rotor arm - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress.

o Distibutor cap - inside and outside - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny, especially between the turrets.

o Plug Leads and Hi-tension connectors - inspect for breaks and contact damage, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny.

o Spark Plugs - Check for recommended type, clean and gap to correct spec, inspect for insulator damage externally and whiskering/crud between central contact and body. Clean externally to a shine.

o The above four items are "zero cost" actions. Many owners replace them all never knowing which of the components may have been faulty.

o Check by swapping is an easy process before buying replacements.

o Looking for spark tracking on a dark night generally reveals faulty hi-tension parts
http://www.v8forum.co.uk/forum/viewtopic.php?t=7801

[LR78]

Le système décrit est de type 35DL8 c'est a dire que l'ampli est un gros "pavé" en métal brillant servant de support à la bobine d'allumage.

C'est la version 35DLM8 qui était montée sur les TVR à partir de la 350 I soit en 1982.... Le principe est le même sauf que l'ampli est un petit rectangle en plastique noir avec un coté en alu servant à son refroidissement. Cet ampli est soit monté sur le coté de l'allumeur jusqu'au chim ou Grif pré-serpentine soit déporté sur le coté droit du plénium a coté de la bobine avec l'aide d'un cordon prolongateur. Ce système n'a plus de condensateur !

Le fils d'alimentation sont :
1 plus contact blanc alimentant la bobine et l'ampli
1 fils blanc/noir allant de l'ampli a la bobine indiquant le signal ainsi que l'info "moteur en route" pour l'injection. Selon les montages ce fils peut servir aussi pour le compte tour quand il n'est pas sur le "W" de l'alternateur.