Ignition System - Bosch Breakerless Volvo 240 I

DESCRIPTION

The Bosch electronic ignition system consists of an ignition control unit, a breakerless distributor, a single or dual ballast resistor, a high output ignition coil, an ignition switch, and battery.

Some models may use a resistor wire rather than a ballast resistor. Standard centrifugal and vacuum advance/retard mechanisms are used.

The distributor contains a rotating trigger wheel and a stationary magnetic pick-up coil (unless it is repositioned by vacuum diaphragm).

OPERATION

A trigger wheel turns with the distributor shaft. The trigger wheel has one tooth or lug for each engine cylinder.

As the trigger wheel rotates past the pole of the magnetic pick-up coil, a magnetic field is created that continually builds and collapses. This produces a low voltage electrical signal.

This signal passes to the control module, which controls the dwell angle and at the same time interrupts the ignition coil's primary circuit. This induces the high secondary coil output voltage that fires the spark plugs.

ADJUSTMENTS

No adjustments should be attempted on ignition system, except spark plug gap and initial ignition timing.

760 GLE

1. Disconnect hose to vacuum advance diaphragm. Start and run engine at idle. Ensure ignition advance is 10 degrees at idle. Increase engine speed to 2000 RPM. Ignition timing should be 21-25 degrees.
2. Increase engine speed to 3000 RPM. Ignition timing should be 19-25 degrees. Increase engine speed to 4000 RPM. Ignition timing should be 27-34 degrees. If ignition timing is not as specified, remove distributor and bench test.

1. Connect vacuum pump to vacuum advance diaphragm and apply 20 in. Hg of vacuum. Vacuum may drop 4 in. Hg within one minute. Replace diaphragm if it leaks excessively. Connect iming light to engine. Start and run engine at idle.
2. Ensure ignition advance is 10 degrees at idle. Apply 6 in. Hg of vacuum. Ignition timing should be 18-23 degrees. Increase vacuum to 7 in. Hg. Ignition timing should be 25-30 degrees. Increase vacuum to 9 in. Hg. Ignition timing should be 28-32 degrees. If ignition timing is not as specified, remove distributor and bench test.

Preliminary Checks

1. Before testing ignition system, be sure battery is fully charged and in good condition. Ensure starter and fuel systems are operating properly. Ensure engine is in good mechanical condition.
2. Ensure all electrical connections are clean and tight. Due to high voltage, use care when working on electronic ignition system. Connect or disconnect ignition system wiring ONLY with ignition off.

Volvo Turbo

1. Remove coil tower high tension lead and hold 3/4" (19 mm) from ground. Crank engine. If spark is present, go to step 10). If no spark is available, go to next step.
2. Check voltage at terminal No. 15 of coil. If no voltage is present, check ballast resistor, ignition switch and wiring. If voltage is present, go to next step.
3. Check voltage drop across transistor by connecting voltmeter to terminal No. 1 of coil and ground. Voltmeter reading should be .50-2.0 volts. If voltage is incorrect, go to step 6). If voltage is correct, go to next step.
4. Check pick-up coil resistance by connecting ohmmeter across terminal No. 7 and 31d at distributor. Resistance reading should be 950-1250 ohms. If reading is incorrect, replace pick-up coil. If reading is correct, go to next step.
5. Check pick-up coil for grounds by connecting ohmmeter to either terminal of pick-up coil and ground. Resistance reading should be infinity. If reading is incorrect, replace pick-up coil. If reading is correct, replace ignition control module.
6. If voltage drop is more than .50-2.0 volts, go to next step. If voltage drop is less than .50 volts, check for 1-2 ohms resistance in ignition coil by connecting an ohmmeter across coil terminal No. 1 and 15. If reading is correct, replace ignition control module. If not, replace ignition coil.
7. Turn ignition on. Connect voltmeter between terminal No. 15 of ignition control module and ground. If voltage is not present, repair wire coming from ballast resistor. If voltage is present, go to next step.
8. With ignition on, connect voltmeter between terminal No. 16 of ignition control module and ground. If voltage is not present, repair wire coming from terminal No. 1 of ignition coil. If voltage is present, go to next step.
9. Ensure ignition control module is properly grounded by disconnecting connector plug at module. Connect voltmeter across plug terminal No. 31 and ground. If reading is zero volts, replace ignition control module. If reading is incorrect, repair ground wire.
10. Check ignition timing. If timing is incorrect, adjust as necessary. If timing is correct, check voltage across coil terminal No. 1 of ignition coil and ground. If voltage is incorrect, replace ignition control module.
11. If voltage is correct and if the engine does not start, check and/or replace spark plugs, rotor, cap, ignition wires, and fuel system. If voltage is correct and engine starts, go to next step.
12. Check dwell angle. If dwell angle is incorrect, replace ignition control module. If dwell angle is correct, ensure coil output 20,000 volts by holding coil high tension lead about 3/4" (19 mm) from ground.
13. If coil output is correct, ignition system is okay. If coil output is incorrect, check and replace spark plugs, rotor, cap, and ignition wires. If output voltage is now correct, ignition stem is okay.
14. If output voltage is still incorrect, install a known good ignition coil. If output voltage is now correct, replace ignition coil. If output voltage is still incorrect, install old coil. Replace ignition control module.

ROTOR

Set ohmmeter to x1000 scale. With ignition off and distributor cap removed, connect ohmmeter leads across rotor. Compare reading with specification.

ROTOR SPECIFICATIONS

SPARK PLUG WIRES

1. If the spark plug connectors have sheet metal jackets, identified by the following symbol (two diodes facing each other), they contain "air gap" resistors. Wires cannot be checked for resistance using an ohmmeter. An oscilloscope must be used.
2. On Volvo, connect ohmmeter to ends of spark plug wires. Wire resistance should be 4600-6600 ohms per 3 feet.

BALLAST RESISTOR

Disconnect wiring at ballast resistors and connect ohmmeter across resistor terminals. Resistance must be .80-1.1 ohms.

IGNITION COIL RESISTANCE TEST

1. On all models, turn ignition off. Remove coil protective cap (if used). Remove coil wires and connect an ohmmeter across ignition coil primary terminals. (Scheme 1) Take primary winding resistance reading.
2. Set ohmmeter to x1000 scale. Connect ohmmeter leads to negative coil terminal and coil tower. Take secondary resistance reading. If either primary or secondary winding reading are not within specifications, replace coil.

Ignition Coil Resistance Tests. Scheme 1

IGNITION COIL RESISTANCE SPECIFICATION

Place pick-up coil and trigger wheel tips opposite each other. Using a non-magnetic feeler gauge, measure air gap between tips. Air gap must not be less than .012" (.30 mm).

PICK-UP COIL RESISTANCE TEST

Disconnect pick-up coil connector. Connect ohmmeter between connector terminals. On Volvo Turbo, resistance must be 950-1250 ohms. On 760 GLE, resistance must be 540-660 ohms. If incorrect reading is obtained, or an open circuit is detected, pick-up and coil must be tested separately.

DISASSEMBLY

1. Remove distributor cap, rotor and dust cover. Remove vacuum advance diaphragm and cap clips. Remove screw and plug on side of distributor.
2. Remove trigger wheel snap ring, shims (if used) and washer. (Scheme 2) Carefully pry upward on trigger wheel. Remove snap ring.
3. Remove pick-up coil mount screws. Pull out carrier plate. Note position of pick-up coil in relation to carrier plate. Remove pick-up coil screws and coil from carrier plate.

Note. Keep screws with components they attach, as screws are different lengths. Distributor may be damaged if screws are installed in wrong location.

Exploded View of Bosch Electronic Distributor. Scheme 2

REASSEMBLY

1. To assemble distributor, reverse disassembly procedure. Install only undamaged insulators between pick-up coil and carrier plate. Check position of plug connecting lug.
2. Align trigger wheel cut out with groove in distributor shaft. (Scheme 3) Install lock pin. Install washer, shims (if used) and snap ring. Check pick-up-to-stator air gap. Attach vacuum advance rod with pin and lubricate with grease. Ensure distributor rotates freely.

Installing Wheel & Lock Pin Be sure lock pin is properly installed. Scheme 3

DWELL ANGLE

Check dwell angle, at idle, and compare it with specification. Dwell angle is controlled by electronic control module and is nonadjustable.

DWELL ANGLE SPECIFICATIONS