F. Quick-Start Preglow System (Model 123.1)

Checking Preglow System

Conventional tools
Voltmeter (measuring range 0-3 volts/0-16 volts)
Ammeter (measuring range 0-60 amps)

Note
Battery charged mm 60 % (acid density approx. 1.22 g/cc).

F. Quick-start preglow system engine 615, 616, 617.91 in model 123.1

Wiring Diagram:

Note: On engine 615, 616, pencil element glow plug G5 is not required.

1. Test bulb and its line

Complaint:
Preglow indicator lamp not lighting up when preglowing system is switched on, in spite of ready-for-starting condition.




Remedy:
Pull 4-point coupler from preglow time relay, turn key into position "2", bridge lack 1 and 3 for coupler.

If preglow indicator lamp is not lighting up, check bulb or renew, if required.




If bulb is in order, check black line from coupler of lack 3 of preglow time relay up to preglow indicator lamp for interruption, repair interruption.

If preglow indicator lamp is lighting up, the preglow time relay is detective and should be replaced.

2. Test main current circuit of preglow system for interruption

Complaint:
Preglow indicator lamp not lighting up, engine cannot be started.




Remedy:
Measure voltage at terminal 30 of preglow time relay against ground by means of voltmeter.

If no voltage is indicated, check red line from starter terminal 30 up to preglow time relay terminal 30 for interruption, and, repair interruption, if required.

If voltage is indicated (approx. 12 volts), test 80-amp fuse for tight seat or interruption and renew, if required.




If so far no fault has been found, test voltage at jack 1 of 4-point coupler of preglow time relay against ground.




If no voltage is indicated with preglow system switched on, test black/blue-green line from fuse box terminal 15 up to coupler jack 1 of preglow time relay for interruption and repair interruption, if required.




If voltage is indicated (approx. 12 volts), connect voltmeter to jack 1 (terminal 15) and jack 4 (terminal 31) and test voltage (should be approx. 12 volts).

If no voltage is indicated, test brown line from jack 4 to ground for interruption and repair interruption, if required.

If so far no fault has been found, preglow time relay is defective, replace preglow time relay.

3. Test pencil element glow plugs and their lines

Complaint:
Preglow indicator lamp not lighting up, engine firing poorly, one or several pencil element glow plugs or their lines to pencil element glow plugs may be inter- rupted.

Complaint:
Preglow indicator lamp lighting up, engine firing poorly after attaining ready-for-starting condition, a pencil element glow plug or a line to pencil element glow plugs of cylinders 2-4 (2-5) may be interrupted.

Pull 6-point coupler from preglow time relay




Measure resistance against ground (engine block) by means of ohmmeter one after the other as follows:

Jack 1 of coupler = pencil element glow plug cylinder 1
Jack 2 of coupler = pencil element glow plug cylinder 2
Jack 3 of coupler = pencil element glow plug cylinder 3
Jack 4 of coupler = pencil element glow plug cylinder 4
Jack 5 of coupler = pencil element glow plug cylinder 5

If resistance is measured, the respective pencil element glow plug or supply line or connection may be interrupted.

If measured resistance is smaller (e. g. at 20 °C/68 °F <1 ohm), thesupply line and the pencil elementglow plug is in order.

Note: It is possible that (as the result of unfavorable tolerances) the indicator lamp will indicate a fault only after 2 pencil element glow plugs in cylinders 2-5.

To make sure that the fault indication in preglow time relay is not defective, disconnect 2 pencil element glow plugs of cylinders 2-4 (2-5) in such a case and repeat preglow procedure.

If warning lamp now indicates a fault (not lighting up), the preglow time relay is in order.