Bosch LH Jetronic Starting Difficulties. B23F, also 2.0/2.1 litre

By Club Member John Hall, who worked for Volvo USA for many years.

December 1996

The Engine does not start

Presuming the manual ignition system has been reviewed, the most likely cause is problems with the wiring harness, between the distributor and the ignition control unit. Poor connections ie. crimping. It is wise to solder all connections where possible.

Erratic idle and/or stalling - warm engine.

Check the fuel system (L.H. Jetronic). Check the throttle switch adjustment -- open the throttle valve and a 'click' (idle switch opens) should be heard when the throttle moves (refer to manual). Adjustment (if required) --loosen the switch (3mm int. hex.) -- turn the switch clockwise then anti-clockwise to the stop but not so far that the valve begins to open, tighten the screws. Check function. Check ignition timing, CO content and basic idle speed.

Engine misfire and/or stalling but the engine can be restarted.

(a) Ignition control unit -- ensure that all electrical connections are free from corrosion and fitted correctly. Check all cable crimps.

(b) Centrifugal advance -- check disconnect vacuum hose from control unit - run the engine at 2,500rpm - check ignition advance (use timing light) - ignition advance should be 16 -24 degrees BTDC. If incorrect, then replace the ignition control unit.

(c) Check the vacuum advance -- run the engine at 1500rpm - record the advance in degrees then reconnect the vacuum hose and ensure that the advance alters - if it does not, check that there is vacuum at the control unit (check suction at the hose) - if there is vacuum but no advance, then replace the control unit.

(d) Ignition coil -- check for clean, firm connections terminals nos. I & 15. Also check HT cable between coil and distributor.

(e) Check tank pump current with ammeter - consumption should be 1 - 2 amps. If it is too high, it indicates that the filter is blocked or the pump is seized. (Turn off the ignition). With pressure gauge # 999-5230-1 check the operating pressure. This should be 13.5 kpa or 1.9 psi. (Turn off ignition). I have found that most of the problems were in connections, either being dirty or loose.. Earth connections especially! Wherever possible, try to solder as many connections as you can.

(f) Check the multi-pin connections at the bulkhead for corrosion and loose terminals - ensure continuity (use ohm meter) - with current switched off

Fuel system

Ensure that all earth connections at the manifold are clean and tight. Check the 25 amp blade fuse in the engine compartment - check for being free from corrosion. Check fuel system relays on bulkhead -- ensure no discoloured pins or connectors.

Main fuel pump wiring.

The wiring under the rear seat, earth connection could be loose (it is only held by a self-tapping screw). Ensure that it is clean and secure and that the rear seat cushion does not foul the cable. Check for voltage at the tank pump (if fitted) which should be 11.5 volts.

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