Petrol engines intermittent 2.1

General

Beaker: Check that you have 12v on pin 30 in the distribution box left side front of engine as this supplies the fuel and ecu relays, then check the outputs from both the relays, if the ecu doesn't get it's ignition switched 12v it won't start.

Check spark at plugs

Check connections on temp2 sender and afm

Check connector to ECU (maybe the wind and damp got to it)

Check that air inlet not blocked somewhere (eg birds nest material in cyclone)

Check trigger signals to injectors

Check fuel pump running

Check connections hall sender and isv and idle control unit - try taking the idle out of the system too - a faulty control unit may affect the start up, the ecu is told it's starting by the ignition switch and throttle switch and adjusts accordingly

Classic 'Vanagon' syndrome

Vanagon syndrome can take a variety of forms, but originally intended to cover cases of injected US origin MVs misfiring after a considerable mileage from start of journey right up to stopping. Symptons usually disapear after stopping for a while. But do not assume that the fix is always the std. vanagon syncdrome fix which only works in some cases.

Std. Vanagon was usually a VW replacement sub-harness for the AFM (see links below) which removed potentiometer voltage 'spikes'.

There was an identified cause covered in the following links, AFM potentiometer tracks, AFM trigger signal instability etc. However, on both DJs and MVs electrics/electronics can become flaky after 15 ~20 years from new. Check and remake good engine and engine bay earths, main engine star-earth, connectors, and on MVs always think 'Lambda sensor' (O2 sensor failure) or its wiring. ECU or Ignition Control Unit intermittent. It has also been suggested that floating engine potentials of up to a volt can be a problem when the alternator is charging at high amperage, so a very heavy earth wire from alternator body to engine-bay firewall could resolve this.

vanagon syndrome

capacitors for above fix

Non-vanagon syndrome intermittent cut-outs or bad running

Symptons like vanagon syndrome but not cured by the normal vanagon syndrome fixes...

On both DJs and MVs electrics/electronics can become flaky after 15 ~20 years from new. Check and remake good engine and engine bay earths, connectors, and on MVs always think 'Lambda sensor' (O2 sensor failure) or its wiring (IIRC - a bad sensor can be disconnected to trouble-shoot)

Fuel pump, fuel pressure regulator or fuel filter (blocked)

But always first check for:

Dirty fuel tank, water in fuel, dirty fuel filter

Then:

Decent plugs, decent connections to injectors, and to Ignition Hall unit...

Fuel pressure, 28~30 psi

Blackdog: Bad multi-connectors behind AFM (corrosion) - Fuel pump supply connector General - fuel pump supply wiring, trace and check condition.

Throttle idle-cut-off position sender and cable adjustment (unless been verified OK recently)

Possibly Idle Stabiliser Unit (check function and cleanliness, can be bypassed (see Bentley) or IS Control Unit (check for signs of damp exposure)

ECU (substitute to test)

Ignition - Hall sender in distributor (usually completelty u/s), igntion control unit (substitute) Leads/plungs - usually if load or weather dependent, not truly intermittent - problem may come and go but generallybgets progressively worse!

Bad starting/flooding/rough running until hot

Usually the T2 temp sender fails or its wiring from under or behind the thermostat. Can be intermittent and can stop the engine through flooding, usually when starting. Sometimes the ISU (idle stabiliser unit), or the IS control unit on the n/s bulkhead or behind the o/s tail-light (Syncros)can prevent running