Consistent engine misses

Step 1: Is ignition system in proper condition?

Check battery voltage, ignition distributor, spark plugs, ignition coil, ignition timing, etc.

  • Yes: Go to Step 2
  • No: Repair or replace damaged ignition components

Step 2: Is engine in proper mechanical condition?

If engine misses still occur after the electrical test, check for mechanical problems: Compression, basic adjustment of valves and engine oil pressure.

  • Yes: Go to Step 3
  • No: Repair or replace damaged components

Step 3: Are the wiring harness plug connections in proper condition?

Check for engine misses caused by loose contacts as follows: Start engine with tachometer connected. Hold the engine speed constant while observing the reading and/or listening for engine misses. Move the wiring harness and the plug connections. The reading must not vary and engine misses must not occur. Check the plug connections for correct seating and corrosion. Test ground cables 5, 6, 17 and 49 for continuity and loose contacts.

  • Yes: Go to Step 4
  • No: Repair loose contacts

Step 4: Is the voltage supply for the fuel injection system in proper condition?

Detach both wiring harness plugs from the double relay. Check that all plug sleeves and electric cables are in proper condition. Check all connector cables for continuity. Move the wiring harness when doing this (suspicion of broken cables). See also preceding test step with wiring harness.

  • Yes: Go to Step 5
  • No: Repair cabling

Step 5: Is the start valve in proper condition (no leaks)?

  • Yes: Go to Step 6
  • No: Go to Step 5-A

Step 5-A: Does the cold start valve leak fuel?

Test the start valve for leaks. For this purpose clamp the fuel intake line closed with a clip. Does engine then run evenly?

  • Yes: Replace start valve

Step 6: Are the alternator and regulator in proper condition?

Engine misses may be caused by voltage peaks.

With the engine stopped, remove the plug from the alternator. Start the engine. If this eliminates the engine misses, check the alternator and regulator.

  • Yes: Go to Step 7
  • No: Check alternator/regulator

Step 7: Is the quantity of fuel delivered by the fuel pump correct?

In order to test the quantity of fuel delivered detach the fuel hose at the start valve. Extend the hose and lead it to a measuring vessel of 5 liters capacity with a graduated scale. Remove the top section of the air filter, open the air-flow sensor flap by hand until the pump operates. Measured value for correct delivery (after 1 minute of operation) about 1.5-2 liters per minute.

  • Yes: Go to Step 8

  • No: Check for the following conditions and repair as necessary:

    • Fuel filter clogged (replace)
    • Fuel-pressure regulator defective (replace)
    • Fuel pump power too low (replace)

Step 8: Is the quantity of fuel delivered by the injectors correct?

Remove one valve at a time and inject fuel into a graduate for 30 seconds while engine idles. Compare quantity with that delivered by a known good injector. If quantity deviates from good injector, original valve was defective.

  • Yes: Go to Step 9
  • No: Replace defective injector

Step 9: Is the air flow meter in proper condition?

For testing, see under Engine does not start under Step 9.

  • Yes: Go to Step 10

Step 10: Is the control unit in proper condition?

Connect tachometer and let engine run. Tap lightly on the control unit and move the multiple plug. Watch the reading and listen for engine misses. Replace the control unit with a known good one. If the problem is solved, original control unit was defective.