Peugeot 405 Manual

Fuel injection system - testing and adjustment
Fuel/exhaust systems - multi-point fuel injection models / Fuel injection system - testing and adjustment


Testing
1 If a fault appears in the fuel injection system, first ensure that all the system wiring connectors are securely connected and free of corrosion. Ensure that the fault is not due to poor maintenance; ie, check that the air cleaner filter element is clean, the spark plugs are in good condition and correctly gapped, the cylinder compression pressures are correct, the ignition timing is correct, and that the engine breather hoses are clear and undamaged, referring to Chapters 1, 2 and 5 for further information.

2 If these checks fail to reveal the cause of the problem, the vehicle should be taken to a suitably-equipped Peugeot dealer for testing.

On later models a wiring block connector is incorporated in the engine management circuit, into which a special electronic diagnostic tester can be plugged. The tester will locate the fault quickly and simply, alleviating the need to test all the system components individually, which is a timeconsuming operation that carries a risk of damaging the ECU.

Adjustment
Bosch L3.1 and MP3.1 systems 3 Before attempting to adjust the idle speed or mixture (CO), ensure that the following conditions are met.

a) Ignition system is in good condition and correctly adjusted.

b) Air filter is clean.

c) Throttle initial positions correctly adjusted.

d) Throttle switch correctly adjusted.

e) Engine must be hot, the cooling fan having cut in at least once, but the fan must not be running during the actual adjustment.

4 Idle speed is adjusted using the idle speed adjustment screw on the throttle housing (see illustration). Turn the screw clockwise to decrease the idle speed, or anti-clockwise to increase the speed.

11.4 Adjusting the idle speed screw on the Bosch L3.1 system
11.4 Adjusting the idle speed screw on the Bosch L3.1 system

5 To adjust the idle mixture, prise out the tamperproof cap covering the mixture (CO) adjustment screw on the airflow meter unit.

6 Connect an exhaust gas analyser to the vehicle in accordance with the manufacturerТs instructions.

7 Start the engine and allow it to idle. Turn the mixture adjustment screw in or out to obtain the specified CO content (see illustration).

11.7 Mixture (CO ) adjustment screw on the airflow meter (Bosch L3.1 system)
11.7 Mixture (CO ) adjustment screw on the airflow meter (Bosch L3.1 system)

8 Re-adjust the idle speed as previously described.

9 On completion, stop the engine, remove all test equipment and fit a new tamperproof cap to the screw.

Bosch ML4.1 system
10 The idle speed is non-adjustable. It is controlled by the idle speed regulator valve.

11 To check the mixture (CO), first ensure that the conditions in paragraph 3 are met.

12 Connect an exhaust gas analyser to the vehicle in accordance with the manufacturerТs instructions.

13 Remove the tamperproof cap from the mixture adjustment screw on the airflow meter housing.

14 Turn the screw clockwise to increase and anti-clockwise to decrease CO content until the specified CO level is obtained.

15 Remove all test equipment and fit a new tamperproof plug to the screw.

Bosch LU2-Jetronic system 16 Idle speed is adjusted as described for the Bosch L3.1 system (see illustration).

11.16 Idle speed adjustment screw (2) (LU2-Jetronic system)
11.16 Idle speed adjustment screw (2) (LU2-Jetronic system)

17 Idle mixture is not adjustable, and is automatically regulated by the electronic control unit according to signals provided by the oxygen sensor.

Bosch Motronic M1.3 system 18 Idle speed is only adjustable on 8-valve engines; on 16-valve engines it is controlled by the ECU. On 8-valve engines use the procedure given in paragraphs 3 and 4.

19 Adjustment of idle mixture is as given in paragraphs 5 to 9.

MM8P, Sagem-Lucas 4GJ,
Bosch Motronic 5.1,
Bosch Motronic 3.2 systems 20 Experienced home mechanics with a considerable amount of skill and equipment (including a tachometer and an accurately calibrated exhaust gas analyser) may be able to check the exhaust CO level and the idle speed. However, if these are found to be in need of adjustment, the car must be taken to a suitably-equipped Peugeot dealer for further testing. Neither the mixture adjustment (exhaust gas CO level) nor the idle speed are adjustable, and should either be incorrect, a fault must be present in the fuel injection system.


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