Fiat 1998 Marea Weekend, Service Manual

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Engine
Marea- Marea Weekend ft
Fuel system
99 range
10.
ENGINE IDLE SPEED CONTROL
If the engine idle speed is not 750±50/min and the injection/ignition control unit is the self-adjusting
type then it is not possible to carry out any adjustments so it is necessary to check that the accelerator
linkage is correctly adjusted and the cause of the problem should be sought by carrying out a complete
fault diagnosis using the diagnostic equipment.
CHECKING THE CONCENTRATION OF POLLUTANT EMISSIONS
Through the self-adjustment of the system, the Motronic ME 3.1 system guarantees a continuous check
on the idle speed and the CO percentage making any other external adjustment operation superfluous
(there are no longer any adjustment screws). However, a check on the content of the exhaust gases,
downstream of the catalyzer, can provide precious information on the operating conditions of the injec-
tion/ignition system, the engine parameters and the catalyzer.
Checking idle concentration of CO and HC upstream of the catalytic silencer
To check the concentration of carbon monoxide (CO) and unburnt hydrocarbons (HC), upstream of the
catalyzer, proceed as follows:
1. Undo the plug or the nut on the exhaust pipe, upstream of the catalyzer, and tighten the tool in its
place.
2. Connect a suitably calibrated CO tester probe to the tool.
3. Start up the engine and let it reach operating temperature.
4. Check that the speed corresponds to the recommended figure.
5. Check that the CO idle concentration is within the recommended limits given in the table overleaf; if
this is not the case, it is necessay to check:
- that the Lambda sensor is working properly, using the diagnostic equipment;
- for the presence of air penetration in the area surrounding the Lambda sensor housing;
- the injection and ignition system (
in particular the wear of the spark plugs ).
6. Under the same circumstance, check that the concentration of HC is below 600 p.p.m.
7. If these values are not found, proceed with tuning the engine, in particular checking:
the ignition advance angle - the valve clearances - the valve gear timing - the engine compression.
3 8 Print n° 506.763/14