Checking Engine Idle Speed; Checking Concentration Of Pollutant Emissions; Checking Idle Concentration Of Co/Hc Upstream Of Catalytic Silencer - Fiat 1998 Marea Service Manual

Marea-Marea Weekend
98
range
C H E C K I N G E N G I N E IDLE S P E E D
If the engine idle speed is not 850 ± 50 rpm and the injection-ignition control unit is the self-regulating
type, then it is not possible to carry out the adjustment, therefore it is necessary to check that the accel-
erator linkage is correctly adjusted and the fault should be sought through a complate fault diagnosis
using the diagnostic equipment.
C H E C K I N G C O N C E N T R A T I O N OF POLLUTANT E M I S S I O N S
Thanks to the auto-adjustment of the injection/ignition system, the idle speed and the CO percentage
are continuously checked, thereby making any external adjustment operations superfluous (there are no
longer any adjustment screws). However, a check on the content of the exhaust gases upstream and
downstream of the catalyzer can provide precious indications on the operating conditions of the injec-
tion/ignition system and the catalyzer and engine parameters.
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 cap 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 engine speed is correct.
5. Check that the idle CO concentration is within the limits in the table overleaf; if this is not the case, it
is necessary to check:
- that the Lambda sensor is working properly, using the diagnostic equipment;
- the presence of air penetration in the area surrounding the Lambda sensor housing;
- the injection and ignition system (in particular the state of wear of the spark plugs).
6. Under the same circumstances, check that the HC concentration is less than 600 p.p.m.
7. If these figures 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
Pollutant emissions tolerance figures table
Upstream of the catalyzer
Downstream of the catalyzer
Copyright by Fiat Auto
@ 1*
CO (%)
0,4 - 1
^ 0,35
Fuel system
HC (p.p.m.)
CO2
600
«c 90
Engine
10.
(%)
> 12
3s 13
57