Cold Driveaway Diagnosis For 1984-85 900, 900S; 1984 Turbo
Model Years: 1984-85 900, 900S; 1984 TurboSymptoms: Occasional complaint of a brief period of rough idle and power loss during warm-up.
May stall when first put into gear, particularly 900 and 900S. Hesitation on acceleration for the first minute or two of operation, possibly accompanied by backfiring into the intake manifold.
Diagnostic and Repair Details
1. Perform the steps required to check for a Cold start Complaint. Do not skip any of these steps. Cold engine only.
- Check rest position of air flow sensor plate.
*See Warranty Info.
- Check for intake air leaks.
- Check auxiliary air valve (cold engine only).
- Measure and adjust line pressure, if necessary.
- Check the cold control pressure and correct, if necessary.
- Check the cold start circuit.
2. Bridge the cold start injector plug with a 12v test light. Start the engine and observe both the test light and the pulse ratio meter during the 120 second test period. Results will be one of the following, depending on coolant temperatures.
a. Coolant temperature below 77~F (25~C) during the entire test cycle.
Every time the throttle is opened rapidly, the test light should flash briefly. Pulse ratio locked on 60/40.
b. Coolant temperature starts below 77~F (25~C), but goes higher during test.
Test light flashes every time the throttle is opened rapidly until the thermal switch opens, at which point the pulse ratio meter will swing toward 92% each time the throttle is snapped open for the balance of the 120 second test period.
c. Coolant temperature above 77~F (25~C) during the entire test cycle.
The test light will not flash, the pulse ratio meter swings toward 92% each time the throttle is opened rapidly for the 120 second test period.
3. Verify that you no longer get acceleration enrichment through the Lambda System after 120 seconds of operation.
4. If inoperative, check:
a. Power to the RED/WHITE and WHITE wires on the pressure impulse contact.
b. 12v pulse on acceleration at the BROWN wires on the pressure impulse switch.
c. Pin functions of the transient enrichment relay as given below.
d. Test light connected to 12 volts
Pin 31 - ground at all times
TRK - ground with closed throttle (man. trans. only).
e. Test light connected to ground
Pin 50 - 12v during cranking
TIP - 12v pulse on acceleration
87 - 12v when engine is running
11 - pulse ratio of 92% +/- 10% when the pin is grounded
f. Ohmmeter or other continuity test
Pin X2 - continuity with X2 of the decel relay
TKK - continuity with the WHITE wire on the thermal switch at the thermostat housing, also check continuity from the thermal switch GREEN wire to the thermo time GREEN wire.
g. Check the mechanical function of the pressure impulse switch. Connect a vacuum pump and a pressure gauge (Turbo boost checking gauge) in series with the impulse switch. Attach a continuity tester to the electrical contacts of the switch.
Draw vacuum until you reach at least 0.3 bar and release it rapidly and note if there was a brief moment of continuity at the electrical contacts. Repeat the test several times. If continuity cannot be obtained, replace the switch.*
Pressure Impulse Switch P/N 93-15-953
5. Check the Pulse Ratio
Leave the Saab Pulse Relation Meter connected. Start the engine and allow to completely warm up (radiator fan should cycle on a few times).
Note the pulse ratio reading. The pulse ratio should be 45-55% for optimum driveability. Adjust if necessary.
Pulse Ratio (engine warm): Checking and Setting 45-55%
(Note: Any reading from 10-90% is acceptable for exhaust emission compliance.)
*See Warranty Info.