1979-1993 & 94 Conv [Subscribe to Daily Digest] |
1. Cranking power
The objective: RPM should be as high as it's required for effective engine start.
What do we want and what do we have? First of all we want to start the engine. Whatever season we've got right now outside. An engine has several performance specs including minimal cranking rpm for a specified temperature and friction force as a function of temperature. If temperature decreases then minimal cranking rpm is increased since air-gasoline mixture has less ability to get vaporized. And it becomes more hard to turn the crankshaft cause of stiffed oil. FIY the function of power required to turn the crankshaft vs outside temperature is non-linear; it's about logarithmic if I'm not mistaken. But at low temperatures battery performance is also decreased cause of electrolyte stiffening. So what? So this means we'd have margin of safety and if we need the car on a daily basis we'd better check its battery and do oil-service in advance not at the end of fall.
As they've already mentioned battery performance decreases when it's fried. Battery has the optimal performance only at given electrolyte density and if its over the nominal value (when you apply high temperature to the batt making water to boil away thus increasing sulphurid percentage) or under the nominal value (when got your batt discharged thus making electrolyte to contain almost water only) then your battery performance is decreased.
2. Checking battery performance
To find out if the batt is dead or alive we need to know:
- voltage
- electrolyte density (correlated to temperature)
- voltage drop at given load
If you tell me your batt has 12.5V at its output terminals it tells me nothing. If your batt has less volts at its terminals I can tell you only that it's not ok but I can't determine if your batt is simply discharged or completely dead. I need densimeter to check electrolyte and accumulator tester to stress it under load (to check separators and their structure).
Battery can be 100% charged only when taken out of the car and using a special charger not car's alternator. Alternator can charge you batt only to 70-75% level but not more cause further charge requires 15-18 volts to be applied and such voltage can kill other electric components (cheap bulbs as well as expensive ECU's).
3. Onboard electrics
Let's imagine you've got your batt live and say 70% charged. But it cranks sloooowly. Why? The scheme is the following:
- batt supplies starter motor with electric power via cables and terminals
- starter is controlled by its solenoid
- starter turns engine's crankshaft making all its internals move and spin.
Here're possible failures:
- bad terminals either on battery or on starter's solenoid; bad connection of 'ground' cable to engine
- worn solenoid's contacts (inside)
- high-viscosity oil in engine; worn engine (e.g. main bearings failed)
---------------------------------------------------------------------------
Total (or back to the original question):
- check your batt; probably you're to charge it only
- check if you've got a heat-shield installed. Even A-class batt will die soon if it's been heated by turbo-unit.
- check ground cables both to chassis and engine; check '+' cable connectors
- check alternator output voltage (I've got no clue about US specs but for EU cars the nominal voltage is 14.2 +- 0.2V)
- check (better say estimate) alternator's power: having your multimeter hooked on cigarette lighter's wiring and having your engine idling you're to start turning on lights, rear window defroster, cabin fan, etc. You should be able to turn your headlights and cabin fan (middle switch position) on and have nominal voltage on a circuit controlled by ignition switch
- check alternator's ground cable
- do an oil service using winter motor oil (low viscosity)
Zig
posted by 195.146.67...
, Thu, 6 Dec 2007 21:35:51
, Fri, 7 Dec 2007 05:08:25
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
