Question about 1998 Pontiac Grand Prix
What your ssying does not make since so let me explain how it works, the 02 works like this when cold in the morning when the car first starts the car is in open loop meaning that it will run rich until the engine has reached operating temprature, once it has it goes into closed loop meaning the 02 sensor now determines the pulse width of the injector opening or how much fuel to give the car under all driving condtions, if one of the 02 sensors goes bad the computer goes into open loop giving the car the same amount of fuel as if it were a cold engine, (running Rich) if it was to lean out the car it is possible to make the engine run hotter because a lean engine causes the car to run hot, so at that pointthe EGR valve steps in and puts inert gas into the intake chamber (Exhaust Gas) since this won't burn it it makes the fuel mixture lean this can cause the temprature to rise slightly but not enought to over heat. A plugged catalitic converter can cause it to over heat and so can a fan not functioning right can cause itto over heat but not the 02 senor it has a limited range of fuel adjustment, and if it was bad it would actually run cooler because the fuel mix would be rich, causing the car to run cooler, this helP.
Posted on Jun 26, 2009
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Posted on Jan 02, 2017
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Following list of possible faults should help:-
Coolant sensor - engine is signaled as being 'cold' all the
time, not just at start up, causing ECU to set longer injection cycle
? Low coolant level can prevent sensor being able to detect coolant
? Faulty 'open' thermostat allows coolant to circulate without regulation
and perhaps prevents the engine from achieving normal running temperatures.
FPR - broken diaphragm allows fuel to enter
the vacuum line and then into the inlet manifold. Additional source of fuel
makes the fuel air mix richer causing a faster and lumpy idle.
Vacuum leak - 'high oxygen' signal
from O2 sensor causes ECU to set longer injection cycle.
O2 sensor - 'high oxygen' sensor error
causes ECU to set longer fuel injection cycle
MAF - 'over reads' in error the amount of air
entering causing ECU to set longer fuel injection cycle
IAT - 'under reads' in error the temperature of incoming air causing ECU to set longer fuel injection cycle
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