Having problems with your 1999 Saturn SL ?

The car has a hard time starting and taking off from a stop, but drives normal a reg speeds. So I changed the plugs and wires, and put heet moisture remover and filled the tank with new gas but it still starts hard and hesitates or wants to die when taking off or the rpms are low

Posted / edited by AnonymousUser on : 27-06-2022

Answers :

There are 2 problems that you are experiencing: \015\0121- Cold start valve for hard start.\015\0122- Faulty thermal vacuum sensor in assisting throttle body for hesitating at the beginning of taking off.\015\012For # 1All car has a cold start valve to assist the initial start. What is does is to spray extra fuel when it start cranking and shut it it off afterwards. The valve is normal close and only open at start when the temp is below the pre set temperature in ECM when compare to the coolant temperature sensor. There are 3 scenarios as following for this case:\015\012
\015\012A- Either the sensor is bad not sending correct resistance reading to ECM causing the Cold start valve not opened. This one can be checked by measure resistances at different temperature verse manufacturing spec.\015\012B- Or the solenoid inside the cold start valve is faulty so it doesn't open the valve. This one has to test to see fuel sprying out or not. Measure resistance is not a correct method since the coil always has some resistance but it could not activate as a solenoid function to make the valve open inside.\015\012C- Both are bad.\015\012
\015\012 For # 2\015\012Hesitation at the beginning to take off is the case of not having rich gas/air ratio. The correct air /gas ratio is 14.7 :1. At normal speed you have a correct air/gas ratio so the engine is working right as the engine reaches the operational temperature.\015\012But at the beginning, the engine temperature is still low, it needs rich gas mixture to sustain the internal combustion. In order to overcome this, the car is designed to have run rich ( less than golden ratio of 14.7:1 ) by giving more gas until the engine reaches the operational temperature then closing the path of the extra fuel mist. This is achieved by a vacuum thermal valve sensor. This one can be identified by looking at the top block engine to spot a sensor with 2 vacuum hoses leading to the Throttle body. When this sensor is bad there is no remedy functioning for the engine to run smoothly as designed.\015\012Good Luck.
Repair Help & Product Troubleshooting for 1999 Saturn SL

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