Q: Engine run for a few seconds then dies

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Put in new fuel pump cleaned the egr also put in new vacum solenoid checked for air leak with smoke machine ....issue is when I start it it runs fine gives gas fine but after a 10 seconds dies if I unplug the intake it runs non stop but with super low rpms if I barely touch the gas it dies

My car has 90000 miles.
My car has a manual transmission.

Usually a vehicle that won’t rev in the manner you are describing is due to a plugged exhaust system. The most common culprit here is a catalytic converter that has come apart on the inside. If this is the case, creating an exhaust leak before the catalytic converter can confirm this. Also, the amount of air that is coming out the tailpipe when the car is idling low. Compare this to another vehicle that is idling normally. If there is very little, a plugged exhaust is likely the issue. Even so, create an exhaust leak to confirm this. Often times, simply removing the EGR valve is enough, but sometimes it is necessary to remove the down pipe coming off the exhaust manifold. Once you have created an exhaust leak, the motor should idle and rev normally, confirming the plugged exhaust theory. Expect it to be very very loud, so don’t do this late at night or in a neighborhood that is sensitive to noise issues.

My first explanation is heavily dependent on the fact that it dies when you touch the throttle, but there are a number of other possibilities here that are not as easy to explain:

  • Flooded motor: A vacuum leak adds more air into the fuel mixture. If this is the case in your situation, I would suspect that the ECT (Engine Coolant Temperature) sensor has failed. When they fail, they usually indicate to the computer that it is -40 degrees Fahrenheit, which makes the computer dump fuel for a cold start. If this is the case, "clear flood" the motor by flooring the gas pedal while cranking. Not only does this allow more air into the motor, but it signals to the computer to go into clear flood mode and it cuts off the fuel injectors until the vehicle begins to run. This often will require extended cranking until the motor starts. Expect black smoke out the tailpipe and some rough running. A scanner that can monitor data will show you what the ECT is reading. If it not ambient air temperature, this is a sure bet.

  • Rich running condition: If the MAF (Mass Air Flow) sensor is failing, it can cause this. The diagnosis of a MAF can be challenging or obvious. It’s also common to have a 5 volt reference problem created by another failed sensor. If this is the case, you will need a scanner to watch the 5 volt reference while unplugging sensors one at a time. You will only need to unplug the sensors that use the 5 volt reference. A wiring diagram will be necessary to identify the correct ones.

  • Jumped timing belt: If this is the case, it can cause all of these symptoms. This is easily checked by taking a compression check of all the cylinders. If the timing has jumped, at least one cylinder will be significantly lower than the others. Then check the cam timing to be sure.

A diagnosis such as this can be challenging, so you might want to enlist the help of a qualified technician, such as one from YourMechanic, who can come out to your home or office and run a thorough inspection to find out what is causing your car to start then quit.

Good luck and don’t give up.

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