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Car engine fades off and then fades back in when started when engine is warm

AceGamingAceGaming Member Posts: 9
edited May 2020 in Pontiac
Whenever I start my car when the engine is warmed up, it'll crank like normal
and the starter will work fine and you'll hear the combustion. But, the sound
immediately fades away and it sounds like it just died, but then it will quickly
fade back up and sound normal again. Sometimes, it will just die and I have
to start the car again. When the engine is warm, I give it some gas on the
throttle to make sure it doesn't fade out like it does when I don't give it gas.
I've had someone tell me it could be a bad sensor, a bad starter, bad fuel
injectors, etc. I have a video of how it sounds to show what I'm talking about,
but obviously i can't attach it here.
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    imidazol97imidazol97 Member Posts: 27,154
    Nothing comes to mind other than the car needs to be connected to a full ability scanner when it's started with an expert mechanic looking for what it's doing in the few seconds after it starts.

    Could be so many things from crankshaft position sensor, to coolant temperature sensor, to oh so many things.

    It'll save money spent hanging parts from guessing to find a good mechanic and pay for the analysis.

    2014 Malibu 2LT, 2015 Cruze 2LT,

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    AceGamingAceGaming Member Posts: 9
    imidazol97 said:

    Nothing comes to mind other than the car needs to be connected to a full ability scanner when it's started with an expert mechanic looking for what it's doing in the few seconds after it starts.

    Could be so many things from crankshaft position sensor, to coolant temperature sensor, to oh so many things.

    It'll save money spent hanging parts from guessing to find a good mechanic and pay for the analysis.

    I've seen a couple of different solutions from other Pontiac cars. Some people saying it was bad coolant temp sensor, crank sensor, bad fuel/air mixture, etc.

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    AceGamingAceGaming Member Posts: 9
    AceGaming said:

    imidazol97 said:

    Nothing comes to mind other than the car needs to be connected to a full ability scanner when it's started with an expert mechanic looking for what it's doing in the few seconds after it starts.

    Could be so many things from crankshaft position sensor, to coolant temperature sensor, to oh so many things.

    It'll save money spent hanging parts from guessing to find a good mechanic and pay for the analysis.

    I've seen a couple of different solutions from other Pontiac cars. Some people saying it was bad coolant temp sensor, crank sensor, bad fuel/air mixture, etc.

    Also forgot to mention bad MAF/MAP sensor.
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    imidazol97imidazol97 Member Posts: 27,154
    edited May 2020
    Could be a lot of different things. I recall one Buick I had with the 3300 engine that after a year or so would die after being started. The cure was they reprogrammed the PROM. The car would be learn when started but the carbon and other buildup on the intake valves would absorb the mixture at first and the cylinders were too lean. It would die. But always restart immediately.

    BUT that was a problem that can be verified by watching the fuel mixture adjustments the computer was making as the oxygen sensors were getting symptoms of a lean mixture and trying to compensate.

    Again, before hanging any more parts, you need to verify that that part is the problem. A scanner like mine that's several years old can follow the fuel mixture adjustment. Find someone that can use their scanner to look for the symptoms and look for the actual cause.

    Disconnecting the MAF or MAP is often tried as a test to decide if they are the problem. Could be. The MAF can be cleaned with a spray cleaner and a camel hair artists brush to light clean particles that stick to the wires.
    BUT disconnecting them can affect other things and that will seem to cure problems. A friend and our shadetree mechanic neighbor found that his MonteCarlo with the 32 valve engine would improve if MAP was disconnected. But that wasn't the problem Took a transmission guy using his scanner to determine what it was.

    Find a professional shop to at least diagnose or find a good shadetree mechanic with a full scan ability that KNOWS what they are looking at.

    2014 Malibu 2LT, 2015 Cruze 2LT,

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    AceGamingAceGaming Member Posts: 9
    So I've done a bit of research and I'm coming to some possibilities, and I've also done some personal maintenance as well.

    Maintenance done:
    -Cleaned MAF sensor
    -Cleaned throttle body
    -New air filter
    -Spark plugs changed to iridium a year ago

    Possible reasons for issue:
    -The car muffler isn't stock (straight through muffler)
    -The car sometimes has a funky smell after turned off after being warm
    -The car pops when revved after warmed up
    -It takes just a bit on the throttle right after the starter successfully turns over to get it running

    Belief:
    -Due to the muffler not being stock and it being a straight through muffler, it could be causing a lean A/F mixture that the car does not adjust to, which would explain the exhaust popping when the engine is warmed up on revving.
    -Too much fuel going into the engine after it is warmed up could cause the engine to be flooded, which is why starting it some time after it sits is unsuccessful and letting the excess fuel into the exhaust which causes it to pop
    -Bad fuel pump
    -Bad fuel injectors
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    AceGamingAceGaming Member Posts: 9
    edited May 2020
    imidazol97 said:

    Could be a lot of different things. I recall one Buick I had with the 3300 engine that after a year or so would die after being started. The cure was they reprogrammed the PROM. The car would be learn when started but the carbon and other buildup on the intake valves would absorb the mixture at first and the cylinders were too lean. It would die. But always restart immediately.

    BUT that was a problem that can be verified by watching the fuel mixture adjustments the computer was making as the oxygen sensors were getting symptoms of a lean mixture and trying to compensate.

    Again, before hanging any more parts, you need to verify that that part is the problem. A scanner like mine that's several years old can follow the fuel mixture adjustment. Find someone that can use their scanner to look for the symptoms and look for the actual cause.

    Disconnecting the MAF or MAP is often tried as a test to decide if they are the problem. Could be. The MAF can be cleaned with a spray cleaner and a camel hair artists brush to light clean particles that stick to the wires.
    BUT disconnecting them can affect other things and that will seem to cure problems. A friend and our shadetree mechanic neighbor found that his MonteCarlo with the 32 valve engine would improve if MAP was disconnected. But that wasn't the problem Took a transmission guy using his scanner to determine what it was.

    Find a professional shop to at least diagnose or find a good shadetree mechanic with a full scan ability that KNOWS what they are looking at.

    So I've done a bit of research and I'm coming to some possibilities, and I've also done some personal maintenance as well.

    Maintenance done:
    -Cleaned MAF sensor
    -Cleaned throttle body
    -New air filter
    -Spark plugs changed to iridium a year ago

    Possible reasons for issue:
    -The car muffler isn't stock (straight through muffler)
    -The car sometimes has a funky smell after turned off after being warm
    -The car pops when revved after warmed up
    -It takes just a bit on the throttle right after the starter successfully turns over to get it running

    Belief:
    -Due to the muffler not being stock and it being a straight through muffler, it could be causing a lean A/F mixture that the car does not adjust to, which would explain the exhaust popping when the engine is warmed up on revving.
    -Too much fuel going into the engine after it is warmed up could cause the engine to be flooded, which is why starting the car is unsuccessful after is sits while warm
    -The funky smell could be unburnt fuel sitting in the engine/exhaust slowly being burnt by the heat of the engine and/or exhaust
    -Bad fuel pump
    -Bad fuel injectors
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