Engine hesitation quick fix
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Joined: Jul 2001
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From: Far Away Land
Engine hesitation quick fix
I see posts from time to time reporting engine hesitation at part throttle/low rpm. Well, I do get that from time to time, but now I know why. Bad gas. I had an obvious case of slight engine hesitation until I got a full up.
So if you experience engine hesitation, I suggest you try another gas station (yes, some gas station cheat and dilute higher octane fuel with regular), or try changing a brand altogether.
I think that hesitation is most obvious is due to the fact that the ecu tries to lean out the mixture at low rpm/part throttle to get more efficient burn/save fuel, and when you mix in some subpar gasoline you get detonation.
So if you experience engine hesitation, I suggest you try another gas station (yes, some gas station cheat and dilute higher octane fuel with regular), or try changing a brand altogether.
I think that hesitation is most obvious is due to the fact that the ecu tries to lean out the mixture at low rpm/part throttle to get more efficient burn/save fuel, and when you mix in some subpar gasoline you get detonation.
Pro
Joined: Jan 2013
Posts: 571
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From: SoCal
I see posts from time to time reporting engine hesitation at part throttle/low rpm. Well, I do get that from time to time, but now I know why. Bad gas. I had an obvious case of slight engine hesitation until I got a full up.
So if you experience engine hesitation, I suggest you try another gas station (yes, some gas station cheat and dilute higher octane fuel with regular), or try changing a brand altogether.
I think that hesitation is most obvious is due to the fact that the ecu tries to lean out the mixture at low rpm/part throttle to get more efficient burn/save fuel, and when you mix in some subpar gasoline you get detonation.
So if you experience engine hesitation, I suggest you try another gas station (yes, some gas station cheat and dilute higher octane fuel with regular), or try changing a brand altogether.
I think that hesitation is most obvious is due to the fact that the ecu tries to lean out the mixture at low rpm/part throttle to get more efficient burn/save fuel, and when you mix in some subpar gasoline you get detonation.
Evidently, I've gotten bad gas at every single refill over the last 2 1/2 years. What are the odds of that?
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Joined: Mar 2013
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From: Atlanta, GA
Agree that bad gas can contribute to acceleration issues. Have had bad throttle hesitation fixed by some software upate, had a bad gas experience (with the car 
) and now live with a slight, but livable, throttle hesitation usually in normal mode (Sport is way better).
) and now live with a slight, but livable, throttle hesitation usually in normal mode (Sport is way better).
Advanced
Joined: Feb 2013
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The only gas you have available is 91 octane, these cars are designed for 93 octane. While it isn't the end of the world, you will get some type of hesitation and even engine knocking if you put a high load at a low rpm.
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Instructor
Joined: Jul 2001
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From: Far Away Land
I was just going to say the same thing. I'm in ny, so my bad gas is probably is like CA gas. We have 93 octane and when it is diluted, probable closer to 91 that you have in ca
Considering you live in California, your odds are 100% chance of getting bad gas.
The only gas you have available is 91 octane, these cars are designed for 93 octane. While it isn't the end of the world, you will get some type of hesitation and even engine knocking if you put a high load at a low rpm.
The only gas you have available is 91 octane, these cars are designed for 93 octane. While it isn't the end of the world, you will get some type of hesitation and even engine knocking if you put a high load at a low rpm.
Pro
Joined: Jan 2013
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From: SoCal
Considering you live in California, your odds are 100% chance of getting bad gas.
The only gas you have available is 91 octane, these cars are designed for 93 octane. While it isn't the end of the world, you will get some type of hesitation and even engine knocking if you put a high load at a low rpm.
The only gas you have available is 91 octane, these cars are designed for 93 octane. While it isn't the end of the world, you will get some type of hesitation and even engine knocking if you put a high load at a low rpm.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
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By your logic, all 991s in CA should exhibit stumbling/hesitation. Most definitely not the case.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
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Joined: Jan 2013
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From: SoCal
"Flush the system"? What does that mean?
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
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Joined: Jun 2012
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"Flush the system"? What does that mean?
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
Thread Starter
Instructor
Joined: Jul 2001
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From: Far Away Land
I had exact same symptoms you are describing. It is very easy to test my theory. Find the closest gas station that sells 100 octane unleaded gas and see if you are still having the same issue. You can usually find 100 octane pumps at the race tracks (drag strips or circuits). There may be something else going on with your car, sure, but why not try this?
By your logic, all 991s in CA should exhibit stumbling/hesitation. Most definitely not the case.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
RL Community Team
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Rennlist Member
Joined: Sep 2005
Posts: 18,846
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"Flush the system"? What does that mean?
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
Many brands of race fuel (i.e. 100 octane gas) can sometimes contain more additives and detergents than premium octane gas.
Thread Starter
Instructor
Joined: Jul 2001
Posts: 234
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From: Far Away Land
"Flush the system"? What does that mean?
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
The simple fact you're missing is that if, in fact, bad/low octane gas is the cause of the hesitation, then there is a 100% probability that the hesitation would occur under high load. There is no possibility bad gas could cause a hesitation under light throttle but not at moderate to heavy throttle - just doesn't make sense.
Advanced
Joined: Feb 2013
Posts: 62
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By your logic, all 991s in CA should exhibit stumbling/hesitation. Most definitely not the case.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
The stumble/hesitation problem occurs ONLY under light load/light throttle, and ONLY between 2500-2800 rpm.
Otherwise, when prompted, my car runs like a striped ape with zero hesitation.
Bad gas and/or 91 octane have absolutely nothing to do with the infamous stumble/hesitation.
Now I know this is the internet and there is no tone of voice when you are looking at only words. But your tone in this whole thread hasn't been very helpful, a bit snarky and borderline hostile.
The OP in this thread is only trying to help other people and he found a solution that worked for him. Yet your only contribution to refute suggestions that other people are trying to give you help on.
The risk from running a lower octane than the minimum is the ECU may not have the range to dial back the timing enough to prevent detonation.
The backing off of the timing lowers the peak pressure generated in the combustion chamber/cylinder which reduces the chances of detonation -- the ECU normally dials back the timing until it no longer senses detonation vibrations from the knock sensors -- but this also decreases the amount of work obtained from burning the fuel. Exhaust gas temperature is increased too.