So if you do mostly around town driving in the suburbs with some occasional short distance highway driving, how much gas do you really save with the Auto Idle Stop feature. Maybe a cup every tank full. The whole thing seems ridiculous to me considering the minute amount of gas savings vs the possible excess wear and tear on the car,

 

I think there are two bigger issues than fuel savings:

• Pollution: a gasoline engine at idle runs very rich and as such, pollutes more per unit of gasoline burned than does a car tooling along at freeway speeds.
• Oil dilution: here again, due to how rich the idle circuit is, oil dilution with gasoline is an issue in cars which spend a lot of time idling.

 

it was recently found that if you spend more than 7 seconds* idling; it's beneficial to stop the engine, as start-ups use less fuel.
said in another way; you use more fuel idling for 7 seconds* than you do starting and stopping the car.

* Seconds not minutes

 

Per the video it's 7 seconds, not 7 minutes.

 

my memory has failed me. LOL thanks

 

it's also noted that auto manufactures take in account for the extra abuse and fortify or make sure the components can withstand extra engine starts. You have no worries, RDXguy!

 

If automakers have such good insight and are so good at fortifying the cars, why do we take them in for repairs?

 

really, guy? does your house need maintenance and repairs? do you need maintenance and repairs? you werent born yesterday. everything needs maintenance and repairs to live a long life.

I think you misconstrued my words... the auto manufactures have accounted for the extra starts and stops and have engineered an item to withstand the extra starts and stops. doesnt mean it wont die eventually.

 

 

Pretty common on forums like this to think engineers are all idiots or that all car companies are driven by accountants first and engineers second. The good news is AZ seems to be more often in support of OEM engineering compared to other forums.

 

Do you have a link that supports this? Everything I've read on the subject states that fuel injected engines are designed to maintain a chemically-correct 14.7 to 1 fuel/air ratio at idle. This ratio produces the least pollution possible and results in 100% of the fuel mixture being burned. There is no reason I can think of that would make a rich mixture at idle desirable. As an aside, my six cylinder 3.5 liter Toyota was tested with an inline flowmeter a few years ago. It burned a measured .30 gallon (38.4 ounces) per hour at idle after warm up. This amount of fuel is insignificant to me and certainly not worth dealing with an engine start/stop system.

 

I'm not sure where you got that little tidbit if information and as such, I'm not even sure where to begin...

• In most conditions, 14.7:1 is a terrible ratio as it can cause detonation and/or burned valves.
• The best air to fuel ratio for any given condition is extremely dynamic, ranging from as rich as 10.x:1 in idle conditions to as lean as 16.x:1 for light throttle steady-state/high vacuum/low throttle cruising conditions (of course dependent upon engine design, I don't know of any one engine capable of both extremes).
• If you have a resource which claims constant stoichiometric conditions across the dynamic operational capabilities of an automobile engine, I would love to review it.

 

Now I suspect you're either BS'ing or haven't done your research. !4.7 to 1 (stoichiometric combustion for those who like big words) is desirable at idle rpm simply because engines can tolerate a lean mixture during low-stress operation and this mixture at idle is virtually mandated by EPA in order to meet their CO2 limits. When the drive train is turning the engine during coasting even a leaner mixture is acceptable and some designs drastically lean the mixture in these conditions. At higher power settings a richer mixture is needed and the fuel injection system automatically compensates to provide this. I'm unaware of any modern fuel injected engine that isn't capable of adjusting the fuel/air ratio to match the existing conditions and am mildly surprised that you think they don't exist. As far as having a reference to an engine that maintains stoichiometric combustion across all power bands, I don't have such a reference because none exists as far as I know. But, it might be worth pointing out that I never said, hinted, or suggested such a thing.

 

 

Sorry buddy, you've got it way-WAY wrong, time to get educated.

 

Here's a Cars Direct article on the subject. I've got a ton more if you don't like this one: https://www.carsdirect.com/car-repai...air-fuel-ratio

"From a strictly scientific point of view, a perfect Air/Fuel ratio will be 14.6:1, or 14.6 parts air for 1 part fuel on a gasoline engine. In the real world however, this perfect number changes quite a bit depending on air temperature, engine configuration, and especially on whether your engine is naturally aspirated or turbo/supercharged. Throttle position will change these values as well; with naturally aspirated engines hovering closer to 14.6:1 during idle or light load cruising. Suggested numbers below are what should be found at wide open throttle.For naturally aspirated engines, 13.0:1 is a relatively safe Air/Fuel ratio. Factory-tuned cars however may run more richly than this at higher RPM to make sure they are as reliable as possible. Using a newer Honda Civic Si as an example, Air/Fuel ratio begins at around 13.0:1 until about 5,000rpm and then drops to a range of around 12.0:1 to compensate for advanced ignition timing, more aggressive valve lift profiles and higher heat. Most factory cars will be somewhere in this range, perhaps a bit leaner on lower compression or older engines.For turbocharged engines, 12.0:1 is a relatively safe Air/Fuel ratio. Most factory tuned cars will run even richer than this, sometimes in the 11.0 to 11.5:1 range. This is because turbocharged engines can be a lot less forgiving to auto-ignition due to the increased amount of airflow and generally hotter temperatures due to the compressing of intake air. In general, turbocharged engines will run a bit leaner before peak boost pressure is reached to help spool up the turbocharger more quickly, and then increase fuel as boost and engine speed increase. As an example of turbocharged Air/Fuel ratio, the 2003 Mazdaspeed Protege starts as high as 14.0:1 at low rpm before boost rises, and then plummets to an Air/Fuel ratio of 10.5 to 11.0 at peak boost to redline. This is known to be excessively rich and can cause hesitation and throttle response issues. A factory reflash to the fuel mapping resets this closer to 11.5:1 and 12.0:1 which gets rid of many of the problems previously encountered."

 

So you've just proven my point, why would I want a ton more?

 

Apparently you missed the part about fuel/air ratios being leanest at idle and when cruising at low engine loads. No person with any auto education or experience would state the exact opposite as you did. Air/fuel ratios aren't hard to research, so why don't you do a little reading before posting nonsense.

 

jesus.. i lost brain cells reading this...


I don't even know where to begin to discount this premise but I doubt you'll listen to any sense so I'm not even going to waste my energy..

 

For cruising at low engine loads that confirms what I said above, for idle circuit operations, not a chance. Don't believe me, hook a wide band monitor up to your engine and see for yourself.

 

Oh! I thought "you've just proven my point" somehow meant that you thought the article that stated that fuel/air mixtures were leanest at idle supported your post that stated the opposite.


Your post:

• "Pollution: a gasoline engine at idle runs very rich and as such, pollutes more per unit of gasoline burned than does a car tooling along at freeway speeds."
• "Oil dilution: here again, due to how rich the idle circuit is, oil dilution with gasoline is an issue in cars which spend a lot of time idling."

Little did I know that in your world up is down and richest means leanest. And, in your world not only is idle mixture excessively rich, it is so rich it results in fuel diluting the oil. You're not honest enough to acknowledge that your opinion has no basis in fact and further post that a professional article that disputes your opinion somehow supports it. Have a great life!

 

Are you for real? Time to take a course on combustion my friend.

 

From what I've read, 3% fuel savings is about average with start-stop systems.

 

This may have been somewhat accurate in 1965, but it's far from accurate on today's modern cars. Not sure if you've ever seen an exhaust analyzer printout, but many states have used them for years to conduct emissions inspections and HC specifically, are at or very near zero on any car made after 1990. And of course those tests are done at idle. That right there alone indicates that modern engines don't at all run rich at idle.

 

Well, the fact remains, the idle circuit runs rich. Like I wrote before, hook up a wide band monitor to the OBD-II port and read the fuel trims for yourself. I cannot say it any plainer than that.

 

And, after some preset number of starter operations is exceeded, the auto idle stop system will stop functioning and the starter motor and starter cut relays will need to be replaced.

From the service information:

"Number of Starter Operations

PCM counts the number of starter operations.
If the number of starter motor operations exceeds the setting limit, the auto idle stop is disabled, and the auto idle stop indicator (amber) blinks*. In this case, both starter motor and starter cut relays need to be replaced.
When replacing the starter motor and the starter cut relays, it is need to clear the counter of "STARTER and STARTER CUT RELAY" with the HDS.
When replacing the PCM, the number of starter motor and starter relays operations, those are stored in previous PCM, need to be transferred to the new PCM.

*: When the auto idle stop system is turned to off by the idle stop off switch, the auto idle stop indicator (amber) comes on"

 

I'm interested in the rich vs. lean mixture when idling, cruising, high throttle, etc. largely because my understanding was that idling caused a rich A/F ratio, especially when cold. My understanding was that you don't want to let the car continually idle until fully warmed up because it's running rich the whole time, which would result in a faster fuel dilution of oil over time. I've heard that from an endless number of mechanics - let the car warm up for a moment (15-60 seconds depending on ambient temperature) then get going. Then just take it easy on the throttle and RPM's until fully warmed up.

Another observation (take it for face value) is that my fuel trim is right on 0, or at most +/- 1 when cruising on the freeway or during city driving during non-rush hour where you're moving most of the time. During rush hour, where's there's a good deal of start and stop, my fuel trim gets as high as 6 or 7. This indicates a rich mixture of course.

I suppose my question is; why does the long term fuel trim slowly kick upwards during stop and go driving but stay around 0 otherwise? That would seem to validate the idea that idling would result in the ECU adjusting fuel trim rich.

 

A POSITIVE LTFT indicates that the system is ADDING fuel to reach the desired air-to-fuel ratio.
A NEGATIVE LTFT indicates that the system is REDUCING fuel to reach the desired air-to-fuel ratio.

A positive LTFT doesn't mean the engine is running rich. It means it's running LEANER than desired and is compensating by adding more fuel to reach the desired A/F ratio.

The air-to-fuel ratio can vary above and below stoichiometric (14.7:1) while STFT and LTFT are both zero depending on the ratio the system is desires. On a cold start and during WOT, the system will run richer than 14.7:1. If conditions permit, a mixture leaner than 14.7:1 is commanded.

A positive LTFT indicates that the programmed values aren't sufficient to achieve the desired A/F ratio, so the system is commentating by increasing the on pulse width of the injectors to compensate. It's normal to see fluctuating fuel trim values. What you don't want to see is the LTFT staying at its extremes at which point the system can no longer compensate and will set a rich or lean DTC.

 

Fuel use is absolutely minimal at idle. The only time you'll see less fuel being used is under deceleration (only because it basically shuts the fuel pulse down completely on many vehicles) or when the engine isn't running. I think that's the main point of this discussion.

 

You missed the point; while fuel use is minimal, the air to fuel ratio is relatively rich.

 

This is the best post in this entire thread. Finally someone who understands fuel trims and what they mean.

 

I don't have a problem with what was written, however, that post in no way indicates how the air to fuel mixture is set when at idle. Like it or don't, believe it or not, virtually all cars, even modern fuel injected cars, run fairly rich at idle.

 

Incorrect. You must have your terms confused. A "rich" mixture means that the ratio is a mixture that's higher than normal in fuel. But anyway, it is you who missed my point, which is this--at idle, with or without a "perfect" fuel ratio, the amount of fuel used is absolutely minimal. Said in simpler terms, your engine just isn't using a lot of fuel to idle and that much should be obvious. Start/Stop systems will save fuel for sure, but it's insignificant for an individual. Collectively, if you consider every car on the road with an active Start/Stop system, it can certainly be significant....but for a single person, it's really not very meaningful, even over a long period of time. If I save three gallons of gas per year because of Start/Stop, is that really meaningful? Not for me it's not.

 

Here's an idea....instead of regurgitating the same of BS over and over again, why don't you post some data? Tell me how rich or lean YOUR car runs at idle, versus coasting, cruising, accelerating at different throttle openings, etc...

I suspect your idea of "fairly rich" is still very insignificant. No matter how you slice it, an idling engine uses very little fuel. The only time an idling engine really runs rich is during a cold start, while still in open loop.

 

Here's an idea, since you don't seem to want to believe me, hook up a wide band monitor to your car of choice and look for yourself. Clearly I have no credibility, I mean really, I'm only an engineer and have consulted to three of the world's automakers on various issues over the years, but hey, I have no idea what I'm talking about Right?

 

This is less about saving money for the consumer. It is more about auto manufacturers meeting CAFE requirements to avoid paying hefty fines.

 

 

 

Yep, separated at birth, but the dude on the left has crooked ears