Quick rev before shutting off motor?
Jun 30, 2006, 12:02 PM
#47
Originally Posted by vboy425
this thread is a waste of server space
Originally Posted by EVOgasmIX
Look, I'm not all hardcore about doing this. I simply wanted to get some more opinions on this. INSIGHTFUL opinions without any sort of attacks, worthless comments, etc. I'M HERE TO LEARN. Not to be a punching bag to boost your ego, because your life in the real world is unsatisfying.
Some arguements against doing this in this thread were insightful, but I can say most weren't. I'M NOT ARGUING THIS, FOR THE SAKE OF ARGUEMENT; I'm arguing this to have a discussion where many viewpoints are comming together. Thanks to anyone who took the time to read and discuss this in an intellectual fashion.
For the rest of you.
Some arguements against doing this in this thread were insightful, but I can say most weren't. I'M NOT ARGUING THIS, FOR THE SAKE OF ARGUEMENT; I'm arguing this to have a discussion where many viewpoints are comming together. Thanks to anyone who took the time to read and discuss this in an intellectual fashion.
For the rest of you.
Jun 30, 2006, 12:19 PM
#49
Originally Posted by nigletsyz
You don't have to take it personally that I want to throw a rock at my computer after reading this thread, its just how I feel.
I'm not a moron; quite the contrary. I'm simply asking a question TO LEARN. At least, I'm providing some reasoning why this might be beneficial. Most of the posters here, not all, either doesn't understand, but thinks they do or posts useless BS about thier feelings or just said it was bad and/or unnessesary without reasoning why it was so.
So unless you have anything useful to add that pertains to the topic, well, stop posting here. Please. Do it as a personal favor to me. Thanks.
Last edited by ITEM9; Jun 30, 2006 at 03:19 PM.
Jun 30, 2006, 12:24 PM
#50
Originally Posted by machron1
I believe the ECU uses MAF and TPS sensor rate-of-change thresholds to calculate the acceleration enrichment. Considering how quick the throttle response is, and how rich the car runs in closed-loop, I would imagine both thresholds are pretty low. Carbs have something similar but I forget what it is called or how it works. Anyway, I'm pretty sure what affects acceleration enrichment isn't how much you blip the throttle but rather how quickly.
So if a proper technique was used to blip the throttle, can this transient enrichment be minimized?
Like I said before: Blip, un-blip, let revs fall, shut-off, as revs continue to fall go WOT to cycle more air through. The fuel system is off remember so WOT won't add fuel, just more air.
Jun 30, 2006, 01:52 PM
#54
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People used to do that with carburated motors but its pointless in our cars.
Yeah even the RX-8 will have the old rotary flooding issues if you don't do that. I think there is a TSB out on it. As for our cars, no I don't think we need to do it. If anything it dumps more fuel in there than there normally would be, because in open-loop mode (idle) the engine is trying its hardest to make a stoichiometric fuel mixture for emissions purposes. However, if you gun the engine it switches to closed loop, which in the Evo's case is PIG RICH to keep from detonating. Also, in addition to closed-loop operation, there is an enrichment algorithm the ECU uses to predict the future fuel load needed, so if you mash the gas the ECU predicts you want lots of fuel for higher rpms than you currently have. So, needless to say as soon as you lift your foot you are ultra-ultra rich. That's why when we gun it then let off we get huge puffs of smoke and/or backfires and/or gigantic flames. Lots of raw fuel is being dumped in for cooling and enrichment which is never burned.
So, I don't know if having a little excess fuel in the engine really that bad. I can see how it might be bad if you didn't change your oil frequently because it might saturate the oil. But, I've never heard of that being a huge problem in EFI engines. That said, if your goal is to have the least amount of residual fuel in the cylinders as possible, I think your best bet is to shut it down while it is hunting for stoichiometric in open-loop and not after you just gunned it. Any fuel left over from near-stoichimetric combustion should evaporate at those elevated temperatures anyway, wheras if you just gunned it and there was enough fuel to pool in the cylinders, it wouldn't necessarily all come out simply because the engine was still spinning, as it is probably a liquid at that point and not a gas or vapor. That's how I see it anyway...
As mentioned earlier, THIS IS NOT A GOOD THING AND WAS DONE in the 50's - 70's with Carbs (left fuel in the system to facilitate startups). This had NOTHING TO DO WITH "CLEARING THE SYSTEM."
You should not do this with FI cars.
Maybe we could get some Mitsubishi engineers to come on occassionally and answer these sorts of questions, along with the more technical questions such as ECU programming ....
this is not a good practice unless you have carburetted engines. it makes no sense at all except waste gas, unless you want to hear your engine hum or your fart muffler. the owner's manual advised against doing it just before shutting down so as my lexus and honda owner's manual.
Its not necessary... Don't know if it can do any harm or not.. HOWEVER the moment you shut off the engine you cut off the fuel injectors and ignition.. There is nothing in the cylinders as it comes to a stop... Therefore not a problem..
Guys If we had carbs. on our cars this would be fine...But since we dont theres no reason. Its only to help start later. It just leaves some fuel in the intake and the gravity does the rest. Any fuel injected car dosent need this help beacuse gravity has less of an effect to a fuel inj. car . It would do more harm than good. If this would be a help to a fuel injected car the factory would set it to do so.
I just talked with one of the engineers in the fuel systems group and he said for fuel injected cars it's not necessary.
On rotary engine's it is necessary in certain situations. He does it on his RX-8 only when the engine hasn't had enough time to fully warm up before shutting it off. (i.e. moving it in the driveway).
The proper way to do it is shut off the engine before it comes back down to idle.
Yeah even the RX-8 will have the old rotary flooding issues if you don't do that. I think there is a TSB out on it. As for our cars, no I don't think we need to do it. If anything it dumps more fuel in there than there normally would be, because in open-loop mode (idle) the engine is trying its hardest to make a stoichiometric fuel mixture for emissions purposes. However, if you gun the engine it switches to closed loop, which in the Evo's case is PIG RICH to keep from detonating. Also, in addition to closed-loop operation, there is an enrichment algorithm the ECU uses to predict the future fuel load needed, so if you mash the gas the ECU predicts you want lots of fuel for higher rpms than you currently have. So, needless to say as soon as you lift your foot you are ultra-ultra rich. That's why when we gun it then let off we get huge puffs of smoke and/or backfires and/or gigantic flames. Lots of raw fuel is being dumped in for cooling and enrichment which is never burned.
So, I don't know if having a little excess fuel in the engine really that bad. I can see how it might be bad if you didn't change your oil frequently because it might saturate the oil. But, I've never heard of that being a huge problem in EFI engines. That said, if your goal is to have the least amount of residual fuel in the cylinders as possible, I think your best bet is to shut it down while it is hunting for stoichiometric in open-loop and not after you just gunned it. Any fuel left over from near-stoichimetric combustion should evaporate at those elevated temperatures anyway, wheras if you just gunned it and there was enough fuel to pool in the cylinders, it wouldn't necessarily all come out simply because the engine was still spinning, as it is probably a liquid at that point and not a gas or vapor. That's how I see it anyway...
As mentioned earlier, THIS IS NOT A GOOD THING AND WAS DONE in the 50's - 70's with Carbs (left fuel in the system to facilitate startups). This had NOTHING TO DO WITH "CLEARING THE SYSTEM."
You should not do this with FI cars.
Maybe we could get some Mitsubishi engineers to come on occassionally and answer these sorts of questions, along with the more technical questions such as ECU programming ....
this is not a good practice unless you have carburetted engines. it makes no sense at all except waste gas, unless you want to hear your engine hum or your fart muffler. the owner's manual advised against doing it just before shutting down so as my lexus and honda owner's manual.
Its not necessary... Don't know if it can do any harm or not.. HOWEVER the moment you shut off the engine you cut off the fuel injectors and ignition.. There is nothing in the cylinders as it comes to a stop... Therefore not a problem..
Guys If we had carbs. on our cars this would be fine...But since we dont theres no reason. Its only to help start later. It just leaves some fuel in the intake and the gravity does the rest. Any fuel injected car dosent need this help beacuse gravity has less of an effect to a fuel inj. car . It would do more harm than good. If this would be a help to a fuel injected car the factory would set it to do so.
I just talked with one of the engineers in the fuel systems group and he said for fuel injected cars it's not necessary.
On rotary engine's it is necessary in certain situations. He does it on his RX-8 only when the engine hasn't had enough time to fully warm up before shutting it off. (i.e. moving it in the driveway).
The proper way to do it is shut off the engine before it comes back down to idle.
Jun 30, 2006, 02:11 PM
#55
Originally Posted by EVOgasmIX
Cool man. THANK YOU for a civil intellegent reply.
So if a proper technique was used to blip the throttle, can this transient enrichment be minimized?
Like I said before: Blip, un-blip, let revs fall, shut-off, as revs continue to fall go WOT to cycle more air through. The fuel system is off remember so WOT won't add fuel, just more air.
So if a proper technique was used to blip the throttle, can this transient enrichment be minimized?
Like I said before: Blip, un-blip, let revs fall, shut-off, as revs continue to fall go WOT to cycle more air through. The fuel system is off remember so WOT won't add fuel, just more air.
I believe this is the method a previous poster was referring to for the RX-8 when it is running under cold-start enrichment and shut off before it leans out the mix, leaving fuel in there which makes a rotary nearly impossible to start. I would say blipping the throttle would be worse for getting fuel out as it may be running on an acceleration enrichment at the point in time when it is shut down, which is the opposite of what you are trying to do. Also, if you let the RPMs drop to the point the ECU is starts to adjust the air-fuel mix to keep it from stalling and then turn it off, you may catch it at an overly rich condition as well.
If you really wanted to get scientific about it, you could hook up a wideband O2 sensor and log your throttle position, rpms, and O2 levels while blipping.
EDIT: Oh yeah, after everything is shut off your throttle position shouldn't let more or less air in, because even with the butterfly all the way closed enough air can get in to let it idle.
Last edited by machron1; Jun 30, 2006 at 02:17 PM.
Jun 30, 2006, 03:11 PM
#56
Originally Posted by vboy425
EVOgasmIX , I'M JUT PULLING YOUR STRING BRO. IT'S ALL GOOD. SORRY IF I TOOK IT TOO FAR. BEER ON ME 
Cool.
Jun 30, 2006, 03:17 PM
#57
Originally Posted by machron1
EDIT: Oh yeah, after everything is shut off your throttle position shouldn't let more or less air in, because even with the butterfly all the way closed enough air can get in to let it idle.
I've tried this a few times and it seems, as the engine isn't trying to pull on a vacuum, the motor seems to cycle a few more times. I'll try to see if the motor cycles more from shutting off and going WOT with no blip at all.
