Dumb question about rev-up shut-down
08-01-2006, 07:11 AM
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Dumb question about rev-up shut-down
So, I was discussing this with someone (local non-Mazda garage tech') and we couldn't figure it out...
The logic says that you rev-up the engine and turn off the key. This cuts the fuel pump, so the engine then revs down by itself and burns off any remaining gas to prevent it sitting in the chambers, so you don't flood for the next start-up.
However, doesn't turning the key also cut the ignition/spark? If so, then you're not really burning off gas, you're just dumping un-burned gas down the headers and into the cat. The cat must be taking a real big burden of un-burned gas when this happens (thereby possibly shortening its life)?
So, is our logic correct and the rev-up/shut-down actually dumps un-burned gas into the cat? Or has Mazda done something clever to the ECU so that the engine continues on sparking long after the ignition key is turned, to combust any remaining gas? How does the relative timing of fuel pump vs. sparks occur at shut down?
The logic says that you rev-up the engine and turn off the key. This cuts the fuel pump, so the engine then revs down by itself and burns off any remaining gas to prevent it sitting in the chambers, so you don't flood for the next start-up.
However, doesn't turning the key also cut the ignition/spark? If so, then you're not really burning off gas, you're just dumping un-burned gas down the headers and into the cat. The cat must be taking a real big burden of un-burned gas when this happens (thereby possibly shortening its life)?
So, is our logic correct and the rev-up/shut-down actually dumps un-burned gas into the cat? Or has Mazda done something clever to the ECU so that the engine continues on sparking long after the ignition key is turned, to combust any remaining gas? How does the relative timing of fuel pump vs. sparks occur at shut down?
08-01-2006, 07:22 AM
#2
I did the rev method for 2 years. One day I had to move my car from the garage (someone was routing some stuff in there) and I had to get my RX-8 out of the way. I started the car up, moved it out of the garage, reved it for longer than 10 seconds, switched it off. When the installer left, I tried starting the car, and couldn't. It was the weekend, and the dealership was closed. The day after, it still wouldn't start. Ended up getting it towed for deflood.
What I got from this is that the rev method does not help. Just because I didn't flood for two years doing it doesn't mean it did anything for me.
What I got from this is that the rev method does not help. Just because I didn't flood for two years doing it doesn't mean it did anything for me.
08-01-2006, 09:05 AM
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My 04 Flooded occasionally until I got the R-Flash.
It fever flooded again even with cold shut-downs.
If your flashes aren't up-to-dater, I highly suggest
you have them taken care of. They're free and you'll
probably avoid these difficulties in the future.
Of coarse nothing is guarantied.
EBF
It fever flooded again even with cold shut-downs.
If your flashes aren't up-to-dater, I highly suggest
you have them taken care of. They're free and you'll
probably avoid these difficulties in the future.
Of coarse nothing is guarantied.
EBF
08-01-2006, 11:53 AM
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Whether it actually always works or not, the method stated by Mazda is to raise the RPM, let it drop to idle, THEN turn off the ignition. Not to turn off the ignition while you have the RPM up. Some people here have sworn by doing it the second way so you'll have to choose who to trust, I guess. You may be right about it not burning all the fuel if the ignition is cut before letting the RPM drop. I've never done such a short run time so I've not had the problem yet.
08-01-2006, 12:39 PM
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After buying the car a few weeks ago, I took it to the Mazda dealer. A mechanic who seems to have a good reputation, has a lot of experience with rotary engines, and is very familiar with my car, heard me rev, then shut off the engine. He smiled knowingly, then told me that this procedure wouldn't be necessary for my car since he had taken the necessary steps to fix (at least, minimize) the flooding issue. I've continued to do it as a precaution, but I may stop. I get the impression there are things you can do to help with certain "high maintenance" issues of the 8, but that there will still be one-off situations where the precautions don't do the trick.
08-01-2006, 03:44 PM
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All I know is I have done this following short trips since I owned the car (three years). The car very clearly starts up faster after doing the rev up-shut down procedure than it does without doing the procedure.
I always thought the rotors spinning down helped to clear the chamber of excess fuel.
I always thought the rotors spinning down helped to clear the chamber of excess fuel.
08-01-2006, 03:54 PM
#8
I don't buy Kool-Aid
Originally Posted by ALP22
So, I was discussing this with someone (local non-Mazda garage tech') and we couldn't figure it out...
The logic says that you rev-up the engine and turn off the key. This cuts the fuel pump, so the engine then revs down by itself and burns off any remaining gas to prevent it sitting in the chambers, so you don't flood for the next start-up.
However, doesn't turning the key also cut the ignition/spark? If so, then you're not really burning off gas, you're just dumping un-burned gas down the headers and into the cat. The cat must be taking a real big burden of un-burned gas when this happens (thereby possibly shortening its life)?
So, is our logic correct and the rev-up/shut-down actually dumps un-burned gas into the cat? Or has Mazda done something clever to the ECU so that the engine continues on sparking long after the ignition key is turned, to combust any remaining gas? How does the relative timing of fuel pump vs. sparks occur at shut down?
The logic says that you rev-up the engine and turn off the key. This cuts the fuel pump, so the engine then revs down by itself and burns off any remaining gas to prevent it sitting in the chambers, so you don't flood for the next start-up.
However, doesn't turning the key also cut the ignition/spark? If so, then you're not really burning off gas, you're just dumping un-burned gas down the headers and into the cat. The cat must be taking a real big burden of un-burned gas when this happens (thereby possibly shortening its life)?
So, is our logic correct and the rev-up/shut-down actually dumps un-burned gas into the cat? Or has Mazda done something clever to the ECU so that the engine continues on sparking long after the ignition key is turned, to combust any remaining gas? How does the relative timing of fuel pump vs. sparks occur at shut down?
Dont do it. Your car will flood.
08-01-2006, 03:56 PM
#9
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^^^ I too thought the same. Since it wouldn't be injecting any more fuel the rotors would just clear out the remaining fuel in the chamber. Is this a bad or good thing to do? I used to not do it but now do and now I am starting to really get concerned over what to do.
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