Just wondering what you guys think of revving the car up and then shutting it off as the motor is decelerating. I thought it was just for show but I didn't do it this morning and the car was hard to start, wasn't getting fuel for some reason. I tried starting it, nothing. Floored the pedal let off and tried again, nothing. Finally I cranked it with the throttle fown about 10% and it started right up. No real terrible smoke or anything like I was expecting and the car drove fine after that. I revved it before I shut it down at home so we'll see what happens when I try to go to work in 5 minutes...

 

Sounds like your engine got a little flooded. It's a bad idea to rev before shutting down because it dumps some unburned fuel into the exhaust. Since your engine is stock until summer, I'd assume your first monolithic cat has puked intself into the 2nd one. Perhaps your TPS is out of adjustment. Do GSL-SEs have a MAF? Maybe yours is working like a rusty gate?

Reving before shutting down serves no purpose other than making a ricer feel good about hearing his fart cannon exhaust one last time before getting out of the car. I know of a guy who would do it religiously to his '01 Eclipse. He wasn't mechanically inclined so I can see why someone like him would do something like that. Anyway there is no reason to rev before shuting down. If you find it's something your engine requires you to do, then something is wrong somewhere. Ask Long Duck since he's the GSL-SE guy around here.

 

Well,

If it does no good, then why does Mazda recommend it for the RX8 in the latest video they sent out?

- Tech

 

Do they? That's disturbing.

 

Where this originated from was the old hand-cranked engines like Ford Model T's. If you knew the trick, you could sometimes start the engine without having to get out and crank-'er up. Old cars like that had the throttle and ignition timing on the steering column. If you revved up your engine and shut the ignition off while it was still spinning, you essentially flooded the cylinders with raw, unburned fuel (being that the spark is no longer lighting the cylinders and the engine is still spinning). When you got back in your car, you could turn-on the ignition and move the timing lever so that one of the cylinders would actually get spark and ignite. When that cylinder ignited, it would cause the engine to rotate and start running all by itself. Pretty cool huh?

Well, for some reason, hot rodders and ricers find a need to do this same thing except we don't have to get out and hand crank our engines any more. Remember I just said that when you do this, it floods the cylinders with raw, unburned fuel? Yeah, what happens to oil when you pour gas on it? It dissolves it. I mean, if you dip a piece of metal in oil and then dip it in gasoline, the oil comes-off. So what it the only thing protecting your cylinder walls from being scuffed by the pistons? or in our case, the side housings from being scuffed by the side seals? The thin layer of oil on them. When you douse the inside of the engine with raw fuel, you wash-off that protective layer of oil and cause cylinder scuffing plus you lose your ring seal. This is a common occurrence with engines that run too rich and get what is called "cylinder wash-down". This is caused by too much fuel in the cylinder that can't all get burned, so what is left over is a wet mixture of raw fuel that literally "washes" the oil right off the cylinder walls/side housings which in turn causes the rings/side seals to lose their seal which in turn results in a major drop in compression, plus the scuffing going-on from the piston/rotor not having a protective layer of oil between it and the cylinder wall/housing.

 

Ah, I didn't even think about that. I only worry about it when and if I ever flood an engine. Heh, I sometimes clean parts with gas if all they need is a quick rinse without any sort of detergent or strong solvent action.

Yet another reason why ricers are the new bottom rung of our mobile society, right behind SUV drivers.

Hey Greek, who produced the new RX-8 video? Do you have a way to upload it somewhere so we can all view it?

 

It came from Mazda so maybe Mazda, but you're only supposed to rev it when your engine hasn't heated up all the way (short trips, moving car, etc).

Here's my question, if gas washes away the oil, then why are we pre-mixing? I just recently STOPPED pre-mixing and my smoke has stopped now and my car dropped a 1/2 second in the 0-60 MPH now and I'm actually in worse conditions then I was back when I got my best for the pre-mixing runs. I might have been over using the oil but I was never properly showed how much to use per tank (I suck at ratios) so I did a better safe than sorry thing.

I don't rev my car either, unless it hasn't warmed up when I go to turn it off.

- Tech

 

No flodding for me, even with a cold engine.

I have a cut-off swich, so I just flip of the switch right before I turn off the ignition.
Cuts the fuel a split second before the spark, so all the excess fuel is always burned off.

No flooding, so backfires after shutdown (as my old -SE used to)

 

what do you mean? your switch controls the fuel going from the carb to the combustion chambers? because if it's just a cut off switch for the fuel pump, the average carb will have enough to run for several seconds after the fuel pump has been switched off.

 

Mazda recomends holding the engine at 4k rpm for 4-5 seconds and shuting it off to clear unburnt fuel out of the engine. Leaving less carbon deposits in the engine and causing less wear on the apex seals. I've been doing this for years! Can't really belive that this is the first time this is comming up here. lol

 

well after further review of the post i see conflicting info. I wonder who's right Mazda or so internet guru? Tough decision, seriously...

 

no one ever does that?

weird.......

on 87 turbo 2nd gens its allmost mandatory. if you dont they will often flood.

 

I thought the T's had magnetos firing the ignition- which won't fire until the crank is turning? Same as on my 1946 Farmall A (which is a hand-crank incidentally). Did they have some direct battery line? I know my Farmall can run a (stock) 6V, but that has barely enough *** to turn the starter for 15 seconds, so I simply crank'er up..

(By the way- I DO NOT throttle my tractor prior to shutting down. I don't like fireballs coming out of a muffler near my face )

 

I know on fuel injected rotaries when you blip the throttle and the revs are coming down, in neutral or not, the injection duty cycle is zero.

 

My car seems to start fine cold but is difficult to start warm. When I slowly and progressively give it gas as it cranks it seems to start fine. I no longer think the revving has anything to do with my car being difficult to start because it idles high anyway so something is probably wrong with the tps or throttle body or I have an air leak somewhere. It was idleing at 2000 this morning and I didn't even have to give it gas to drive around in a parking lot, just let the clutch out.

 

Well,

What we are talking about is holding it at 3k RPM and then killing the engine and when the engine stops turning letting off the gas.

You'll notice a difference when you do it and don't do it.

- Tech

 

That sounds reasonable. What was mentioned before, reving before shutdown, is a rodder/ricer thing where they run the RPMs up for a second or two, and kill it mid-rev. Not 3,000 RPM, but closer to redline.

 

Yeah,

That's just ghey...period.

- Tech

 

I don't think that I'd do this on a carb'd car, but on my '88 TII, I rev it and kill the IGN while holding it at WOT to clear the crap out of the engine. I also hold it at WOT when cranking, and it almost NEVER EVER floods!

before I started doing this it would flood pretty frequently.

 

When i had my Air Cooled VW's If i reved a little before shutting down it made the next cold star MUCH Easier...like turn key and even before one rev it would start. But when i didnt rev before ignition cut off my cold satrts would be a pain in the ***!!!

But with the H4 engines oil stays up by the pistons more so than a V or I engine so oil washing was never really a problem.


I havnt had my rotary long so i got a lot of experimenting and reading to do!

 

EFI, not carb. My car is an -SE
And there's about enough pressure for 1-2 seconds tops.
I don't like to run it completely dry as that makes a hard start, but I find between .5-1 second makes sure there is no flooding...

 

I always thought it was done on piston engines to increase oil pressure before shutoff so when restarted there was maximum oil coverage on components... but oil washing on cylinder walls with unburnt fuel contradicts that...

 

There is no way to keep oil pressure in an engine that is not running. My friend's 510 takes several seconds before the aftermarket kechanical oil pressure guage reads any pressure. Scary, actually. My rotary comes up in pressure is a second or two after it started, even with a large oil cooler to pressurize!

Ah, so that earlier thing in this thread about the RX-8 is indeed different from the ricer revdown. Thank goodness.

 

yes very different. lol

 

ok i think we got 2 things going on here. EFI and Carbs. on Carbs the cylinder walls will get washed by revving before shutting down. on EFI cars there is enough presure in the fuel rail for injection but the ignitions in the off position so it's not going to inject fuel. Mazda does recommend this but about 3500 - 4000 rpm. if you ever see a fuel map for these cars, around 3750 rpms is the point in the rpm range where the car is most efficiant in the combustion. I don't know about rx8's but on first and second gens the oil injection worked off of throttle position and intake vacum. so on an EFI motor with the ignition cut off the excess fuel is ejected and a very light ammount of oil is put it. on carb motors this doesn't work. you will infact wash the walls away.