Car in a coma

[Breakdown]

I think there's a rev limiter for when the car is in park, at least my car (93 cutty) cuts out at like 2000 or somewhere around there.

 

Mine goes to at least 3,500, I'm sure I can get it up to 5,000, but it's not something that I want to do just for the hell of it, I just don't think that there's a cutoff for me.

[carkhz316]

Wow, holy flame war dude. Guess I haven't watched 'em too close on decel then. It's been awhile for me to do any real scan tool monitoring lately. Too busy painting cars at school instead of working on 'em

[AL]

You would think that if the engine stopped getting fuel, it would shut off... I did NOT click the links... I know about the RPMs dropping while going downhill or rapid deceleration but I have always been taught that the injectors dont STOP giving fuel but they are cut to an extreme minimum... Just enough to keep the car running. Both of my GP's (not the 03) have a rev limiter of 3k while in park or neutral.

[Addicted To Boost]

Thank you, Jamie.

[Night Fury]

The idea is that the wheels turn the motor when in gear, therefore completely eliminating the need for gas. It's just flawless and unnoticeable though because the engine is already turning when gas is added back into the cylinder!

[carkhz316]

Make sure to gloat in spite of my lapse of attention, because apparently we were thinking of two different situations.

[CSI_MuNkY]

Oh... mine hits the limiter in N and P at 4000

 

 

My Jeep is auto and it engine brakes in D

Engine braking doesn't occur in regular automatics because they are all fluid powered. In order to get the engine braking effect you need a fully mechanical transmission. In the case of my Jeep, its a CVT2L transmission, fully automatic and fully mechanical. I don't know the exact fluid dynamics of a hydromatic transmission to explain how it happens, it was just something I read when I was researching the CVT2L.

 

Jamie

[carkhz316]

Well, I think on the 'ol GM TH350 and 400, there may be engine braking in 3rd. I have a 350 apart right now outta a Camaro, I'll have to look at it closer.

[oldscsc]

I'm not going to argue either way, just trying to understand for myself. Fuel injectors shut down? How does that matter? If I'm in D at 1500 RPM going down a hill and I put it in N and the engine drops to 900 RPM...explain to me how I'm using less gas in D

[Addicted To Boost]

I'm not going to argue either way, just trying to understand for myself. Fuel injectors shut down? How does that matter? If I'm in D at 1500 RPM going down a hill and I put it in N and the engine drops to 900 RPM...explain to me how I'm using less gas in D

When you put the car in neutral, the car is basically idling. To idle, the fuel injectors have to inject fuel into the engine to keep it running.

 

When you are coasting down in D, the engine doesn't need fuel to stay running, it stays running on the momentum it already has, the wheels driving the transmission, which is in turn keeping the engine going. That is why during this time, the fuel injectors are shut off, until the ECM deems it necessary to start adding fuel again.

 

I hope that makes sense.

[oldscsc]

I'm not going to argue either way, just trying to understand for myself. Fuel injectors shut down? How does that matter? If I'm in D at 1500 RPM going down a hill and I put it in N and the engine drops to 900 RPM...explain to me how I'm using less gas in D

When you put the car in neutral, the car is basically idling. To idle, the fuel injectors have to inject fuel into the engine to keep it running.

 

When you are coasting down in D, the engine doesn't need fuel to stay running, it stays running on the momentum it already has, the wheels driving the transmission, which is in turn keeping the engine going. That is why during this time, the fuel injectors are shut off, until the ECM deems it necessary to start adding fuel again.

 

I hope that makes sense.

 

That cleared it up, thanks Nick. It was just confusing to me that the engine uses less fuel at 1500 RPM (in rapid whatever) than it does at 900 RPM.

[Addicted To Boost]

No problem, glad to help!

[w-bodys_are_the_best]

As for the braking thing... some of you gotta drive a car in a Canadian winter. Dropping the car into neutral and then applying the brake will in fact help the car slow sooner. Don't believe me? Come on up and give it a shot, we should have some ice to play on in the next couple months. I do this all the time, and it is actually taught in some driving schools up here.

 

Jamie,

 

100% agree with you,

 

I do this in the winter before letting the ABS get working, that's just me though.

 

I do this too, it especially helps with a RWD vehicle. It's made the difference of stopping before the instersection or sliding through it many times. I drove my stepdad's 88 Mercury Grand Marquis throughout most of HS, even with good tires, you had to throw that beast into N to stop, it was downright scary. I'd hate to drive antoher one in the winter, they're fun for sliding around and messing around in the winter, but they have no traction even with good snow tires, I don't know if it had to do with the weight distribution or the soft suspension in them, but every LTD/Grand Marquis of that generation I've been in are like that.

[Euro]

mmk....back to the topic?

[Breakdown]

mmk....back to the topic?

 

I don't think that it's too much of a hijack as long as we're discussing something relevant to the discussion. To me the discussion in terms of what is wrong with the car is pretty much over, until he gets his update from the mechanic and then it begins anew. Anything we say is purely speculation.

 

Just my two cents.

 

I also don't think that it's a bad idea to discuss the merits of jamming the car into neutral, positive and negative, since that's what the original other felt was a catalyst in causing these issues; as long as those discussing it can remain CIVIL aboot things, tossing insults around and mocking people isn't respectful - it's just ignorant.

 

If the original poster had said that he was street racing and tried to start from a 4,000 RPM from standing in Neutral I would have much less compassion for them. Stupid is stupid, in the end it wasn't that the guy put the car into neutral when descending the hill that may have hurt the car, it was the fact that he made a mental error - we all do these, and didn't remember to throw the car back into Drive prior to hitting the gas / didn't let the RPM's fall before shifting again.

[93cutty]

I shut my car off in neutral down hills to save gas...oh then I have to stop at the bottom and restart my car.

[CSI_MuNkY]

I shut my car off in neutral down hills to save gas...oh then I have to stop at the bottom and restart my car.

 

Your kidding, right?

 

Jamie

 

 

[1990lumina]

As for the braking thing... some of you gotta drive a car in a Canadian winter. Dropping the car into neutral and then applying the brake will in fact help the car slow sooner. Don't believe me? Come on up and give it a shot' date=' we should have some ice to play on in the next couple months. I do this all the time, and it is actually taught in some driving schools up here.

[/quote']

 

Jamie,

 

100% agree with you,

 

I do this in the winter before letting the ABS get working, that's just me though.

 

I do this too, it especially helps with a RWD vehicle. It's made the difference of stopping before the instersection or sliding through it many times. I drove my stepdad's 88 Mercury Grand Marquis throughout most of HS, even with good tires, you had to throw that beast into N to stop, it was downright scary. I'd hate to drive antoher one in the winter, they're fun for sliding around and messing around in the winter, but they have no traction even with good snow tires, I don't know if it had to do with the weight distribution or the soft suspension in them, but every LTD/Grand Marquis of that generation I've been in are like that.

 

I normally slam the shifter down to first gear if I need to stop faster on ice. I was taught the neutral thing is driving school to but in personal experiences it isn't as effective as hitting first gear. Yes I know it's hard on the transmission, but if it can't take a little abuse then I don't want it - so far it's held up fine.

[Night Fury]

GREAT point!^^

[GOT2B GM]

at this thread

 

+1 for Jamie and Nick

[Addicted to eaton]

GTP in p- 3500

 

SE in park 4000

 

Monte carlo in P 4000 lol

[Breakdown]

GTP in p- 3500

 

SE in park 4000

 

Monte carlo in P 4000 lol

 

WTF??

 

Did you actually find the keys for the '95??

 

If you did . . . . congrats??

[PCGUY112887]

FYI for those who care... in a Grand Prix at least, this whole Fuel Cutoff On Decel thing will only happen when you are well over 55mph and will never happen below 55mph. Example, I run up fast to 100mph then let off and coast down, as soon as I let off it cuts off all fuel (wideband in dash showing no fuel) and it does not add fuel back in unless you hit the brakes, tap the gas, or fall below 55mph.

 

It scared me at first since it is very noticeable in my car, you can feel it happen and hear it in the exhaust and see it in the dash.

[Addicted to eaton]

GTP in p- 3500

 

SE in park 4000

 

Monte carlo in P 4000 lol

 

WTF??

 

Did you actually find the keys for the '95??

 

If you did . . . . congrats??

 

LOL when i sold the cutty.

[Breakdown]

My theories (based on logic, not car knowledge) this is where I'll have to be corrected (not proven wrong) many of these things I haven't actually done.

 

I live on a hill, my house is near the top, and then there's a gentle free-fall from there, you're probably 50-100 feet lower at the bottom of the street.

 

So if I have the car at the top of the street and the car is for all intents and purposes off, keys are in but engine is not started.

 

I ghost-ride the car down the hill in drive, then I ghost ride the car down the hill in neutral. The car goes faster in neutral - correct?? (I'm asking, but also assuming).

 

I would assume that this would happen because if I did take the car down the hill in drive that the serpentine belt would be rotating, along with the alternator all of the way down the street. The simple equivalent would be a bicycle that is not be pedaled and one of those light generator things that absolutely no one in their right mind would use when we have batteries available for headlights on bicycles.

 

By the same context, if I had a longer hill to free-fall with and a dead battery, at the bottom of the hill I might just have a chance in hell that at the bottom of the hill my battery just might have enough juice to turn over the engine.

 

So taking this common knowledge into have the car go down the hill. Logically a car's engine has two priorities. 1.) Maintain idle / running and 2.) Respond to user's demand for acceleration. While at the same time minimizing resources (fuel) in accomplishing those goals.

 

If you have the car in neutral, the car is responsible for maintaining idle, and running an alternator.

 

If you have the car in drive without accelerating, the car is responsbile for maintaining idle and pushing forward, either against an invisible wall (you have the brakes on) or rolling forward because you are not on an upslope, nor do you have the brakes on.

 

So, if you have your foot off of the gas and are going down a big hill in neutral, all of the responsibilities above for being in neutral are in play.

 

If you have the car in drive and have your foot off of the gas while going down the big hill. Your engine is engaged to your wheels, therefore it should take less fuel to maintain an idle (not none because if you had to brake abruptly, you'd stall the car), but the drive wheels should be rotating the engine themselves at a faster rate than idle to start with - obviously the car isn't stupid and doesn't let the speed of the drive wheels get the motor running at 8,000RPM. And therefore would use less fuel.

 

However!!

 

If you were stop and go down a massive hill using the priorities outlined above, I believe that you would save money by disengaging the drive and having the car in neutral.

 

BTW - Has anyone taken a lego motor and connected it to a lego motor with no batteries in between. If you rotate the blades or wheels on the one motor, the other one follows suit. . . . . no I do not feel like a genius for discovering this, but some of these dynamics apply to cars and how they run.

 

Thoughts? Counter-theories? Death-threats???