How to drive a protege, Stick.

[SocialStealth]

This is possible but it would be hell on your transmission to not rev-match at all, which is what would be required. As soon as you touch the throttle the car goes back in closed loop control and tries to maintain the 14.7:1 air:fuel ratio. In my opinion, you're better off just leaving it in the gear you were last, winding it all the way down to almost stall and then push the clutch in. To me, that makes for the best compromise between a smooth and quick stop. The only time I downshift is when I'm driving in slippery conditions or I know I'll be accelerating soon.


Man, I'll tell you - it's very different from the Protege. Long gears, long throws and the clutch pretty much has to be all the way out to be engaged. When I still had the P5 it always felt like I was driving a big rig after switching back to the truck. It's nice because it actually have a pretty tall, and therefore useful first gear.

Someone said the engine only reduces the fuel until 1500 rpms?

 

[magnumP5]

Someone said the engine only reduces the fuel until 1500 rpms?

That was me. My old P5 was turbocharged so I had a wideband oxygen sensor and gauge installed. When I let off the throttle completely above 1500 RPM or so the gauge would read "---", which corresponded to air:fuel ratios above 18:1. While cruising around the stock computer tries to maintain the stoichiometric ratio for gasoline of 14.7:1. Obviously less fuel = better fuel economy. This is why it is much better to coast in gear going down a hill than in neutral.

It's tricky to explain how this works because even though the throttle plate is shut, air still enters the intake manifold and fuel is still added (this is how the engine stays alive). The throttle adjustment screw (TAS) controls how much air bypasses the throttle plate and works in conjunction with idle air controller (IAC) to maintain the idle.

 

[thecrash91]

^you make my head hurt with all that knowledge

 

[SocialStealth]

That was me. My old P5 was turbocharged so I had a wideband oxygen sensor and gauge installed. When I let off the throttle completely above 1500 RPM or so the gauge would read "---", which corresponded to air:fuel ratios above 18:1. While cruising around the stock computer tries to maintain the stoichiometric ratio for gasoline of 14.7:1. Obviously less fuel = better fuel economy. This is why it is much better to coast in gear going down a hill than in neutral.

It's tricky to explain how this works because even though the throttle plate is shut, air still enters the intake manifold and fuel is still added (this is how the engine stays alive). The throttle adjustment screw (TAS) controls how much air bypasses the throttle plate and works in conjunction with idle air controller (IAC) to maintain the idle.

...so am I saving gas when I keep it in gear until 20 mph//1000 rpms? Or is it pointless to leave the car in gear under 1500 rpms?

And thank you for all the knowledge. Your spitting it out like day old gum and at this rate, I think I'm starting a used gum collection.

 

[magnumP5]

...so am I saving gas when I keep it in gear until 20 mph//1000 rpms? Or is it pointless to leave the car in gear under 1500 rpms?

And thank you for all the knowledge. Your spitting it out like day old gum and at this rate, I think I'm starting a used gum collection.

Honestly, at that point the savings are probably pretty small. You should be able to feel the ECU kick in the idle control somewhere around 1000-1500 RPM. On my P5 it was a little harder to feel (with all the modifications) but my truck does the same thing around 1200 RPM. It literally feels like the car will drive itself and keep from stalling but I don't think there's enough power to keep it going for too long without some input. With my P5 I always let the RPM drop to around 1000 RPM because that's where the control kicked back in. It will be different for yours because I imagine it's probably stock. Also, any load on the engine (A/C, turning, etc.) the control will kick back in sooner and "harder" (ie, more noticeable). Below this point it isn't really that you're not saving gas or not but you're no better off than you would be in neutral, if that makes any sense.

As for knowing all this I owned my P5 for 4 years and I've been a member here for nearly four years as well. Lots of reading and searching and I still don't know as much as some members (though we are a little harder to find these days). I'm still kind of sad I sold the P5, but I should have fund with the RX-7.

 

[SocialStealth]

Ha if you ever get bored with it, I'll trade you a p5 for an rx-7 any time

But yet another question I've stumbled upon while driving is...


Is it more economic to maintain a steady speed? (staying at 40 mph // 5th gear@ 2000 rpms)

Or to accelerate and take your foot completely off the gas repetitively ?
(45mph // 5th gear@2500 rpms, take foot off gas until 40 mph // 5th gear@ 2000 rpms, repeat)

I'm going to make up some numbers to further explain this...
Lets say with your foot keeping a steady 40 mph, the engine requires a 10/1 fuel/air ratio.
Now lets say slowly accelerating from 40 mph to 45 mph requires a 9/1 ratio.
Taking your foot completely off the gas lets the engine take an 18/1 ratio.

Therefore, using the completely made up numbers mentioned above, the short moment of coasting with an 18/1 ratio obtained from accelerating @ a 9/1 ratio saves more gas than if you maintained a 10/1 ratio.

Once again, all the numbers mentioned above are completely fictional. Does anyone have any ideas on the real numbers? I'm very curious to find this answer!

 

[magnumP5]

^^^ No, it's definitely better to cruise at a constant speed. When driving around normally, the ECU is in what is called closed-loop control. The air/fuel ratio is maintained by preset values stores in the ECU, which are then modified based on information from the mass air sensor (MAS) and primary oxygen sensor. At wide-open throttle (WOT) and high RPM driving (above 5500 RPM or so) the ECU switches into open-loop control in which the air/fuel ratio is controlled completely by preset values (no input from sensors). This latter control state is where Mazda's characteristic rich tune comes into play.

Anyhow, getting back to your question about maintaining speed vs accelerating/decelerating. All engines have set efficiencies and it's almost never the lowest RPM. I've always said miles per gallon (mpg) is not a good indicator of an engine's efficiency and that rather a specific fuel consumption (volume per time per power). You'll see that a given power output there is a given "sweet spot" engine speed for efficiency. I've always said 2500 RPM is a good speed to cruise at for these cars.

 

[SocialStealth]

ok, so 2500rpms is more efficient than 2000rpms.

So when going down a slight hill with the intentions of continuing your drive and not stopping, is it better to coast in gear down the hill (even if it means slowing down slightly) or to just maintain the RPMs? (which would mean increasing speed slightly)

 

[magnumP5]

I personally think 2500 RPM is best but that is me; you'll find a lot of differing opinions here. As for your last question you're really nitpicking here. I have to ask, why are you so concerned with fuel economy that you're debating between the difference between 2000 and 2500 RPM? I drive in a manner that my speed remains constant to what I desire. If the hill is steep and I start to speed up, I let off the gas, if it's shallow and reduce throttle input. Honestly, out of all the questions you are asking you will not notice a difference in fuel economy either way, and a lot of the actions you mention really seem like inconveniences to me. You should drive the car in a manner that feels best to you. When I had my P5 I kept the engine speeds at or above 2500 RPM at all times while moving, unless I was slowing down coming to a stop. I still easily managed over 25 mi/gal city and well over 30 mi/gal highway, which exceeds the EPA estimation for the car. Now when I first got the P5 and was getting used to the manual transmission those numbers were more like 19 and 24 mi/gal. It takes time, but you get used to the car.

 

[SocialStealth]

At the beginning of this thread I was averaging 25-28 mpg.
After having these questions answered and 'nit picking' my driving habits, I've managed to triumph with 33 mpg today. But I still think I can do better.
(driving has been constant through the same daily commute)
They might sound like inconveniences but its is rather easy to manipulate the rpms to a certain degree.

As for another question...

Is it more economic to use cruise control to maintain your speed or is a steady foot the best method? I'm afraid cruise control might run a little rich just to make a smoother ride, but I honestly have no idea.

Sorry for all the stupid questions, but they really do help

 

[magnumP5]

Unless you are in open loop or off throttle above ~1500 RPM the ECU is in closed loop and will try to maintain a 14.7:1 air:fuel ratio regardless of engine speed (as long as it's below ~5500 RPM). It's only when you mash on the gas or go above 5500 RPM that the ECU goes into open loop control and starts running rich.

So to answer your question, cruise control has no impact on the air:fuel ratios. Unless you are really skilled it is unlikely a "steady foot" would net better fuel economy. I got pretty good at that because I had removed the CC altogether and I still managed 30+ mpg on the highway.

What I think you're getting yourself into here is called hyper-miling and I believe they have their own forum (they call themselves Gas Savers or something like that). I don't believe in 90% of the crap they do/claim but whatever floats your boat.

 

[SocialStealth]

This is totally off topic, but my j-pipe heat shield is missing. Is it important enough to replace? both the upper and lower part are missing. Its not gonna hurt anything to just leave it like that, is it?

 

[SocialStealth]

And do you happen to know where I can get some ZFR5F11 spark plugs from?

And this is going to sound stupid but uhhh how many spark plugs are in my car?

 

[Rockin03mp5]

to answer both of your q's....

the heat shields missing will not hurt anything. added weight savings

and you can find the plugs at any auto parts store. (advanced auto, napa, autozone ect.)

they come in a pack of 4, and that is all you need. 1 plug for each of your 4 cylinders.