Is it bad for your tranny?

[Don Hatfield]

It seems to me that your thinking is, if the engine is turning higher than idle

rpm, it must be using fuel to do so. Not so. When going uphill, it takes fuel

to make the engine turn higher rpm. When going down hill with the throttle

closed, the car forces the engine to turn higher rpm. It doesn't matter

what rpm the engine is turning, if the throttle is closed, you are burning

minimum fuel. growe3, careful on that Bass Lake Hill. Don Hatfield

[JasonA]

There is a mode of decel fuel cutoff used to protect the cat converter during long decels. The PCM turns the fuel off completely. I don't know where the idea of the PCM cutting off selected injectors or "up to 4 injectors" came from (that is not correct, BTW). If the PCM sees the correct overrun conditions it will turn off all the injectors and the car will be using no fuel at all during the coast.

Bbobynski:

I noticed something like this in a Taurus I was driving one time. After cresting a hill and going back down, with my foot totally off the gas, the car would gain speed for a few seconds, then it almost felt like a slight brake was applied, and the car maintained speed or even slowed down some. Do you think that Taurus was probably doing the same thing -- total fuel cutoff during a coast to save gasoline?

I can say that I haven't noticed quite the same transition from fuel-to-no-fuel during coasting in my Cadillac, but I of course attribute that to the Northstar being a much more sophisticated drivetrain than the Vulcan V-6 is in that Taurus. I would admit that that Ford did a great job of maintaining speeds down hills, and I often have to shift down into 3 in my Seville on longer steeper hills so as not to ride the brakes -- and even then I have to use some brake. The Seville is also a much heavier car than those Tauri are...

[adallak]

I often have to shift down into 3 in my Seville on longer steeper hills so as not to ride the brakes -- and even then I have to use some brake

so do I . I have to switch even to the second gear, and the car still speeds up. Never noticed the comp cutting off the fuel...

[jinxed45]

bbobynski,

Thank you.. you gave me the answer I was looking for with an explanation of why you say what you say. (Not just, "it's not good.. no explanation") I WILL actually try the self diagnostic.. and will post results for various hills. Although it may be UNSAFE for my engine, it's ok, I'm trading it in for a newer ETC within the month.

[Ranger]

The PCM turns the fuel off completely. I don't know where the idea of the PCM cutting off selected injectors or "up to 4 injectors" came from (that is not correct, BTW).

I haven't read the manual recently. I new there was a fuel shut off during decel but thought it was selected injectors. Sorry for the misinformation. Do I get points for being close?

[rmac-etc]

No one will probably see this or care, but I have been interested in the 70 mpg reading max that is displayed on my 95 etc. I had an 89 Lincoln mk7 lsc and it would sometimes show more than double that for inst mpg. I think that the 70 is the number that the software maxes out at.

I have done this at 60mph down a hill and it reads 70 mpg, then done it again at 80 (or more-not going to be more specific- ok? ), and it still reads 70mpg, that smells like a software limit to me and I have done this in gear and 'horror' in neutral also (for the sake of science) and 70 is all it will display.

fyi

[JasonA]

Yes, 70 is as high as the INST MPG will display. I was interested in that, too, one day and decided to play around with it. On I-77 near the Virginia/North Carolina border, there is a LONG hill (probably 5-6 miles) and we were heading southbound this particular day, which is downhill. At the top of the hill, I reset my AVG MPG and headed down the hill. While the INST MPG displayed a maximum of 70 mpg, at the bottom of the hill, my AVG MPG was much higher, at 80 or 90. So the computer does calculate it. It just uses dist traveled/fuel used. That's pretty easy to calculate. I don't know how it calculates INST MPG...maybe it just polls it every second or something? I don't know.

[STS Scott]

I am one to put it in "drive" and leave it there, but I have always questioned downshifting with an automatic to slow down. Is this not hard on the Torque Converter?

A friend of mine has a Geo Metro with an auto trans. (he's not a car guy!), but drives the hell out of it. He had to replace the transmission, because the thing would not go into gear one day. I assume this is because he drove the thing like a stick (always down shifting, and holding the gear he was in). I havn't even thought of downshifting to slow down since, in my STS.

Am I right to assume this, or is downshifting designed to be one of an automatics duties?

[JasonA]

I'd say the automatic went out in your friend's Geo Metro because it was a Geo Metro. Sometimes, parts just fail, and something happened in that transmission that probably was unrelated to the downshifting (had he changed his transmission fluid, or recently had it flushed?). I drive my Cadillac in '3' most of the time. If I get out on the Interstate, I'll put it into 'D'. Manual downshifting, in my opinion, is just asking the transmission to do something it'll do anyway as you slow down. Actually, by keeping my transmission in '3', it never shifts into overdrive. Does that help "save" it by shifting less often? I don't know. Does it "hurt" it by keeping it in 3rd gear? Nah.