This is the one thing I'm still confused: if the O2 sensors see too much oxygen in the exhaust, shouldn't the PCM increase the fuel dispensing towards the stoechiometric ratio? Too much O2 means lean mixture ... too little gas for the amount of air that's sucked in ...

...unless, similarly to what you said about Diesels, the Scangauge is cheating here by estimating the fuel economy through MAF and O2 readings instead of RPMs and fuel trims. I would have thought that the fuel trims tell the scanner how much gas is injected in one cylinder during one cycle ... multiply that by no of cyls and the (RPMs divided by 2 to account for the four cycle engine) ... and volia .. here's the instant fuel consumption. Take car speed into account (to get the travel distance) and you should know your instant mileage. But apparently not so

All in all, it's been great going through this with you guys. You'll hear more from me, I'm not leaving the forum anytime soon.

Cheers,
Dan

 

You think you're confused ! Just when I thought I was becoming an expert , I came across this definition That describes me to a tee.
Definition of expert- A person who continues to learn more and more about less and less until he knows practically everything about almost nothing at all.
When I can get my marbles collected, maybe I will try to digest some of the info you and greasemark presented after which I could offer some more worthless 2 cents.

 

Dan:
Unfortunately, you're thinking like a rational person, and that doesn't quite describe HOW the engineers programmed the darned thing. You would think that fuel trims, and o2 sensors would be the primary inputs, but they're not. The programming relies primarily (but not always, and it changes from car to car) on accelerator pedal position (TPS input), Vehicle Speed, and Caluclated engine load. The Diesel engines rely on APP (acellerator) and calculated engine load.
To give a quick example, I took my old crappy 5 spd. manual, 1.9L 1992 Escort into the mountains one Labor day weekend. It always ran great, and since I had the Next Gen. Star tester in the car, I hooked it up to monitor PIDS while driving (I know, I lead such an interesting life). It used about 1/2 a tank of gas going up into Rocky Mountain National Forest (which goes up to about 14,500 feet). However, on the downside, the injectors were shut off the entire time. It didn't use a drop, as the engine became a big air pump that was shut off, and i was using compression to slow the car down.
I used to love that car. But, then I got old and lazy and started working on Auto trannies, and I got tired of shifting between 2nd and 3rd gear on the backed up highways out here, so the next car was an automatic trans.
The new hybrid powertrains are really quite amazing also. The new Fusions (which are really bulletproof little cars) show a vine with leaves that sprout up when you drive it more effiecently. In town, I have no problem getting 35 m.p.g. It all depends on how you drive them (and also on the type of gas, what kind of shape the drivetrain is in, and a million other things). I guess I'm trying to say "it depends on the nut behind the wheel."
mark

 

One other thing:
Hanky, I've NEVER stopped learning about new things. That's one of the spices of life that keep you going.
However, I just sometimes wish I didn't HAVE to know so much just to fix todays cars!
When I stop learning new things, it's time for me to swallow a gun!

mark

 

I hear you, Mark ... but you know what? There's life beyond learning new things. This is when you start digesting what you've learned, sorting stuff out, understanding the meaning of life. We worry about fixing cars. A rocket scientist may be looking down on guys like you and me ... what a waste of time and energy to fix something that can be easily replaced ... why bother? Lease the next one, right? WRONG! Having to know so much makes people like you and hanky stand out from the crowd. You don't have to regret having to learn. Appreciate the chance you've been given.

I'm an electrical engineer, but my profession doesn't give me half of the joy I get from fixing my car or doing woodwork around the house. I'm more proud of my car than of the high tech gimmicks I come up with on a daily basis at work. Learning isn't everything - making use of your gifts for the good of the guy next to you IS.

Dan

 

Interesting that you mentioned this ... my Cougar does something similar: if I drive over about 50 mph and the speed stays or increases without me touching the gas (as in coasting), the injectors are SHOWN as cut off (zero liters / 100 km), and the PCM puts the transmission in neutral so the car runs freely, you can feel it going faster and faster ... I wish it were engine-braking but it isn't ... However, the zero fuel consumption is fake because the engine is still idling. So yes, you're absolutely right: what the Ford designers came up with is amazing, and many times beyond our normal logic.

BTW: can you tell the PCM to cut off the fuel completely (engine-brake) by issuing a command on the OBD bus? I know it's easier to just cut the injectors' power but that's not as fun as talking the car into doing it

 

BTW: can you tell the PCM to cut off the fuel completely (engine-brake) by issuing a command on the OBD bus? I know it's easier to just cut the injectors' power but that's not as fun as talking the car into doing it [/quote]

Dan:
Actually, that idea would be really wonderful, and a great idea, but it would murder the transmission. The only way I could think of (and I'm not blessed to have the 150 plus IQ needed to be an engineer), would be to lock up the torque converter on decel. This is the weak spot of this powertrain, and the engine is idling to keep it running, which takes gas, as you mentioned. I don't think the Torque convertor clutch could take it for long. The trans itself wouldn't be my first choice for this either, as these had a really long, long history of direct clutch faiiures, and in my normal work, I've found that never tempting fate with this transmission is a good thing. I would bet with what little knowledge I do possess about auto transmissions, that you could design an automatic to do exactly this, but I don't think it would pay the designers/engineers or the automaker to do it.
I kinda thought you were really smart from the way you talked, but I never dreamed you'd be an electrical engineer. I liked the nuts and bolts end of it more. As I told people, I have a double major in Business and Economics, with a minor in music, but it's the 2 years of Physics I use every single day at work. But to be fair, I made a little money with the music minor. Certainly more then at the econ and business.
So, does this mean I should address you as "Lord Dan, Master of the atom?".
Just wondering...

mark

 

So did I, Mark, so did I .. but I was born and raised in a (now former ...) communist country in Europe, and options were quite limited back then. I've always loved mechanisms and engines a lot more than the electrons and the wires they run through, however mechanical engineering involved an enormous amount of technical drawing (done with rulers and black-ink Rotrings on paper, back in the late 80s when I went to university), which I hated ... so here I am, enjoying my spare-time passions for cars and woodwork more than my daily engineering job. I'm no lord, by any means, but a mortal like anybody else, who tries, as best as he can, to help his fellows ...

Dan

 

Actually, it is interesting that some people do look down on us 'greasemonkyes', but I really don't pay attention to that. In fact, at one of my college reunions, I took a lot of heat for that, but I didn't care. I'm still a tech with a stable job, which is something that not many of the people I went to school with could say they had, or ever had had.
As I mentioned, it really was the physics I took that has save my hide many, many times. As I tell aspiring new techs, "take all the electrical and electronics you can. You'll make money at it." And that's more true now then ever before, as a processor sits and monitors everything.
I started out doing driveability. I loved electronics, and had many credit hours in it. I'm amazed that so many new techs think they don't need to do this. I'm one of the very few that actually doesn't mind working on electronic steering and suspension (air ride). Then I got into diesels when the Powerstroke first came out in '94. They really had a gas driveabilty type fuel injection that used high pressure oil to control the fuel injection, that was very similar to gasoline fuel injection. Then came electronic automatic transmissions, and electronic anything on the interior, and so, and so on.
I know I sound like a tired old mechanic, and there's some truth to it. But I aged about 20 years in 5 seconds when one of my apprentices years ago opened the hood on a '65 Mustang and said "points and a carburater, I've read about these!"
There are many times when I wish I had my '67 Galaxie converitble to drive around it. It ran so well, and got relatively good gas milage with the 289 engine it had. And it had lots of room, which was nice, becuase I have a big ***!
A

 

And, I was only kidding. I try to help everyone I can. You never can tell when the person you help will repay the favor. I think its really wonderful that you kept another great old classic on the road. It sure beats always buying a new car. I just keep mine running forever, even if they look not-so-new. They don't look good, but they would pass a state inspection at any time.
I would never denegrate anyone by calling them "master of the atom". It was only a joke. Please take it as such!

mark