Gas economy

Just as an aside.

I recently made a round trip, virtually all highway at continuous 65 to 75 mph, of abot 1300 miles.

According to my EDU on return the average milage was 32.3.

The car: '92 900S. The milage 165000 plus

I am very pleased.

Any comment?

Malcolm

Just as an aside.

I recently made a round trip, virtually all highway at continuous 65 to 75 mph, of abot 1300 miles.

According to my EDU on return the average milage was 32.3.

The car: '92 900S. The milage 165000 plus

I am very pleased.

Any comment?

Malcolm

Reply to
Malcolm William Mason
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Reply to
Smoky

I thought it was comparing miles driven and gas consumed aka mpg ?

Bob

Reply to
'nuther Bob

I defer to your knowledge over my speculation (i.e. my previous post elsewhere in this thread). I just assumed that the EDU is a dumb display driver, but you say it has signal acquisition and computational abilities, is that right?

This description implies to me that there is another method of determining fuel used - maybe the fuel tank sender, to compensate for diffeences in fuel injector characteristics. Is that what you are saying or am I just reading more into this than I should?

AndyH '94 9000 CDE

Reply to
Andy Hookins

The EDU that I am familliar with is the one used on the 9000. That EDU had a wire directly wired to one of the injectors (for the injector open time) and one wire to the speedometer (for the speed signal). All numbers shown on the EDU was calculated inside the EDU itself.

The injector characteristics must be known. How else is the engine management computer supposed to determine the correct time to keep the injector open?

The fuel pressure over the injectors is determined by the fuel pressure regulator. It should be constant and fixed. Knowing the characteristics of the injectors and the time they are open allows the EDU to calculate the fuel consumption. The engine management computer can not read the fuel pressure, so if it is wrong then both the amount of fuel injected, and the values shown on the EDU, will be wrong.

I can't answer that as I don't know what you are reading that shouldn't be read.

Reply to
Goran Larsson

Nice economy, just to back up the EDU you can use gallons added/miles taken down on paper.

Have a great one!

Bush

Reply to
Bush

Reply to
ma_twain

That's amazing to me.... My 92 900 is in tip-top shape, with 94k, and it gets about 19mpg combined city/highway- mostly city....

I always thought that was reasonable, considering you really have to step on it to get going, and its only a 3 speed auto, meaning high revs anywhere above 55mph...

Reply to
Chris O'Malley

I have a 2000 9-5 wagon and the displayed MPG is always within +- 1 MPG of the calulated value.

Reply to
Barry Test

Us is drivin a 92 9000 5 spd @ 100K miles, summer city milage 24-25 mpg highway 32 ish. Winter city drivin 20 mpg.

Reply to
Bowser

Why is there a difference between summer and winter?

Reply to
Chris O'Malley

I have "checked" the EDU values by using the trip odometer and gallons fromFull to Full. The values I get are comparable. The gallons ar4e checked reularly by the jurisdiction's (state or province) Weights and measures departments and mileages on major highways in the U.S. and Canada are posted in 0.1 mile or 100 metre increments by the Departments of Highways and are very accurate.

True, the fuel injectors wear with time but this is compensated for by the fuel management system. The data are empiric and "jibe" with the EDU. My best guess is that it is quite accurate.

Malcolm

Reply to
Malcolm William Mason

I have "checked" the EDU values by using the trip odometer and gallons fromFull to Full. The values I get are comparable. The gallons ar4e checked reularly by the jurisdiction's (state or province) Weights and measures departments and mileages on major highways in the U.S. and Canada are posted in 0.1 mile or 100 metre increments by the Departments of Highways and are very accurate.

True, the fuel injectors wear with time but this is compensated for by the fuel management system. The data are empiric and "jibe" with the EDU. My best guess is that it is quite accurate.

Malcolm

Reply to
Malcolm William Mason

I have "checked" the EDU values by using the trip odometer and gallons fromFull to Full. The values I get are comparable. The gallons ar4e checked reularly by the jurisdiction's (state or province) Weights and measures departments and mileages on major highways in the U.S. and Canada are posted in 0.1 mile or 100 metre increments by the Departments of Highways and are very accurate.

True, the fuel injectors wear with time but this is compensated for by the fuel management system. The data are empiric and "jibe" with the EDU. My best guess is that it is quite accurate.

Malcolm

Reply to
Malcolm William Mason

Cool, I didn't know that.

Agreed, the nominal characteristics must be known, but doesn't the ECU compensate for deviations from nominal using feedback from other sensors, not least the Lambda sensor ?

I thought the FPR regulates fuel pressure wrt manifold pressure such that the fuel rail pressure is 2.8 bar above boost/vaccum.

Agreed.

No, but it measures air mass and/or manifold pressure and extrapolates from that.

Comes back to closed loop correction. It's clear to me that the closed loop system compensates for injector variations as far as getting the air/fuel mixture right, but not how the absolute volume of fuel used is determined. Is it 'simply' that all the different corrections that might need to be made for correct air/fuel ratio metering tend to factor in such a way that they cancel each other out when it comes to injector opening time? I wouldn't have thought that to be the case.

What I wondered is this; is the fuel injector time part of the fuel consumption calculation moderated by some other longer term factor, say the reading from the fuel sender.

Come to think of it, IIRC when I refuel the car after a few long trips (i.e. better MPG), the range displayed by the EDU seems to be higher than when the car is refuelled after use around town with lots of short stop/start trips (i.e. worse MPG). I'll keep a better watch on this - perhaps I've answered my own question if this is indeed a correct observation.

AndyH '94 9000 CDE

Reply to
Andy Hookins

That's only part of it, warm up only accounts for a few minutes of my 45-60 minute commute. There's got to be more to it. BTW the owner manual has a nice graph depicting relative engine efficiancy against engine deperature.

Oh yeah :-) the Trionic-5 system works to a fixed boost pressure - although intake temperature is measured it is only used for fuel metering purposes. Cooler - denser air at the same pressure > greater air mass > more fuel to get the right mixture > more power :-)

Later T-7, I suppose T-8 on the 9-3 sport sedan too, aim to deliver a fixed engine torque, so boost pressure is slightly lower in cold weather :-(. I don't know if the 'hot-wire' AMM used in the APC system behaves like the older T-5 or the newer T-7/8.

AndyH '94 9000 CDE

Reply to
Andy Hookins

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