Date: Sun, 02 May 2004 21:30:25 -0300
From: Dexter J <lamealameadingdongnospamlamelame.org>
Subject: Re: Fuel consumption figures computer wrong


Salutations: On Sun, 02 May 2004 23:12:21 +0100, Colin Stamp <colinnospamp.plus.com> wrote: > > Anyone still awake and reading by this point will twig that this means > the SID is actually, in a really roundabout way, telling us something > worthwhile(!) - the fuel flow through the injectors is different from > SAABs expected figure. Others have said their readings tally up, so it > looks like SAABs figures are reasonable and there must be a difference > with our particular car. > Who knows, correcting the error may actually improve the fuel > consumption for real ;o) > > Colin. One of the most wonderful things I once loved about my 9000 was the dash computer. I was struck with the true distance variable you note when I actually started really using the dash CPU as outlined in the manual while traveling around the city - 'it, or something under the hood, just had to be wrong' - on several distance and time calculations. However - I then did a series of direct 1,800 kilometer hops to and from central Canada on the TransCanada and was even more deeply surprised about how accurate it suddenly became over relatively straight tankfuls of 4 lane on cruise or off. My take is that it's not a digital problem, it's physical variable that can't be gauged while the machine is measuring driveline speed on the bell housing. It simply can't accurately correct for things like wheel spin, clutch/torque converter slip and the amount of extra wheel travel taken up turning corners - you know - over time. The system, as advanced as it is, reads upstream of true differential output, which changes the distance a car/tire actually travels quite a bit relative to the engine management system - and over surprisingly short distances. It's the same thing that makes everyones three spokes fall out of lock step over time. My old KZ-Z1R Rickman sled reads the true wheel travel extremely accurately given that it is driven from a gear on the front wheel itself. I can accurately flip to the reserve dimple based on the trip clock or time averages as I treated her to a factory calibrated police issue tac/speedo when I cleaned her up. I did the run a few times on it and it came within 1% on the highway as read by the stock SAAB system. Anyway, it has since been my opinion that SAAB trip/dash electronics were driven by SAAB avionics logic - which very accurately corrects for everything but slide-slip - which is/was corrected by advanced GPS. But - as traveling through the air is not the same as rolling wheels down a road - they kinda missed a step by not correcting the data stream using the ABS tickover as a variable. I guess it would have screwed the computer control system completely when the system ABS lights up and never gets properly repaired though. Anyway, I often find myself with about another 20 kilometers in the tank after a tank of city driving - but - when I'm on a long run (like four or five highway tankfuls in a row), the system is pretty accurately tripping the pump light. I've taken to checking inspection stickers for last official date on the actual pumps on the other point. Never put down to malice what can easily be explained by 'service rationalization' as they say.. :/ .. -- J Dexter - webmaster - http://www.dexterdyne.org/ all tunes - no cookies no subscription no weather no ads no news no phone in - RealAudio 8+ Required - all the Time Radio Free Dexterdyne Top Tune o'be-do-da-day Glen Frey - All She Wants to Do Is Dance http://www.dexterdyne.org/888/045.RAM

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