93CutlassSupreme Posted September 26, 2005 Report Share Posted September 26, 2005 how accurate is the average fuel economy function on the Cutlass Supreme DIS? the best I can get on mine is 21 mpg city driving, not exceeding 2200 rpms. That seems pretty bad to me. Quote Link to comment Share on other sites More sharing options...
pwmin Posted September 26, 2005 Report Share Posted September 26, 2005 they arent very accurate from what i've heard. fill your tank, write down the current mileage, then when you fill it back up, write down the mileage then and how many gallons it took to fill and that will tell you how many miles/gallon you went. then compare that to your dis by resetting the mileage and fuel used and mpg (i'm not meaning to come across rude or that youre stupid by saying that you dont know how to do that, just explaining it if youve never done it before). Quote Link to comment Share on other sites More sharing options...
sl3196 Posted September 26, 2005 Report Share Posted September 26, 2005 Just do it with the trip meter/odometer and see what your really getting. My DIC is a few mpg high compared to what I really get. Quote Link to comment Share on other sites More sharing options...
93CutlassSupreme Posted September 26, 2005 Author Report Share Posted September 26, 2005 they arent very accurate from what i've heard. fill your tank, write down the current mileage, then when you fill it back up, write down the mileage then and how many gallons it took to fill and that will tell you how many miles/gallon you went. then compare that to your dis by resetting the mileage and fuel used and mpg. i know how to figure mpg, i was just wondering if these units are known to be off Quote Link to comment Share on other sites More sharing options...
sl3196 Posted September 26, 2005 Report Share Posted September 26, 2005 Yes. Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted September 26, 2005 Report Share Posted September 26, 2005 Well, mine is not, at least not by much. The instant MPG readout is a bit optimistic to me, but if I reset the average function when I fill up the tank, my calculated MPG number is almost identical to what the DIS is telling me. Usually around 1-1.5 MPG off. Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted September 26, 2005 Report Share Posted September 26, 2005 I don't remember on the 89, but on the 94 whose injector flow constant I programmed myself, the AVG MPG is accurate to within 1%. Quote Link to comment Share on other sites More sharing options...
Psych0matt Posted September 26, 2005 Report Share Posted September 26, 2005 I don't remember on the 89, but on the 94 whose injector flow constant I programmed myself, the AVG MPG is accurate to within 1%. speaking of which, that was one of the things in my inbox that got removed that I was gonna talk to you about PM sent Quote Link to comment Share on other sites More sharing options...
john99gtp Posted September 27, 2005 Report Share Posted September 27, 2005 both of mine are high. ive been keeping a running track of the GTP, and its constantly 1-1.5mpg higher then actual Quote Link to comment Share on other sites More sharing options...
Justin Posted September 27, 2005 Report Share Posted September 27, 2005 A friend of mine drove his '90 CS back to ND from OH, kept track of his mileage on the DIC and on paper, and it was pretty close, maybe 1 MPG off. I hope mine is that close, I've been hitting 31-32 hwy lately. Quote Link to comment Share on other sites More sharing options...
pwmin Posted September 27, 2005 Report Share Posted September 27, 2005 (i'm not meaning to come across rude or that youre stupid by saying that you dont know how to do that, just explaining it if youve never done it before). Quote Link to comment Share on other sites More sharing options...
99RegalGS Posted September 27, 2005 Report Share Posted September 27, 2005 The one that is in the Cutlass is WAY high (8mpg high). Shaun, don't ever use that for gas milage. lol Quote Link to comment Share on other sites More sharing options...
bartonmd Posted September 27, 2005 Report Share Posted September 27, 2005 They will get you in the ballpark most of the time, but there are several things that effect the readout #... I believe it calculates mileage from knowing what the injectors are supposed to flow and what the fuel pressure is supposed to be, and calculating it from that... so the things that can throw is off are: 1. fuel pressure 2. injector size 3. injector cleanliness With #3, that's where people get the idea that fuel injector cleaning REALLY helps out their gas mileage... They see their mileage go up 5mpg or so after the cleaning and think it worked... Fact of the matter is, as long as you are in closed loop control, you're mileage is the same, but the injectors flow more freely and therefore, don't have to be open as long (pulse width) to flow the same amount of fuel... This makes the computer think it's flowing less fuel when it's actually not. Mike Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted September 27, 2005 Report Share Posted September 27, 2005 The 88-93 systems calculate mileage using 3 inputs: 1. Injector flow rate constant. 2. Injector pulse width (well not the actual pulse width, but a rapidly increasing number that increments proportionately with the pulse width). 3. Speed. So yes, fuel pressure, injector size, and cleanliness will affect the actual flow rate and therefore affect the MPG readout. 94-96 don't get an injector flow rate constant from the ECM, so either that value is hard-coded into the trip computer (making each engine-specific) or they calculate it a different way. To get the DIS working in my 94 Cutlass w/3.4 DOHC, I had to reprogram the MEMCAL to transmit the injector flow rate constant. Quote Link to comment Share on other sites More sharing options...
frusciante fan Posted September 27, 2005 Report Share Posted September 27, 2005 like somebody else said in another topic. DIS=$ 3rd grade math = free Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted September 27, 2005 Report Share Posted September 27, 2005 like somebody else said in another topic. DIS=$ 3rd grade math = free That's what guys with base models always say. Quote Link to comment Share on other sites More sharing options...
GP1138 Posted September 27, 2005 Report Share Posted September 27, 2005 like somebody else said in another topic. DIS=$ 3rd grade math = free That's what guys with base models always say. My DIC was free... Quote Link to comment Share on other sites More sharing options...
john99gtp Posted September 27, 2005 Report Share Posted September 27, 2005 :withstupid: Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 27, 2005 Report Share Posted September 27, 2005 My fuel gauge will start flashing when i'm two bars from the bottom. I think the DIC gives you 32 Miles left before it starts going crazy. Quote Link to comment Share on other sites More sharing options...
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