adallak Posted June 13, 2005 Report Share Posted June 13, 2005 Here is some interesting fuel used data. According to the receipts I have collected I have bought 123 gallons of fuel in six months (for average $2.21 per gallon). The computer shows 112 gallons plus 4 gallons in the tank. What happened to 7 gallons of fuel? A bad gas tank cap, leaking injectors? The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Ranger Posted June 13, 2005 Report Share Posted June 13, 2005 With the way fuel prices jump around, maybe the 7 gallons can be accounted for by calculating actual price instead of average. It might add up over 6 months. Just a thought. Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 With the way fuel prices jump around, maybe the 7 gallons can be accounted for by calculating actual price instead of average. It might add up over 6 months. Just a thought. Ranger, There are actual gallons pumped on the receipts. I used that data and the average price was calculated later. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
mike5514 Posted June 13, 2005 Report Share Posted June 13, 2005 I have noticed the same thing, the pump shows more fuel than the dic does 98% of the time, it could be incorrect tire size, dic, pumps or me.Mike Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 I have noticed the same thing, the pump shows more fuel than the dic does 98% of the time, it could be incorrect tire size, dic, pumps or me.Mike I do not think the tire size has something to do with "Fuel Used" calculated by the ECM. It could affect fuel economy data but not fuel used. Right? In my case the difference is about 5% which is a lot. Hate to think the fuel went to the atmosphere...The cap is one year old but the filler neck does not look smooth. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Ranger Posted June 13, 2005 Report Share Posted June 13, 2005 I thought maybe you just averaged them and used that for the calculation. At todays prices it would not surprise me to see stations setting their pumps off by a tenth of a gallon. No one would no and it would add up to a nice profit over time if they pump a lot of gas. Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 I thought maybe you just averaged them and used that for the calculation. At todays prices it would not surprise me to see stations setting their pumps off by a tenth of a gallon. No one would no and it would add up to a nice profit over time if they pump a lot of gas. You might be right. Looks like it makes sense switching on gas stations from time to time. I used to fill up my car at local Shell... The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
JIMDTS Posted June 13, 2005 Report Share Posted June 13, 2005 I only use the fuel used on the dic when I fill up I reset it every fill up it is usually pretty close the how much fuel I take onboard Just to make sure I'm not getting screwed on the fill up. Jim Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 I only use the fuel used on the dic when I fill up I reset it every fill up it is usually pretty close the how much fuel I take onboard Just to make sure I'm not getting screwed on the fill up. Jim If they underfill say, some 1-2% you will never notice that way... I still think these 5% are lost mostly by the car. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
chriskoc1 Posted June 13, 2005 Report Share Posted June 13, 2005 There was recently a news report by one of my town's news stations. They said they uncovered some gas stations in the metro area actually setting the pumps off. They were fined a lot and had to give gas away to customers. I will see if I can get the report on their website. Link to comment Share on other sites More sharing options...
JIMDTS Posted June 13, 2005 Report Share Posted June 13, 2005 Hi adallak I hear ya at least I'm close. One time back in the late 80's I had a new fleetwood If I recall it hatok about 20 gallons to fill it up I was pumping fuel at the gas station and cleaning the windows glanced at the pump and I had already took on over 25 gallons I shut the pump off and went in and stared bitching and I did not pay for the 5 extra gallons I told the guy Hey FU this darn car only holda about 20 gallons empty and I had a few gallons before I filled up You never really know if you are over payong and at some places I'm sure you do.. Jim Link to comment Share on other sites More sharing options...
chriskoc1 Posted June 13, 2005 Report Share Posted June 13, 2005 Here is a great article on how my state is using my tax to not check to see if gas station owners are being truthful when they say I am buying premium. http://www.jsonline.com/news/metro/apr05/317263.asp Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 Hi adallak I hear ya at least I'm close. One time back in the late 80's I had a new fleetwood If I recall it hatok about 20 gallons to fill it up I was pumping fuel at the gas station and cleaning the windows glanced at the pump and I had already took on over 25 gallons I shut the pump off and went in and stared bitching and I did not pay for the 5 extra gallons I told the guy Hey FU this darn car only holda about 20 gallons empty and I had a few gallons before I filled up You never really know if you are over payong and at some places I'm sure you do.. Jim This one was too obvious. I believe other gas station owners act smarter...Well, what can we do? Just accept gas cost us some 5% more than we think it does. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
bobnsue2 Posted June 13, 2005 Report Share Posted June 13, 2005 My 91 STS was doing the same, reporting less fuel used than really used. I replaced the injector for other reasons after measuring the resistance of them and finding some were around 6-8 ohms instead of 16 ohms. Now it reports a lot more accurately. Bbobinski suggested this was the reason as the computer knows how much fuel goes through on each pulse, but when the injector is acting up the measurement comes out wrong. My injectors went to he** because I added two cans of injector cleaner in one tankfull of gas. Apparently when the injector coils begin shorting out they act differently. Bob B Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 My 91 STS was doing the same, reporting less fuel used than really used. I replaced the injector for other reasons after measuring the resistance of them and finding some were around 6-8 ohms instead of 16 ohms. Now it reports a lot more accurately. Bbobinski suggested this was the reason as the computer knows how much fuel goes through on each pulse, but when the injector is acting up the measurement comes out wrong. My injectors went to he** because I added two cans of injector cleaner in one tankfull of gas. Apparently when the injector coils begin shorting out they act differently. Bob B Can I measure the injectors' resistance through the DIC? The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
bobnsue2 Posted June 13, 2005 Report Share Posted June 13, 2005 Not unless the newer caddys are a LOT better. Mine is a 91 STS. I used a digital ohm meter at the plugs in the harness by the side of the engine. Didn't have to go to the injector connectors. ON the 4.9 they are on the drivers side under the airbox/filter. Bob B Link to comment Share on other sites More sharing options...
mike5514 Posted June 13, 2005 Report Share Posted June 13, 2005 Going a little deeper into this subject and the reason for this discrepency I did some reserch by process of elimination of course it was not me dont make mistakes and I never take the blame when I do (accused). I then shifted the blame over to the most likely suspect the pumps. I marked a 5 gal can and filled it up at different gas stations in my area both pumps were the same to the naked eye. This is not very scientific its very basic but it gives us something to work with. I check the tire size with the book and found them to be the same this also is basic for measurements could be made etc. This leaves the dic there are a lot of variables within that read out , one thing that comes to the front is wind speed does the dic account for wind speed. I live in a windy area. Mike Link to comment Share on other sites More sharing options...
adallak Posted June 13, 2005 Author Report Share Posted June 13, 2005 Going a little deeper into this subject and the reason for this discrepency I did some reserch by process of elimination of course it was not me dont make mistakes and I never take the blame when I do (accused). I then shifted the blame over to the most likely suspect the pumps. I marked a 5 gal can and filled it up at different gas stations in my area both pumps were the same to the naked eye. This is not very scientific its very basic but it gives us something to work with. I check the tire size with the book and found them to be the same this also is basic for measurements could be made etc. This leaves the dic there are a lot of variables within that read out , one thing that comes to the front is wind speed does the dic account for wind speed. I live in a windy area. Mike Mike, The tire size, wind etc. have a lot to do with fuel economy in miles per gallon. The discussion I have started concerns rather the fuel used and the actual fuel used may be based on the numbers provided by a gas station receipts (actual gallons pumped, not the price!). But the ECM calculates the Fuel Used based on the data associated somehow with fuel injectors (pulse width integrated over the time or something like that). The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
JasonA Posted June 13, 2005 Report Share Posted June 13, 2005 This leaves the dic there are a lot of variables within that read out , one thing that comes to the front is wind speed does the dic account for wind speed. I live in a windy area. Mike The fuel used according to the DIC is the fuel used. Period. No ifs, ands, or butts. The fuel mileage according to the DIC is calculated by distance driven / fuel used. On most cases, that's miles/gallon. It can be affected by many things, as you say. If your tires are the same nominal size as what's supposed to be on the car (225/60R16), it should be pretty close. The DIC can only rely on the odometer to figure out how far you went, so if your tires are wrong, the odometer will be wrong. But...assuming your tires are the correct size, the fuel mileage according to the DIC should be your actual fuel mileage. If you live in a windy area, and use more throttle, then it will show up as more gallons used. If you live in a hilly area, and use more throttle, then it will show up as more gallons used. If you drive on the Interstate the whole trip, and be moderate with the throttle, it'll show up as more miles driven and fewer gallons used. It's really a very simple calculation. If something is WRONG...like if your tires are the wrong size, then that can affect the number. If your injectors are leaking, then you're actually using more fuel than the computer thinks, and that can affect the reading. But under normal circumstances, that reading should be exact. I would never trust a calculation at a gas pump, because you never know how full you get the tank, how accurate the pumps are, etc. Over time, like over a period of a few months, your personal calculations should match the computer pretty close. But specific variables can affect the result each time and cause you to think something's wrong, if you look at each individual fill-up separately. Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
Oldgamer Posted June 14, 2005 Report Share Posted June 14, 2005 Let say calculations based on time of opened injectors will correct if fuel pressure measure is correct. Theoretically calculations should take into attention injector size, pressure difference and time. I assume that injector size is always same. Fluctuation of pressure in cylinders is minimal too. I believe that time can be calculated very precisely, but not so sure about fuel pressure. I don't know how PCM "knows" current fuel pressure. For correct calculating it should measure it all the time. It should not be based on some "base" or "assumed" value. If PCM has that data (fuel pressure), how come we can't see it? So, possible PCM just assumes that fuel pressure is always the same, for example 41 PSI. Possible, Guru can give us some more info on that. Talking about gas stations, with prices like this I believe they try to get what they can. Link to comment Share on other sites More sharing options...
KHE Posted June 14, 2005 Report Share Posted June 14, 2005 Let say calculations based on time of opened injectors will correct if fuel pressure measure is correct. Theoretically calculations should take into attention injector size, pressure difference and time. I assume that injector size is always same. Fluctuation of pressure in cylinders is minimal too. I believe that time can be calculated very precisely, but not so sure about fuel pressure. I don't know how PCM "knows" current fuel pressure. For correct calculating it should measure it all the time. It should not be based on some "base" or "assumed" value. If PCM has that data (fuel pressure), how come we can't see it? So, possible PCM just assumes that fuel pressure is always the same, for example 41 PSI. Possible, Guru can give us some more info on that. Talking about gas stations, with prices like this I believe they try to get what they can. The fuel pressure regulator maintains a constant pressure drop across the injectors. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
Oldgamer Posted June 14, 2005 Report Share Posted June 14, 2005 That's right, it the same across the injectors, but it fluctuates. If you'll install gauge to measure fuel pressure you'll see that it will different from car to car. Not too much, but enough to make a noticable difference. And it will change a bit when you accelerate. That what I'm talking about. As I was reading posts, some owners report 39-41 PSI, and some report 42-45 PSI. Link to comment Share on other sites More sharing options...
Bill K Posted June 14, 2005 Report Share Posted June 14, 2005 A couple of things come to mind. If you are not resetting the DIC ea. time before leaving the station it could add up. Also if someone else was in your car and "accidently" reset the gal. used it would mess it up. I use the same pump at the same station and the results are very close to the DIC ea time. Now your gonna make me take a closer look...... Link to comment Share on other sites More sharing options...
Ranger Posted June 14, 2005 Report Share Posted June 14, 2005 Oldgamer, I am sure the PCM uses factory spec fuel pressure for the calulation. I don't think it can measure fuel pressure. I would guess that the difference would be minimal anyway. Link to comment Share on other sites More sharing options...
KHE Posted June 15, 2005 Report Share Posted June 15, 2005 That's right, it the same across the injectors, but it fluctuates. If you'll install gauge to measure fuel pressure you'll see that it will different from car to car. Not too much, but enough to make a noticable difference. And it will change a bit when you accelerate. That what I'm talking about. As I was reading posts, some owners report 39-41 PSI, and some report 42-45 PSI. The fuel presure is controlled by the FPR, not the ECM. The FPR operates off engine vacuum. When engine vacuum changes, the pressure will change slightly - when you accelerate, the engine vacuum changes. What you described sounds normal. Have you ever done an injector leakdown test? Each injector is activated for 1/2 second and the drop on the fuel pressure is recorded. You will notice a slight drop in pressure. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
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