Russtoy Posted June 12, 2012 Report Share Posted June 12, 2012 Hi Everyone. I have a new question. Is there anyway to recalibrate the fuel gage/and computer? My wife has run out of gas twice. The gage is above E and the please feed me ding/light is not on, then the car goes ding and it runs out of gas. The computer says the car has only used 12 gallons but it takes 19 to fill it up. So how do I recalibrate this thing, I know my wife would appreciate any info, so I don't laugh any more when she runs out. yea I know she should let me know before it gets that low, HAHAHAHAHAHAHA. Thanks Russtoy. opps I almost forgot, The car is a 96 Eldorado ETC. I fixed the trans a few months ago, bad shift soleniods. Great advice. Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted June 12, 2012 Report Share Posted June 12, 2012 The fuel sender is a maintenance item on these cars, so if the fuel gauge doesn't read properly I think fuel sensor. However, the gas used since last fillup is actually a calculated value based on the injector open duration and fuel pressure. So if that is off then either the fuel pressure is off, or an injector is leaking. So I would look for other clues, starting with checking the fuel pressure regulator. Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
rockfangd Posted June 12, 2012 Report Share Posted June 12, 2012 ALso a good maintnence for the fuel level sender is to run a bottle of chevron techron through a tank of gas to clean the deposits, See if that helps. Even small deposits can cause misreadings GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Ranger Posted June 13, 2012 Report Share Posted June 13, 2012 Most likely a bad fuel level sensor. Bruce, Fuel pressure has nothing to do with the fuel used calculation. The PCM simply counts injector pulses and pulse width (injector open duration) and then does the calculations. A leaky FPR should not affect the fuel gauge. Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted June 13, 2012 Report Share Posted June 13, 2012 Bruce, Fuel pressure has nothing to do with the fuel used calculation. The PCM simply counts injector pulses and pulse width (injector open duration) and then does the calculations. A leaky FPR should not affect the fuel gauge. when the computer counts injector pulses and pulse width wouldn't it have to assume that the fuel pressure was at spec to reach a value sprayed at those pulse characteristics? Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
JimD Posted June 13, 2012 Report Share Posted June 13, 2012 when the computer counts injector pulses and pulse width wouldn't it have to assume that the fuel pressure was at spec to reach a value sprayed at those pulse characteristics? YES! Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
Ranger Posted June 14, 2012 Report Share Posted June 14, 2012 True, but fuel pressure is not part of the calibration. Link to comment Share on other sites More sharing options...
JimD Posted June 14, 2012 Report Share Posted June 14, 2012 Most likely a bad fuel level sensor. Bruce, Fuel pressure has nothing to do with the fuel used calculation. The PCM simply counts injector pulses and pulse width (injector open duration) and then does the calculations. A leaky FPR should not affect the fuel gauge. A faulty FPR cannot affect the fuel gauge. However, when you introduce "fuel used" into the thread, fuel pressure becomes an issue. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
JimD Posted June 14, 2012 Report Share Posted June 14, 2012 Most likely a bad fuel level sensor. Bruce, Fuel pressure has nothing to do with the fuel used calculation. The PCM simply counts injector pulses and pulse width (injector open duration) and then does the calculations. A leaky FPR should not affect the fuel gauge. A faulty FPR has nothing to do with the fuel gauge. However, when you introduce "fuel used" into the thread, fuel pressure becomes a variable. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
JimD Posted June 14, 2012 Report Share Posted June 14, 2012 Whoops! Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
Ranger Posted June 14, 2012 Report Share Posted June 14, 2012 Most likely a bad fuel level sensor. Bruce, Fuel pressure has nothing to do with the fuel used calculation. The PCM simply counts injector pulses and pulse width (injector open duration) and then does the calculations. A leaky FPR should not affect the fuel gauge. A faulty FPR cannot affect the fuel gauge. However, when you introduce "fuel used" into the thread, fuel pressure becomes an issue. True, but the OP said "The computer says the car has only used 12 gallons but it takes 19 to fill it up". That's a 7 gallon difference. I don't think a faulty FPR could leak that bad. If somehow it was, wouldn't you think that the car would be running terribly bad and billowing black smoke Jim? Link to comment Share on other sites More sharing options...
CoupeDTS Posted June 14, 2012 Report Share Posted June 14, 2012 My fleetwood is quite a bit off since i put a new sending unit in. I can get to completely empty and have 5 gallons left in the tank every time. GM sending units are 0 ohms to 90 ohms. So I can calculate what ohms i should be at compared to the reading at the gauge and add a resistor so the gauge reads correctly. But your problem is more likely just a bad sensor. * 1966 Deville Convertible * 2007 Escalade ESV Black on Black * 1996 Fleetwood Brougham Black on Black V4P -Gone* 1983 Coupe Deville Street/Show Lowrider -Gone* 1970 Calais 4dr Hardtop GONE* 2000 Deville DTS - Silver with Black Leather and SE grille GONE* 1999 Seville STS - Pearl Red GONE Link to comment Share on other sites More sharing options...
bobbnsueb@sbcglobal.net Posted June 15, 2012 Report Share Posted June 15, 2012 When our 91 STS did the same thing as the computer reported less gas then actually used, I ended up finding the injectors were going bad. The resistance with a digital ohmeter was 5-6-8 ohms on 6 of the 8. Should be 16 ohms. (This from memory) This means they were opening differently than expected so the computer was calculating the fuel used with faulty info. They were already going bad, but I may have added to the problem. If one can of Techron is good then I added two cans. Well the windings started shorting out and one even went to zero ohms. (shorted) This made a miss so I got the meter out and unplugged the two common plugs on the side of the engine thew rest was obvious. Techron disolved the varnish on the windings. New injectors fixed the faulty mileage reporting. Link to comment Share on other sites More sharing options...
Russtoy Posted June 15, 2012 Author Report Share Posted June 15, 2012 Thanks for the info everyone, I will start with some techron and go from there. The car runs very good, so I am not sure about bad injectors. It runs a bunch stronger then the 98 SLS we have, and the mileage is the same. Link to comment Share on other sites More sharing options...
bobbnsueb@sbcglobal.net Posted June 16, 2012 Report Share Posted June 16, 2012 Thanks for the info everyone, I will start with some techron and go from there. The car runs very good, so I am not sure about bad injectors. It runs a bunch stronger then the 98 SLS we have, and the mileage is the same. ____________________________________________________________________- Well mine ran good until the one went to zero ohms. Then it had a noticeable miss. But all it takes is a decent ohmmeter and go to the common connectors. On mine (4.9) the connectors are on the left side of the engine compartment. The rear of the engine, Easy to get to and it was a shock to see that most were only 6-8 ohms and not the normal 16. You don't have to remove the injectors to do this it was running good up to that point but the real mileage was not as good as it should have been and the computer reported better mpg than it really was. Bobb Link to comment Share on other sites More sharing options...
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