42 Miles until empty, but out of gas!
#21
03-11-2010, 03:09 PM
See this is getting kind of interesting.. The trip odometers do not reset when you turn off the car.. But, the computer just might be doing things based on a rolling set of numbers... Here is something pretty easy for everyone to see... You have two sets of trip odometers..A and B... A I use to check by the tank or week...B I keep until I service the engine. I notice when I compare the two, they will display different average speeds and different MPG..Yet if I reset one to 0 while driving, it won't just match the average MPG on the other, nor will it display the Instant MPG as the average like older trip computers used to do... It comes up with it's own average. That average does adjust real quick as miles are added to that trip..So, I wonder if it is just doing calculations on a preset rolling range of numbers to determine DTE and Average MPG...
I'm going to jot down some readings today on the way home and in the morning....
I'm going to jot down some readings today on the way home and in the morning....
#22
03-11-2010, 03:17 PM
Veteran Member
See this is getting kind of interesting.. The trip odometers do not reset when you turn off the car.. But, the computer just might be doing things based on a rolling set of numbers... Here is something pretty easy for everyone to see... You have two sets of trip odometers..A and B... A I use to check by the tank or week...B I keep until I service the engine. I notice when I compare the two, they will display different average speeds and different MPG..Yet if I reset one to 0 while driving, it won't just match the average MPG on the other, nor will it display the Instant MPG as the average like older trip computers used to do... It comes up with it's own average. That average does adjust real quick as miles are added to that trip..So, I wonder if it is just doing calculations on a preset rolling range of numbers to determine DTE and Average MPG...
I'm going to jot down some readings today on the way home and in the morning....
I'm going to jot down some readings today on the way home and in the morning....
It's easy to prove this (that DTE is dynamic) .. Especially when there are less than 100 miles left in the tank.
Floor the car on an open stretch of road for a few seconds. Or come off a light or a stop hard. I bet it costs you 5 miles. Then coast / be gentle with it, you'll gain them back. Now the average MPG is probably spot on based on miles traveled and calculated actual fuel consumption. (From the last reset of that computer). Those are measured facts.
Trip A and B are completely independent. However they have a max capacity of 9999 miles, at which point they will reset to zero.
The DTE calculation is speculation into the future. I could get stuck in bumper to bumper traffic and get 5 mpg on the rest of the fuel supply, or I could coast all the way down a descent and barely take the engine off of idle. (I know these are extremes, but DTE is definitely affected by instantaneous MPG and recent history).
George
#23
03-11-2010, 04:58 PM
Senior Member
It's not brain farting. It's calculating your distance to empty based on the fuel economy figures you achieved over the last 30 or so miles. For me, when I come home from work, I have a 15+ mile highway commute, and 2 miles off the highway into my neighborhood.
Now there can be at least a 10mpg difference between highway and city driving, especially in overdrive etc. The next morning when you start the car the trip resets. You back out of your driveway and start heading 25-30 mph on local roads, it knows how much gas it has left (besides the reserve that you aren't supposed to get into) and recalculates based on the slow city speed (or your average mpg). Until you develop a history with this trip.
The more fuel you have onboard - the greater the potential discrepancy in miles. 15 gallons on the highway will take your 150 miles give or take more than than the same 15 miles burned in the city.
Oh and Jeff... This would also prob explain your DTE figure being off. Were you driving stop and go or slowly? That 66 miles was prob calculated over 4 or so gallons of fuel. Plus I think the computer thinks zero = 2.5 gals aboard. Under 1 gallon = potential overheating of the pumps, so while the reserve is "1.5" gallons, I think there trying to hide a gallon to save the fuel pumps.
As to the OP taking on 18.83 gallons after running the car bone dry. Does the filler neck count as fuel capacity? If it's an 18.5 gallon tank you could easily be holding 1/3 of a gallon in the filler neck. Especially if you get a gas attendant that's trying to round up the total to the next dollar..
George
Now there can be at least a 10mpg difference between highway and city driving, especially in overdrive etc. The next morning when you start the car the trip resets. You back out of your driveway and start heading 25-30 mph on local roads, it knows how much gas it has left (besides the reserve that you aren't supposed to get into) and recalculates based on the slow city speed (or your average mpg). Until you develop a history with this trip.
The more fuel you have onboard - the greater the potential discrepancy in miles. 15 gallons on the highway will take your 150 miles give or take more than than the same 15 miles burned in the city.
Oh and Jeff... This would also prob explain your DTE figure being off. Were you driving stop and go or slowly? That 66 miles was prob calculated over 4 or so gallons of fuel. Plus I think the computer thinks zero = 2.5 gals aboard. Under 1 gallon = potential overheating of the pumps, so while the reserve is "1.5" gallons, I think there trying to hide a gallon to save the fuel pumps.
As to the OP taking on 18.83 gallons after running the car bone dry. Does the filler neck count as fuel capacity? If it's an 18.5 gallon tank you could easily be holding 1/3 of a gallon in the filler neck. Especially if you get a gas attendant that's trying to round up the total to the next dollar..
George
Its good to know its not the car having brain farts, just me..lol
I knew there is some sort of mathematical explanation for all this,but when I try to figure it out my math challenged brain has a break down.
#24
03-11-2010, 05:55 PM
#25
03-14-2010, 02:57 PM
Veteran Member
I had a kinda..sorta ..related problem in Nov. 2008. My gas guage needle went back and forth between ~3/4 and ~3/8 full. One morning I went about some errands and saw the needle around the 3/8 mark and went to fill it up. I hadn't been driving it much so I lost track of the last time I filled it up. Anyway, it took only about 4-5 gallons, (IIRC), and...whatttt??? Things that make you say WTF!!!!.Then the fun began, it went from full to ~3/8 to ~3/4 and back and forth.
OK, called dealer and took it in for repair (still under factory warranty).
. They had a rental car waiting for me which was nice..
Here's the writeup...
""Customer states the fuel gauge seems to be inaccurate and will fluctuate when filled with fuel. It will not read full, it will read approx. 3/8 full and eventually go to full but will drop again to empty or low. Check and advise fuel pump sender failure.
Checked codes, got B2627, B1202. Checked raw fuel thru inst. pack. Raw 1 91, raw 2 255.2 open circuit. Gauge was reading full but dropped to 1/4 tank. Checked resistance at pump. RH side at 300 ohms and left at 3.6 kohms. Replaced both pump and jet pump.
Parts replaced..(1) XR852870 Assy sender; (1) ZR852864 sender; (2) XR848118 gasket""
Service guy said it would have been about $950 without warranty..
The "range" or distance left on the computer display is directly tied to the position of the gas needle and not how many gallons are in the tank. The display varied as the needle varied.
OK, called dealer and took it in for repair (still under factory warranty).
. They had a rental car waiting for me which was nice..Here's the writeup...
""Customer states the fuel gauge seems to be inaccurate and will fluctuate when filled with fuel. It will not read full, it will read approx. 3/8 full and eventually go to full but will drop again to empty or low. Check and advise fuel pump sender failure.
Checked codes, got B2627, B1202. Checked raw fuel thru inst. pack. Raw 1 91, raw 2 255.2 open circuit. Gauge was reading full but dropped to 1/4 tank. Checked resistance at pump. RH side at 300 ohms and left at 3.6 kohms. Replaced both pump and jet pump.
Parts replaced..(1) XR852870 Assy sender; (1) ZR852864 sender; (2) XR848118 gasket""
Service guy said it would have been about $950 without warranty..
The "range" or distance left on the computer display is directly tied to the position of the gas needle and not how many gallons are in the tank. The display varied as the needle varied.
#26
03-14-2010, 04:19 PM
Veteran Member
#28
03-14-2010, 08:40 PM
Veteran Member
Basically 6 of 1 half a dozen of the other.
The car has a sender in the fuel tank that sends an electronic representation of how much fuel is in the tank. The car's electronics have no other way of knowing how much fuel is in the tank. The instrument cluster uses this to display how much fuel is left (gas gauge) and supply the trip computer with remaining fuel amount to calculate distance to empty. And yes all the logic is in the cluster, there is NO other place that the fuel sender connects to.
The gas gauge is not an independent entity, but rather driven by the in tank level sender.
What happens is if the in tank sender is sending erroneous info. I.e. alternating between 3/8 and full, the gas gauge and DTE calculations have no choice but to follow.
George
The car has a sender in the fuel tank that sends an electronic representation of how much fuel is in the tank. The car's electronics have no other way of knowing how much fuel is in the tank. The instrument cluster uses this to display how much fuel is left (gas gauge) and supply the trip computer with remaining fuel amount to calculate distance to empty. And yes all the logic is in the cluster, there is NO other place that the fuel sender connects to.
The gas gauge is not an independent entity, but rather driven by the in tank level sender.
What happens is if the in tank sender is sending erroneous info. I.e. alternating between 3/8 and full, the gas gauge and DTE calculations have no choice but to follow.
George
#29
03-14-2010, 10:15 PM
#30
03-16-2010, 02:33 PM
I have an 03 S-type. Dealer told me the tank is "humped" in the middle with a sensor on each side. The computer reconciles the two readings. One of mine didn't work for a while and when i got down to 1/4 tank the needle dropped to below E and the range read computer error. I was quoted $450 by the dealer to replace both and decided to take my chances. After a while it came back and has worked well ever since.
#31
03-16-2010, 05:18 PM
Veteran Member
I have an 03 S-type. Dealer told me the tank is "humped" in the middle with a sensor on each side. The computer reconciles the two readings. One of mine didn't work for a while and when i got down to 1/4 tank the needle dropped to below E and the range read computer error. I was quoted $450 by the dealer to replace both and decided to take my chances. After a while it came back and has worked well ever since.
Hold down the trip computer button (on the edge of the turn stalk) and start the car while holding it down. Keep holding the button till the instrument cluster says test mode.
Tap the trip computer button, the first thing it will say is test guages. Keep tapping and go through, you'll see a bunch of sw version stuff. Keep tapping. You'll go through and eventually see the two fuel levels. There's also instantaneous rpm, and instantaneous battery voltage. But the two fuel levels should be close.
George
#32
03-16-2010, 05:19 PM
You learned a lesson. When it hits the last quarter, buy gas.
#33
03-16-2010, 06:14 PM
I generally reset the avg mpg and avg speed when the low fuel indicator comes on and it seems to adjust the DTE almost immedietely based on my current driving. It also gives my an idea of my current mpgs. So if you know how many gallons are left when the low fuel light comes on you'll have a pretty good idea how many more miles you can drive based on those current driving conditions.
I started to use this when I had a Prius where the MPGs could vary by +/- 25 mpg depending on what kind of driving I was doing (hwy/city, uphill/downhill, etc). Those last few gallons could last anywhere from 50 miles up to 130 miles. I learned the hard way that people like to laugh at Prius drivers who run out of gas.
In the Jag I can barely average in the teens so I just stop and fill-up soon after the low fuel light comes on.
For those who fill-up at a quarter tank, they obviously don't drive very much. That wouldn't even get me 200 miles.
I started to use this when I had a Prius where the MPGs could vary by +/- 25 mpg depending on what kind of driving I was doing (hwy/city, uphill/downhill, etc). Those last few gallons could last anywhere from 50 miles up to 130 miles. I learned the hard way that people like to laugh at Prius drivers who run out of gas.
In the Jag I can barely average in the teens so I just stop and fill-up soon after the low fuel light comes on.
For those who fill-up at a quarter tank, they obviously don't drive very much. That wouldn't even get me 200 miles.
Last edited by DTB; 03-16-2010 at 06:17 PM.
#35
03-17-2010, 07:31 AM
Veteran Member
I'd love to say I figured that out on my own, but credit goes to Brutal on that one. He told me about it in another thread about X-types, and I happened to ask him if it also applied to S-Types and he said yes!..
You can also drive around with the car displaying whatever "test" value you want on the dash, so you can watch reported fuel levels in real time.
The dash will not come out of test mode until you turn the car off and back on again.
George
You can also drive around with the car displaying whatever "test" value you want on the dash, so you can watch reported fuel levels in real time.
The dash will not come out of test mode until you turn the car off and back on again.
George
#36
03-17-2010, 09:13 AM
Veteran Member
#37
03-17-2010, 09:39 AM
Veteran Member
(Most of this shamelessly grabbed from the UK forum.)
It's known as ETM - Engineering Test Mode. TSB JTB00014 covers it and is here:
http://jaguar.bttlxe.com/xtype/Addit...%20Cluster.pdf
(it's not 100% but good enough)
You can read useful things like the ECT (engine coolant temp) (called TEMP IN) on there, in tenths of degrees C.
It can help also to know the ICM is a variant of Ford's HEC (Hybrid Electronic Cluster) - www.fordwiki.co.uk/index.php/Instrument_Cluster_Self-Diagnostic_Mode
You can display DTCs (OBD codes) using it, but only the ones the ICM knows about, I think, and you have to decode them (they're shown in hex so in effect raw as per the OBD standards). Just do this to decode ICM DTCs:
1xxx => P1xxx
9xxx => B1xxx
Axxx => B2xxx
Dxxx => U1xxx
Exxx => U2xxx
(if you know hex, the top 2 bits determine whether a P,B,C or U code, the rest are the code)
It's known as ETM - Engineering Test Mode. TSB JTB00014 covers it and is here:
http://jaguar.bttlxe.com/xtype/Addit...%20Cluster.pdf
(it's not 100% but good enough)
You can read useful things like the ECT (engine coolant temp) (called TEMP IN) on there, in tenths of degrees C.
It can help also to know the ICM is a variant of Ford's HEC (Hybrid Electronic Cluster) - www.fordwiki.co.uk/index.php/Instrument_Cluster_Self-Diagnostic_Mode
You can display DTCs (OBD codes) using it, but only the ones the ICM knows about, I think, and you have to decode them (they're shown in hex so in effect raw as per the OBD standards). Just do this to decode ICM DTCs:
1xxx => P1xxx
9xxx => B1xxx
Axxx => B2xxx
Dxxx => U1xxx
Exxx => U2xxx
(if you know hex, the top 2 bits determine whether a P,B,C or U code, the rest are the code)
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tomfurie (06-25-2018)
#38
03-17-2010, 10:35 AM
#39
03-17-2010, 11:06 AM
#40
03-17-2010, 08:38 PM
(Most of this shamelessly grabbed from the UK forum.)
It's known as ETM - Engineering Test Mode. TSB JTB00014 covers it and is here:
http://jaguar.bttlxe.com/xtype/Addit...%20Cluster.pdf
(it's not 100% but good enough)
You can read useful things like the ECT (engine coolant temp) (called TEMP IN) on there, in tenths of degrees C.
It can help also to know the ICM is a variant of Ford's HEC (Hybrid Electronic Cluster) - www.fordwiki.co.uk/index.php/Instrument_Cluster_Self-Diagnostic_Mode
It's known as ETM - Engineering Test Mode. TSB JTB00014 covers it and is here:
http://jaguar.bttlxe.com/xtype/Addit...%20Cluster.pdf
(it's not 100% but good enough)
You can read useful things like the ECT (engine coolant temp) (called TEMP IN) on there, in tenths of degrees C.
It can help also to know the ICM is a variant of Ford's HEC (Hybrid Electronic Cluster) - www.fordwiki.co.uk/index.php/Instrument_Cluster_Self-Diagnostic_Mode
Raw Fuel 1 - 112
Raw Fuel 2 - 46
Filter Fuel 1 - 205
Filter Fuel 2 - 0
Fuel % - 120
Fuel Driver - 660
Please help me out with this. Shouldn't Raw Fuel 1 & 2 be close? Can any one of our "experts" tell from these results?
Thanks for your help!