[font size="3"]I thought I'd start a new thread on this subject since it looks like David/Merlin/others might get long winded and involved ;) .
David said: [font size="2"]"Hmmm! Your explanation actually makes the discrepancy worse. My Pathfinder pulling our 16TBS gets 13-13.5 mpg at a steady, flat 60 mph. So call it 13 mpg for your heavier TV in 4wd. 60/13 * 12 = 55 hp.
Since I doubt that the OBDII connector reports actual hp, as it can only infer hp from the gph of fuel used, does your Scangauge report instantaneous fuel consumption? I am sure that it reports instantaneous mpg which can easily be converted to gph. Also Sean reported that his OBII connector reported instantaneous torque and hp. I can't believe that there are strain gauges that measure actual torque. I am pretty sure that it is inferred by fuel rate as well.
FWIW, the above knowledge comes from electronic controlled marine diesels. These report pct load, which is directly related to hp produced. But that load and hp is inferred from instantaneous fuel consumption. I suspect that modern auto engines are the same.
Any thoughts, or is this getting too deep for a camper forum?
David" [/font]
Merlin said: [font size="2"]"What the heck, nothing's too deep for this forum! :) I'll bet you're right and the ECU reports several parameters based on inferences. And yes, torque, fuel flow rate, and mpg are among those reported instantaneously. I wouldn't want to guess at the algorithm the computer uses, but there are several parameters observable with the Scanguage that may go into calculating HP. One thing I noticed is that HP drops each time the transmission shifts into a higher gear and rpm drops. That of course is consistent with the fact that HP is basically torque times rpm. However, the throttle position doesn't change at each shift, so fuel demand is almost constant. Therefore the HP algorithm is more than just fuel flow rate."
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I also have a ScanGauge and have been trying to get good readings to confirm or refute David's numbers. I'm towing a CL 21RBS with a 4.0L Tacoma. Generally my ScanGauge HP numbers seem higher than David's on flat ground @60mph, but it's really hard to get a good instantaneous number. Any slight hill or wind will throw it off. The ScanGauge will report instantaneous and average MPG and instantaneous fuel flow (GPH). The averages run around 11MPG; the instantaneous MPGs are all over the place. I think the Scangauge uses fuel flow rate plus some other parameters to compute HP. It can also display % load, whatever that may be. I have not tried to watch and correlate these parameters to HP. No torque reported. I have watched HP and, at the same speed and hill climb it will be higher in the lower gears as expected. It also can approach 300HP when climbing a steep hill at 60MPH. I can't quantify "steep" yet, but I'm still trying. I also don't have a good feel for altitude effects other than my supercharger seems to be working. The ScanGauge doesn't display boost and I don't have a separate gauge for it.
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Smart move on the new thread. I'm now messing about on the Land Cruiser forum to see if others with a Scangauge have had similar readouts. So far, it looks like a yes.
I know what you mean (Charlie) about how hard it is to get the instantaneous readouts steady enough to have a good number.
Are you aware (Charile again) that the Scangauge II allows for custom programming for parameters not normally standard in the readouts? For example, I programmed mine to report transmission temperature, a parameter not in the standard scan. You may fine torque is a programmable parameter for the Tacoma.
[quote timestamp="1471564822" source="/post/23960/thread" author="@sandroad"]Are you aware (Charile again) that the Scangauge II allows for custom programming for parameters not normally standard in the readouts? For example, I programmed mine to report transmission temperature, a parameter not in the standard scan. You may fine torque is a programmable parameter for the Tacoma. [/quote][font size="3"]I am aware of that and have programmed mine to display both transmission temps. However, I doubt torque is reported from the ECU (no strain gauges) and I can't find anything on boost. I too have been all over the Tacoma forums. I'd love to see boost, but not found so far. Good info on what the ECU reports is nowhere to be found :( .[/font]
I've investigated the horsepower calculations by Toyota ECUs and I'm now very confident in the numbers I see reported on my Scangauge. I don't pretend to understand the algorithm(s) completely, but I know now what goes into the calculations for percent engine load, which is used along with rpm in the HP calculations.
The full suite of parameters used to calculate load include ambient temperature, barometric pressure, air flow, manifold pressure, throttle position, coolant temperature, peak torque available at wide open throttle, total engine volume, and volumetric efficiency (how much of the volume is actually used). Some of these parameters are variable reported by sensors and some are constants already in the computer that were determined in initial engine testing.
Gas engines don't use fuel flow rate in the calculations, but diesels do.
My bottom line is that when the Scangauge reads 104 horsepower, I think the engine output is very very close to that. An anecdotal confirmation on my Land Cruiser engine comes from the reading of 229 horsepower I had when climbing a mountain pass in 3rd gear with the engine very close to wide open throttle for a couple minutes. The 4.7L engine in my vehicle is rated at a maximum of 235 horsepower and 320 ft-lbs of torque.
Ok, let's analyze what you just said- the engine produces 104 hp to tow at 60 mph steady state on flat land and you get something more than 10 gph. I posited earlier that you probably get 13 gpm under those conditions because that is what my Pathfinder gets while towing the same trailer. Mpg and speed are pretty accurate readings. The average mpg shown on my display is within 0.5 vs fill up calculations and the speed is within 1-2 mph range of accuracy.
I have no idea how your 104 hp is calculated. You say it is not related to fuel burned but I don't understand why not. It is the only real parameter that is directly related to horsepower produced. All of the other parameters you mentioned are rather indirect such as throttle position and manifold pressure. The engine ECU has to directly measure fuel rate to be able to calculate mpg, so why not use it to infer hp produced?
So let me go back to the 104 hp produced while going a steady state 60 mph and getting a posited 13 mpg. The latter two values directly indicate 60/13 = 4.6 gph of fuel burned. If you divide that value into 104 hp you get more than 22 hp per gph of fuel burned.
That value is higher than any modern diesel. Marine diesel manufacturers are very transparent (unlike auto manufacturers) and they publish curves of gph burned and hp produced vs rpms. They peak at about 20 and average 18-19. We know that gasoline engines do much worse, so how can your engine be producing 104 hp. When I look at gasoline boat engines, instrumented tests indicate 12 gph at wide open throttle. A gasoline engine can do somewhat better at lighter loads, maybe 14 hp per gph at best.
So my guess is that it is closer to 60 hp for your TV/trailer, which is a big difference. I can't explain the difference, as I can only explain why I think a lower 60 hp is more likely correct.
Thoughts?
David
[font size="3"]FWIW, I just tried to get a representative set of numbers this afternoon. Towing a 21RBS with a 4.0L Tacoma at 60MPH I average 10-11MPG. So watching instantaneous gph, instantaneous MPG, and instantaneous HP it appears to come out to ~16HP/gph. It was reassuring to note that, on the ScanGauge, MPG times gph = MPH=60. Always heartening to see the gadgets making sense. That said, it normally looks like around 90-110 HP to maintain 60MPH, but it varies so much and so fast depending on road condx, wind, inclination, etc. that's it's a guess at best.
Also I'm running the A/C and burning 91 octane gas. The "experts" say higher octane doesn't affect MPG, but I've seen it add 2-3 MPG on my Honda and most vehicle mfg'rs recommend higher octane when towing. I can't experiment with low octane gas in the Tacoma due to the supercharger requirements.
Thoughts?
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[quote timestamp="1471658931" author="@david" source="/post/23996/thread"]Ok, let's analyze what you just said- the engine produces 104 hp to tow at 60 mph steady state on flat land and you get something more than 10 gph. I posited earlier that you probably get 13 gpm under those conditions because that is what my Pathfinder gets while towing the same trailer. Mpg and speed are pretty accurate readings. The average mpg shown on my display is within 0.5 vs fill up calculations and the speed is within 1-2 mph range of accuracy.
I have no idea how your 104 hp is calculated. You say it is not related to fuel burned but I don't understand why not. It is the only real parameter that is directly related to horsepower produced. All of the other parameters you mentioned are rather indirect such as throttle position and manifold pressure. The engine ECU has to directly measure fuel rate to be able to calculate mpg, so why not use it to infer hp produced?
So let me go back to the 104 hp produced while going a steady state 60 mph and getting a posited 13 mpg. The latter two values directly indicate 60/13 = 4.6 gph of fuel burned. If you divide that value into 104 hp you get more than 22 hp per gph of fuel burned.
That value is higher than any modern diesel. Marine diesel manufacturers are very transparent (unlike auto manufacturers) and they publish curves of gph burned and hp produced vs rpms. They peak at about 20 and average 18-19. We know that gasoline engines do much worse, so how can your engine be producing 104 hp. When I look at gasoline boat engines, instrumented tests indicate 12 gph at wide open throttle. A gasoline engine can do somewhat better at lighter loads, maybe 14 hp per gph at best.
So my guess is that it is closer to 60 hp for your TV/trailer, which is a big difference. I can't explain the difference, as I can only explain why I think a lower 60 hp is more likely correct.
Thoughts?
David
[/quote]The Toyota engineering site I used didn't explain why fuel burn rate was not used in the algorithm, but did very clearly state there was a difference in the way the calculations are made between gas and diesel engines and referenced a formal federal standard for those calculations. The equations used in gas engines calculate %load, which I presume (and my PhD is not in mechanical engineering!) is used along with rpm in some way to calculate HP.
[quote source="/post/23961/thread" timestamp="1471565899" author="@charliem"][quote timestamp="1471564822" author="@sandroad" source="/post/23960/thread"]Are you aware (Charile again) that the Scangauge II allows for custom programming for parameters not normally standard in the readouts? For example, I programmed mine to report transmission temperature, a parameter not in the standard scan. You may fine torque is a programmable parameter for the Tacoma. [/quote][font size="3"]I am aware of that and have programmed mine to display both transmission temps. However, I doubt torque is reported from the ECU (no strain gauges) and I can't find anything on boost. I too have been all over the Tacoma forums. I'd love to see boost, but not found so far. Good info on what the ECU reports is nowhere to be found :( .[/font]
[/quote]I agree that complete info on what the ECU reports is hard to find, but here's what I know about the Scangauge and it's applications to Toyota. (And I note that I was wrong in an earlier post that torque is reported; it's not.)
Scangauge Readouts for Toyota
Standard Instantaneous Parameters
Horsepower
Miles per gallon
Throttle position sensor
Battery voltage
Intake air temperature
Fuel pressure
Ignition timing
Gallons per hour
Engine loading
Manifold absolute pressure
Revolutions per minute
Miles per hour
Programmable Instantaneous Parameters
Transmission temperature
Catalyst temperature
Exhaust gas temperature
Barometric pressure
Fuel level
Engine run time
Air/fuel ratio
O2 sensor data
Fuel trim (both short term and long term)
Programmable Trip Parameters
Fuel costs per mile
Trip fuel costs
Average miles per gallon
Distance traveled
Trip fuel used
Fuel remaining
Distance remaining to empty
Time remaining to empty
Trip mpg
Average speed
Maximum speed
Trip time
Diagnostic Trouble Codes Displayed
P0100 to P1780 (4 pages worth!)
And I should add a quick edit that I haven't actually tried all the above, so some may not be available on my Land Cruiser.
[quote source="/post/24014/thread" timestamp="1471744230" author="@sandroad"]I agree that complete info on what the ECU reports is hard to find, but here's what I know about the Scangauge and it's applications to Toyota. (And I note that I was wrong in an earlier post that torque is reported; it's not.)
Scangauge Readouts for Toyota
Standard Instantaneous Parameters
Manifold absolute pressure
And I should add a quick edit that I haven't actually tried all the above, so some may not be available on my Land Cruiser.
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[/font][/quote][font size="3"]Merlin,
Thanks for the prod. I checked my firmware and it's at 4.06. Looks like I can update to 4.22 for $25. Don't know what that buys me though. I see where the book says it displays Manifold Pressure either as absolute or boost, but mine doesn't display any data in that field. Not sure the Tacoma ECU is reporting this. I'll play with it further on trip home, but just sitting in the driveway I can't get it to display data. I get the MAP or BST label, but no data. Do you have a specific web reference that confirms or denies this parameter is reported on the OBD II bus? [/font]
[quote timestamp="1471746659" source="/post/24016/thread" author="@charliem"][font size="3"]Merlin,
Thanks for the prod. I checked my firmware and it's at 4.06. Looks like I can update to 4.22 for $25. Don't know what that buys me though. I see where the book says it displays Manifold Pressure either as absolute or boost, but mine doesn't display any data in that field. Not sure the Tacoma ECU is reporting this. I'll play with it further on trip home, but just sitting in the driveway I can't get it to display data. I get the MAP or BST label, but no data. Do you have a specific web reference that confirms or denies this parameter is reported on the OBD II bus? [/font]
[/quote][font size="3"]P.S. Best I can find only 50% of Toyotas/Tacomas report MAP, even less for newer trucks. I guess I'm in the non 50%.[/font]
In a series of side-bar conversations with members of Land Cruiser forum, we all concluded there is no reason for Toyota engineers to design and program a vehicle ECU to purposefully or incidentally report inaccurately on any parameter, including horsepower. In fact, given the VW scandal, there is every reason to make certain parameters are accurately reported! So, even though I don't understand completely how it's calculated, I'm going to say that when the ECU on my Land Cruiser reports 100 horsepower, the engine really is making a 100 horsepower (or any other reading).
On my 700 mile trip coming up this week sans trailer, I'm going to record again all the parameters I looked at on the recent trip with the trailer and do some comparisons. I'm looking forward to being able to say exactly what it means to tow a 16 Camplite!
[quote timestamp="1471791924" source="/post/24020/thread" author="@charliem"]
Quote from: @charliem" source="/post/24016/thread" timestamp="1471746659[font size="3"]Merlin,
Thanks for the prod. I checked my firmware and it's at 4.06. Looks like I can update to 4.22 for $25. Don't know what that buys me though. I see where the book says it displays Manifold Pressure either as absolute or boost, but mine doesn't display any data in that field. Not sure the Tacoma ECU is reporting this. I'll play with it further on trip home, but just sitting in the driveway I can't get it to display data. I get the MAP or BST label, but no data. Do you have a specific web reference that confirms or denies this parameter is reported on the OBD II bus? [/font]
[font size="3"]P.S. Best I can find only 50% of Toyotas/Tacomas report MAP, even less for newer trucks. I guess I'm in the non 50%.[/font]
[/quote]MAP would be an interesting parameter on a supercharged engine!
MAP goes positive and is called Boost when the SC kicks in. ScanGauge accomodates it, but Toyota doesn't report it