Your intake manifold's original black nitrile (synthetic rubber) gasket is most likely hard compacted and leaking, even if you think it isn't... Look for any dark grimy leak residue along the edge of gasket on engine head's aluminum surface.
A/F sensor??? on 04 model?? My understanding was that until model year 2005 both 02 sensors were in fact O2 sensors, and from 05 on, the upstream O2 sensor was replaced with an A/F sensor. And what I ordered from ROckauto last year and installed for the new upstream O2 sensor was called and O2 sensor, not an A/F sensor.
I got the scantool OBDII laptop interface (from scantool.net). Took it on a 30 mile drive. logged about 10 parameters. Works great, and is very easy to use. The dashboard display---for hwy miles only and cruising at 65---showed 36.4 MPG average! THis is a real puzzle. For many fill-ups I have calculated the MPG based on total gals. pumped and the miles driven since last fill-up on the trip meter. This has been showing abt 31 or 32 MPG for months, and I fill up at least twice a week.
So one or the other is in error by 4-5 MPG! I hardly think the cars' odo/trip meter would be off---I have std. size Perelli 13 in. P6 tires----and supposedly the gas pumps are kept pretty accurate.....but how could the scantool data be lying?
I also have a new intake manifold gasket from Rockauto, and will change it out tomorrow. Will reset the computer, and drive it again on same route, same speed, logging with the scantool. Will see if there is any change in the average MPG. If it improves I will know I did have a manifold leak. But what I am not sure about is how long the system has to "re-learn" in order to optimize the MPG again?
I am looking long and hard at getting a Toyota Yaris/Echo...there is a youtube video of a guy getting about 48 mpg hwy in one!
Scan tools have to calibrated. I have an UltraGauge and it needed a few fill ups before it was accurate (off by around 4-5MPG). Does your software have a calibration section for mileage and/or true fuel used?
You said you have 13" wheels? What size tires? That will definitely throw your speedo off. A smaller will make it seem as if your car has gone further than it really has making your fuel economy look better than it really is.
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My bad! They are Perelli P185 SR-15!
I would like to know the details of how the scantool is determining MPG, of course its from the gal/min readout and distance travelled...but there is really no fuel flow meter per se. Does it infer this from the duty cycle of the four injectors over time, which would be proportional to throttle setting? No I didn't see a fuel usage calibration tool in the software provided. I will have to go to the scantool.net forum and find out about this.
It has to be calibrated and if it can't it's inaccurate. I am almost positive it uses MAF readings, load readings, and speed sensors to determine economy.
Which parameters did you enter to set calibration initially? Engines size & number of cylinders?
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Last edited by hardtopte72; 02-22-2013 at 04:34 PM.
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in the OBDwiz software setup, there is only an option to choose either english or metric units. ALso in the fuel setup window, there is an option to choose different calculation methods, it defaults to "MAF sensor" (that is what it was using for the tests), but there are two other methods to select--- direct fuel rate and IMAP. Whichever one is chosen, it won't work or work right unless the required parameter IDs for that method are available and selected. Maybe MAF method is not as accurate as some other? To use the IMAP method, when setting that up, you have to enter the engine size in liters. No problem. But you also have to enter the "volumetric efficiency" of the engine, which is a complete unknown! How can I find this out? This is the only place in the software I have found where you enter info on specific engine, BTW...there is nothing about the engine in general setup for instance. (if the software is a UK product, it could be using imperial gallons, I guess, not US gallons)
"English" units : In modern UK usage, the term is considered ambiguous, as it could refer either to the imperial system used in the UK, or to the US customary system of unit. The common term used in the UK for the non-metric system is imperial units or imperial measurements...
We could confirm if it's imperial or US gallons by converting metric litres/100 km or km/litre to miles/US gal.
You don't have a MAP sensor (Manifold Absolute Pressure) for IMAP. That is for older MAP sensor cars.
MAF (Mass Air Flow) is a much more accurate reading anyway.
Direct fuel is only with fuel sensors.
All of these options are available on my UltraGauge. I have a separate option to calibrate it against the factory settings by comparing the gallons the UG thought too what I actually used. It then adjusts to multiplication factor.
Example the UG says I used 10 gallons of fuel. I actually used 20 gallons of fuel. I enter 20 and the UG multiplies every reading it would get my 2. If I used 5 it would multiply by .5.
It works the same way for mileage. You need to calibrate both for the most accurate reading. Mileage is calculated against mile markers on the highway and fuel on the reading at the pump.
Without that you would either have to do your own internal calculation or deal with the incorrect reading.
Like I said mine was also off 4-5 MPG without calibration.
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Okay. Well there seems to be something not right configuring FUEL SETUP for IMAP method. it is defaulted to 3.4 liter engine, and 65% efficiency. But the decimal number you gave would be 5.5 percent. So small compared to a bigger engine? This doesn't seem right.
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