Overhead MPG computer..

[Fuzz]

The MPG on overhead computer was very accurate. . checking against miles traveled and fuel used... in fact read a little less mileage than was actually getting... Installed 275's and EZ and the darn thing reads about 4MPG better than actually getting. .

I do it the old fasioned way,but kinda wondering why the additions fooled the computer.

TIA

Fuzz

 

[KatDiesel]

Your adding "more" fuel then the computer thinks your adding. It can't compensate for the injectors dumping more fuel, anytime you "upgrade" the power and add more fuel the overhead computer is worthless.



I really don't know how else to try and explain it. Been up too long I guess... ...

 

[chuck3]

Overhead Computer.

Kats right , Mine worked allmost perfect till I installed the EZ now its allways off several MPG's

 

[Okie-Go]

Mine was to within a tenth of a gallon till I put in the injectors and the edge ez. Now I can't even count on it till the miles to empty part. Oh well the price of power.

 

[work2muchplay2little]

My suspicion is that it is keyed off the throttle position sensor and calculates fuel used by using a formula that assumes a constant fuel delivery through the stock injectors and fueling curves. When these are "overriden" via a minor or major fueling box or larger injectors, then as Kat said, you're putting in more fuel at the same relative position of the throttle and the mileage computer doesn't know the difference, and actually thinks you're using less fuel than you really are. Maybe as the intracies of the ECM and PCM are better known this can be recalibrated... hopefully.

 

[tgbol]

work2much hit right on the nailhead. In a training class I took from Chrysler it was explained that the computer knew the volume of fuel of each shot and added it up to figure the mileage. when we put a fueling box on our trucks the computer doesn't know the correct amount of fuel injected so it is off a bit.

 

[Fuzz]

Thanks All

Thanks for the info,all,and it would be nice to come up with a recalibration fix.

Thanks again

Fuzz

 

[FJ40Cruisn]

Distance to empty ...

Greetings! (My first post. )



I've been interested in getting one of the replacement fuel tanks that I've seen in advertisements on the site here and have wondered how the Trip Computer would be affected by the 60 gallon replacement tank.



I guess the Transfer Flow system would probably be a good choice if you only want to know the distance to empty on the factory tank, but my current preference is to replace the factory tank with a larger one where I can keep the full space available in the bed and not lose the spare tire.



Is the trip computer programmed with a constant value for the volume of the factory tank? Or, does the computer calculate consumption (on unmodified engine) and use movement of the fuel guage to derive capacity and then determine distance to empty. It seems to me that should be a reasonably easy way to have it set up.



Does anyone know how the factory trip computer is set to calculate the distance to empty?

 

[Ray J]

Greetings and welcome FJ40. I have the TF 54-gal. replacement tank and am very happy with it. The same sending unit is used and so far my fuel-gauge readings are pretty much dead on. I've filled to check at quarter-tank intervals and its been as accurate as any needle reading can be.



I don't use the DTE (don't trust it) and would rather rely on miles driven and gauge reading. But, that said, I don't think the computer will recognize the larger tank. Normally my DTE reading with a full tank would be in the high 500's. The extra 19 gal's. didn't change that. My "low" light would come on with about 7-8 gal. left in tank. Now when it comes on, there are about 12-14 still in tank. I try not to let it get below 1/4 so the DTE really isn't a factor.



Bottom line is, the trip comp. doesn't appear to recognize the extra fuel, BUT the fuel gauge IS accurate. Given the extra range the extra fuel provides, it would be hard to imagine not having diesel available in most normal circumstances.



Of course if you want to get it down to the last 1/2 gal... ... ...