_MFB_ Posted July 18, 2009 Share Posted July 18, 2009 Hi Guys, I recently had my injectors replaced to 650cc and upgraded the fuel pump as well. Having had a previous map done with my stock set up, a second map was done to reflect the changes which includes a vf52 turbo. Powers good, no complaints here except for the now inaccurate reading of the fuel economy gauge. What parts/sensors do I check? What could be faulty? It shows im getting 12/100km when its really 18/100km once I compute after a full fill up upon empty. It used to be spot on or just a little bit off. Ok, here's what I got so far: As I've read, The computer calculates it from how many km on the trip and the estimated liters from the injector pulses. The tune is perfectly fine, only that the fuel economy meter does not adjust to the injector pulse for the 650cc. So question now is how I can make the fuel economy meter understand the the injector pulse time used for the 650 cc injectors. Link to comment Share on other sites More sharing options...
lawl Posted July 18, 2009 Share Posted July 18, 2009 i dont think you'll ever get it to read correctly. i looked for a bit (not realy hard though) and no dice. the little things you gotta put up with... u gotta pay to play. car for sale. PM me! Link to comment Share on other sites More sharing options...
Max713 Posted July 18, 2009 Share Posted July 18, 2009 Hmmm, so thats why my mpg has been so good after going stage 3 with DW 740cc's. So far Im averaging 32mpg mixed driving... wonder what Im really averaging Link to comment Share on other sites More sharing options...
_MFB_ Posted July 18, 2009 Author Share Posted July 18, 2009 Hmmm, so thats why my mpg has been so good after going stage 3 with DW 740cc's. So far Im averaging 32mpg mixed driving... wonder what Im really averaging Use scan gauge 2 instead? Link to comment Share on other sites More sharing options...
praedet Posted July 18, 2009 Share Posted July 18, 2009 Take the mpg displayed and multiply it by stock injectors/your injectors... so 32*520/740=22.5 real mpg Link to comment Share on other sites More sharing options...
jim1969 Posted July 18, 2009 Share Posted July 18, 2009 the stock injectors for an 05 LGT are 520cc? Link to comment Share on other sites More sharing options...
DiscoPete Posted July 18, 2009 Share Posted July 18, 2009 My MPG meter is inaccurate without any modificaions. It is usually in the range of 6% to 11% too high compared to the actual mileage. The closest it ever got to accurate was 2.1% high. Once it read 5.6% low, the only time it was ever low. Is there some way to calibrate these things? Maybe a trim pot on a circuit board or something? Link to comment Share on other sites More sharing options...
praedet Posted July 18, 2009 Share Posted July 18, 2009 the stock injectors for an 05 LGT are 520cc?I think that is what the ECU treats them as... Let me go check Link to comment Share on other sites More sharing options...
John M Posted July 18, 2009 Share Posted July 18, 2009 Yep, 520 is the stock value in the ECU. Link to comment Share on other sites More sharing options...
slimjoe Posted July 18, 2009 Share Posted July 18, 2009 Hmmm, so thats why my mpg has been so good after going stage 3 with DW 740cc's. So far Im averaging 32mpg mixed driving... wonder what Im really averaging Fill up your tank, drive around. When you go back for gas, take your miles driven and divide by gallons needed to fill the tank. That'll be more accurate than the trip computer any day. Stock, it's about 1 mpg too high. Link to comment Share on other sites More sharing options...
_MFB_ Posted July 19, 2009 Author Share Posted July 19, 2009 Take the mpg displayed and multiply it by stock injectors/your injectors... so 32*520/740=22.5 real mpg Wow, it seems spot on. Could this be correct and that simple? No consideration for pulse time and flow rate of the injectors? The pulse time we used is not the same time as stock, as per DW manual for the 650cc. Link to comment Share on other sites More sharing options...
_MFB_ Posted July 19, 2009 Author Share Posted July 19, 2009 Yep, 520 is the stock value in the ECU. Will subaru allow to change value in the ecu to just make the economy meter read correctly? I've been reflashed already. Thanks Praedet, I can use the fuel eco meter again. Hopefully Subaru have a way of changing the default value. :-) Link to comment Share on other sites More sharing options...
praedet Posted July 19, 2009 Share Posted July 19, 2009 Wow, it seems spot on. Could this be correct and that simple? No consideration for pulse time and flow rate of the injectors? The pulse time we used is not the same time as stock, as per DW manual for the 650cc.Yes, it is that simple. A 650cc injector, open for the same amount of time as a 520cc injector, will put out 650/520ths more fuel You did not adjust "pulse time", you adjusted latency, which is basically how long it takes for the injector to open. That might be the same, but the amount of fuel delivered per increment of time is different... Link to comment Share on other sites More sharing options...
_MFB_ Posted July 19, 2009 Author Share Posted July 19, 2009 Yes, it is that simple. A 650cc injector, open for the same amount of time as a 520cc injector, will put out 650/520ths more fuel You did not adjust "pulse time", you adjusted latency, which is basically how long it takes for the injector to open. That might be the same, but the amount of fuel delivered per increment of time is different... Wow, thanks!!! So in the meantime I just manually convert what's displayed then. haha At least its usable now. No need for sg2 just for this. Now question is, can subaru change the default value the fuel economy meter reads to reflect 520 to 650 injector change? Link to comment Share on other sites More sharing options...
02rusWRX Posted August 2, 2009 Share Posted August 2, 2009 As some mentioned, my MPG reading was always 1-2MPG's higher than what I was actually getting ... which was frustrating. After going to Stage 2 with 820cc injectors and a high flow fuel pump, the reading is about 10MPG off. I also converted to E85, so I'm wondering if preated's calculation would still work. I'll have to try next time. Link to comment Share on other sites More sharing options...
tingtang Posted August 2, 2009 Share Posted August 2, 2009 i dont think mines ever read correctly.... everytime before i fill up i look at my mpg and its usually around 27... im stage 2.... i can get about 400 miles each tank... and probably have a couple miles more because the gas light still doesnt come on.... i dunno.... wierd... Link to comment Share on other sites More sharing options...
John M Posted August 2, 2009 Share Posted August 2, 2009 Will subaru allow to change value in the ecu to just make the economy meter read correctly? I've been reflashed already. The ECU has to know the injector size to compute pulsewidth. The MPG display calculates the economy by using puslewidth only; it doesn't know what injector value is in the ECU so all its results are assuming 520 injectors. You'd have to hack the display's code to correct the calculations. Link to comment Share on other sites More sharing options...
_MFB_ Posted August 3, 2009 Author Share Posted August 3, 2009 The ECU has to know the injector size to compute pulsewidth. The MPG display calculates the economy by using puslewidth only; it doesn't know what injector value is in the ECU so all its results are assuming 520 injectors. You'd have to hack the display's code to correct the calculations. Now making this work will surely benefit a lot of us here. Hack..hack.. hack.. Link to comment Share on other sites More sharing options...
_MFB_ Posted April 11, 2010 Author Share Posted April 11, 2010 Does the fuel economy meter get its a/f value (rpm vs load) from the open loop table and compute that with injector latency? Link to comment Share on other sites More sharing options...
desibeatz101 Posted April 11, 2010 Share Posted April 11, 2010 Subscribed to see who hacks Link to comment Share on other sites More sharing options...
kinder Posted April 22, 2010 Share Posted April 22, 2010 Bump? I too would like to reset mine for my injectors if possible. Link to comment Share on other sites More sharing options...
John M Posted April 22, 2010 Share Posted April 22, 2010 This thread turned into this: http://legacygt.com/forums/showthread.php/gi-re-calibrator-mpg-display-122593.html?t=122593 lossol has figured out how to do it but has put it on hold, presumably for more profitable ventures -- which is understandable. Link to comment Share on other sites More sharing options...
kinder Posted April 28, 2010 Share Posted April 28, 2010 I saw his but would rather have the code changed so my navi/ si drive all works. Thx though! Link to comment Share on other sites More sharing options...
John M Posted April 29, 2010 Share Posted April 29, 2010 The "fix" would be a device placed between the ECU and the display, whether that be the clock readout I have or the nav display. The signal manipulation would be done exactly the same way. The only other way for you to do it would be to reprogram the nav unit and I think we all know that isn't happening. Our only choice is to lie to it to make it display actual fuel use. Link to comment Share on other sites More sharing options...
_MFB_ Posted April 29, 2013 Author Share Posted April 29, 2013 Finally solved by Dshultz! :-) http://www.romraider.com/forum/viewtopic.php?f=34&t=9530&p=90949#p90949 Link to comment Share on other sites More sharing options...
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