crazy question...

Discussion in 'Sportster Models' started by BrettG, Apr 21, 2010.

  1. BrettG

    BrettG Member

    Ok, I understand fuel injection.
    I have been reading past posts here, and the system on my 2009 seems to work well, it just has limitations as to the range it can adjust for in its basic form.
    People who put less restrictive exhausts on, and/or open up the air cleaner run into a problem with lean running, as the system has limited range and only under some conditions, at other times, it just uses maps (open loop).

    The system looks at air intake temps, engine temps, and other things to adjust the mixture, it sometimes looks at the oxy sensors.

    People spend lots of money to have the maps changed, or buy gizmo's to 'fool' the ecu into thinking things are different to correct the lean burn.

    What about changing things yourself, like, the engine or air intake temp sensors to tell the ecu the intake air, or engine temp is just a little bit cooler than it is?

    Most temp sensors vary resistance with temp, so would it be possible to add a resistor to make a sensor read that the temp is just a little bit cooler than it is and the ecu will adjust the mixture (slightly) richer?
    The sensor would still have a lot of input, the oxy sensors would still control things, etc.

    I don't have the shop manual, which may or may not say what does what, but say the engine temp sensor is used to set the mixture, and it reads 1000 ohms hot, and 100 ohms cold. Could you not put a 1500 ohm, or 2000 ohm resistor across it, and have it read say 800 ohms hot instead of 1000 ohms, and it would still read 100 ohms cold, or about 99 ohms....

    Does the shop manual go into details about the sensor resistance, and what the sensor controls (engine temp, air temp).

    On some older fuel injection systems, the air intake temp sensor just retarded the ignition timing on intake temp rise to eliminate ignition knock, on modern setups it has an input on the mixture control.

    If a system was to use both the engine temp, and air intake temp for mixture control, it would likely use engine temp as the major mixture control input, with the air intake for fine adjustments, which would allow one to play with the air intake reading for changing the mixture a bit....

    I am sure the bikes run on the lean side stock, any mods would just make it worse...


    NEWHD74FAN Experienced Member Retired Moderators

    One of the technological advances that made EFI possible for the everyday vehicle was converting mechanical fuel injection developed in the 50's & 60's (anyone remember the first fuel injected Chevy Corvette and such)?...and found it too complex to keep running right...and analog sensors were limited to fuel pressure and centrifugal "advance" technology to try and sync the ignition system to the fueling.

    It was Bosch that developed the first successful EFI system using old fashion TTL (transistor transistor logic) electronic processor to control the duty cycle of the electric solenoid injectors with ceramic tips (they looked like spark plugs)...and the air flow sensor, throttle position sensor, temperature sensor and oxygen sensor made it possible, rather than synchronize with the ignition system.

    Most EFI and EC ignitions systems developed and were integrated together based on that system. The advances have been in the microprocessor...starting with 2 dimensional mapping to 3 and 4 layer mapping. What your asking is can you change the various bits...probably could, but then most of us do not have the background or "scratch" to do the deed without an R&D group to back us up.
    Last edited: Apr 21, 2010
  3. Hoople

    Hoople Account Removed

    Why would you want to change the engine temp sensor to fake out the ECM. That would lead to a global change in A/F ratio. Some map cells may be better but others would be far far worse. The ECM would never go closed loop and your gas mileage would likely sink.

    It is more involved than just making the engine think it's always warming up.
  4. Crocker

    Crocker Active Member

    No need to go through all that. if your or just looking to drop your A/F from the stock 14.6 all you need to do is drop the voltage on your 02 sensors thats where the ecm gets its A/F info from. There are inline plug and play set ups that plug in between your 02 sensors on the market with very good reviews that are in the 80.00 - $120.00 range that will get you 14.2 - 13.5 depending what you are looking for , it will provide you with better response and a drop in your engine temp.and some HP and TQ gain.
  5. Iceman24

    Iceman24 Well-Known Member

    13 yourself a whole lot of $$$ & time by buying & installing a TFI (~$200). I think you're putting way too much thought into a simple fix for self-tuning your ride. Also, tweaking the wiring/sensors could end w/drastic results that might not be covered by your OEM warranty.
  6. kemo

    kemo R.I.P

    I have to agree with the Iceman, buy the tool for the job and be done.
  7. BrettG

    BrettG Member

    I am not thinking of making big changes, like the engine is cold all the time, just a slight change. I have done things like this on cars, even with the transmission control, changing the downshift points in the sport mode of an automatic transmission. It worked great.

    Yes, the best bet is likely to spend money on it, but it would cost me nothing to experiment, and you can not damage anything as long as you dont short something out.

    I figure you could slightly enrich the maps, and still allow oxy sensor control when they do....

  8. Jack Klarich

    Jack Klarich Expert Member

    I dont get this one, I see it every day tho some one trying to reinvent the wheel, and as NEWHDFAN said without R D and alot of money AH, I would leave it alone or say bye bye to your warranty and possible severe engine damage. JMO
  9. cedarbrook63

    cedarbrook63 Junior Member

    Beautifully put IM.
    Dopeck's TFi is a super little unit that gives you Carb-like control of your FI system. Works really well, very good support and if you let them know you're a member of this forum - they give you a discount.