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Thread: 1227747 with DEKA injectors

  1. #1
    Electronic Ignition!
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    1227747 with DEKA injectors

    Hi there,

    I'm using the Affordable Fuel Injection TBI injector tree which is using 2 Deka 840cc@43.5 psi injectors. (80#)

    I'm using a BPW spreadsheet to calculate what my BPW should be and it gives me ~134 which is close to the BPW I see in most of the stock bins for a relatively stock GM 7.4L. I'm running a moates emulator to start the engine and I can only get the engine to idle with 165 BPW, 65 psi, and the fuel table in the 50% range. This doesn't quite seem right given that many of these engines seem to do fine with 80lb injectors running with much less fuel pressure. It just seems to want much more fuel than expected and make me think something is not right.

    I wonder if there are some injector settings in the BIN that I might be overlooking given that these injectors are quite different than the originals? I see posts about injector voltage bias, and PW, but am not familiar enough with those to know if that's what I need to adjust.

    Appreciate any pointers.
    Brian

  2. #2
    Super Moderator dave w's Avatar
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    Is this what you have? See link: https://www.ebay.com/i/252865497725?chn=ps

    Seemingly AFI should have the injector parameters you need? I can't imagine why AFI would not have the parameters you need?

    dave w

  3. #3
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    Quote Originally Posted by dave w View Post
    Is this what you have? See link: https://www.ebay.com/i/252865497725?chn=ps

    Seemingly AFI should have the injector parameters you need? I can't imagine why AFI would not have the parameters you need?

    dave w
    AFI can provide tuners with the injector characteristics required for your calibration.....

  4. #4
    Electronic Ignition!
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    Quote Originally Posted by Freak View Post
    AFI can provide tuners with the injector characteristics required for your calibration.....
    i did get some info, but Iím not sure if it is directly applicable to the 7747 ECM. Iíve been able to make some guesses on which data can be directly input into tunerpro. Iím not a total noob with tuning but I somewhat am in this case.

    Theres a voltage offset set and what looks like a minimum pulse width. I guess I could directly ask if they have any mapping available for the 7747. Seems like such an obvious question now that I think about it. Hereís what I did find for info:

    http://www.siemensdeka.com/wp-conten...t-Brochure.jpg

  5. #5
    Super Moderator dave w's Avatar
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    Interesting Data in the link above.

    Injector flow is based on 300 Kilo Pascals = 43.5 PSI = 80 lb/hr. Factory TBI injectors flow is based on 13 PSI

    Perhaps the Base Pulse Width (BPW) needs re-calculated with 43.5 PSI fuel pressure?

    Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

    The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

    dave w

  6. #6
    Electronic Ignition!
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    Quote Originally Posted by dave w View Post
    Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

    The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

    dave w
    Thatís entirely possible. By changing the injector pulse width vs voltage and minimum injector pulse width to that on the chart Iíve gotten it to run OK above idle (BLMís in closed loop are able to be adjusted to stay around 128) Now the idle doesnít want to settle down below about 1000 RPM and the IAC count is over 100. Iím wondering if the minimum pulse width or injector bias is a little too much and maybe I should turn that down to see if I can get less fuel at idle?

  7. #7
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    The chart appears to show minimum PW at 1.7 ms. I don't believe I'd go lower.
    The voltage offset chart is also present at the link above. Having the correct voltage offsets is very important for consistent idle.

  8. #8
    Electronic Ignition!
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    Quote Originally Posted by 1project2many View Post
    The chart appears to show minimum PW at 1.7 ms. I don't believe I'd go lower.
    The voltage offset chart is also present at the link above. Having the correct voltage offsets is very important for consistent idle.
    I had the same thought so I did experimently lower the injector bias from 1.4 to 1.0 and it wonít idle at any temperature so Iím hoping thereís a sweet spot around 1.2. Or lower the fuel pressure a bit and hope I donít lose too much fuel at the top end.

  9. #9
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    Quote Originally Posted by bp71k5 View Post
    I had the same thought so I did experimently lower the injector bias from 1.4 to 1.0 and it wonít idle at any temperature so Iím hoping thereís a sweet spot around 1.2. Or lower the fuel pressure a bit and hope I donít lose too much fuel at the top end.
    On second thought, Iím not sure whatís going on. When engine is cold, itíll start up ok and then die unless I give it throttle. That seems to tell me it needs more fuel at idle.

    Once it warms up it would idle, but too high with too high IAC counts.

    Since the openloop AFR fueling level is set from the VE1 table and then adjusts the AFR to be richer during a cold start, there would have to be a very large fueling difference needed between cold and normal operating temperature, a larger difference than the openloop AFR vs coolant table is asking for. Is that a logical conclusion? Itís hard to believe changing the injector bias from 1.4 to 1.0 would expose that large of a cold vs hot fuel requirement difference.

  10. #10
    Super Moderator dave w's Avatar
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    It might be a good plan to include a Wide Band O2 Sensor (WBO2) to the information collection process.

    One possible option for a WBO2: https://www.aemelectronics.com/produ...uego-afr-gauge

    dave w

  11. #11
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    Quote Originally Posted by dave w View Post
    It might be a good plan to include a Wide Band O2 Sensor (WBO2) to the information collection process.

    One possible option for a WBO2: [url]https://www.aemelectronics.com/products/wideband-uego-air-fuel-controllers/digital-wideband-uego-afr-gauge/digital-wideband-uego-afr-gauge[/url


    dave w
    Thatís not a bad option for the price. May be time to do that.

  12. #12
    Fuel Injected! brian617's Avatar
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    Quote Originally Posted by dave w View Post
    Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

    The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

    dave w

    I'm with Dave here, has this been proven to work with 7747 or 7427 ECM/PCMs?
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  13. #13
    Electronic Ignition!
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    There is a big difference in impedance, but I’m not convinced yet that it won’t work. It’s somewhat fun experimenting.

    I did increase the injector bias back up to 1.2 and adjusted the minimum air setting and tried again but then the fueling was almost 20% too lean so after increasing that it’s idling pretty well now. IAC floats around 16. I did find a scalar called “IAC kick down steps” what’s supposed to be set to one digit higher than the idle IAC count. I’m wondering if that was my real problem earlier rather than being too rich at idle.

    I still need to check the cold start again tomorrow and do some data logging but the 30-40 kpa VE table looks pretty close up to 3200rpm and the engine starts right up and idles where it should so I’m hopeful.

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