electrical load and AFR changes

  • #1

    electrical load and AFR changes

    im a bit hesistant to post this question here considering the quality of the questions and replies on this forum over the past few months, but i guess it worth a shot…

    just a little background.. i have an 86 na2t with an 88t computer, dsm 450cc injectors with dropping resistors and a z32 AFM.. i have a boost referencing 1-1 aeromotive adjustable fuel pressure regulator with the pressure set at just around 43 psi.. i am using nistune and an LM1 to control things.. my problem relates to my electric fan. its a fairly large fan that takes a 30 amp fuse, and has popped 25 amp fuses.. when the fan kicks in i have huge drops in air fuels across the board. they drop as much as 4 full points.. if im idling in the 14s with the fan off, it will drop to the 10s with the fan on.. the fan is powered directly from the battery and i have tried grounding it in several different places with the same results.. with the fan on, battery voltage drops about 1 10th of a volt (13.8 to 13.7). no other logged values in nistune change with the fan coming on.. the fan is controlled by a painless wiring thermostatic fan controller. the stock O2 sensor is turned off in nistune.. i have not yet rewired the fuel injectors to account for the differences between the NA and turbo harnesses.. i certainly plan on doing this, but i dont see how it could relate to my problem.. i have never been too good at diagnosing electrical problems, and this one certainly has me stumped. my only guess is that the slight drop in battery voltage has an effect on injector latency.. but i dont see how 1/10 of a volt could be making such a huge difference..

    if you have an insightful and educated idea as to what i should try please let me know..
  • #2
    Just getting a little more info… What alternator are you running? Where does your nistune get its voltage reference from? Is there a separate map for the voltage like this one below? Does your car run stupid rich on startup also? On my current map there isnt even 1 millisecond difference for the entire voltage range 0-26vdc.

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  • #3
    Something to consider. Since your using 450cc fuel injectors, your injector pulsewidth is very low at idle. Small changes within 1/10th of a millisecond is going to make huge changes in your AFRs.

    Have you tried turning "off" the battery voltage latency scale?

    This is just speculative, but maybe the battery voltage latency function is actually more of a current sensing function. The fuel injectors a driver by current, not voltage anyways.

    Also, to rule out these prossible issues, you should really change your fuel injector wiring and match the right fuel injectors to the ECCS.
    1984 300ZXT
    1986 300ZX 2x2 NA2T
    2000 Porsche Boxster
    2007 Toyota Yaris
  • #4
    Typically, when there's a large drain in the voltage of the car, the ECU will bump the injector pulswidth to make up for the voltage drop. Since you have larger injectors, the bump may be overkill when it's still on the stock setting. Is there a way to change the voltage compensation?


    (I'm just speaking from general standalone experience. No experience on the Nistune)
    1987 300ZX Turbo - http://z31performance.com/forum/vie … php?t=3114
    2001 Tiburon Turbo 60-1 270whp/268tq

    No cupholders? Where am I gonna put my beer????

  • #5
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  • #6
    thanks guys, this has been helpful…

    Racinjitter: i have a 90 amp maxima alternator. nistune gets its voltage reference directly from the ecu… the nistune software does have a latency/battery voltage scale, but i dont know what the values mean or how to use it.. (hopefully bernardd or bemis can help me out with that one) unfourtunatly nistune is not always descriptive as to what everything does and how everything works.. well at least its not descriptive enough for someone like myself to comprehend it..

    Bemis: do you think the fuel injector wiring is playing a big part in this problem? if it is, then i wont waste my time trying to fix this until i have the wiring corrected. also, how would i go about "turning off" the voltage latency scale? in the nistune software there is a single value (184 if i remember correctly) that is adjusted with a sliding scale just like the regular latency adjustment. should i set that to its max or min?

    bernardd: i know the address of this scale, but i dont know how it works.. what do the values mean?

    thanks again everyone
  • #7
    You know, this just came to me, but I'm still on stock injectors/ECU and my idle dips pretty bad when the FAL fans kick on, and I also have the Maxima alternator.
    So the stock vs. bigger injector theory could be eliminated. Although, I should really get my wideband and voltmeter hooked up to see why it dips.
    1987 300ZX Turbo - http://z31performance.com/forum/vie … php?t=3114
    2001 Tiburon Turbo 60-1 270whp/268tq

    No cupholders? Where am I gonna put my beer????

  • #8
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  • #9
    Chris86NA2T wrote:
    Bemis: do you think the fuel injector wiring is playing a big part in this problem? if it is, then i wont waste my time trying to fix this until i have the wiring corrected. also, how would i go about "turning off" the voltage latency scale? in the nistune software there is a single value (184 if i remember correctly) that is adjusted with a sliding scale just like the regular latency adjustment. should i set that to its max or min?
    Discussion between NA and Turbo fuel injector wiring
    viewtopic.php?f=6&t=7925

    To turn OFF the voltage latency coefficient, you can "null" it. In other words, put value to zero so that no correction takes place, no matter what the read voltages are. Of course, this is just for testing. I wouldn't suggest that you keep it OFF.
    1984 300ZXT
    1986 300ZX 2x2 NA2T
    2000 Porsche Boxster
    2007 Toyota Yaris
  • #10
    problem solved… i was grossly off in my latency estimation.. i had it way too low.. i spent two full tanks of gas and i dont know how many hours to get this solved.. i dont know why ive had such a hard time with latency and k value, but i think i got it for good this time.. heres how it worked.. the lower i set the latency, the richer the afrs became when the fan turned on.. if i had the latency way too high the afrs leaned out.. eventually i found a good value and the problem was gone.. so in effect the problem i thought i had actually helped me to solve my real problem..

    mathematically the actually null time of my dsm 450cc injectors comes out to 1380us.. i plugged this number into nistune and figured it couldnt be too far off.. i figured that all the other problems i was having were related to k value and ttpmin/max and things like that.. in the months that ive had nistune i never thought the null was an issue.. i finally settled on 2600us for the null time.. with 3 bar fuel pressure and a z32 afm i settled on 235for the K. the fuel map matches the wideband within 1/2 to 3/4 of a point under all conditions, including when the fan is on or off.. thats good enough for me.. thanks for all the advice
  • #11
    Yup, it's good that you found the solution and this is good info to remember.
    1984 300ZXT
    1986 300ZX 2x2 NA2T
    2000 Porsche Boxster
    2007 Toyota Yaris