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Thread: Injector impedance and max amps Stinger V4

  1. #1
    ethanol sniffing Backyard Mechanic adamaw11's Avatar
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    Default Injector impedance and max amps Stinger V4

    I'm running a Stinger V4, have been running it with batched injection.
    Running big injectors of 800cc which are low impedance (2.2ohms as measured), they were wired in in series, 2 injectors per channel - batched firing.

    There's been issues trying to tune it with this setup, running rough, especially on light throttle, but running fairly well under full load and boost - still an occasional misfire it seemed.

    So realising the ECU is capable of full sequential injection, I decided to re-wire the injectors for sequential firing. And have the ECU set for 3.5ohms for the injector resistance setting.
    It idles better and smoother at light load, but now has significant misfire on boost and up in the revs.

    What I've found out is the ECU says it can only take 4 amps max per injector channel.
    With my injectors being 2.2ohms, they'd probably be drawing more than this. (V=IR) 13.8volts / 2.20Ohms = 6.3amps.

    I need to find out whether this is causing my problem,
    and if it is, does it mean I'm going to have to get another ECU if I want to run low impedance injectors?
    I would have thought 4 amps per channel would be enough, but do most modern ECUs support more than this to allow running low impedance injectors?
    Surely most ecus could run injectors of 2.2ohms.
    If I need to bite the bullet and get a new ECU i want to be sure its worth it, and that this problem with max injector amps is the cause of the problem here.
    Even with the injectors in series for batched injection, I wonder if that was still too much current for the ecu to allow, and it was current-limiting, as it says it can do below.


    Quote stinger manual:
    The STINGER 4 ECU controls injectors by pulling to ground. This means that all injectors have a common positive 12 volt rail. The injectors are fired sequentially.
    You must ensure that the combined injector resistance for each output is not less than 1.2 ohms. For example connecting 2 X 1.2 ohm injectors in parallel will give a resistance of 0.6 ohms. This would cause the injector output drivers to current limit, if this were to happen then the injectors would not open consistently. All STINGER 4 ECUs automatically adjust the injector duty to compensate for battery voltage fluctuations ranging from 7 to 16 volts.

    quote stinger manual:
    The ECU uses this value to determine the injector latency and compensate for it. Low ohm injectors have a faster response time than high ohm injectors. So by setting the correct injector resistance will allow the ECU to compensate for injector latency more accurately. This also works in conjunction with battery voltage. As the battery voltage varies from 13.8 volts, the ECU will adjust the injector duty to compensate. This enables the ECU to work with battery voltages from 7 volts up to 16 volts while maintaining a steady air/fuel ratio.
    You can do a test by using a Multi-Meter. Unplug the electrical harness of one of the injectors and place the Multi-Meter's probes on the injector pin outs (where the electrical harness clips on) and measure the resistance. When you have a reading adjust this parameter to the closest setting. Note: If you are using staged injectors with a different value of Ohms, set the Ecu to the value corresponding to the primary injectors.
    http://www.toymods.org.au/forums/showthread.php?t=83259
    '88 A.D.M aw11 '98 4age 20v blacktop
    NA: 14.745@150kmh at willowbank. On E85 with 6psi boost: 13.573@165kmh. ~8psi: 13.187 @169.9kmh. >10psi: 12.9 rod fragments @ 174mm holes in block
    daily: '93 ae101 Levin coupe. Motorbike: '09 Suzuki GSR600: 12.358@179kmh at Willowbank

  2. #2
    Chookhouse Chooning Automotive Encyclopaedia Hen's Avatar
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    Default Re: Injector impedance and max amps Stinger V4

    My understanding is that when an ECU is driving low impedance injectors they will be actively controlled. In that they may get the full 12V (or really 14V) for a few ms when opening, but then the current is reduced to hold the injector open for the rest of the injector opening time. So the current is not simply voltage / resistance.

    The first quote seems to support that running 2.2ohm injectors directly shouldn't be a problem. The second quote makes me think that the injector ohm value set in the ECU is just used for battery voltage adjustments, not anything critical.

    While I am no Stinger expert I'd be surprised if the it was the ECU and injector combination that was causing your misfire. I'd be looking at other more boring things like wiring/earth issues, bad plugs, etc first.
    I need a working 4AGE bottom end. Pref smallport GZE, but all others considered. Also complete motors.
    Drift Volvo. Was fun. 2JZ next time.

  3. #3
    ethanol sniffing Backyard Mechanic adamaw11's Avatar
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    Default Re: Injector impedance and max amps Stinger V4

    Thanks, yeah I guess even if it draws 6amps briefly when the injector opens it wouldn't be a continuous 6 amp draw.

    I suppose I immediately thought it was caused by the sequential injector setup since it was after that when I really started getting the on-boost misfire. But yeah its possible it just aggravated a bad-earth issue or something from the extra current draw.
    I can try gapping down my plugs, but I'll try and make sure its not a wiring issue first.
    http://www.toymods.org.au/forums/showthread.php?t=83259
    '88 A.D.M aw11 '98 4age 20v blacktop
    NA: 14.745@150kmh at willowbank. On E85 with 6psi boost: 13.573@165kmh. ~8psi: 13.187 @169.9kmh. >10psi: 12.9 rod fragments @ 174mm holes in block
    daily: '93 ae101 Levin coupe. Motorbike: '09 Suzuki GSR600: 12.358@179kmh at Willowbank

  4. #4
    1MZ > 2JZ Carport Converter knightrous's Avatar
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    Default Re: Injector impedance and max amps Stinger V4

    If you are indeed hitting a current limit on opening the injector, it might induce a delay or stutter in opening as the injector driver suddenly sees the over current and pulls it back. Maybe throw some resistors inline with each injector to turn it into a "Hi-Z" injector and see if you get the same issue.

  5. #5
    ethanol sniffing Backyard Mechanic adamaw11's Avatar
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    Default Re: Injector impedance and max amps Stinger V4

    That was a good suggestion Knightrous, I added a 1ohm resistor on each of the 4 injector channels, and it changed the problem, it was actually back to how it was with the injectors wired in series on two channels - which is poor response under sudden load(no response, just goes lean and doesn't accelerate), but revs ok once up in the range and on boost with only slight misfire.
    I then adjusted the ECU settings to say 4.5ohm injectors, and it seemed to be a 'happy' medium between the two problems- response ok, and revs ok, but something definitely not right.

    This leads me to think it is indeed to do with how much current the injectors are getting. - either they don't get enough and aren't very responsive, or they draw too much and the ecu doesn't like it when up in the revs with higher duty cycle.

    I guess it could still be a voltage/earth wiring issue with the ecu, yet to check that, maybe I can hard wire 12v and an earth to test how it goes. But I've tested out my battery earth, don't think that was the problem.

    I actually called EMS today, the guy said the ECU should be able to run injectors with that low impedance, but agreed that current-limiting could be possible.
    He also said that they recommend using high impedance injectors, and that these days new high impedance injectors are much better.
    So I guess one thing to consider is trying to get some high impedance side-feed injectors of about 700-800cc


    edit: dunno how to link to other threads, but just found a comment which is relevant:
    Quote Originally Posted by MWP
    Do you know that using a ECU that doesn't handle low impedance injectors (ie doesnt do peak & hold) and using low impedence injectors + resistors will limit your tuning ability?

    It'll mainly effect your idle and cruise tuning ability, which = more fuel use if it's a daily.
    I was definitely finding this when trying to tune with the injectors running in series on two injector channels. On cruise, semi load, light accelerating uphill etc, it couldn't tune it any leaner than a certain point, which was still too rich 11.5 ish AFR
    Last edited by adamaw11; 31-08-2018 at 08:55 PM.
    http://www.toymods.org.au/forums/showthread.php?t=83259
    '88 A.D.M aw11 '98 4age 20v blacktop
    NA: 14.745@150kmh at willowbank. On E85 with 6psi boost: 13.573@165kmh. ~8psi: 13.187 @169.9kmh. >10psi: 12.9 rod fragments @ 174mm holes in block
    daily: '93 ae101 Levin coupe. Motorbike: '09 Suzuki GSR600: 12.358@179kmh at Willowbank

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