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Thread: Newbie tuning saga of my LS Jeep TJ

  1. #31
    Fuel Injected!
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    I believe I found the original tune that was on the computer that I believe to be the stock 2000 Silverado computer. It was OS 09381344. In table B4001 it shows the injector flow rate at 3.1250.

    In the current OS on that same computer it shows the same flow rate table as 3.1797.

    So should I change the flow rate in my 12212156 OS to match 3.1250 instead of 3.1797?

  2. #32
    Fuel Injected!
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    That would be a good start to see if anything changes. I have a good working original copy of 12212156 here and an already edited copy with VATS removed, etc if you need it.

    Rick
    1970 Chevy El Camino, LM7 Engine, 4L60E - Two 896 and two 0411 PCM's

  3. #33
    Super Moderator dave w's Avatar
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    according to the injector calculator I'm using:
    3.125 g/sec = 24.8 lb/hr
    3.1797 g/sec = 25.2 lb/hr

    Injector base pulse width (BPW) is calculated using injector flow. Increasing the injector flow will cause the computer to lower BPW = Less Fuel. Decreasing the injector flow will cause the computer to increase BPW = more fuel.

    If you want more fuel change the injector flow to 3.125.

    Maybe we shouldn't be so quick to say the flash is 100% correct? Let's see what happens when the injector flow is set to 3.125

    dave w

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  5. #35
    Fuel Injected!
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    I just verified changing the flow rate did not correct my lean condition. I then did a MAF fail to see it maybe the second used MAF is contributing to the lean condition. It is not. I am still running lean as soon as I go above idle for a second or two.

  6. #36
    Super Moderator dave w's Avatar
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    Quote Originally Posted by steveo View Post
    a difference in injector flow of less than 2% wouldn't be causing fueling errors in the range of 20%
    I agree 100% with you steveo, 2% wouldn't be causing 20% errors.

    Now, I have to wonder what fuel pressure regulator is being used, return-less or vacuum referenced? The injector flow rate for a return-less fuel pressure regulator is linear with different flow rates in each cell. If a Corvette fuel filter / pressure regulator is being used, then having all fuel injector cells the same flow rate 3.125 would be incorrect.

    dave w

  7. #37
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    It is a new return style vacuum referenced regulator.

    Would the MAP sensor play into this at all? How would I test it? What is a "normal"reading for a stock engine at idle and say 2000 rpm?

  8. #38
    LT1 specialist steveo's Avatar
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    the map sensor is not a likely failure point. i’ve seen a dead one once in my life. the correct way to test the sensor would be to apply vacuum to it and datalog with engine not running, or use a mechanical gauge while observing the data. also when off it should be whatever your atmosphere pressure is, about 100 kpa near sea level.

  9. #39
    Super Moderator dave w's Avatar
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    I suppose there is the option to set the injector flow rate to 3.00 or lower to see what happens. The odd thing is, setting the injector flow rate lower than the factory specification on the factory stock injectors would mean .... the engine likes a rich mixture. Why would a stock engine need a rich mixture?

    I wonder what cylinder balance test might indicate?

    dave w

  10. #40
    Super Moderator dave w's Avatar
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    Quote Originally Posted by jeeper View Post
    It is a new return style vacuum referenced regulator.
    I wonder what would happen if the vacuum line was disconnected from the fuel pressure regulator? Would anything change with the ARF's at different RPM's?

    dave w

  11. #41
    Fuel Injected!
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    I've been playing with this for a few hours today. I actually set the flow rate lower by 20% thinking that may help. It didn't. I tried all sorts of things. I tried modifying the VE by 20% by both adding and subtracting 20% from the stock table. Nothing seems to be allowing it to run rich.

    At this point I am disabling vats and reloading the original OS back on the computer and testing it (if it will run at all due to the manual trans swap). My thinking is if it will start and run on the original OS I can see what the AFR is then. I'm guessing it will start because I am not using the GM computer to start it I am using the Jeep computer to crank it over.

    Before I do anything though I will unplug the vacuum line from the new regulator to see what happens.

  12. #42
    Fuel Injected!
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    edit: I did unplug the vacuum line but that didn't change anything. I tried it before and after OS change.

    Quote Originally Posted by jeeper View Post
    At this point I am disabling vats and reloading the original OS back on the computer and testing it (if it will run at all due to the manual trans swap).
    This didn't help either. It runs fine with the "stock tune" but is even more lean now including at idle... edit: when I say runs fine I mean idles smooth as glass and sounds really good.

    I'm 100% confident I'm getting good fuel pressure and I'm 95% sure I'm getting enough volume to the rail because the pressure doesn't drop when I rev the engine with the gauge connected.

    That seems to leave only the injectors left? Or maybe I have a faulty wideband?

    This isn't really "fun" anymore it's frustrating...
    Last edited by jeeper; 07-02-2020 at 10:32 PM.

  13. #43
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    Quote Originally Posted by jeeper View Post
    This didn't help either.
    Wait a minute. Time for a dumb luck update.

    I was ready to step away from this for a couple days. I decided I'd take my dog to the park for a swim in the river. My dog loves to swim and it is hot here for the last few days. I took the Jeep. It still has the stock original Silverado 9381344 OS on it with VATS removed and some automatic transmission parameters changed. I watched the wideband hover around 14.7 to 15 all the way there.

    Since I was low on fuel I decided I'd better fill up before I went home so I drove from the park to the gas station. Again it was running between 14-15. I wasn't really watching it that close. On the way home from the gas station is when I noticed (and was probably the first time I tried) at WOT I was running 12 AFR. I was a little stunned so I tried it several more times. Sure enough on this OS when I go WOT it goes rich.

    Now I have a starting point? I can now be sure I am getting enough pressure and fuel flow to the engine at least...

  14. #44
    Fuel Injected!
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    So at this point I don't really understand why I would be running lean at every RPM/throttle position except WOT. What could be broken? If it goes rich at WOT doesn't that prove I'm getting enough fuel and enough pressure? I suppose I can hook the gauge back up and record it again but I'm pretty sure it isn't a "fuel delivery" problem.

    Anyone have any suggestion on what I should be looking for? I'm probably going to step away from this for the weekend but that doesn't mean I won't be thinking about it...

  15. #45
    Super Moderator dave w's Avatar
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    Most members would agree, when cruising, AFR's ranging between 14.2 to 15.2 are good. AFR's going above 15.5 are lean. Warning: Prolonged AFR's above 16.2 will eventually damage the engine.

    dave w

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