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Thread: Obligatory first post introduction from a newbie to EFI

  1. #1
    Fuel Injected!
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    Obligatory first post introduction from a newbie to EFI

    Hello all.
    I am trying to learn as much as I can about tuning an engine using a computer. I have been into vehicles/engines for many years but mainly have dealt with carburetors for fuel mixing. I have also spent some time with naturally aspirated IDI diesel engines mainly the GM/Detroit 6.2.

    I have moved into the end of the last century as far as computer control goes. I am currently working on learning to tune a Chevy Vortec 5.3 from a 2000 Silverado that I have transplanted into my 2000 Jeep Wrangler. I am able to drive the Jeep at this point but am struggling with getting it fine tuned.

    I am pretty comfortable at the keyboard as far as using a PC goes. What I am trying to learn now is the science of internal combustion engines and how the PCM/ECU controls the engine. I am feeling overwhelmed and feel like a baby steps are still too big for me...Some of the terminology and abbreviations are still new to me. I am hoping that once the terminology sinks in the tuning will become easier.

    I'm guessing I will be lurking around for a while before I muster the courage to start asking questions.

  2. #2
    LT1 specialist steveo's Avatar
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    cool swap. i have a 2000 jeep and haven't had the guts to swap to a real engine yet.

    all reasonable gas injection systems pretty much work the same.

    the ecm reads a timing reference (usually a cam and/or crank sensor) so it knows both what position the engine is in, and how fast it's moving. on older engines those are in the base of the distributor

    it has various inputs like directly measured airflow (MAF), engine vacuum (MAP), throttle position (TPS), coolant and intake temperatures, etc.

    it takes the engine position and speed and those various inputs, using various 1, 2, and 3 dimensional tables that the ECM has (the calibration) and running math on them to figure out how much fuel to squirt.

    a calculation might use a MAF for direct airflow, which doesn't really involve a lot of math, but a vehicle without a MAF would use speed density (manifold vacuum, intake temperature, and RPM together with a table of how much airflow an engine can produce at each point)

    it then opens the injector(s) for a certain amount of time to inject that much fuel

    a sequential system opens each injector individually for each cylinder, a batch fire system opens whole sets of injectors.

    when it's in 'closed loop' that means it gets feedback from an oxygen sensor in the exhaust to figure out how close its calculation for fuel quantity is, and adjust it (short term fuel trims) and if that adjustment is helpful on later injections, it will remember (long term fuel trims)

    it does the same with spark, uses various inputs and tables to determine when to fire the coil(s). obviously with spark you want to burn the whole air/fuel shot off without going too far.

    some ECMs form a closed loop with spark too, with knock sensor(s). when it sparks and there's a knock, it removes some timing advance and if that helps, some ECMs remember that knock retard for next time.

    the goal of the injection is to keep fueling within a certain reasonable range for the condition (flooring it, cruising lightly, or limping along with a failed sensor) and also keep spark advance within a range where the air/fuel charge can be burned completely without going far enough to cause knock

    if you understand that stuff you pretty much know enough to tune, the tools you already have (the ecm's narrowband sensors and knock sensor) are good instruments for basic tuning, you just need to datalog them and learn to read those logs

    of course there's idle control, transmission control, air conditioning control, and all sorts of other accessories that ECMs are responsible for

  3. #3
    Fuel Injected!
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    Thanks stevo. I appreciate the synopsis. I guess I have made a few baby steps so far. I am really trying to figure out how the different tables interact with each other.

    I have done some industrial automation in my past. I have integrated plc's and robots on assembly lines. It's basically inputs controlling outputs. Current or voltage (4-20ma or 0-10v) control of electric motors that sort of thing.

    In the terms of engines I am trying to first learn all the abbreviations that get used. On top of that I am hoping to get a grasp on how making changes to certain tables in the program can affect how rich or lean the engine runs and how much power can be achieved without damaging the engine.

    I have purchased EFI Live and have used that to disable VATS in my PCM. I also have a wideband O2 sensor to monitor the air fuel ratio. But trying to get help at the EFI Live forum feels like a slow process. I've decided I need to do a bunch more reading before I go back there to ask for more help.

    I have also started looking at some free alternatives. I'd like to understand this stuff well enough that I can use whatever tool I'm in front of to make alterations to my "tune" in the future.

    It feels like a lofty goal right now. If only I knew what I don't know I should be reading...

    I have my Jeep running fairly well now but I know some of the tables (or at least one table) are off because I can watch the wideband gauge show lean (between 17-18 AFR) while I'm accelerating. When I'm cruising at a constant speed it does settle right around 14 AFR. I'm hoping to get the tune closer sooner than later so I'm not burning up my pistons.

  4. #4
    LT1 specialist steveo's Avatar
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    I have my Jeep running fairly well now but I know some of the tables (or at least one table) are off because I can watch the wideband gauge show lean (between 17-18 AFR) while I'm accelerating.
    that's very lean for acceleration indeed,

    do you see that when gently accelerating, briefly when stabbing the throttle, or flooring it?

    what modifications have been made to your engine?

    if you floor it and it goes lean, you are running a stock-like calibration for the engine, and few modifications have been made, you need to back right off, it's not your tune that's the problem.

  5. #5
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    Thanks for the help stevo. It really helps to have input from someone that will ask the questions I didn't know I should be thinking about.

    The engine is completely stock. I did mount the MAF directly to the intake and it has a high flow air cleaner in a cold air intake setup.

    It runs lean the entire range of acceleration. I just took it for a test drive to be sure before I responded.

    It idles (cold) around 15 AFR. Just off idle it jumps to around 17 and as I increase pedal it creeps up from there. If I stab it WOT it drops to between 15-16. This morning was the first time I noticed on deceleration it was going above 23 briefly. My gauge stops displaying over 20 if it stays there for more than a second or so. It will just display --- when it is that much too lean.

    So based on that I'm wondering if I have a fuel delivery problem? I used the stock Jeep fuel pump but bypassed the pressure regulator at the tank. I don't have a fuel pressure gauge but I've read multiple places that the stock Jeep pump can deliver enough pressure and fuel once the regulator is bypassed. I also used the stock Jeep fuel supply line to the engine. It is only 5/16" and the stock GM fuel supply line is 3/8". Could 1/16" difference in size be a problem?

    I suppose I should probably start a thread in the proper section to be asking questions?
    Last edited by jeeper; 06-23-2020 at 06:01 PM.

  6. #6
    LT1 specialist steveo's Avatar
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    you almost certainly have a fuel problem

    do not tune around it

    run a fuel pressure gauge under load to see if it drops pressure

  7. #7
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    Quote Originally Posted by steveo View Post
    run a fuel pressure gauge under load to see if it drops pressure
    Thanks steveo. I really do appreciate the tips.

    I will get a fuel pressure gauge but I'm already wondering how I will be able to see the gauge while I'm driving to produce a load. I assume I can buy an electric gauge and not a mechanical gauge? I'd prefer not to run a pressurized fuel line into the cab from the engine bay.
    Last edited by jeeper; 06-25-2020 at 02:22 AM.

  8. #8
    Fuel Injected!
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    Get a mechanical fuel pressure gauge with a long enough hose that it can exit at the rear of the hood.
    Close the hood and tape the display just under your most common driving line-of-sight.
    THEY are NOT Lying to You.
    You are NOT Even Lying to Yourself.
    You ARE Being Lied to ... by Your SELF.
    The Last Psychiatrist, aka ... Alone ...


  9. #9
    LT1 specialist steveo's Avatar
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    yeah that's the best cheap way. i also just rev the piss out of it in neutral in the driveway to see what happens. fuel pressure should peak and level out almost immediately when opening the throttle, and never drop until you let off.

    think of it this way, you hit 18:1 and the stock cal is probably like 11:1!?

    that is a massive error in the area of 60% (too lazy to open a calculator)

    there should be really obvious evidence of the problem that should stick out like a sore thumb. i'm not talking about a difference in fuel line size here, i'm talking a dead or way too small fuel pump.

  10. #10
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    I will probably go to Hardly Freight and pick up a gauge today.

    I'm assuming I will be replacing my fuel pump soon. And also upgrading the fuel line. What are others running for fuel pumps in their swaps?

    I bought a Walbro 450 LPH pump for my other Jeep swap project I have been working on but the price has gone up a LOT since I bought the first one. I haven't installed it yet so I could use it on this project but I'm sure it will be needed on the project it was purchased for. That project is using a rebuilt 6.0 LQ4 that should be capable of around 450-500 HP and I will be attempting to set it up with flex fuel capability.

  11. #11
    Fuel Injected!
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    I picked up a Cheap gauge today and tested the pressure in my driveway. Clearly I am not getting adequate fuel.

    Video of results:

    https://youtu.be/sVji3PU9bdA


    I will be dropping the tank soon I guess. Thanks for the help steveo! Maybe some day I can buy you a beer or something.

  12. #12
    LT1 specialist steveo's Avatar
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    it looks like it's being regulated to your original jeep's fuel fuel pressure. my 2000 jeep uses static pressure from a regulator that is built into the fuel filter. i think you are running two regulators.

  13. #13
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    The Jeep fuel filter/regulator at the tank has been removed. I put a solid 3/8" line in its place. I attached rubber line between the new 3/8 hard line I installed, and the stock Jeep fuel line. The rubber line is rated for (I think) 4 bar which is right at its limit if I were actually getting 58 psi from the pump.

    I believe I read the stock Jeep regulator is rated at 49 PSI. That does seem suspiciously close to the 50 I was seeing on the gauge but I assume that has to be the GM regulator doing that. I plan to try to attach the gauge ahead of the GM regulator to see if the Jeep pump is putting out even close to enough pressure before the GM regulator.

    Yesterday I also purchased an external fuel pump (Walbro clone) rated at 255 LPH. It unfortunately doesn't say what pressure it puts out at that rating though. It should be here Monday. Today in my parts stash I found a new Bosch fuel pump I purchased for my last TJ but never installed. I may try dropping the tank and throwing that in to see if it's any better. I'll try to get a picture of the bypass I did of the Jeep regulator too if I do end up dropping the tank.

  14. #14
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    Another update just in case anyone is interested. Today I disconnected the vacuum line between the intake manifold and the fuel rail mounted regulator and recorded the results.

    I don't think the fuel pump is my problem. I'm leaning towards the GM regulator or a vacuum leak.

    Video of the test this morning are here:



  15. #15
    Fuel Injected!
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    I have started a thread of this engine swapped Jeep here in case anyone wants to follow along:

    http://www.gearhead-efi.com/Fuel-Inj...3090#post83090

    I have added a follow up video showing a short drive with the vacuum line disconnected. I will continue to update that thread so future searches may possibly benefit from my struggles just as I have benefited from others posting their progress on their swaps.

    Also thanks again to steveo and LeMarky Dessod for your help so far.

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