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Thread: Initial Setup of TBI, TPI and MPFI systems. Min Air Adjust, TPS set and Fuel Pressure

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    EFI GearHead ! EagleMark's Avatar
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    Initial Setup of TBI, TPI and MPFI systems. Min Air Adjust, TPS set and Fuel Pressure

    Initial EFI Conversion System Setup for TBI systems, works with TPI/MPFI as well.

    I know the first thing guys want to do when hooking up their fuel injection set up is to start it up and hear it run....
    Well there are a couple things that need to be done after the installation.

    1. Timing
    Disconnect the bypass wire and set timing to 0 at idle when warm. Procedure- warm up motor then turn off. Unplug bypass. Start motor. Set timing to 0. Turn off motor. Reconnect bypass. Unplug ECM to clear fault code.

    2. IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. It should be set to 100-125 RPM below idle commanded in bin file. At ALDL connector you need to put a jumper between pins A and B of the connector. These are pins A9 (what/blk) and A12 (blk/wht) on the ECM. This puts the ECM into ALDL mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the TunerPro running up and running on your laptop, or a Scan Tool you should see the IAC went from 145 to 0. Now unplug the IAC connector. Turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It will probably be behind a silver plug. If so just use a drill bit slowly to drill a hole, not to deep as to damage the torx screw behind it, just enough to use a punch to grab it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed in bin. If 600 then set to 500 rpm. You are looking for the lowest consistent idle your motor will do. When set, turn off motor and reconnect the IAC. I try to keep the IAC count to at least 10-20 with the motor warm and idling. Higher number are OK but more air pushing gas past throttle blades on TBI engines is better!

    3. TPS Throttle Position Sensor. With the idle set, you need to set the TPS idle voltage. This need to be set to about .54V to .60V
    The TPS is on the passengers side and will have 2 screws holding it on. The factory TPS will not have much room in the holes for adjustments so I use a drill bit or file to elongate the holes as needed. Or bend tang on throttle shaft. To adjust, just loosen the screws and twist the TPS. You can monitor the voltage on Pin B of the connector with the key on or at pin C13 of the ECM. You can also see it in TunerPro or Scan tool! Anything away from .54V will also show as a percent of throttle on 1227747 ECM like .2 percent or 1.7 percent...depending on how far from .54 you are. But otherECM/PCM set to 0% when key on. I try to keep the idle setting to within 1 percent do to settings in bin file.

    This is also a good time to check your TPS voltage. Once it is set, just watch the voltage as you open the throttle. you should see a steady rise in voltage up to about 4.5-4.8V at WOT-wide open throttle. If it jumps up and down or skips some then you will need to replace it.

    4. Fuel pressure The systems calculates the fuel needed based on the initial settings for injector size at a specific pressure. If the pressure changes then the fuel calculations will be off. I recommend checking the feed and return line pressures at the very beginning. This can save a lot of time later. The pressure on TBI should be 13 psi and 43.5 on TPI/MPFI with stock regulaters.
    These are feed side pressures and should not change with rpm or load.

    The return should be near 0 psi.

    These are basics that need to be done before any tuning or data logging can begin.


    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  2. #2
    Fuel Injected! JeepsAndGuns's Avatar
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    Though I have not tried it since I have installed it. I have read that the 7427 (and simmilar pcm's) do not drive the iac closed when the pins are jumpered.
    Any advice for setting min idle on those? Only thing I can think of would be run engine till warm, then watch iac steps in tunerpro and adjust idle screw untill desired number of counts is reached.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 99+ intake, SS header, dynomax exhaust, 5 speed, 8.8 rear, WJ front brakes, hydroboost, P-pump conversion, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  3. #3
    Quote Originally Posted by JeepsAndGuns View Post
    Though I have not tried it since I have installed it. I have read that the 7427 (and simmilar pcm's) do not drive the iac closed when the pins are jumpered.
    Any advice for setting min idle on those? Only thing I can think of would be run engine till warm, then watch iac steps in tunerpro and adjust idle screw untill desired number of counts is reached.
    That would be my best guess. I never tried it, however. I'll have to take a look at a log and see what my IAC is doing when at idle...
    Familiar with 1227747 and 16197427 PCMs

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    EFI GearHead ! EagleMark's Avatar
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    I must have lost my post? I was going to check this when the kids IH TBI 16197427 Conversion is done.

    When doing it this way you may have to turn engine off, wait a minute and restart to see actual results as it resets during start. If you make changes while running and IAC hooked up. Bigger throttle opening = less IAC counts.

    Then have to check TPS voltage. Although some say it's OK under 1 volt, I like factory spec per ECM/PCM.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Here's a homegrown way to set minimum air that I learned with carbs and still works today. Get a strip of paper about 1/4" to 3/8" wide and maybe 5" or more long. Open the throttle and insert the paper into the throttle bore past the throttle plate and shaft. The paper should be perpindicular to the throttle shaft. Release the throttle and gently try to pull the paper. If the paper has a slight drag then the throttle angle is ok. If it's too tight you risk stalling and a sticking closed throttle when the engine's cold. If it's too loose you risk having a high idle the ecm is unable to control. Ensure IAC counts are 30-35 and tps volts are below .75 and you're usually good to go.

    If you want to set minimum air while the engine is running there are a few ways to do it. You can remove TPS or use a substitute TPS to fool the ecm into thinking the throttle is closed, then increase engine speed slowly until the ecm / pcm tries to command the IAC all the way closed. Disconnect IAC, close the throttle, and check your RPM. Or you can get an IAC test tool and use it to drive the IAC closed. Or you can get a special rubber plug designed to plug the IAC passage (known as a dog turd to GM dealership techs).

  6. #6
    Fuel Injected! JeepsAndGuns's Avatar
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    Quote Originally Posted by 1project2many View Post
    Or you can get an IAC test tool and use it to drive the IAC closed.
    I have often wondered if there was a way to "bench" test a IAC. Any more info on this tool? Is it electrical or what?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 99+ intake, SS header, dynomax exhaust, 5 speed, 8.8 rear, WJ front brakes, hydroboost, P-pump conversion, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by JeepsAndGuns View Post
    I have often wondered if there was a way to "bench" test a IAC. Any more info on this tool? Is it electrical or what?
    I've done that on my test bench, the plunger extends all the way and pops out!
    Attached Files Attached Files

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Fuel Injected! JeepsAndGuns's Avatar
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    So basicly 12 volts has to be "pulsed" to either extend or retract it? Like grounding one wire, then quickly touching and releaseing the other to a hot wire?
    I have a couple spare ones from a old dodge tb, I may play with them, if I burn it up there is no loss...lol
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 99+ intake, SS header, dynomax exhaust, 5 speed, 8.8 rear, WJ front brakes, hydroboost, P-pump conversion, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  9. #9
    EFI GearHead ! EagleMark's Avatar
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    My test bench is not running, I'm in the middle of building a harness or I would check for you. Pretty sure 12 volts will burn it up. It's a 5 volt signal... IIRC

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  10. #10
    Fuel Injected! JeepsAndGuns's Avatar
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    Ahh, good to know.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 99+ intake, SS header, dynomax exhaust, 5 speed, 8.8 rear, WJ front brakes, hydroboost, P-pump conversion, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  11. #11
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    This article explains pretty well how the various types work: http://www.megamanual.com/ms2/IAC.htm. Just read around the megasquirt configuration stuff that you dont care about :)

    - Frank

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    A stepper motor like the IAC need to have power and ground applied to different terminals to make the armature turn a complete revolution. Look at the gm wiring diagram for your system and you'll see two connections for coil A and coil B. Each of these needs to be connected to 12V in turn on order to make the IAC move. When the ECM shows IAC counts, that's how many times the ecm has applied power to one or the other coils to make the IAC move. I have an old tool made by Thexton but I couldn't find it in their current tool lineup. Here's a thread that gives a homegrown way to check the IAC: http://www.chevytalk.org/fusionbb/sh...96c4b37436442/ There's also a mention of an OTC3320 IAC tester but I really think those old tools are only going to show up in Ebay auctions or swap meets now.

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    EFI GearHead ! EagleMark's Avatar
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    You sure it's 12 volt? I wasn't... then read the IAC procedure .pdf and it says do not apply 12 volt... ?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  14. #14
    Fuel Injected!
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    I tried this procedure and when the A/B pins were shorted the IAC made noise and never stopped. Just kept sort of buzzing. Well, I didn't wait forever, but 30 seconds or so. Should it take a long time to bottom out, or is something wrong with my IAC?

    Also, you specifically said to have almost no pressure on the return line. Why is that important? I've never checked it, but I am using a section of my original 1/4" steel return line, which may be on the thin side.

  15. #15
    EFI GearHead ! EagleMark's Avatar
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    Yes when it's buzzing it is completly closed and ready to pull the connector.

    Any pressure on return line directly increases pressure on feed line. Remember when you pinched your return line?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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