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Thread: Help with fresh start up. Olds 455 MPFI $0D

  1. #1
    Fuel Injected!
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    Help with fresh start up. Olds 455 MPFI $0D

    Can anyone help me adjust the crank, start and run, iac and idle settings? What do you guys do when starting from zero? The below paragraph is just issues I'm having and can be disregarded if it's to long, I guess I really just need a step by step of what to do to get things close enough to start driving to tune it. Maybe a link to a .bin that has the pe hack and all the cool mods installed?
    I have my Regal running but its using so much fuel its unreal. Just starting and trying to get the Idle off 10afr has used 1/2 a tank In several start ups. I'm just wondering if I took to much off the idle ve and the computer is compensating. its in open loop so I didn't think it would But I have gone back and forth with the injector settings and ve settings trying to get it from not starting because not enough fuel at start up to straight 10's on the meter. I have 48# accel ls style injectors and a 400lph (or close) boche fuel pump so I wouldn't have to upgrade later if need be. Fuel pressure is at 43#'s or close. It idles at 1200 rpm 10afr but goes to 19 afr if I hit the throttle. Ive moved the ae settings and always get the cough at first touch of the throttle. I started with a .bin my dad is running his olds 403 mpfi with but I have a ls throttle body, he has a 4 barrel carb type TB. I took the iac motor out and plugged the hole and the iac is all the way up and when i hit the throttle it pushes the valve in. I am in the opinion that the iac is doing the opposite of what it should b doing, so I checked the wiring and is correct. Would making a log and running through the spreadsheet help with these issues? My dad did not tune his the way I have read you are supposed to, he made the afr meter read what he wanted from the ve and didnt use pe at all. Throttle blade is closed all the way and dies if i plug the iac inlet hole.
    Thanks for the help

  2. #2
    Super Moderator dave w's Avatar
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    Re: Help with fresh start up. Olds 455 MPFI $0D

    The attached show how to set the TBI IAC.

    Possibly the below procedure will verify the IAC is working correctly / wired correctly by verifying the IAC pintle is fully extended. Seems likely the IAC will need to be removed to verify the pintle position.
    1- Engine warmed up, key OFF, tranny in PARK
    2- Put a jumper wire from pin “A” to pin “B” on the ALDL
    connector (should be the black wire & white wire) A metal
    paper clip works good for this.
    3- Turn key to ON, do not start engine, wait 10 seconds. This
    will extend the IAC pintle and close off the air passage in the
    body of the TBI. Remove the electrical connection to the IAC
    by pulling it straight out. Turn the key to OFF and remove the
    jumper from the ALDL connector.
    Attached Files Attached Files

  3. #3
    Fuel Injected!
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    Re: Help with fresh start up. Olds 455 MPFI $0D

    That's great, very helpful to know what the counts and tps voltage should be! This helps with my truck as well. Thank you I will update after i try this. Not knowing the target data or correct readings is my main issue... Again thank you very much!!

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    Re: Help with fresh start up. Olds 455 MPFI $0D

    Can anyone help me adjust the crank, start and run, iac and idle settings? What do you guys do when starting from zero?
    We can try. cranking and startup can be tough. Luckily idle and running settings are usually a little easier.

    That's great, very helpful to know what the counts and tps voltage should be!
    TPS should be below .72V. IAC counts stock are usually around 25-32 but in the beginning of tuning this isn't as important. And the more modified your engine is, the more likely you won't see stock IAC numbers.

    I have 48# accel ls style injectors and a 400lph (or close) boche fuel pump so I wouldn't have to upgrade later if need be. Fuel pressure is at 43#'s or close.
    Did you change the injector constant to match the injector? Did you change the injector corrections as well? These can make a big difference in fuel delivery. Some people spend years chasing their tails b/c they don't get these right in the beginning. I usually set the injector values then leave them alone.

    I took the iac motor out and plugged the hole and the iac is all the way up and when i hit the throttle it pushes the valve in. I am in the opinion that the iac is doing the opposite of what it should b doing, so I checked the wiring and is correct.
    That definitely seems backward. Are you able to see IAC direction or IAC counts in the scan data to confirm which way the ECM is commanding the IAC to move? Dave's method to check IAC operation is pretty easy. If the IAC really is operating backward you need to swap two wires in the IAC connector. It doesn't matter which two, just swap two. I usually swap the blue and blue/white or blue/black. Some IAC motors are wired differently internally and require this change.

    I'm just wondering if I took to much off the idle ve and the computer is compensating. its in open loop so I didn't think it would
    The computer does not compensate for AFR issues in open loop so no need to worry about somehow adding issues to the tuning process.

    Would making a log and running through the spreadsheet help with these issues?
    It sounds like you have some more troubleshooting to do, but it can be very helpful to take time to write down changes and settings. First, it gives you time to sit and think. Second, you can end up changing so many things that you forget what you've done.


    As far as the actual tuning, Cranking can be very challenging. With a "completely from scratch" build I like to have a fuel pressure gauge available to put on the system during cranking, at least in the beginning. Why? I once spent an entire day trying to make a car start by adjusting everything I could think of in the ecm when it turned out the way the fuel pump was wired, it wasn't getting enough power during cranking.

    Are you using a wide band O2 or just the stock style O2 sensor? Is the sensor heated? Is it getting warm enough to read accurately? Either can work, but I like using O2 voltage for a NB sensor instead of AFR. NB sensors are not accurate for AFR outside of stoich.

    Timing is a really big player in cranking. What is your timing set to? Setting the distributor more advance during cranking is ok, just be careful not to go too much. I've worked on engines that liked 10 degrees base timing. If that's what works best, I'm ok with using it.

    I like to get the VE and timing good at idle and off idle then work on cranking after the fact. It's ok to use a little starting fluid or a starting aid to get the engine to light off, just keep safety a priority.

    Do you have something like "desktop dyno?" I've used that to create a starting VE table before. The shape of your VE curve will end up close to the shape of your torque curve. DD doesn't generate a torque curve at low rpm but if you start with 0 VE at 0 RPM you can fill in th emissing numbers to create a rough calibration.

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