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Thread: No start ~ start and stall issue

  1. #1
    Carb and Points!
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    No start ~ start and stall issue

    I have a 1995 Chevy 2500 5.7 TBI that is hard to start, and when it does, it stalls immediately. I bought TunerPro because this vehicle is one of those interim year vehicles, meaning that in 1995 it could have been either OBD 1 or OBD 2, and mine turns out to be OBD 1. Sooo, now that I can communicate with it, I have questions but mainly about TunerPro.
    I am trying to find information on:
    1) term definitions
    2) normal indication limits on TunerPro
    3) startup indications
    and probably others. I am new to TunerPro, but, I don't seem to have the series of problems (comms) that others are experiencing. I just don't know what is normal and what is not. For example, TunerPro is indicating "160 : IAC Present Motor Position" and "33.51 : Injector Base Pulse Width", and I don't know if these are good or bad. I am trying to troubleshoot a "no start ~ start and stall" problem. Here I thought TunerPro was going to help and instead, this is what I feel like. I have tried looking through the index with no luck.

    Items changed prior to TunerPro: EGR, IAC, Rotar and cap, Wires and plugs
    Items changed after to TunerPro: Ignition module (called out by TunerPro),

    Vehicle smells of gas when cranking, so, I don't have a fuel problem. Changing the ignition module changed nothing. I'm tired of changing random parts.
    After >$300 in parts and no improvement in performance, I am tired of guessing. I want "know" what is wrong with my truck.

    Any help you could provide would be greatly appreciated. Thanks.
    Last edited by PDD33734; 11-07-2017 at 07:07 PM. Reason: added vehicle information

  2. #2
    Fuel Injected! steveo's Avatar
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    Quote Originally Posted by PDD33734 View Post
    After >$300 in parts and no improvement in performance, I am tired of guessing. I want "know" what is wrong with my truck.
    ironically, you only find out what's wrong with something by guessing. diagnosis is always guess work, but you'll want to rule things out one-by-one.

    I just don't know what is normal and what is not.
    most sensors read real-world values, and you can confirm with common sense, such as:

    your coolant temp or CTS or whatever your adx calls it should be near-ambient before you start, then climb up as the engine warms. if the engine will not run, you can remove the sensor and heat it while logging to ensure that the value is changing to reasonable values.

    map sensor senses engine vacuum, so it should be around ~100kpa (or whatever your local atmospheric pressure is) before the engine starts when there is no vacuum, then it should match intake vacuum when running, say 30-40kpa. you can use a mechanical vacuum gauge to verify on a running engine, or you can unhook the map sensor, stick a hose on it, and apply vacuum with a hand pump too.

    the iac valve moves in steps, which is confusing, but 0 is closed and 160 is damn near wide open. the wider the opening, the more idle speed it's trying to attain. your engine being TBI, i'd expect it to be very far open on a cold engine and for cranking, progressing to nearly closed on a warm engine. the IAC adds air to what comes through your throttle plate(s) to attain the idle speed, so if your plates are too far closed with the idle screw, the iac will tend to stay open and still never attain its target idle speed, and if your plates are too far open, it'll hang out at zero all the time.

    throttle position (tps) should be near-zero at closed throttle and 100% at open, you should be able to slowly move it from closed to open a few times and watch the number move, if it jumps around or drops while moving the throttle, TPS is bad

    i think those are the only sensors necessary for starting that engine.

    Vehicle smells of gas when cranking, so, I don't have a fuel problem
    that's very far from good detective work,

    are you sure the 'smelly fuel' is coming out of the injectors?

    are you sure your fuel pump running constantly once the engine starts? what's your fuel pressure like?

    have you physically removed the air cleaner and looked at the injectors?

    when the engine dies, do the injectors shut off dead?

    if you drizzle a bit of fuel into the intake once the engine catches, can you keep it running?

  3. #3
    Carb and Points!
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    "no start ~ start and stall" problem

    Quote Originally Posted by steveo View Post
    ironically, you only find out what's wrong with something by guessing. diagnosis is always guess work, but you'll want to rule things out one-by-one.

    most sensors read real-world values, and you can confirm with common sense, such as:

    your coolant temp or CTS or whatever your adx calls it should be near-ambient before you start, then climb up as the engine warms. if the engine will not run, you can remove the sensor and heat it while logging to ensure that the value is changing to reasonable values.
    Sadly it seems this is the norm in automotive electronics and diagnostics in general.

    Speaking of the CTS, if I knew how to add my "list view" I would post the entire thing, and on it you would see the following (except bracketed comments) :
    -=TEMPERATURE=-
    73.4 Engine temperature (the actual ambient temperature before starting engine)
    23.0 Coolant temperature (No clue)
    -40.0 Manifold air temperature (I do not have a manifold air temp sensor)

    The "engine temperature" reading is derived from the intake manifold "coolant temp sensor", and changes with the application of a flame. The "Coolant temperature" reading however does not change, and so I'm sure you can see my dilemma. Which one is relative to the CTS information? If 23 degrees F is what the computer thinks is the "Coolant temperature", then I understand why it smells and looks like the engine is flooding. [Yes, the injectors are spraying] The tables are telling it to do that, so, given the disparity of these "labels", how do I determine if a reading being provided even matters? After all, I would tend to think the ADX file knows what information I need to see.

    map sensor senses engine vacuum, so it should be around ~100kpa (or whatever your local atmospheric pressure is) before the engine starts when there is no vacuum, then it should match intake vacuum when running, say 30-40kpa. you can use a mechanical vacuum gauge to verify on a running engine, or you can unhook the map sensor, stick a hose on it, and apply vacuum with a hand pump too.
    My MAP sensor was disconnected when I acquired the vehicle and it ran for 4+ years that way. The MAP sensor connected reads 11.1. Connected or disconnected, nothing changes the startup problem.

    the iac valve moves in steps, which is confusing, but 0 is closed and 160 is damn near wide open. the wider the opening, the more idle speed it's trying to attain. your engine being TBI, i'd expect it to be very far open on a cold engine and for cranking, progressing to nearly closed on a warm engine. the IAC adds air to what comes through your throttle plate(s) to attain the idle speed, so if your plates are too far closed with the idle screw, the iac will tend to stay open and still never attain its target idle speed, and if your plates are too far open, it'll hang out at zero all the time.
    This makes sense.

    throttle position (tps) should be near-zero at closed throttle and 100% at open, you should be able to slowly move it from closed to open a few times and watch the number move, if it jumps around or drops while moving the throttle, TPS is bad
    I forgot to mention that this was changed also, and confirmed to be bad at the time. And now with TunerPro its a quick and easy check. It responds as expected.

    i think those are the only sensors necessary for starting that engine.
    Does the O2 sensor provide a (reliable) reading during startup or is it disregarded for a period of time while warming up? I think I already know the answer but just checking. I'm assuming open loop.

    are you sure the 'smelly fuel' is coming out of the injectors?
    Yes.

    are you sure your fuel pump running constantly once the engine starts? what's your fuel pressure like?
    I have fuel at the injectors, cannot find my pressure tester.

    have you physically removed the air cleaner and looked at the injectors?
    Yes. They spray while cranking, and the pattern looks good.

    when the engine dies, do the injectors shut off dead?
    Yes. An oil pressure sensor controls that.

    if you drizzle a bit of fuel into the intake once the engine catches, can you keep it running?
    As I recall. yes.

  4. #4
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