Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Fuel injector logic? '91 ECM

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KRAZIE87K5, Aug 30, 2003.

  1. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Fuel injector logic? \'91 ECM

    I've just gotten to turn the key on this '91 setup that I dropped in the K5. Its a STOCK motor from a '91 K5, harness and all the rest is intact with the motor. I'm cranking it for the first time, and the injectors aren't firing.

    Can anyone assist here? I'm pulling what little hair I have left out here... /forums/images/graemlins/rotfl.gif /forums/images/graemlins/1zhelp.gif

    I even wired in the secondary pins on the ECM to fire the injectors! See below for details...

    Click here for the secondary pinouts!!!

    -Dan
     
  2. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Re: Fuel injector logic? \'91 ECM

    BTW - If I spray a good amount of carb cleaner down the TBI it starts. Keep in mind, this is the FIRST TIME I am starting this engine in my truck, and I am not real excited about running it on carb cleaner. Secondly, I am not sure that the timing is PERFECT, but rest assured its close. I had it idle for 3-4 seconds on the carb cleaner.

    Finally... I'm running open exhaust manifolds, SO I am done for tonight, as I really don't want to piss off the neighbors THAT bad! /forums/images/graemlins/eek.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif

    IDEAS???

    -Dan
     
  3. zcarczar

    zcarczar 1/2 ton status

    Joined:
    Feb 10, 2002
    Posts:
    2,495
    Likes Received:
    0
    Location:
    Apple Valley California
    Re: Fuel injector logic? \'91 ECM

    Ok, the injectors work off of a pulse ground. The ECM pulses the ground to the injectors, thus causing them to fire. They also recieve power from the positive lead on when the key is on. So check and make sure you are getting proper pulse and have power to the injectors when the key is on. Also, is the fuel pump running for 2 seconds when you turn the key on?
     
  4. zcarczar

    zcarczar 1/2 ton status

    Joined:
    Feb 10, 2002
    Posts:
    2,495
    Likes Received:
    0
    Location:
    Apple Valley California
    Re: Fuel injector logic? \'91 ECM

    O yeah, if the fuel pump isn't providing enough volume or pressure the truck wont start, and when you crank it do you have fuel firing from the injectors?
     
  5. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Re: Fuel injector logic? \'91 ECM

    [ QUOTE ]
    Ok, the injectors work off of a pulse ground. The ECM pulses the ground to the injectors, thus causing them to fire. They also recieve power from the positive lead on when the key is on. So check and make sure you are getting proper pulse and have power to the injectors when the key is on. Also, is the fuel pump running for 2 seconds when you turn the key on?

    [/ QUOTE ]

    I've got voltage to the injectors with the key on, and I also hear the FP run for a short while as well. I've gone as far as to jump the relay, causing the pump to run endlessly. This should also tell the ECM that the pump is running correctly, which I would only think would urge the ECM to fire the injectors.

    I have checked pin A6 (switched 12v to the ECM), and it reads just fine. I tutorial I have says, "With 12v here, as soon as the distributor turns, the injectors will start firing." I have a definate problem with that statement... /forums/images/graemlins/rolleyes.gif

    I need more information I think...

    -Dan
     
  6. zcarczar

    zcarczar 1/2 ton status

    Joined:
    Feb 10, 2002
    Posts:
    2,495
    Likes Received:
    0
    Location:
    Apple Valley California
    Re: Fuel injector logic? \'91 ECM

    Ok, you need to see if your getting fuel from the injectors while cranking.
     
  7. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Re: Fuel injector logic? \'91 ECM

    There's a spark reference pulse that comes from the distributor to the ECM. The injectors will fire once for each time this pulse is received from the distrbutor. Without the pulse, the injectors won't fire.

    BTW, do you know what application the ECM came from? If it came from an application that had a VATS (Vehicle Anti-Theft System), then it's a bit more tricky to get the injectors to fire. /forums/images/graemlins/eek.gif

    It would help to find out if the injectors are getting a signal to fire. 12 volts is applied to one side of the injector coils constantly in crank and run. The ECM applies ground to the other side of the coils to fire the injectors.

    Also, even though the pump is running, are you sure that it is actually creating fuel pressure? Without pressure, nothing will come out of the injectors. /forums/images/graemlins/wink.gif
     
  8. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Re: Fuel injector logic? \'91 ECM

    OK, I took a look at your drawing... Does your harness only have wiring to C16 and D14? (I'm asking because you mentioned that you hooked up the "secondary" pins). From the drawing, it looks like they use injector drivers in parallel for 5.7 and 7.4 liter engines. This would infer that a single driver can't handle the current draw of the injectors for those engines. It looks like the wiring for your engine should have one injector wired to both D15 and D16 and the other wired to both C15 and D14.

    An analog volt meter will make it easier to check for pulses, as the needle will swing a bit for each pulse. It's harder to tell what the heck is going on with a digital meter as the numbers will just change too fast to see what's happening.
     
  9. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Re: Fuel injector logic? \'91 ECM

    Harry, I did wire in BOTH drivers from the ECM to the injectors. /forums/images/graemlins/wink.gif

    -Dan
     
  10. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Re: Fuel injector logic? \'91 ECM

    Time to break out the ohm meter and some long test leads... I ohmed out the circuits on my 'vette harness before installing the engine and found that there was no continuity to one entire bank of injectors. /forums/images/graemlins/eek.gif I traced it out and found that one of the injector wires from the ECM had been yanked loose from the spot where in connected to the 4 wires for that bank. I had to upwrap part of the engine harness to find the break and fix it, but it would have been pretty hard to get it running on just 4 cylinders. /forums/images/graemlins/wink.gif I was VERY happy when it started the very first time that I turned the key! /forums/images/graemlins/thumb.gif
     
  11. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Re: Fuel injector logic? \'91 ECM

    Harry-

    I actually had this harness out on the table prior to installation, and I DID ohm out every lead. The wires to the injectors are good. /forums/images/graemlins/confused.gif

    -Dan
     
  12. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

    Joined:
    Feb 23, 2001
    Posts:
    3,369
    Likes Received:
    0
    Location:
    Chicago, IL
    Re: Fuel injector logic? \'91 ECM

    Good news! The truck is running! Long story short, I had the feed and the return lines to the TBI reversed! This mistake was made easier simply due to the fact that I am not using the standard steel flex lines to the TBI... I am using the stuff from the old BBC fuel injection setup.

    ANYWAYS... I now have all the troubleshooting technique down PAT for the electrical side of the system... and I obviously now know which side of the TBI is which at this point. /forums/images/graemlins/grin.gif So if anyone needs this stuff, check out my site!

    Thanks y'all! /forums/images/graemlins/thumb.gif

    -Dan
     
  13. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Re: Fuel injector logic? \'91 ECM

    Glad to hear you got it running! Like I told ya this morning [ QUOTE ]
    Without pressure, nothing will come out of the injectors.

    [/ QUOTE ] /forums/images/graemlins/wink.gif /forums/images/graemlins/thumb.gif
     

Share This Page