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My TBI swap is complete but only starts when primed ***UPDATED***

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BlueOx, Oct 16, 2002.

  1. BlueOx

    BlueOx 1/2 ton status

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    I got the swap all finished and I tried to start it and nothing happened. I poured a little gas in the TB to see if it would start and it did so, I waited for the thing to die and it never did. I looked at the TB and saw the injectors spraying fuel and it stayed running until I turned it off. I tried to start it again and nothing happed so, I did the priming thing again and it started right up.
    Can anyone that has done the swap or know way this is happening help me out?

    Thanks,
    Charles
     
  2. RedBrute

    RedBrute 1/2 ton status

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    Re: My TBI swap is complete but only starts when primed

    Tbi engines use a relay fired buy the computer to "prime" or pressurise the fuel system. The relay only runs 2 sec's or so. When the engine starts, the oil pressure switch takes over to keep the fuel pump running. You need to add something to prime the system with. A hidden momentary awitch would work and be a cheap anti theft device. By the way, does it start if you crank it till oil pressure comes up? My '87 would only start when the pressure came up, drove me nuts for a month till I found the relay thing in a haynes manual. New relay, starts right away now.
     
  3. BlueOx

    BlueOx 1/2 ton status

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    Re: My TBI swap is complete but only starts when primed

    I’m not following you on the switch you are talking about. When I turn the key to RUN, I hear the fuel pump kick on for about 2 seconds. Does the oil pressure have something to do with it not starting?

    Charles
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Re: My TBI swap is complete but only starts when primed

    Make sure that the coolant temperature sensor is connected and working correctly. This is the one for the ECM, not the one for the gauge. If that wire is shorted to ground, then the ECM will think that the engine is VERY hot and won't kick in the fuel enrichment program, which is the EFI equiavalent of a choke. If you have a scanner, like the Auto X-Ray or WinALDL, you can read the temp that the ECM sees for the engine. It has to know when the engine is cold, or it won't spray the extra fuel required for a cold start.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: My TBI swap is complete but only starts when primed

    That should be covered in the wiring manual. AFAIK, all GM injection setups (electronic anyways) use an oil pressure switch. If there is no oil pressure, the pump won't continue to run.
     
  6. RedBrute

    RedBrute 1/2 ton status

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    Re: My TBI swap is complete but only starts when primed

    Guess I should have asked if the pump runs with key on first... oh well. Still sounds to me like the system isn't getting enough pressure to get the injectors to squirt right off. You can "jump" the pump by jumpering the pump at the oil pressure switch, ornge and grey wire if i recall. this'll run the pump all the time. See if it starts and runs then. If it does, the system isn't getting enough pressure from the 2 sec "prime" cycle I think.
     
  7. jimmy88

    jimmy88 1/2 ton status

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    Re: My TBI swap is complete but only starts when primed

    Don't know what year your TBI setup is from, but this is from the 88 service manual:

    "When the key is first turned "ON" the ECM turns on the fuel pump relay for two seconds, and the fuel pump builds up pressure to the TBI unit. The ECM checks the coolant temperature sensor, throttle position sensor (TPS), manifold absolute pressure (MAP) sensor, and crank trigger signal, then determines the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36C (-33F) to 14.7:1, at 94C (201F) running temperature."

    Hope that helps.
     
  8. jimmy88

    jimmy88 1/2 ton status

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    Re: My TBI swap is complete but only starts when primed

    dyeager have you looked at the wiring diagrams? If so, do you think the oil switch and the fuel pump relay are wired up in parallel? Looks that way, but why would that be?

    If the fuel pump relay fails while the engine is running will the fuel pump still run until a loss of oil pressure, kind of a get back home mode?
     
  9. BlueOx

    BlueOx 1/2 ton status

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    I noticed the TB was not injecting any fuel when the engine was cranking and therefore not starting. I was checking the oil pressure switch and I saw that the distributor was loose so I started moving it back and forth and saw the injectors firing. I thought my problem was in the distributor so I took off the cap and hooked up a remote starter switch to find TDC on #1. As the engine turned over the injectors started to fire fuel. I put the cap back on and tried to start it with the key but it didn’t start. I went back to try the remote and the truck started. To make and long story longer. The HOT wires that go to the injectors and the ECM were plugged into the fuse box in a HOT in RUN and when I turned the key to START the injectors would lose power. When I changed the wires the engine started right up.
    Thanks for all the help guys


    Charles
     
  10. imiceman44

    imiceman44 1 ton status

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    /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
    I love it when it turns out o be something like that.
    Still we all learn a lot because of stupid mistakes like this, again I say:
    /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  11. BlueOx

    BlueOx 1/2 ton status

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    I wouldn't say it was a stupid mistake. It was just a mistake
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Oh no, that was STUPID! Oh man was that dumb. J/K /forums/images/graemlins/smile.gif Glad it wasn't something serious or more complex!

    So what do you think now that its running and presumably driving??
     
  13. BlueOx

    BlueOx 1/2 ton status

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    HAHAHA Yeager, thanks for everyone’s help on this project and answering all my questions. The swap was very easy (I say that now that it's done) it only took 2 days. One day for the install one for trouble shooting. I still need to fine tune the thing and am now looking to get the Auto Xray to help.

    For the one’s that have used the Auto Xray is it easy to use and will it help diagnose the little problems I’m having.


    Thanks again,
    Charles
     
  14. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">Thats the SAME thing I did when I put my TPI on!

    </font><blockquote><font class="small">In reply to:</font><hr />
    all GM injection setups (electronic anyways) use an oil pressure switch. If there is no oil pressure, the pump won't continue to run.

    [/ QUOTE ]
    <font color="blue">I beg to differ. I dont have an oil pressure switch and mine runs just fine /forums/images/graemlins/grin.gif
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Yeah auto x-ray is nice. You REALLY need the service manual for the year of ECM/components you are using though, as diagnosis is covered VERY well in them. Coupled with the scanner, it should make troubleshooting a breeze.

    I like the Auto Xray, to be honest, I haven't used it a whole lot to monitor "live data" while troubleshooting, but I have watched as the vehicle is running, and it spits out some good data. At worst, its an expensive voltmeter! : ) But along with system voltage, of course there are things like O2 millivolts, closed/open loop indicator, lockup indicator, and a bunch of other stuff.

    Wish I had something to hook mine up to, eventually I will.

    Another couple of things to consider. http://www.winaldl.webhop.net/ if you've got a laptop, make the cable and its even better than autoxray. Also, since I end up helping friends and family work on their cars, I wish I would have gotten a newer scanner, one that will handle both OBD1 and 2.

    The scanner IMO has already paid for itself. (two diagnosis, one suspect piece alone would have cost $150 is the owner had guessed wrong, more than the scanner was, used) Not sure what route I will take, haven't been looking for an OBD2 laptop based program, (if there is such a thing) one of these days I'll have a laptop to use, and may not ever need a dedicated scanner again.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    No, but if it was set up stock, it would have one, right?

    Why would you remove it anyway? If the relay dies, then you've got no fuel pump. (again, in stock setup) At least thats what I gather from http://92b4crs.tripod.com/86wiring/dia-pics/22-2.jpg and other discussions.
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: My TBI swap is complete but only starts when primed

    Parallel as a failsafe would be my bet. It's been discussed on other injection forums, usually gets pretty ugly.

    As I just stated in the previous post, from the wiring diagrams, my interpretation is that once the pressure switch closes, (from oil pressure, IE cranking) the fuel pump works, regardless of what the relay does, and whether it works or not.
     
  18. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Here is something else to consider if you have access to a laptop. It's what I use.
    http://www.winaldl.webhop.net/
    As already stated, get a service manual. The "driveability" manual is also great. Also, I believe it was BlazzinOR that pointed me to "Chevrolet Fuel Injection" (ISBN 0-7603-0422-x) which taught me allot (I'm an EFI/TBI noob).
     
  19. BlueOx

    BlueOx 1/2 ton status

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    I have a laptop but that cable on Winaldl looks like a pain to make. If I was able to make the cable and use the laptop would the Winaldl be easy to use? I downloaded the program and looked at it and it really looked confusing.

    Charles
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    wait wait wait....you can do a TBI swap but not make a simple cable? Give yourself some credit! /forums/images/graemlins/smile.gif

    I looked at that cable design myself, and it did look kind of complex. But its just wiring and plugs.

    For what you can buy pre-made ones for, it would seem they are extremely complex to make, but apparently such is not the case. Believe someone on here made the cable, was it you baddog?
     

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