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New TBI first run debug help

Discussion in 'The Garage' started by Mastiff, Jun 17, 2004.

  1. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Okay, so I got my new TBI installed and fired it up, got the timing and idle set. The O2 sensor is currently disconnected because the harness I bought had the wrong connector, so I'm plunging ahead while I wait for an adapter in the mail.

    Anyway, it runs okay, but once it heats up, it starts surging in and out at a very periodic interval. Every 6 seconds or so, it'll go from 650 to 800 RPM and back. I put a light on the timing, and it doesn't seem to be moving around. The only way I've found to make it stop is to remove the vac line from the MAP and plug it. Then it runs fairly smooth.

    Any ideas where to start looking?
     
  2. jjlaughner

    jjlaughner 3/4 ton status

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    mines done the same thing for a couple years /forums/images/graemlins/dunno.gif
     
  3. Wingnutt

    Wingnutt 1/2 ton status

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    You didn't mention what type of TBI you idnstalled (ie: Holley, Turbo city, stock), but after fighting my Holley 670 TBI install, the first thing I would do is hook up an O2 sensor, your computer is basically clueless without it's input. Second thing I would check would be to make sure your TPS is set correctly (.50v-.54v). Then take a second look for vacuum leaks. Because of the Delphi injectors that Holley is now using (stock GM units will NOT interchange /forums/images/graemlins/angryfire.gif) I had to have a custom chip burnt by TBI Chips because Holley's injectors flow MUCH more than the stock units. What will have to be done is to shorten the base pulse width, lean it out throught the entire RPM range (including the power enrichment and cold start cycles) and add a bit of timing to take advantage of the increased air and fuel flow capabilities of a larger TBI.

    If you have any more questions please ask, do a search (the whole sorted story of my install is in there) or join the parade of TBI folks heading over to http://www.thirdgen.org/ and start asking questions. Now there are a few members over there who are very, very adament about burning your own chips (which I plan on doing as soon as I gain some more ECM knowledge and the equipment) so be prepaired.

    All this can sound a little bit intimadating, but the rewards are more than worth it. For a quick example my '88 with 160k miles on it with 3:43's and 33's has surprised a quite a few Mustangs not to mention being able to blow the doors off 99.99% of the ricers in this area. The downside (if you want to call it that) is that I now have traction problems on damp pavement if I nail it to hard from a stop or slow speeds. /forums/images/graemlins/thumb.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/thumb.gif
     
  4. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I'm going stock GM all around. I bought a full kit from CustomEFIs.com (another long story in itself). The chip should be fairly close to stock, but not exactly, since I blew off the knock sensor. My motor is not exactly stock without the EGR and I've got headers.

    Well, I guess I can just wait for the adapter for the O2 sensor. I tried to just jumper it for now, but it didn't seem to work. /forums/images/graemlins/confused.gif

    I don't even really know what to ask at this point. I should be getting tech support from the guy I bought from, and I kind of do, it just takes longer than getting help at CK5. /forums/images/graemlins/grin.gif
     
  5. realsquash

    realsquash 1/2 ton status

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    Well when the engine is cold it ignores the O2. After it warms up it's going to want to see the O2 signal-if it doesn't then it tries to do whatever it can to keep it running.

    Andy
     

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