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Open Headers with TBI

Discussion in 'The Garage' started by Jeromy Gibson, Feb 17, 2005.

  1. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    Could this be why my engine is running bad? would putting on some header extensions help?
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    You mean you've got no exhaust past the collector?

    It could be, depending on where your O2 sensor is located, but what is it doing that is "bad"?
     
  3. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    the o2 is about 5 inchs from the collector and there is nothing past the collector, this is the first time I have been able to test this after my Fuel injection swap. the motor idols well but once you give it gas it just pukes all over itself, with a load on it after about 3000 it just starts poping and won't pull. dies if I don't feather the throttle to start off. I am about to replace the MAP and TPS tonight. and check fuel pressure this weekend.
     
  4. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Timing check out? On OE TBI you need to disconnect a plug to get an accurate reading. Wouldn't about 3k be when the dist mech advance really starts kicking in? That would make incorrect timing really bad.
     
  5. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    not had a chance to put a timing light on it, but it should be very close.
     
  6. K5MONSTERCHEV

    K5MONSTERCHEV 1/2 ton status

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    And its prolly running dead ass rich.
     
  7. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    seems to run rich on the bottom and lean on the top end.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, the O2 sensor is essentially ignored on acceleration, so that shouldn't be the issue. Need a scanner on it to see if it goes closed loop. Really no way to tell otherwise whether the sensor is cooling off and staying/going open loop, or not enough "pure" exhaust flow past it to work correctly. But thats going to be an idle/cruise thing, not acceleration.

    I'd be thinking more along the lines of timing with the symptoms you provide...is TPS within specs?
     
  9. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    will check the tps this weekend, is there any difference between TPS I have one throtle body that has a differnt connector pattern than the other.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    Well I thought folks here were saying that TBI TPS "base" voltage is in the .6V range, while TPI etc I *know* is in the .5V range. Seems odd to me that they would be different but what do I know?

    If the wiring is different on two TPS', you could probably figure out which wire goes where with a multimeter, then de-pin the connector, and re-pin it to match the different TPS, but I can't say with certainty that there is no difference other than wiring pinout. I suspect no, there is no difference, but there always could be.

    Used TPS is almost always a bad idea though, it seems that more often than not they are screwed up when you get them used. Just from my experience.
     
  11. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    Everything came off an engine I was told was good, and thats the story of my life about right now, So I will be changing the TPS and MAP this weekend to see if that help.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    If someone has a 1987-1991 service manual they want to let me cut up, I would be more than willing to scan it into PDF format for the benefit of all.

    Anyone that knows me also knows that I really, really, really dislike replacing parts before diagnosing, even if it is a $10 or $20 part, because it doesn't teach you anything. The factory service manual troubleshooting sections are invaluable, and are a must.

    I believe on the MAP setups winALDL will show the MAP values, which would tell you if its working right or not, and will also show if TPS is working right or not. As crappy as aftermarket parts are now, replacing a piece that is old, but good (and GM) is not really a better solution than leaving it, IF its working correctly.

    Most people don't just replace a motor because it has 100K miles on it, it gets replaced because there is noise coming from it, it smokes, etc. An EFI system can have a problem that seems at first wholly unrelated to whats going on, which leads to a lot of parts replacing if no diagnosis is done.
     
  13. Thunder

    Thunder 3/4 ton status

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    So I am wondering. Have you bothered to check for trouble codes? After you do a FI swap, that should be the first thing you do after you get it running.
     
  14. sweetk30

    sweetk30 professional hooker Premium Member

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    1 wire non heated o2 need to be close to heads. if in colector area need to use heated o2 .
     
  15. SUBFAN

    SUBFAN 1/2 ton status

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    Tell us about the rest of the engine....If you are running open headers, I am assuming that this motor is far from stock. The cam might not be computer friendly.


    Unless the motor is modified, you are shooting yourself in the foot powerwise running those headers open like that....

    If the motor is stock enough for the TBI, I think there is no way the O2 sensor is getting and staying hot enough for it to work right.
     
  16. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    the rest of the engine is fairly stock, its is a rebuilt 355 flat tops, stock heads off the 91 engine, cam came with the el cheapo rebuilt kit that my friend already had. When we fist got the engine running it was not throwing any codes. but now I do not have a scanner avalible. I guess I will get a heated O2 and see if that helps. The only reason I am running the open headers is this started out being a beater truck I bought for $300 and I can't seem to keep it running long enough to worry about exhast.
     
  17. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I don't believe TBI uses a mechanical advance distributor.
     
  18. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Your neighbors must HATE you......



    :D
     
  19. Jeromy Gibson

    Jeromy Gibson 1/2 ton status

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    Well, I rent a small shop with a buddy of mine and thay hate his alot more than mine, he has straight pipes ran into 5 inch truck stacks.
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    Huh. My truck doesn't seem to have a problem with a one wire, exhaust being fed from only 4 cylinders, and being located behind the collector. Another expensive part to be throwing at a problem.
     

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