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Thread: vss and tbi questions

  1. #1
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    vss and tbi questions

    ive managed to thouroughly confuse myself. doing a tbi setup in my 64 el camino. i am now using all the components that came with my stock 89 truck motor. the wiring aspect is fairly simple (at least to me). will start out completely stock to eliminate variables and make things go smoother.

    i know i need a VSS. truck is running a 700r4, cable driven. mechanical speedo is accurate with the bowtie overdrive gears installed.

    there seems to be a lot of confusion on what number of pulses and what sensors to use. im trying to go for cheapest way possible, as having to buy another engine due to someone elses incompetence has really ste the budget back.

    so, what sensor, and why?

    additionally, there seems to be a lot of confusion out there about wether or not a properly functioning egr helps or hurts fuel economy. whats the truth?

    lastly, im attempting to use the cruise setup from the same engine donor truck. again, info seems awfully thin on the ground. what it seems is that the cruise uses the same 2000 pulse per mile signal the ECM uses. does this seem right?

    thanks guys. the signal to noise ratio on this forum is the best of any im on.

    michael

  2. #2
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    If you're taking a '7747 computer then it takes a 2000 pulses per mile signal. The speedometer cable turns 1000rpm/mile or 1000rpm @ 60mph so you need 2 pulses per revolution of the cable.

    I'm cheap so I once made my own sensor with 2 small cylinder shaped magnets drilled and pushed into the gear and a hall effect sensor to detect them passing by. I had to buy another magnet so it cost me about $5 to make.

    The cruise control should be the same but it might be 4000 pulses per mile.

  3. #3
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    Quote Originally Posted by dusterbd13 View Post
    additionally, there seems to be a lot of confusion out there about wether or not a properly functioning egr helps or hurts fuel economy. whats the truth?
    i've never seen correctly implimented EGR hurt fuel economy...

    i've seen some vehicles where it might make an improvement that is within the margin of error for fuel usage and distance traveled.

    and then i've seen the freaks that see a solid 10% bump, some more.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  4. #4
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    The homemade might be the cheapest way to go if you're up to it. Or, you should be able to get a 2000 pulse inline adapter from Stealth Conversions (Jags that Run) in the $100 range. This would give you the VSS info you need, but you can't run the DRAC with it, so I'm not sure if you'll be able to get the cruise to work. Another alternative would be to swap the mechanical stuff for electronic, then you could run a DRAC and have cruise output. Or you could try to adapt the '89 gauge cluster and use it's output for the VSS and cruise.
    1973 K-5 Blazer, TBI 350, TH400, 1 ton axles & 38" SSRs'
    1975 280Z, TBI 350, 700R4
    1953 M-38A1, TBI Buick 231
    1951 Ford Panel, 5.3 with 4L80E

  5. #5
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    Do you have more details on the homemade? And any reason that it's a bad idea?

    THANK YOU for the help so far guys.

  6. #6
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    Quote Originally Posted by fastacton View Post
    The homemade might be the cheapest way to go if you're up to it. Or, you should be able to get a 2000 pulse inline adapter from Stealth Conversions (Jags that Run) in the $100 range. This would give you the VSS info you need, but you can't run the DRAC with it, so I'm not sure if you'll be able to get the cruise to work. Another alternative would be to swap the mechanical stuff for electronic, then you could run a DRAC and have cruise output. Or you could try to adapt the '89 gauge cluster and use it's output for the VSS and cruise.
    Could I run an 8k dakota digital vss by using a drac? Thereby getting both the ecm and cruise signals while retaining the mechanical speedo?

    Or would it be better to find a 4 pulse vss and use a drac?

    Im just having a hard time swallowing a hundred bucks for the jtr unit.

  7. #7
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    The Dakota Digital ones are a bit cheaper, but I haven't tried one out with a 7747. The inline ones that I've used haven't been compatible with a DRAC/VSSB, I've had to wire them straight to the ECM. I'm using a 4k inline VSS adapter (used to have TPI) with a 7747/700R4 and it's been working okay once I changed the lockup speeds. Since I'm using a 4k where you'd normally use a 2k, I had to pretty much double all of the speeds and now that I think about it, I don't think there's enough adjustment left to compensate for an 8k.
    1973 K-5 Blazer, TBI 350, TH400, 1 ton axles & 38" SSRs'
    1975 280Z, TBI 350, 700R4
    1953 M-38A1, TBI Buick 231
    1951 Ford Panel, 5.3 with 4L80E

  8. #8
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    Ok, another idea. Im seeing a bunch of driveshaft mounted pulse generators for cheap. Dakota digital suggested one. Anyone tried these? They said with two magnets it should be close enough to a 2k pulse.

  9. #9
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    I'd probably just spend the $85 to get a 2k inline adapter from Jags That Run. It's pretty much guaranteed to work and then you're done with it.
    1973 K-5 Blazer, TBI 350, TH400, 1 ton axles & 38" SSRs'
    1975 280Z, TBI 350, 700R4
    1953 M-38A1, TBI Buick 231
    1951 Ford Panel, 5.3 with 4L80E

  10. #10
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    Took your advice and ordered one. Just spent soo much time trying to reinvent the wheel to save thirty bucks. Just not worth it.

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