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Ripping out the computer....HELP?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fjleiter, Aug 22, 2004.

  1. fjleiter

    fjleiter 1/2 ton status

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    Getting ready to put a new motor in my 90 K5, looking at two ways to go here. I can put it all back with the computer/TBI etc but would need a new TBI unit, Intake etc.. to get the performance I'm shooting for. OR.... I can deep six the computer, go with a carb setup (which I prefer) and save some money on parts and hassle. Question is..

    1) what exactly is involved with getting this sucker to run without a computer, what will be affected without one? (such as gauges etc...)

    2) Tranny is a 700r4, what do I need to keep the lockup function and keep my speedo working. I want to switch it out for a TH350 or TH400 next year so don't want to dump too much into getting it working right.

    3) It's not a daily driver, only a snow runner in winter and mud runner/ trail runner in summer, with occasional crusing here and there. Little to no highway driving. Gas mileage as such is not a concern.

    Anyone that's done this that can give me a step by step walk through? (I know I need an old style distributor etc...)

    Anyone intrested in trading a carb/intake for a TBI/Intake?
    Or how about a 700r4 for a TH350?
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Why not keep the computer on there , tape the wires you aren't using to the harness for later use , and cover with black conduit so it doesn't look bad , and run a new 12 volt fot the HEI . That way when you want to reap the benefits of EFI ( if I had it I'd keep it ) its already ready already /forums/images/graemlins/k5.gif

    And as for the lockup , you may be able to use a lockup th350 , I just don't know what needs to be done with output shaft , I thought th350's with lockup were in 2wd cars . And as for speedo , I thought it was run of the transfercase electronically . Someone else can answer this one /forums/images/graemlins/k5.gif
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    [ QUOTE ]
    [ QUOTE ]
    Why not keep the computer on there , tape the wires you aren't using to the harness for later use , and cover with black conduit so it doesn't look bad , and run a new 12 volt fot the HEI . That way when you want to reap the benefits of EFI ( if I had it I'd keep it ) its already ready already /forums/images/graemlins/k5.gif

    And as for the lockup , you may be able to use a lockup th350 , I just don't know what needs to be done with output shaft , I thought th350's with lockup were in 2wd cars . And as for speedo , I thought it was run of the transfercase electronically . Someone else can answer this one /forums/images/graemlins/k5.gif [/quoteThe ignition wire to the coil is not in the ECM harness.

    [/ QUOTE ]

    The ignition wire for the coil is separate from the ECM harness.

    The speedo is electronically controlled running off the T-case but it does goes through the ECM so if the ECM gets removed/disconnected the speedo will no longer work.
     
  4. Blue85

    Blue85 Troll Premium Member

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    [ QUOTE ]
    Anyone intrested in trading a carb/intake for a TBI/Intake?

    [/ QUOTE ]

    Ummm...yeah. But to do something like that the trucks would have to be in the same place and at least one of them would be down for a while.
     
  5. botboy

    botboy 1/2 ton status

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    I did a full computer retrofit along with a 454 TBI setup and performer intake into my '72 C10 and did all the wiring and computer stuff myself so I'm a bit of an expert here.

    My personal recommendation would be to leave the ECM in place along with the distributor and wasted spark coil. This way the computer controls your advance and you don't have to mess with re-timing your vehicle after putting in a non-computerized HEI coil from a '74-84 GM V8 vehicle, although you'll have to re-time anyway since you're going to change the intakes out to go from 2-bbl TBI to a 4 barrel Q-jet or something along those lines. You'll also need to install a pressure regulator to keep the pressure down from the 14-16 PSI the TBI unit needs to the 4-7 a carb will need otherwise you'll constantly flood it and maybe break the carb or risk an engine fire.

    Not seeing input from the TPS, MAP, and responses from changing the mixture values (injector open/close timing) will make the computer set values and keep your SES light on constantly. You will want to keep the temp sensor hooked up, most if not all aftermarket intakes will have a bung you can screw this into. This is necessary because the computer won't allow for very aggressive advances in timing unless the engine is warmed up, and you will also need to leave the knock sensor along the bottom of the block hooked up or else the computer defaults to a dummy mode and won't allow for more than a very small amount of advance because its feedback device is gone.

    There's a lot of useful information at www.chevythunder.com and www.gmecm.com and diy-efi.org if you need it, or you can email me if you have further questions at botboy60 (at) hotmail (dot) com.
     
  6. 84_Chevy_K10

    84_Chevy_K10 Banned

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    My only comment is that you're a complete fool if you remove a simple, user friendly, cheap to repair, and highly effective fuel injection system like TBI for a carburator.
     
  7. botboy

    botboy 1/2 ton status

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    [ QUOTE ]
    My only comment is that you're a complete fool if you remove a simple, user friendly, cheap to repair, and highly effective fuel injection system like TBI for a carburator.

    [/ QUOTE ]

    Yeah, because on any even slightly modified engine, 470 CFM (stock 4.3/5.7 2-bbl TBI) should be more than enough! And that TBI intake manifold flows so amazingly well too!
     
  8. Blue85

    Blue85 Troll Premium Member

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    [ QUOTE ]
    My personal recommendation would be to leave the ECM in place along with the distributor and wasted spark coil. This way the computer controls your advance

    [/ QUOTE ]

    How in the world can the computer control timing without knowing throttle position, MAP, O2, coolant temp and intake temp? Are you suggesting to keep all of these sensors connected while running a carb? I can see O2 and temp being easy to keep (+ knock) and there should be a way to retrofit MAP, but how do you get TPS?

    [ QUOTE ]
    Yeah, because on any even slightly modified engine, 470 CFM (stock 4.3/5.7 2-bbl TBI) should be more than enough! And that TBI intake manifold flows so amazingly well too!



    [/ QUOTE ] There are ways to get more flow out of a TBI system that are easier than retrofitting to carb, especially if you are going the "double unreliable" path of electronics + carb.
     
  9. botboy

    botboy 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    My personal recommendation would be to leave the ECM in place along with the distributor and wasted spark coil. This way the computer controls your advance

    [/ QUOTE ]

    How in the world can the computer control timing without knowing throttle position, MAP, O2, coolant temp and intake temp? Are you suggesting to keep all of these sensors connected while running a carb? I can see O2 and temp being easy to keep (+ knock) and there should be a way to retrofit MAP, but how do you get TPS?

    [ QUOTE ]
    Yeah, because on any even slightly modified engine, 470 CFM (stock 4.3/5.7 2-bbl TBI) should be more than enough! And that TBI intake manifold flows so amazingly well too!



    [/ QUOTE ] There are ways to get more flow out of a TBI system that are easier than retrofitting to carb, especially if you are going the "double unreliable" path of electronics + carb.

    [/ QUOTE ]

    Yeah, an aftermarket intake manifold for a q-jet, 454TBI and an adapter for 2-bbl 454TBI --> Qjet which is precisely what I did on my '71. You should have noted the sarcasm against 84 K10 for being wrong - if the author of the thread rebuilt the engine he's putting in the truck, I should think that he did so with the intention of getting a few more ponies out of it, and if that is the case then a 470 CFM TBI with a poorly-flowing factory manifold will really limit his engine at the higher end of the RPM scale. The 454 throttle body flows about 670 as I understand it, and I did notice a substancial performance increase when I switched to the larger TBI in my '72 (although I couldn't use the 5.7 chipset anymore).

    According to the DIY_EFI list, the timing is controlled by engine RPM's compared against a map of values for engine temperature and retarded as necessary by preset values based on what input is given by the knock sensor. I said above, keep temp and knock attached or else the system will be crippled.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    Unless you somehow program it out of the system, it will go into limp mode without TPS, plain and simple. Whether or not TPS plays into spark timing I can't comment on without authority, but TPS voltage is one of the criteria that is monitored by the ECM, and will set a code. At that point, you might as well remove all the other sensors, since it will be running on pre-programmed values anyways, which means lame timing for one.
     
  11. botboy

    botboy 1/2 ton status

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    [ QUOTE ]
    Unless you somehow program it out of the system, it will go into limp mode without TPS, plain and simple. Whether or not TPS plays into spark timing I can't comment on without authority, but TPS voltage is one of the criteria that is monitored by the ECM, and will set a code. At that point, you might as well remove all the other sensors, since it will be running on pre-programmed values anyways, which means lame timing for one.

    [/ QUOTE ]

    Had to find it again, but:
    http://www.diy-efi.org/gmecm/papers/747spark.txt
    he suggests that you use the TPS if you can but without it, it will only set the following code:
    error 33's: map sensor high codes.
    but error 33 won't set the ECM in limp mode, as I understand it.
     
  12. fjleiter

    fjleiter 1/2 ton status

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    My problem is that I have a self imposed target of 350 horsepower, with equal or greater torque. (based on some values I played with in DD2000 in the rpm range I want).

    As I understand it, this is unobtainable with TBI setup no matter what I do (at least without spending gobs of money). If anyone can tell me how I can beef up a TBI to support those figures without spending $500-$1000 to do it(just on the TBI, not the whole engine build) , I would be more than happy to keep the electronics and TBI. /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    '88 Camaro TBI (guessing thats the '747?) manual states:

    Code 21 will set if:
    TPS signal voltage greater than 2.5 volts.
    All conditions met for 8 seconds.
    MAP less than 52kPa

    Code 22 (low TPS signal) will set if the engine is running and voltage is less than .2 for 2 seconds.

    Code 33 states that if MAP fails, it will run off of fixed MAP values, which if tied to timing, will certainly mean timing is compromised.

    If the TPS voltage doesn't match expected voltage for the pressure MAP is seeing, the ECM assumes something is broken.

    As noted in the article, you will be modifying things in the PROM to make this work, so all bets are off about codes, etc.

    I can understand the reason for using the ECM to mess with spark, but damn, thats a lot of work to make a "simpl" carb work with a "complex" distributor. Unless restricted by racing class, I can see NO situation where that is worth the time or effort.

    Basically, that guy has done what GM did on the trucks. ESC, which everyone tends to rip off anyways. ESC is just an attempt to control spark without the other engine control sensors of CCC or injection, to save GM money.
     
  14. botboy

    botboy 1/2 ton status

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    [ QUOTE ]
    '88 Camaro TBI (guessing thats the '747?) manual states:

    Code 21 will set if:
    TPS signal voltage greater than 2.5 volts.
    All conditions met for 8 seconds.
    MAP less than 52kPa

    Code 22 (low TPS signal) will set if the engine is running and voltage is less than .2 for 2 seconds.

    Code 33 states that if MAP fails, it will run off of fixed MAP values, which if tied to timing, will certainly mean timing is compromised.

    If the TPS voltage doesn't match expected voltage for the pressure MAP is seeing, the ECM assumes something is broken.

    As noted in the article, you will be modifying things in the PROM to make this work, so all bets are off about codes, etc.

    I can understand the reason for using the ECM to mess with spark, but damn, thats a lot of work to make a "simpl" carb work with a "complex" distributor. Unless restricted by racing class, I can see NO situation where that is worth the time or effort.

    Basically, that guy has done what GM did on the trucks. ESC, which everyone tends to rip off anyways. ESC is just an attempt to control spark without the other engine control sensors of CCC or injection, to save GM money.

    [/ QUOTE ]

    According to the article:
    1) A look up is done on the Main SA table, the value retrieved
    is based on the current rpm and map values. Call this Total
    Spark Advance, or TSA for now.

    2) The Slope, if any, is calculated and added to the TSA.

    3) A look up is done on the Coolant Compensation table using
    the current engine temp and manifold vacuum. Add this to TSA.

    |4) (adjust for any egr spark, SA is added if egr is active).
    | (a lag filter calculation is done here also, but appears
    | to be egr related only. The lag filter allows for the smooth
    | change of SA whenever the EGR is enabled/disabled).

    5) Add in any PE spark to TSA. Calc'd in a separate routine.

    6) Add in any aldl/closed loop spark, to TSA.

    7) Add in any Start-up Spark, to TSA.

    8) Add in any Hi-way Spark, to TSA.

    9) Subtract the Warm Bias spark value, from TSA.

    10) Subtract the Cold Bias spark value, from TSA.

    11) Subtract the Initial spark value, from TSA.

    12) At this point, the TSA value is tested against
    the Max Allowed Spark Value. If it is greater, it
    will be set to the maximum allowed SA value.

    13) Subtract any Burst Knock, from TSA.

    13) Subtract any Knock Retard, from TSA.

    14) The TSA value is tested against the Minimum
    Allowed Spark, and adjusted to this minimum value
    if required.

    15) A Spark Latency correction is made and the end
    value is sent to counters in the ecm. An output from
    the counters control when the distributor will spark,
    relative to the incoming distributor pulse.

    So I was wrong in my original post - leave the map sensor attached because the TSA tables are tied to map values. But I still see nothing about the TPS values being tied to ignition timing, the only thing I see it being tied to (according to the article) being engine RPM, cool/warm changes, map sensor values and knock sensor feedback.

    Almost all 305/350's got the 747 ECM before '91 so you should be correct there. The reason that this was suggested in the first place is to avoid having to deal with the automatic transmission and lockup control (shift control depending on how new it is) and timing, if it were simply timing I think an HEI module would be the simplest solution.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Since a TPS failure is tied into MAP (which means that MAP is compared to throttle position, if it doesn't match a "known" value, it will throw a code) removing TPS from the equation seems to be impossible.

    As well, PE (power enrichment, pump shot to carb guys), #5 in what you just posted, is based off of the change in throttle position, again, TPS.
     
  16. Blue85

    Blue85 Troll Premium Member

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    [ QUOTE ]

    As well, PE (power enrichment, pump shot to carb guys), #5 in what you just posted, is based off of the change in throttle position, again, TPS.

    [/ QUOTE ]

    PE doesn't matter since it is a carb controlling fuel. Another option would be to have a TPS, either by getting one from a CCC or adding one to the throttle linkage. OR you could burn a PROM to ignore the TPS altogether.

    If it was me, I would remove everything and run a distributor with weights and a vacuum can.

    Well, actually, I would try to keep the TBI, but that's another topic.
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    PE doesn't matter since it is a carb controlling fuel.

    [/ QUOTE ]

    It DOES matter, as spark is adjusted for and during PE.
     

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