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Thread: Carb to TBI conversion

  1. #1
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    Carb to TBI conversion

    I am currently putting a TBI unit off a 1995 Chevy pickup with a 5.7 L engine on to a 1974 Chevy pickup with 5.7 L engine and have some questions about VSS and EGR. If anyone has done something like this, I would really like to hear from you.

    Thx a lot
    Dan Brown

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    Super Moderator dave w's Avatar
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    TBI computers use a 2000 pulses per mile VSS square wave signal.

    https://jagsthatrun.com/collections/...ce-holder-4pac

    The original 95 Chevy used a Vehicle Speed Sensor Buffer (VSSB) for the 95 Chevy dash speedometer and ABS braking system. The VSSB is not needed for the 74 Chevy if your using a TH400, TH350, or manual transmission. The 95 Chevy VSSB is needed if your going to use a 4L60E, 4L80E, or 700R4. If you have a 4L60E, 4L80E or 700R4 you should a VSS in the transmission, eliminating the need for the JTR aftermarket VSS. ****Some 700R4 transmissions Do Not Have a VSS.*****

    Direction are supplied with the VSS or contact JTR tech support.

    The EGR can be disabled in the chip programming by setting EGR "ON" at 151 degrees Celsius (304 Fahrenheit) and / or EGR "ON" at 255 MPH.

    dave w

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    Quote Originally Posted by Dan Brown View Post
    I am currently putting a TBI unit off a 1995 Chevy pickup with a 5.7 L engine on to a 1974 Chevy pickup with 5.7 L engine and have some questions about VSS and EGR. If anyone has done something like this, I would really like to hear from you.

    Thx a lot
    Dan Brown
    Don't forget the Park/Neutral input to the ECM. Painless makes a simple relay kit that uses the OEM park/neutral switch and provides both the correct signal for the ECM and Park/Neutral startup protection. Their kit is easy to duplicate with a relay and a diode as well.

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    Super Moderator dave w's Avatar
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    Quote Originally Posted by Fast355 View Post
    Don't forget the Park/Neutral input to the ECM. Painless makes a simple relay kit that uses the OEM park/neutral switch and provides both the correct signal for the ECM and Park/Neutral startup protection. Their kit is easy to duplicate with a relay and a diode as well.
    The 1995 16197427 Second Generation TBI computer does not have a Park / Neutral input wire like the older 1227747 First Generation TBI computer does.

    I agree 100%, a Park / Neutral safety switch is a must have feature!

    dave w
    Last edited by dave w; 01-28-2020 at 01:37 AM.

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    I am using a Muncie SM465 which is a manual transmission, so, if I'm reading dave w right, I don't need a VSS. If this is correct, and I don't use one, will I have any driving problems? Too, as for the EGR, how do I handle that? I didn't bother to worry about an EGR valve when I started this project since the vehicle is over 40 years old and in Texas, it's exempt from any emissions check, but I'm now being told that if I don't use one, the MIL will be on constantly since the ECM isn't seeing an EGR signal. True/False?

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    Quote Originally Posted by dave w View Post
    The 1995 16197427 Second Generation TBI computer does not have a Park / Neutral input wire like the older 1227747 First Generation TBI computer does.

    I agree 100%, a Park / Neutral safety switch is a must have feature!

    dave w
    It does too!!! It uses one of the pressure sensor inputs from the E-Trans when it is in TCC only mode. It is in my wiring change chart.

    The manual trans trucks use a clutch anticipate switch from what I remember too.

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    Quote Originally Posted by Dan Brown View Post
    I am using a Muncie SM465 which is a manual transmission, so, if I'm reading dave w right, I don't need a VSS. If this is correct, and I don't use one, will I have any driving problems? Too, as for the EGR, how do I handle that? I didn't bother to worry about an EGR valve when I started this project since the vehicle is over 40 years old and in Texas, it's exempt from any emissions check, but I'm now being told that if I don't use one, the MIL will be on constantly since the ECM isn't seeing an EGR signal. True/False?
    You will want a VSS. You will not get away without tuning the ECM unless you run a factory 350 cam and factory TBI heads.

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    I actually just took off my jags that run 2000 pulse per mile vss sensor since i switched to the 4l60e and got their 40 pulse per revolution reluctor kit. PM and I'll send the 2000 ppm for $75 shipped.

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    Super Moderator dave w's Avatar
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    Quote Originally Posted by Dan Brown View Post
    I am using a Muncie SM465 which is a manual transmission, so, if I'm reading dave w right, I don't need a VSS. If this is correct, and I don't use one, will I have any driving problems? Too, as for the EGR, how do I handle that? I didn't bother to worry about an EGR valve when I started this project since the vehicle is over 40 years old and in Texas, it's exempt from any emissions check, but I'm now being told that if I don't use one, the MIL will be on constantly since the ECM isn't seeing an EGR signal. True/False?
    What is the computer part number your using for the TBI conversion?

    dave w

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    Super Moderator dave w's Avatar
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    Quote Originally Posted by Fast355 View Post
    It does too!!! It uses one of the pressure sensor inputs from the E-Trans when it is in TCC only mode. It is in my wiring change chart.

    The manual trans trucks use a clutch anticipate switch from what I remember too.
    I can't find 16197427 wiring schematic showing a wire labeled Park / Neutral. Please post a 16197427 wiring schematic showing the Park / Neutral wire.

    dave w

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    Quote Originally Posted by dave w View Post
    I can't find 16197427 wiring schematic showing a wire labeled Park / Neutral. Please post a 16197427 wiring schematic showing the Park / Neutral wire.

    dave w
    Had to reference my old writeup on TGO. When you have TCC only option selected if you input the Park/Neutral wire into pin E5 the PCM will see Park/Neutral or In-Gear just as it should. It will operate the Idle Speed tables correctly and add or remove IAC counts to compensate for the load change. I always add enough steps to keep the engine from having a large RPM drop on the Park to Reverse shift. Reverse has the highest engine load. I set the Park/Neutral table about 75-100 rpm higher than in-gear. Makes the transition feel relatively seamless without the RPM dipping and activating the stall saver routine. I have yet to find a factory application that was TCC only so you would not find this on a wiring diagram. I figured out the TCC was on E10. The TCC only application did not seem to have coding for a High Gear switch or I never found it if it existed.

    https://www.thirdgen.org/forums/tbi/...rting-tbi.html

    4.3 V6 with a 5speed wiring diagram should show where to input the clutch switch too. The PCM uses the clutch signal for the spark smoothing. The PCM will alter timing and IAC counts to help you launch off-idle and shift the trans more smoothly. The clutch switch will also keep the RPM from spiking when you press in the clutch pedal coming to a stop. The factory upshift light control is on pin E2 and is enabled when you select manual trans option. You can adjust the light to come on at various TPS vs RPM and set the NV table correctly for the SM465. I had it programmed correctly and functioning on a 3spd column shift truck. I used a relay to control an amber bulb.
    Last edited by Fast355; 01-28-2020 at 09:24 AM.

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    Super Moderator dave w's Avatar
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    Quote Originally Posted by Fast355 View Post
    Had to reference my old writeup on TGO. When you have TCC only option selected if you input the Park/Neutral wire into pin E5 the PCM will see Park/Neutral or In-Gear just as it should. It will operate the Idle Speed tables correctly and add or remove IAC counts to compensate for the load change. I always add enough steps to keep the engine from having a large RPM drop on the Park to Reverse shift. Reverse has the highest engine load. I set the Park/Neutral table about 75-100 rpm higher than in-gear. Makes the transition feel relatively seamless without the RPM dipping and activating the stall saver routine. I have yet to find a factory application that was TCC only so you would not find this on a wiring diagram. I figured out the TCC was on E10. The TCC only application did not seem to have coding for a High Gear switch or I never found it if it existed.

    https://www.thirdgen.org/forums/tbi/...rting-tbi.html
    Pin E5 on the 16197427 is listed as "Range Signal C" on the Factory Wiring Diagrams. I'm hoping to avoid confusion. The 16197427 upgrade information on TGO has helped and benefited many TBI projects.

    Accurate information is helpful, but sometime too much information is confusing. I agree E5 can be used as a Park / Neutral input, but the chip needs to be reprogrammed (as stated in a previous post). Can confusion be created when re-purposing a computer wire with a custom chip (maybe / maybe not)? It is a 100% accurate statement to say the Factory Wiring Diagrams for the 16197427 DO NOT list a Park / Neutral input wire.

    TBI conversions can be challenging for someone if it's their first time doing a TBI conversion. I created confusion in a previous post on what Transmissions used a VSS and what transmissions used a VSSB. Maybe confusion can be avoided by asking "what transmission is in the 74 Chevy" before answering a VSS is question. In hindsight an answer saying a SM465 requires a VSS could have avoided confusion?

    dave w

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    So dave w, your saying that I WILL need a VSS using the SM465, and if so what do you recommend I do? Too, I am using a 16197427 ECM.

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    A VSS is a must in my opinion because the decelerator fuel cut off (DFCO) and a few other speed controlled things like EGR and stuff. The confusion above is that a 4l60e or 4l80e electronically controlled automatic needs a vehicle speed signal buffer to handle the VSS signal to the ECM to control the trans. Non PCM controlled trans like: TH350, TH400, 700r4, sm465, sm420 and etc would only need a VSS for the engine control like DFCO and etc. In tunerpro, you would specify speed signal not from DRAC and need a 2000 pulse per miles VSS like the 2prs from jags that run and set it for manual transmission options.
    Last edited by c5wagner; 01-29-2020 at 06:47 AM.

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    Quote Originally Posted by Dan Brown View Post
    So dave w, your saying that I WILL need a VSS using the SM465, and if so what do you recommend I do? Too, I am using a 16197427 ECM.
    Needs a VSS and programmed for manual trans option. I will double check the information and wiring diagrams for the clutch switch. The relay option I mentioned to use the OEM clutch safety switch will also work for a clutch input signal from what I remember.

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