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carb to tbi conversion

I'm sure everybody whose responded to my very first inquiry about my project, and I have gotten lots of help from lots of you guys about ESCs and VSSs and I really appreciate all the help you guys have been. As for needing a VSS, I just talked to Troy at Howell efi conversion experts, and he said that since I'm using a manual transmission and not a 700R4 that I don't need a VSS and will have "no problems" by not using one. He, too, said he's done "many" of these conversions and "knows them real well". I guess the reason I'm sending this is to get any reactions from any of you guys. Please feel free to let me know what you think as I'm still a novice at doing this conversion.
 
The ESC I picked up at the junk yard was mounted on the same bracket that the EGR solenoid and MAP Sensor are mounted on, on the passenger side of the intake manifold.
 
Dan Brown said:
The ESC I picked up at the junk yard was mounted on the same bracket that the EGR solenoid and MAP Sensor are mounted on, on the passenger side of the intake manifold.
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yep, that’s where mine was mounted as well.

it’s certainly possible to run without a VSS, but you’ll get better performance when downshifting or engine braking if you install it. It made a nice difference on mine. Kinda depends on what you’re planning to use the truck for. If it’s just for trail riding and blasting through stuff, probably not needed. If you use it on the street or highway, I think you’ll appreciate it being there, especially since it’s not a big deal to hook up. If you plan to use some of the tuning parameters like highway lean cruise, you’ll need a VSS signal for that as well.
 
Okay, I'm gonna use a VSS, so could somebody please tell me what 'buffer' to use and how to wire it. Thx a lot.
 
That appears to be the correct one. But the only way it is going to work is to be hooked up to a gm speedometer of the same vintage.

Unfortunately the best pic I could find of the VSS buffer being bolted to the speedometer (black plug end is what connects, but zooming in looks like it's not actually screwed in on this pic):
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And I believe that not ALL the speedometer heads were designed for VSS, even being the proper vintage. There are specific components for the VSS in the speedometer heads that used this style, and since it was only an optional requirement (cruise control being one) up until TBI, which requires it, GM probably didn't feel the need initially to make all the speedo heads capable of running VSS.

It is certainly possible to run without one. You could always try, and decide after driving for a bit. Manual should certainly eliminate stalling when in gear and decelerating, but I'd be concerned about when I had to hit the brakes, perhaps a bit hard and fast, when I'd be on the clutch and the trans wouldn't be driving the engine.

GM didn't install anything they didn't know was necessary. Some things were necessary for regulations, and some things are necessary for the systems to operate as designed. Some do get away without using VSS, maybe you'd be one of the ones that can, and it doesn't bother you one bit.
 
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There is a guy on this thread called Bent77 who mentioned that he had Howell efi tweak his PROM in his 1227747 ECM removing VSS and pattern off the TPS. I talked to Tony Brown at Howell and he's going to tweak my PROM when I'm ready. If Bent77 reads this, please let us know if both the conversions you've done work okay and I'll have him do mine the same way.
 
You may want to read this, also: https://ck5.com/forums/threads/est-and-esc-diagnostics-for-tbi.237433/. As you're finding out, there are more ways to get this done than one. Often, it's easier to put it together and troubleshoot than try to get it right up front...either way can be a challenge though. There's plenty of help and good advice on here, you'll get it done, you obviously have the ability to research and ask questions and sift through all the answers to apply what is useful to your situation.Trying to help you out has already taught me a few things, it's a two way street. Looking forward to the post where you tell us it's running.
 
Looking at an electrical diagram for a 1991 Chevy K1500 and saw an output speed sensor with two wires going to the ECM. My truck has an NP205, which has no place to put the sensor. Just by the name, I know what it does, but, do I need it, and if so, how have any of you guys handled it.
 
Dan Brown said:
Looking at an electrical diagram for a 1991 Chevy K1500 and saw an output speed sensor with two wires going to the ECM. My truck has an NP205, which has no place to put the sensor. Just by the name, I know what it does, but, do I need it, and if so, how have any of you guys handled it.
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“output speed sensor” = VSS (Vehicle speed sensor)?
 
Okay, that makes sense. Since I have a Jags That Run 2PRS with two white wires on it, I'm I over simplifying by assuming (which usually gets you in trouble) that both white wires go the the ECM, and if so, does it matter which is which?
 
Dan Brown said:
Okay, that makes sense. Since I have a Jags That Run 2PRS with two white wires on it, I'm I over simplifying by assuming (which usually gets you in trouble) that both white wires go the the ECM, and if so, does it matter which is which?
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One is ground (pick either one) and run the other to the ECM.
 
I just talked to a Painless Performance Tech and he said the same thing bp71k5 said. One of the white wires, either one, gets grounded and the other goes to pin A15 (brown wire) on the ECM. Slam, bam, thank you ma'am.
 
Gotta question for somebody in the know about the 1227747 ECM. The schematic I'm using shows pin C2 (brown wire) going to an Air Control Solenoid. What is it, and is it needed? Thx for any help.
 
Dan Brown said:
Gotta question for somebody in the know about the 1227747 ECM. The schematic I'm using shows pin C2 (brown wire) going to an Air Control Solenoid. What is it, and is it needed? Thx for any help.
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For emissions equipment. Need depends on if you are keeping all the smog equipment or not.
 
Is there anybody on this Forum in the Houston, Texas area that can tweak the PPOM from my 1227747 ECM.
 
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