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TBI to LS swap wiring

formercruiserhead

formercruiserhead

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Swapping in an LS 5.3 with standalone harness. Vehicle is 89 k5 with stock 350 TBI and 465 4speed 241c tease with mechanical speedo (cable).
Does anyone know if my speedo signal (which comes off of back of speedo in dash) will work with LS computer? I guess a better question might be what signal spec is coming off of my stock speedo? Then it could be programmed into the LS computer? I thought I needed a vss converter but it already has some type of speed signal for the TBI so why couldn't I use that? And where would I tap into that?
 
Electronic speed sensor or cable driven? If you’re using an aftermarket ls harness, you just need to run the supplied wiring to the speedo.
 
The only ls swap into a tbi truck I have done was with an automatic transmission. The electronic speedo worked with the harness I used. I just had to repin the gauge plug.
 
If your 241 is a mechanical Speedo version, then i believe you must buy a module that goes in between the transfer case and speedometer cable that generates the correct signal?

My K5 was supplied from factory with TBI and 208... and pretty sure the speedo cable drives a signal generator on the back of the speedometer? or its part of the speedometer? man, its been a long time since i played around in there. I swapped a mechanical 241 into place- no issues... not sure if the factory TBI signal would be correct for the LS computer. those modules that go inline with the speedometer cable should be fairly inexpensive and easy to work with? - and do I remember dodge using those type modules as OEM?
 
interested in what you will think of the 5.3 transplant on that drivetrain.

IM an '88 TBI350/sm465/np241 in the k5 right now, and given the California air research board here... I'm still of the mindset to build TBI replacement engines and avoid the smog nazi's and the nightmares of dealing with them AT ALL
 
If you plan on keeping the 465, the ls computer doesn’t technically need the vss signal to operate.

I ran the 5.3 in mine for years with a 700r4 and no vss input to my pcm. Same for my 8.1/4500 combo, no vss input. The 8.1 uses the same pcm as early ls engines (1411) and it doesn’t have any issues.
 
ZooMad75 said:
If you plan on keeping the 465, the ls computer doesn’t technically need the vss signal to operate.

I ran the 5.3 in mine for years with a 700r4 and no vss input to my pcm. Same for my 8.1/4500 combo, no vss input. The 8.1 uses the same pcm as early ls engines (1411) and it doesn’t have any issues.
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Thanks for the response. I have read that with the manuals they tend to die when you come to a stop because the computer doesn't know what going on without the speed signal.
 
scouthead said:
If your 241 is a mechanical Speedo version, then i believe you must buy a module that goes in between the transfer case and speedometer cable that generates the correct signal?

My K5 was supplied from factory with TBI and 208... and pretty sure the speedo cable drives a signal generator on the back of the speedometer? or its part of the speedometer? man, its been a long time since i played around in there. I swapped a mechanical 241 into place- no issues... not sure if the factory TBI signal would be correct for the LS computer. those modules that go inline with the speedometer cable should be fairly inexpensive and easy to work with? - and do I remember dodge using those type modules as OEM?
Click to expand...
I think it does have some type of converter on the back of the speedo head from the factory. Which would make sense since you switched tcases with no issue with the tbi. I was hoping to figure out what is the frequency or revolutions per mile or whatever it is. Then when I have the LS computer reflashed they can program that in. If you are running cruise control it is more important to be accurate I have read. Just haven't found that spec. Was hoping I could figure that out and which wire goes to the tbi computer then connect that to the new LS harness?
 
scouthead said:
interested in what you will think of the 5.3 transplant on that drivetrain.

IM an '88 TBI350/sm465/np241 in the k5 right now, and given the California air research board here... I'm still of the mindset to build TBI replacement engines and avoid the smog nazi's and the nightmares of dealing with them AT ALL
Click to expand...
I have had a few issues with my tbi the last couple of years. Electrical issues. Thought I fixed them and at the end if the summer seemed to come back and tired of it. Plus the fact it is really under powered for me. (37s, 4.10s and a boat in tow don't work too well). Seems best bang for the buck is an LS swap. It will stay stock for now. Just want the added hp and reliability.
 
formercruiserhead said:
Thanks for the response. I have read that with the manuals they tend to die when you come to a stop because the computer doesn't know what going on without the speed signal.
Click to expand...
Nope. My 8.1 doesn’t stall when I come to a stop. Let off the throttle and it transitions back to idle. The 5.3 didn’t either with the 700 and no vss input to the pcm. It acted the same.
 
Blue85 said:
The optical eye in the back of the speedometer was used on all the 80's cruise controls, until the T-case got the electric sender in mid 89 or 90. If the truck didn't have cruise, it may not have one. Apparently, that comes out to 2000PPM if your speedometer is right. https://ck5.com/forums/threads/tbi-vss-signal.141879/
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Cool thanks. So if I tap off that and have my ls ecm programmed to 2000ppm it should work right?
 
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