Author Topic: TBI newbie question  (Read 6489 times)

Offline zieg85

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    • 73-87 GM squarebody extended cab and conversions up to 91 R/V series
Re: TBI newbie question
« Reply #15 on: April 22, 2015, 05:43:34 PM »
The 87 TBI should acquire its VSS signal from the buffer that connects into the back of the speedometer head.  As long as you have a suitable cluster with VSS buffer, Code 24 will not set and the ECM will be able to properly register road speed.  If push comes to shove (and IIRC) there's a software switch accessible to a programmer that will toggle VSS diagnostics OFF.

Code 24 will set if:
  CKT 437 voltage is constant.
  Engine speed between 900 and 4400 rpm.
  Less than 2% throttle opening.
  Low load condition (low air flow).
  Not in park or neutral.
  All conditions must be met for 3 seconds.
These conditions are met during a road load deceleration.

Perfect, I can switch out the speedo cluster or just add the speedometer head.  The clusters are identical being both are dummy lights and not gauges.  I am sure it will be self explanatory when I start the harvest process.  I parted out a 87 TBI truck a couple of years ago and carefully removed the wiring harness to ecm and engine and when I have the trucks side by side it shouldn't be too difficult.   
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline frotosride

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Re: TBI newbie question
« Reply #16 on: April 22, 2015, 09:05:02 PM »
Since you said budget here's a pic of what you will need from a donor. The sensor in my hand has a single screw that attaches it to the back of the speedometer. The green box is the signal converter. It only needs switched power,ground and the brown wire goes to A10 on ythe ECM smaller blue connector.
« Last Edit: August 12, 2015, 11:08:04 AM by Captkaos »
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Offline zieg85

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    • 73-87 GM squarebody extended cab and conversions up to 91 R/V series
Re: TBI newbie question
« Reply #17 on: April 22, 2015, 09:11:04 PM »
Looks like what is used on the newer cruise controls
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline roundhouse

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Re: TBI newbie question
« Reply #18 on: April 24, 2015, 07:18:24 PM »
Wow
$1600 for TBI

Guy near me sells LS motors ready to run with harness and reprogrammed computer for $1100

The frame mounted pump may work or it may not
Worked fine on my 73 bronco to supply 50 psi for the 90 mustang engine

But wouldn't work on our 77 K-10 TBI
We wound up ordering a new 87 tank from rock auto for $80 and buying a new In tank pump at a local auto parts store

We bought the complete TBI system from a running truck for $200



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