gauge help after doing swap...

[Wtfan18]

i remember when i did my 98 swap the Tach, Speedo, and Gas gauge did not work, a guy named Lance (nitrous) on this forum walked me through it. i had to splice wires from my factory harness into certain pins on the New PCM and harness, i cannot begin to tell you which ones they were, i never got the gas gauge worked out because supposedly they had different OHM readings in the 98 and newer sending units which was causing my issue. i know the wiring in the 89-93 trucks are totally different and so are the gauges so it may be totally different. below are some PMS from a WHILE back im not sure if they will help or not.

u get it working yet
Originally Posted by Wtfan18
i grounded pin 9 and it dropped my fuel gage to emply. so i ran a jumper wire and connected pin 13 and 9 and grounded out 19 but it stayed pinned past full still, any ideas?


Originally Posted by beater6.0
sorry i dont explain my self very good lol pins 13 and 19 are on the same plug .and the purple 9 is on another plug. what u can do is take key on and ground pin 9 to verify it is the right plug gas gauge will read empty. then take pins 9 and 13 hook those toghter. then ground 19 and it should work
Originally Posted by Wtfan18
although i did find a #9 purple wire on a different plug. should they all be on the same plug or were they supposed to be on 2 differnt ones?

Originally Posted by beater6.0
no lol pin 9 is out to the gauge and is purple. pin 13 is purple with a white line on it and there wont be voltage just resistance. and pin 19 is a ground for the sending unit.
Originally Posted by Wtfan18

Originally Posted by beater6.0
from your old pcm wiring harness there was to purple wires pins 13 and 9 they need to be spliced toghter and it should work but u need to make sure pin 9 has some where between 0 and 90 ohms 90 should be full and 0 being empty
Originally Posted by Wtfan18
hey bud i just realized something the donor truck my sending unit and fuel pump came off was a 97 gmc sierra 5.7 vortec so is there anyway you can explain to me how to bypass the pcm so i can get my gas gauge working! id really apprecaite it. thanks.

[scarybowtie]

It makes things so much easier for the swap. I left the wires and computer in for all that stuff. My truck is 4x4 so the factory computer in my truck still controls the transfer case, front diff, speedo, volt gauge, air bag & light, and all that stuff. I never even unhooked any of that stuff. The only thing the new harness controls on mine is the 6.0 and the tranny. If you have any questions ask and I'll help all I can bc I just finished my swap. In fact I'm headed to tx to pick the truck up from the exhaust shop now

[PitchBlackC3]

You shouldn't have to run your old ECM for the gauges. It has been so long since I messed with a TBI truck, I don't remember the years they used the DRAC. If your truck has one, you essentially need to remove it and put the PCM output directly to the speedo.
For the fuel gauge you can wire directly from the sending unit to your gauge, the PCM doesn't even need to be involved.

[T-Stark]

been doing some reading on it and they say the DRAC is really hard to take off on my gauges but i could possibly go to a 91-94 style and it would be easier, ill try and mess around on it next time im home i may just say F it and shell out for some aftermarket gauges if i cant get these to work...

any body have reviews on glowshift gauges was thinking about getting some on the pillar but i may just go with a whole set of em

[remauto1187]

been doing some reading on it and they say the DRAC is really hard to take off on my gauges but i could possibly go to a 91-94 style and it would be easier, ill try and mess around on it next time im home i may just say F it and shell out for some aftermarket gauges if i cant get these to work...

any body have reviews on glowshift gauges was thinking about getting some on the pillar but i may just go with a whole set of em

A few of the other guys hit the nail on the head. Your fuel level sending unit doesnt go through the ECM/PCM and the resistance has to be the correct range to make your gauge read correctly. I'll need to look at some schematics but your VSS inputs to the PCM and then the PCM outputs to your gauge but there might be a buffer in between the gauge and the PCM(the newer one).
The buffer takes an average of pulses from your PCM which cleans it up to a usable signal that is not pulsating and send it to your speedo. I think the older gauges are not compatible with the newer system.

[T-Stark]

i appreciate any help man, as in the earlier post i believe i have to bypass the DRAC system in the gauges its self but i have no idea on how to do it.

im sure it can be done but i just don't know much about it

[remauto1187]

Ok let me clarify some of your setup. Do you have your VSS hooked up to your original wiring that goes to your original truck's computer? If you do, then you need to hook it up to the PCM (Engine computer) for the 5.3L. The "buffer" is built into the PCM for your 5.3L. I think your DRAM(Buffer) is behind the glove box(its a module). You wont have to worry about it since your feed wires to the Speedo will come directly from your 5.3L PCM. I would disconnect the DRAM so it cannot feed the speedo anything. You dont want to get into stray outputs or ground loops from one engine computer to the other.

[88stepside]

As you are finding out the 88-90? trucks have the VSS buffer built into the instrument cluster. On our trucks if you change tire s or gear size and want the speedo to read correct you have to change the pin settings in the actual cluster. This is done by burning out factory setting and installing a chip looking thing with pins in it, the number and position of the pins determines the ratio that is read by speedo. In 90 or 91 GM switched to the DRAC module (for ease of manufacture these DRAC modules do the same thing as whats inside our cluster but can be manufactured seperately) which takes the raw hi and low reference signal from the VSS and the sends it to the speedo. I have taken the VSS signal from my transmission and sent it to the PCM, from the PCM I am going to try to send that signal to the speedo. I will send it to the hi reference pin in the cluster and see if it works. As I am still working on the rest of the wiring I havnt reached that part yet. Hope his helps

[T-Stark]

As you are finding out the 88-90? trucks have the VSS buffer built into the instrument cluster. On our trucks if you change tire s or gear size and want the speedo to read correct you have to change the pin settings in the actual cluster. This is done by burning out factory setting and installing a chip looking thing with pins in it, the number and position of the pins determines the ratio that is read by speedo. In 90 or 91 GM switched to the DRAC module (for ease of manufacture these DRAC modules do the same thing as whats inside our cluster but can be manufactured seperately) which takes the raw hi and low reference signal from the VSS and the sends it to the speedo. I have taken the VSS signal from my transmission and sent it to the PCM, from the PCM I am going to try to send that signal to the speedo. I will send it to the hi reference pin in the cluster and see if it works. As I am still working on the rest of the wiring I havnt reached that part yet. Hope his helps

havnt had time to mess with it been having to work weekends and no chance of going home. but heading home this week so hoping to get it working... so are you saying it would be easier to swap to a 90 or 91 speedo with drac other than messing with my moonie gauges? if so looks like i need to make a trip to the local yard

[haveTBIwantLS2]

Yah man the 91 and earlier OBS trucks suck in terms of changing speedo for gears/tires/etc, thanks to the built in VSSB/DRAC/whatever you wanna call it.

I think the best way to deal with it is to swap to a 92-94 cluster with an external DRAC.
You can choose to feed the newer cluster with the speedo output from the 0411 OR from the DRAC.
I chose to feed the cluster with the PCM, to ensure that I know how fast the PCM thinks its going.
I also did this because I have EFILive and can change things whenever I want, to fine tune, etc.
That being said, you can have your PCM sent out and retuned for your wheel tire combo, but if you can't confirm the PCM is correct by seeing on the gauge you can't really tell. Soldering in the DIP switch on the DRAC gives you the ability to change the output to the cruise control to ensure that it operates correctly, so you're good with that, no matter which route you take to feed the speedo...PCM or DRAC.
Bottom line is that you will need to ensure that both the DRAC and the PCM know how fast they're going.

Pitchblack said it, you don't need the ECM to run the speedo. And getting your fuel gauge to work is just a matter of wiring the sender directly to the pin on your cluster. It was purple on my truck (the gauge wire from the tank). That's an easy fix, tho...sounds like you might have just accidentally snipped it.

The wiring scheme basically goes like this in the 91 and earlier trucks

VSS HI/LO feeds --->VSSB in cluster, internal to speedo, then wire to CC unit from cluster and then a feed to the ECM

The VSSB converts the HI/LO AC sine wave feeds from the VSS itself into a 3 different kinds of signals.
The speedo feed is a 4k pulse per mile generated by the VSSB, and the cruise control signals are 2k ppm, not sure what the ECM gets.
Since the 0411 already makes a 4kppm signal output, you can directly connect it to the cluster (92-94, mind you).
The damn cruise control needs its own crap from the DRAC (or cluster in 91 and earlier trucks).

Here is the pinout diagram for our original 91 and earlier clusters (I'm pretty sure the OBS clusters from 91 and earlier are about the same)
No input for a speedo because it is all internal to the cluster.
Couple years ago I remember removing my cluster and hooking up my laptop to datalog with the intention of clearing this up...low and behold, the ECM read 0 MPH when pulling out of my driveway, truck ran like garbage. Promptly threw the cluster back in.

1991 Chevrolet K1500
Instrument Cluster Connector
34 Pin Connector

O
B Wire(s) Colors Circuit Function
17 Brown 437 ECM/PCM <-----tells the ecm how fast it's going
16 Lt Grn/Blk&Lt Gray/Blk 822 VSS-Low <-----from VSS
15 White 121 Gauge-Tach
14 Brown 250 Ignition & RWAL
13 Purple/White 821 VSS-High <-----from VSS
12 White 696 RWAL
11 Black/White 450 Ground-Gauges
10 Not Used Not Used
9 Not Used Not Used
8 Not Used Not Used
7 Not Used Not Used
6 Not Used Not Used
5 Not Used Not Used
4 Not Used Not Used
3 Light Green & White 11 HeadDimSw&DRL
2 Gray 8 Fuse Block
1 Black 150 Ground
B
O


A Wire(s) Colors Circuit Function
17 Not Used Not Used
16 Red/White 818 Cruise Control <----tells cruise control how fast it's going
15 Yellow 237 Safety Belt Lamp/Buzzer
14 Dark Green 35 Gauge-Engine Temp Sender
13 Tan 31 Gauge-Oil Pressure Sender
12 Not Used 507 Not Used
11 Not Used Not Used
10 Light Blue 14 Turn Signals
9 Pink/Black 39 Power-Fuse Block
8 Dark Blue 15 Hazard Flashers
7 Lit Orange/Black 419 DRL Module
6 Tan/Black 592 Upshift Indicator Lamp
5 Brown/White 508 ECM/PCM-Check Engine
4 Not Used 69 Not Used
3 Brown 25 Gauge-Ammeter (Generator)
2 Tan/White 33 Parking Brake-RWAL-Brake Press
1 Purple 30 Gauge-Fuel
A


the tech article for swapping in the 92-94 cluster is over at FSC
http://www.fullsizechevy.com/forum/g...es-w-tach.html

So, basically 91 and earlier OBS clusters suck and you're looking at a some splicing/soldering. Not too bad tho. at least your gauges will work.
O yah, just noticed you have a DBW truck, no biggie. Just looked at LT1swap and it says your speedo output is on C2 Green pin 50.