Needs some help: 91 factory service manual

[Ackattack]

I put a 91 TBI engine into my 69. All seems to be good there. Now I'm trying to get the cruise control hooked up. I do not have a factory service manual for the 91. If someone has one, can you look around and see if you can find what kind of signal the cruise control module is looking for.

I believe it is a 4000 square wave pulse per mile, but I want to confirm this before spending more money.

Thanks

[ChevyTech]

I believe the 91 TBI truck would have a separate DRAC module where the 1988 had it built into the instrument panel. It is my understanding that the signals used for various items would be the same for 1988 and 1991


From 1988 C/K training manual:
The VSS produces 40 pulses per drive shaft revolution.
The DRAC uses an Schmitt trigger to convert the AC wave the a square wave
The DRAC produces 2000 pulses per mile signal for the speedometer
The DRAC produces 4000 pulses per mile signal for the cruise control
The DRAC produces 128000 pulses per mile signal for the antilock brakes

The DRAC sends a 12 volt square wave signal to the RWAL module.

[clay68c10]

For reference, I used a 40 pulse per mile VSS driven by my speedo cable when I converted my 68 c10 to a 1989 TBI. The TBI computer liked it and it did show the correct speed when I viewed it with WIN-ALDL.

Maybe the factory cruise will accept that signal, maybe not.

I will say that the TBI ran much better with a VSS input. Also, it allows for the system to go into lean-burn mode at steady throttle cruise for better mileage.

I piggybacked that speed sensor signal to an Audiovox aftermarket cruise control, it worked as well as any throttle by wire new car cruise control.

[Ackattack]

Originally Posted by ChevyTech

I believe the 91 TBI truck would have a separate DRAC module where the 1988 had it built into the instrument panel. It is my understanding that the signals used for various items would be the same for 1988 and 1991


From 1988 C/K training manual:
The VSS produces 40 pulses per drive shaft revolution.
The DRAC uses an Schmitt trigger to convert the AC wave the a square wave
The DRAC produces 2000 pulses per mile signal for the speedometer
The DRAC produces 4000 pulses per mile signal for the cruise control
The DRAC produces 128000 pulses per mile signal for the antilock brakes

The DRAC sends a 12 volt square wave signal to the RWAL module.

The "speed buffer" was built into the instrument panel on mine (it could be a 90 actually....I misplaced the title but could swear it was a '91, however i found an owners manual that is a '90). Anyways, I was thinking the cruise needed a 4000 pulse per mile signal.

[clay68c10]

You guys are probably right. Maybe you could grab a DRAC out of a later truck and use it to convert the signal.
I've got the 93 wiring diagram if you find a 93 DRAC and want to try it.
Also have an 89 diagram from my old c10 conversion.

I posted over in your build thread too, pretty cool truck. I really liked my old TBI c10 setup. I'm gonna run one on the Caddy eventually.

[tommie]

http://67-72chevytrucks.com/vboard/s...63&postcount=5

some wiring diagrams that i posted on here... don't know if any will help or not

[Mark S]

Hi folks, I have a question for Tommie about the DRAC module that I have.
1st, this is going in my '89 silverado SB 1500, 5.7, 5 speed. I have a '93 cluster, and DRAC. I have the '89 Helms elec. book but was short on info without a 92-94 wireing diagram. Then I came across this post and thought I had every thing I needed. BUT!!! the '93 diagram that I downloaded from your post shows the wires coming out of the DRAC plug in a different order than the plugs (I have two) that I have. The diagram shows the wires, from the top down;
LT BLU-BLK
BRN
PPL-WHT
WHT
BRN
BLK-WHT
LT GRN-BLK
RED-WHT

My plug has them;
LT BLU-BLK
PPL-WHT
BRN
WHT
BRN
BLK-WHT
LT GRN-BLK
RED-WHT
I'll post this on a new thead with more info, your help would be much appreciated. Mark

[tommie]

mark,

i posted in your new thread... lets keep this one on topic with Ackattack's question...

[ChevyTech]

Originally Posted by Ackattack

The "speed buffer" was built into the instrument panel on mine (it could be a 90 actually....I misplaced the title but could swear it was a '91, however i found an owners manual that is a '90). Anyways, I was thinking the cruise needed a 4000 pulse per mile signal.

Are you using the factory cruise control off the TBI truck?