Supernatural

I need the wiring diagram / schematic for the computer for the 1988 TPI (specifically the power, ground and vehicle speed sensor that runs to the ECM, colors and location on the 2 plug-ins).

RonsRed88

I scanned a couple pages out of my electrical manual (88) that may be helpful. They are pretty big so I won't insert them here. You can see them at the following links:
http://myc4.freeservers.com/images/file0043.jpg
and
http://myc4.freeservers.com/images/file0044.jpg

Good Luck,
Ron

Supernatural

I tried both links,but instead of the pictures it came up and said on both of them. Thanks for trying.

steve1ph2

i can send them pdf style to your mail box if you want.

Supernatural

Yes, if you could please send me the schematic / diagrams to my mail box that would be great. I am trying to install a speedo calibrator box in between the speed sensor wire. I swapped 3.07's for 3.45's. The 1988 has a 4+3 in it, if that makes a difference in wire color.

CentralCoaster

Have you considered just changing the speedo gear? It'll cost you about 5 bucks, and take a 1/2 hour at most.

steve1ph2

i dont think i can attach anything here on the forum. you know after all these years i still dont know how to add a pic to my post other than a link to a freebee host? seems its an act of god. not a hoop i want to jump thru. but i understand the admin position on space. if everybody could just copy and past then we would all be paying a monthly fee. i can scan to pdf and email you want you want. pm me with your address.

Supernatural

Is it really that easy, just 30 minutes and a $5.00 part? I thought you had to remove the drive shaft and take apart the tail housing to get to the speedo gear in the trans. Has anyone done this in a 4+3 that can give some detail instruction on this.

CentralCoaster

Well, the closest you can get without changing the tailshaft gear is a 17/45 ratio, optimal for a 26.3" tire, so you'll have about 3-4% speedo error, depending on exactly how tall your tire is (should be 25-25.5 inches)

If you go this route, get GM p/n 25513052. Simply unplug the speedo sensor, remove the hold down bolt, catch the 1/2 cup of ATF that comes out, and slip the new gear on and slap it back together.

A more accurate speedo would require opening the trans, or using the adapter.

Supernatural

Thanks, I will have to give that a try. It does not sound that bad. There are 2 tests that I tried, to see how far off I was. I was driving next to someone. They were doing 45mph and I showed 52mph. That was 1.18 to 1. Then I drove a distance of 1 mile in my other car and then drive the Vette the same exact distance. The trip meter showed 1.2 miles distance, so that is 1.2 to 1. So both tests are very close math wise. I am currently running on 255 50 16's on the stock 1988 16" wheels. I will be upgrading in the future to 2006 ZO6 style 18X9.5 in front and 18X10.5 in the rear.

steve1ph2

check your hotmail

tequilaboy

If you do go with an electronic ratio adapter like the dakota digital SGI-5. You must correct the VSS signal to the instrument cluster. The cluster gets the signal first and then outputs to the ecm.

If you correct the ecm input only, the speedo will still be off.

Personally I think this is the easier approach than swapping the drive and driven gears and possibly the vss. Gears may work out to be a little cheaper depending upon your needs. Others will surely disagree.

The advantage of electronic adaptors is that they can be dialed nearly exactly for any tire gear combination, and can be easily changed to support future tire/gear changes.