Hello everyone. I just got this 1991 z28 with a 5.7. Runs great with only 1 problem the speedo is inop. Im sure its a 700 trans but the guy thinks its not the one that came in it. Anyway I took it to the dragstrip and it did not shift properly in fact i had to let up to get it to upshift and the big problems at about 3/4 track it was done (no power at all) I think the speedo not working is
the problem? If so can you bypass it? I have a gps so i dont need the speedo. The car is all stock with no mods. Any help please!

 

The transmission in these cars is mechanical. The only thing that disconnecting the speedo would do is not allow the ECM to lock the torque convertor.

 

yeah the speedo not working isnt your problem there, might wanna start with adjusting the tv cable and go from there.

 

When you say the speedo is mechical i think of a cable my speedo has 2 wires coming out of the trans were the speedo cable should be. Im just thinking that the ECM would go into some kind of shut down mode if you are wot and the ECM shows your not moving??? Thanks for any help...

 

no, the speedo can be electrical. My 85 berlinetta has an electrical speedometer sender. The transmission is mechanical, meaning that the ECM has no control over the transmission besides locking the torque convertor.

 

and the torque converter lockup wouldnt even be noticeable in a 1/4th mile pass since it wont lockup at WOT, it will be noticeable on the highway though.

 

OK thanks my last thoughts are over with the speedo! I guess i'm back to square one with my problems??? I did shift it manualy 1 time and i had to let up a little for it to shift that time also. But even after in 3rd it lost power like a vapor lock or low fuel pressure. I'm going to adjust the tv cable and put a fuel guage on it and go back next weekend. What fuel pump pressure should i see at idle and wot in 3rd gear???

 

what gear its in shouldn't make a difference, the fuel pressure regulator has a vaccum line on it, when its at idle with high vaccum pressure should be lower, when you go to wot and vaccum is low pressure should go up. Not positive on the numbers off the top of my head but I think its somewhere in the mid 30's at idle and somewhere around 46 or 47 at wot? I'm sure someone knows for sure and will chime in..

 

I just got back from the dragstrip and after adjusting the tv cable my problem is solved!!! Thanks to all... Any way it went 14.93,14.92,14.93 all at 90 mph. with about 125lbs in the trunk to solve my traction problem. (I'm getting some better tires soon) With all the first hand pro's on here can any one let me know the best HP gains for the money??? I'm not rich but can spend some $$$ if it sounds good...Thanks for any help and it is a daily driver...