Ok i have never seen this happen before. But about 4 days ago i was driving down the road only going about 25 and when my car gets into OD the rpms would drop down really hard and it seemed like the car would try to shut it self off. Now no matter what the keep if i get to a cruzing speed where OD kicks in it does the same thing. The RPMS drop to about 300 and the car hesitates bad like it wants to cut off but that picks back up again. Only does it accasionally. Whats going on here. Thanks. By the way i have a 91 Z-28 305 now not an RS.

 

Possibly the 4th gear pressure switch in the valvebody failed (closed) so it can lock up in lower gears... You can change it easy by dropping the pan and filter.

 

It's your converter clutch locking, not shifting into OD, completely normal. If you never noticed it before you were either always driving with too heavy a foot or for some reason it wasn't locking (bad switch/connection, etc.) Basically, it bogs down like that b/c the convert locks up, thus you have a direct connection between the engine and transmission. This is a good thing, it reduces heat in teh tranny and also uses less gas. If it really bothers you that much you can program the minimum lock up speed higher in the chip.

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.8 @ 93.1
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

I don't know what you were trying to get at with this one. The minimum TCC lock speed is 25mph in every stock SD 305 bin i've seen. This has nothing to do with the 4th gear switch. The 4th gear switch input simply switches between the low gear and OD TCC lockup vs. % TPS tables. So it's not a matter of a failed 4th gear switch, cuz it will lock up at 25mph in second gear if you know what you are doing.