up shift light ques
Thread Starter
Racer
Joined: Jun 2001
Posts: 335
Likes: 0
From: MANTEO NC USA
up shift light ques
i have an 86 vette my up shift light comes on and stays on even when the car is already in overdrive if i tap on the gas it will go off but it will come back on in a few minutes what can i do to correct this.
Drifting
Joined: Dec 1999
Posts: 1,319
Likes: 2
From: Douglasville GA
Re: up shift light ques (Jim-K)
DADDY D - have you changed the rear gear ratio?
I believe the way the light works is based on a RPM vs SPEED table and a combination of throttle position and time.
For example, if you are in 3rd, at a steady speed, and say 10 seconds the light will come on. But if you are accelerating in 3rd for 10 seconds, the light will not come on. Also, if you are deccelerating in 3rd for 10 seconds the light will not come on.
I recently upgraded my 86 from 700R4/3.07 D36 to a ZF6/3.45 D44 and the light behaves perfectly before and after. The light will come on until I hit 6th gear, anytime that I am steady state in any gear 1-5 for about 10 seconds. The ECM cannot know that I have a ZF6, as there is no inputs for it (and I connected all the required wires myself).
Had I left the 3.07 D36 in the car, the light likely would not have come on in 5th, as the RPMS would match the 700R4 in 4th.
Make sense?
Tom Melton
82 CE
86 Z51 Coupe
I believe the way the light works is based on a RPM vs SPEED table and a combination of throttle position and time.
For example, if you are in 3rd, at a steady speed, and say 10 seconds the light will come on. But if you are accelerating in 3rd for 10 seconds, the light will not come on. Also, if you are deccelerating in 3rd for 10 seconds the light will not come on.
I recently upgraded my 86 from 700R4/3.07 D36 to a ZF6/3.45 D44 and the light behaves perfectly before and after. The light will come on until I hit 6th gear, anytime that I am steady state in any gear 1-5 for about 10 seconds. The ECM cannot know that I have a ZF6, as there is no inputs for it (and I connected all the required wires myself).
Had I left the 3.07 D36 in the car, the light likely would not have come on in 5th, as the RPMS would match the 700R4 in 4th.
Make sense?
Tom Melton
82 CE
86 Z51 Coupe
Melting Slicks
Joined: Apr 2001
Posts: 2,090
Likes: 215
From: Ca.
Re: up shift light ques (DADDY D)
That irritating light is controlled in the prom programming. Unfortunately I havn't seen any hacks that ID it. Might try posting about it at the prom section. You could always just take out the bulb!? :smash:
Drifting
Joined: Dec 1999
Posts: 1,319
Likes: 2
From: Douglasville GA
Re: up shift light ques (drive it)
Fix it? Somewhere in the chip in the ECM is the table I mentioned. It will need to be modified to make the light work correctly again. This actually is not a true table, but probably one single value. Probably something like a constant. *Guessing here*, The ECM likely takes the RPM and divides by the MPH and compares to the constant. If over the constant value and steady state (no accel/deccel) for X time, then turn on the light.
Hypothetical constant here: 28.6
2000RPM/55MPH = 36.7 higher than constant - turn on light
2000RPM/70MPH = 28.6 equal (auto 4th with 3.07) - no light
2000RPM/35MPH = 57.1 higher ... turn on light
Again, the above is a simple *possibility* of the way it *could* work.
Last question, did you have your chip in the ECM modified for your grar change? If not, then find someone to burn you a new chip with the correct ratio and the light will probably start working correct again.
Tom Melton
82 CE
86 Z51 Coupe
Hypothetical constant here: 28.6
2000RPM/55MPH = 36.7 higher than constant - turn on light
2000RPM/70MPH = 28.6 equal (auto 4th with 3.07) - no light
2000RPM/35MPH = 57.1 higher ... turn on light
Again, the above is a simple *possibility* of the way it *could* work.
Last question, did you have your chip in the ECM modified for your grar change? If not, then find someone to burn you a new chip with the correct ratio and the light will probably start working correct again.
Tom Melton
82 CE
86 Z51 Coupe
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Melting Slicks
Joined: Apr 2001
Posts: 2,090
Likes: 215
From: Ca.
Re: up shift light ques (tommelton)
Last question, did you have your chip in the ECM modified for your grar change? If not, then find someone to burn you a new chip with the correct ratio and the light will probably start working correct again.
Tom Melton
82 CE
86 Z51 Coupe[/QUOTE] His is an 86-it just needs the gear/gears on the tranny speed sensor changed to correct the speedo signal to the dash and the ecm.
Drifting
Joined: Dec 1999
Posts: 1,319
Likes: 2
From: Douglasville GA
Re: up shift light ques (drive it)
His is an 86-it just needs the gear/gears on the tranny speed sensor changed to correct the speedo signal to the dash and the ecm.
-Tom
Racer
Joined: Oct 2000
Posts: 460
Likes: 0
From: Lincoln NE
Re: up shift light ques (DADDY D)
What's the point of that light on an automatic anyway? The owner's manual even says to press the throttle till the light goes away which says to me "We have no idea either why we put this on the car". WTF?
Couldn't they have programmed the PROM to deactivate this light on the automatics? Oh well, then their would have been two different chips for manuals and automatics.
Sorry, didn't mean to rant.
Couldn't they have programmed the PROM to deactivate this light on the automatics? Oh well, then their would have been two different chips for manuals and automatics.
Sorry, didn't mean to rant.
Drifting
Joined: Dec 1999
Posts: 1,319
Likes: 2
From: Douglasville GA
Re: up shift light ques (ToddAT)
Couldn't they have programmed the PROM to deactivate this light on the automatics? Oh well, then their would have been two different chips for manuals and automatics.
ThermoMaster Power Chip 5.7 TPI AH AUTO FED 126022
ThermoMaster Power Chip 5.7 TPI CIH AUTO FED 126032
ThermoMaster Power Chip 5.7 TPI CIH MAN FED 126042
ThermoMaster Power Chip 5.7 TPI AH MAN FED 126062
ThermoMaster Power Chip 5.7 TPI CIH AUTO CAL 156302
ThermoMaster Power Chip 5.7 TPI AH AUTO CAL 156342
ThermoMaster Power Chip 5.7 TPI CIH MAN CAL 156372
ThermoMaster Power Chip 5.7 TPI AH MAN CAL 156382
Note though that Hypertech does not differentiate between the non-performance and performance axle ratios. To fix the light will typically take custom programming -OR- remove the bulb.
-Tom