Upshift Light On C4
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,592
Likes: 3
From: St Louis MO
Upshift Light On C4 Auto Trans
I have an"87 L98 Coupe, auto trans. When cruising at or above 55mph, the "Upshift" light comes on. The trans has been checked and all shift points are correct and the torque converter clutch kicks in and out at the right times. Averages over 21mpg on highway. Contacted 2 diff GM "Performance Parts Techs", (per GM's website) and received 2 diff answers:
1 - "Gee, on a car that old, I don't know".
2 - "You got an automatic, then you don't have an upshift light".
I've got some imagination then, because that sucker lights up everytime. Would appreciate any thoughts or ideas.
1 - "Gee, on a car that old, I don't know".
2 - "You got an automatic, then you don't have an upshift light".
I've got some imagination then, because that sucker lights up everytime. Would appreciate any thoughts or ideas.
Last edited by PierEagle; Jul 27, 2005 at 11:54 PM.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
I would say check your fuses the converter is not locking up.
The plug also falls off the trans at times check both of them.
The 2 prong I think is for the up shift light and the wire is always to short.
The plug also falls off the trans at times check both of them.
The 2 prong I think is for the up shift light and the wire is always to short.
Drifting
Joined: Sep 2004
Posts: 1,961
Likes: 2
From: Fort Knox
Originally Posted by REDC4CORVETTE
I would say check your fuses the converter is not locking up.
The plug also falls off the trans at times check both of them.
The 2 prong I think is for the up shift light and the wire is always to short.
The plug also falls off the trans at times check both of them.
The 2 prong I think is for the up shift light and the wire is always to short.
Wouldnt the light not function if the plug is off the tranny? Im not being a smartass, seriously, my shift light doesnt come on in my 86, and ive kinda always wondered why the idiot light didnt work.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
It all depends on who was doing the wiring for things on the car .
You would not believe what I have found on my 86.
My trans wires were tied into the courtsy lights and light would stay on when head lights came on .
No ground straps.
Horn was hooked to a toggle switch.
And lots more that I did not think anyone was capable of.
The guy that owned the car before me said he was a mechanic.
I think he was butcher.
I just make it a rule to check all things ,even if it does not seem possable.
You would not believe what I have found on my 86.
My trans wires were tied into the courtsy lights and light would stay on when head lights came on .
No ground straps.
Horn was hooked to a toggle switch.
And lots more that I did not think anyone was capable of.
The guy that owned the car before me said he was a mechanic.
I think he was butcher.
I just make it a rule to check all things ,even if it does not seem possable.
Drifting
Joined: Oct 2004
Posts: 1,976
Likes: 0
From: Patchogue NY
Yes, I put a thread in about a similar problem except that my car is a 91, and the light never came on, but it comes on now that I have swapped my gears. I emailed Jesse, the "tuner," and he assured me that he could reprogram a chip to eliminate the light. You might want to give him a shout, he usually lurks around the "scan and tune" thread.
Good Luck.
Joe B.
Good Luck.
Joe B.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Seems like alot of guys are reporting this lately. Another member and myself with 87 autos were having the same thing happen. He said he replaced his fuel pump and it stopped-for awhile, I replaced my fuel pump and haven't had that problem now for over 6 months.After thinking about it-I felt it was tied to the computer for not only shifting
at a certain RPM range-but also had something to do with fuel economy-could a bad fuel pump indicate to the computer not enough fuel in a certain gear at a certain RPM? don't know-but it seems to have worked for me. Besides, didn't know if the pump had ever been changed-and the sock was really clogged.
at a certain RPM range-but also had something to do with fuel economy-could a bad fuel pump indicate to the computer not enough fuel in a certain gear at a certain RPM? don't know-but it seems to have worked for me. Besides, didn't know if the pump had ever been changed-and the sock was really clogged.
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Waka, Waka, Waka!
Joined: Jun 2002
Posts: 2,435
Likes: 2
From: Richmond Virginia
CI 4-6-8 & 10 Veteran
St. Jude Contributor
Originally Posted by rick lambert
...
I felt it was tied to the computer for not only shifting at a certain RPM range-but also had something to do with fuel economy-
...
I felt it was tied to the computer for not only shifting at a certain RPM range-but also had something to do with fuel economy-
...
PierEagle, has your highway milage always been that bad?
Former Vendor
Joined: Jun 2001
Posts: 7,204
Likes: 6
From: St Marys PA
This can be changed in the chip 
The MPG will also be off if you change the injector size. I have not found a way around this yet. Then again I have not really looked at it too closely either. I am sure there is just a simple calculation that could be altered in the code to make it use the correct factor. Just never really cared enough to search around for it. Makes me feel good to have 600+ ponies and look down and see 32mpg
I freak people out that don't know better when they see that. 
The MPG will also be off if you change the injector size. I have not found a way around this yet. Then again I have not really looked at it too closely either. I am sure there is just a simple calculation that could be altered in the code to make it use the correct factor. Just never really cared enough to search around for it. Makes me feel good to have 600+ ponies and look down and see 32mpg
I freak people out that don't know better when they see that.
Team Owner
Joined: Mar 2000
Posts: 83,381
Likes: 87
From: Boston, MA
Have you verified that the transmission is shifting into overdrive and the torque controller is locking up? In an auto that is basically the function of the upshift light, reminding you to go into OD.
There are a couple parameters in the ECM that can be altered to turn it off all the time or to reprogram it for those that are interested. I think the fields are...
% Throttle vs. RPM
Light Delay (in seconds) vs. RPM
There are a couple parameters in the ECM that can be altered to turn it off all the time or to reprogram it for those that are interested. I think the fields are...
% Throttle vs. RPM
Light Delay (in seconds) vs. RPM
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,592
Likes: 3
From: St Louis MO
Upshift Light
Appreciate all the comments. It gives me some things to look at and if none work, I guess I'll to succumb to the "GM Performance Tech" consultation fee of $200.00 - $300.00. I've only owned the car for about 6 mos and highest mpg has been 22.8 during that time. Car has 75k miles, in very good shape and all stock.
Thanks again.
Thanks again.
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,592
Likes: 3
From: St Louis MO
Hey, FOZZY BEAR:
The EPA rating for the '87 was 16 city/25 highway 19 combined. What did you do to get over 28 ?
The EPA rating for the '87 was 16 city/25 highway 19 combined. What did you do to get over 28 ?
Last edited by PierEagle; Mar 6, 2005 at 02:01 AM. Reason: Directing to FOZZY BEAR
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Originally Posted by PierEagle
I have an"87 L98 Coupe, auto trans. When cruising at or above 55mph, the "Upshift" light comes on. The trans has been checked and all shift points are correct and the torque converter clutch kicks in and out at the right times. Averages over 21mpg on highway. Contacted 2 diff GM "Performance Parts Techs", (per GM's website) and received 2 diff answers:
1 - "Gee, on a car that old, I don't know".
2 - "You got an automatic, then you don't have an upshift light".
I've got some imagination then, because that sucker lights up everytime. Would appreciate any thoughts or ideas.
1 - "Gee, on a car that old, I don't know".
2 - "You got an automatic, then you don't have an upshift light".
I've got some imagination then, because that sucker lights up everytime. Would appreciate any thoughts or ideas.
Last edited by 86PACER; Jul 27, 2005 at 12:17 AM.
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,592
Likes: 3
From: St Louis MO
Originally Posted by 86PACER
It's supposed to do that. I don't see what the problem is here. You do not mention it, but is the light not turning back off when you do go into overdrive? Maybe I'm missing something. When it lights up, shift to the overdrive (d with the circle arround it) and it goes out. Or just leave the shifter in Overdrive and it does it for you.
Thanks anyway, for your input.
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Originally Posted by PierEagle
But the light comes on and stays on until I brake or slow down.
Last edited by 86PACER; Jul 27, 2005 at 01:52 AM.
Drifting
Joined: May 2002
Posts: 1,581
Likes: 2
From: The Motor City
This may sound a little far fetched, but do you think you might have a vaccum leak? I could see a rogue vaccum leak setting something like that off, especially if you're saying that you don't have a shift kit or new rear gears, your transmission is functioning fine, and you don't see any electrical issues.
It might be worth checking your vaccum lines, especially those that come in contact with any of the corrigated electrical conduits - vaccum lines easy chaffe in these areas and can go unnoticed for a long time.
Hope that helps. Good luck with it.
It might be worth checking your vaccum lines, especially those that come in contact with any of the corrigated electrical conduits - vaccum lines easy chaffe in these areas and can go unnoticed for a long time.
Hope that helps. Good luck with it.
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,592
Likes: 3
From: St Louis MO
Originally Posted by TheCorvetteKid
It might be worth checking your vaccum lines, especially those that come in contact with any of the corrigated electrical conduits - vaccum lines easy chaffe in these areas and can go unnoticed for a long time.
Hope that helps. Good luck with it.
