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.

REDC4CORVETTE

If you changed the rear end gears or installed a shift kit ,get use to it.
Mine is on until I hit 83 mph ,then it goes off.

PierEagle

Everything is stock. And the puzzle continues..Thanks

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.

snoopdan

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.

REDC4CORVETTE

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.

joe3906

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.

rick lambert

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.

Fozzy_Bear

I was wondering about the mpg number. My 86 with 170,000 miles and 3.07 gears gets over 28 mpg.

PierEagle, has your highway milage always been that bad?

0ski_dwn_it

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.

scorp508

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

PierEagle

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.

johnno!

If its a 4+3, hit the overdrive button. my 86 says upshift when I keep the OD off.

John

PierEagle

Hey, FOZZY BEAR:

The EPA rating for the '87 was 16 city/25 highway 19 combined. What did you do to get over 28 ?

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.

PierEagle

Sorry, it's NOT supposed to do that. As I stated in my original post, all shift points physically check out, the lockup kicks in and out as it should and yes, the shifter is in overdrive and the tranny goes into od. But the light comes on and stays on until I brake or slow down.

Thanks anyway, for your input.

86PACER

You did not say that in any of your posts. Now I see what's going on.

mikey whipreck

Take the light out

TheCorvetteKid

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.

PierEagle

Never thought of that. I'll check. Thanks for the tip. I am about ready to take the cheap way out and put a piece of tape over the light (not really.)