Upshift Light Mystery

[isby]

I've had my '84 3.2L for about a year and a half (125K miles) and, in that time, the upshift light has never worked ... not even once. I'm driving around my neighborhood this afternoon and - all of a sudden - the upshift light starts working. I realize that many will view the operation of this nanny light as a curse rather than a blessing, but I like things to work as intended. Any ideas as to why this light would magically start working?

[pavegeno]

The signal comes from the DME brain (it does on my 88). It stopped working on mine so I sent the DME brain back to ECU doctors and they fixed it under warranty. Could be the connection on the back of the tach or the light bulb in the tach. Any chance you recently tightened these or maybe a good bump got it working.

I actually like the light and like that every component on my 88 works. The upshift light not only comes on under mild acceleration for better gas mileage, but it also comes on at max RPM under heavy throttle.

[Larmo63]

I ignore the one on my tach.

I find it annoying.

[GH85Carrera]

I just ignored my shift light for several years. I too like everything to work as designed, or better. That shift light was just a government mandated fuel economy stupid idea.

I just LOVE having a volt meter in the spot where the shift light was. A volt meter is a million time more useful than the shift light. I prefer my calibrated temperature gauge as well. Knowing an actual temperature at a glance and not just a mark on the gauge is comforting.

[Steam Driver]

I always thought they encouraged short-shifting and lugging.

[megerian]

Mine worked, then stopped working for a little while when my tach wiring was wonky, then started working again when I had the the tach wiring fixed.

[darrin]

Originally Posted by Steam Driver

I always thought they encouraged short-shifting and lugging.

Yep, AND an '84's 915 would shift a LOT smoother if shifted at >3,000 rpm -- If the OP's upshift light never worked at all, wondering whether it's an issue inside of the tach itself. When I disconnected the trigger wire from my tach's wiring harness the upshift light stopped telling me to shift too early and lug my engine, but did continue to illuminate as the tach swept into the redline

[GH85Carrera]

Originally Posted by Steam Driver

I always thought they encouraged short-shifting and lugging.

Back in the early to middle 1980s all cars had to have a way to show a driver how to get better gas mileage. Mercedes and most other makers had a vacuum gauge on the dash, and it showed the driver a green zone of low throttle, and a red area if the loud pedal was pressed.

Porsche decided to go with the shift light and not a stupid vacuum gauge. And for sure, if one followed the shift light suggestion, driving the 911 was as much fun as driving a 40 HP VW bug.

At least Porsche got rid of the idiotic 85 MPH speedometer with the big red 55 on it as soon as the law was changed. I remember the bad old days of 55 MPH national speed limit. Just a few weeks ago I cruised past a state trooper, with my radar detector alerting me of radar, while I was driving 80 MPH. That was the legal and posted speed limit. It was somehow very satisfying to roll by at 80, knowing I was not even bending the speed limit.

[dw1]

Originally Posted by Steam Driver

I always thought they encouraged short-shifting and lugging.

Please remember that the upshift light works in conjunction with throttle position - the more you press on the go pedal, the later the light comes on.

I actually like the upshift light on my '87 3.2, so much so that I disassembled the tach and fixed mine. Well, not just because I find it useful but more because I wanted everything in my 911 working.

As to why one would not be working and then start working, I can only guess:

• As previously posted, the light works from a signal from the DME. if the harness connectors (on the DME or tach end) and/or the DME itself were recently cleaned, fixed or replaced, that might do it.
• Another less likely possibility is an intermittent connection to the upshift light bulb (and yes, it is a bulb and not an LED) within the tach.

[redridge]

I actually want to disable the shift light... anyone know which wire to pull off? Is the bare wire on the multi wire connector the shift light? Or pull out the bulb?, I can't seem to find access to the bulb. 1986 Carrera.

[rokemester]

In my 10 years of ownership the shift light seems to follow the moon and the tides. It amuses me when it works and I forget about it when it doesn’t.

[GG Allin]

Originally Posted by pavegeno

The signal comes from the DME brain (it does on my 88). It stopped working on mine so I sent the DME brain back to ECU doctors and they fixed it under warranty. Could be the connection on the back of the tach or the light bulb in the tach. Any chance you recently tightened these or maybe a good bump got it working.

That's odd, because mine works and my car has no DME, it's been completely removed along with the harness. First time I saw the shift light come on I thought it was odd and figured it was just a function within the tach.

[rgrimm]

Mine seemed to work accasionally in the early Spring and late Fall, when it was cooler out. Never in the summer heat. But I haven't seen it at all in the last few years. One of life's little mysteries!

[brianlay]

That light is driven by two inputs
The input from the DME indicates the rev limiter
The fuel economy function indicates high intake manifold vacuum, but only above approx 2k rpm
I disconnected the economy function years ago but it still indicates the limit

[thsupernge]

I love the fact that you guys know this stuff!