My mostly stock '87 TII's 'shift up' light sometimes flickers if I'm cruising at light load above ~2500 RPM in any gear, but the truly strange part is it's usually either on constantly or flickering when I'm coasting with and without cruise control in 5th gear at all normal highway speeds. Is there a sensor that should be tested/replaced, is this causing the ECU to make any changes, and what purposes exactly is the light supposed to serve (how is it supposed to operate?)? Thanks, guys.

 

search for cpu cold soldering points.

 

http://fc3spro.com/TECH/PROBLEMS/DT/TRANS/shiftup.htm


-Ted

 

that is there for the "best economy" once you have reached a certian RPM the light comes on.. so if you are above that rpm and u even lightly depress the gas it will come on.. if you have it on cruise control it will come on anytime the cruise accelerates to get up to speed..

You do realize that cruise control is actually worse for economy MPG then just using yrou foot to keep it steady!

 

On cruise or off it still comes on at highway speeds, maybe even lower. Once I have the '7 back together and running I'll have to do a few more tests.

The fc3s article explains it. That's probably the problem then. The shifter bushings were replaced by the PO, maybe he messed up the sensor then... Thanks, Ted.

 

If the car is in 5th gear, the light should not come on above 2200rpm

Vince

 

The CPU has nothing to do with the shift light

 

if the car is in 5th gear the light should not come on at any point.

 

So then, how, exactly, is this light supposed to operate?

 

The shift up indicator light is to help the driver get the best mileage out of the car. It is based on the system found in many 82-89 Porsche products with manual transmissions.

It comes on at the optimal (for gas mileage) shift point based on throttle position in the first 4 gears (as obviously 5th gear is already the highest gear for best gas mileage).

For example if you are accelerating in 2nd gear with only half throttle, the light should come on somewhere around 2600-2800 RPM, indicating shifting to 3rd will give you better mileage than 2800 RPM in 2nd.

If you are at full throttle, the shift point switches to around 4000 RPM.

So full throttle acceleration, (say for example) in 3rd gear... around 4000 RPM it is going to come on, telling you to shift up to 4th gear.

If it is coming on in 5th gear. The Over The Top switch (or otherwise called 5th gear switch) is disconnected.

The only other reason it can be coming on, is if the alternator is failing, however all the idiot lights should also be flickering at the same time.

 

Thank you much! I'll look up where to find that switch.

 

on the transmission. As I recall it has ground on it when the car is in 5th gear

You can test it at the ECU or the Split Air Solenoid. With the Key off, the Black/Blue wire (pin I at the ECU) or the White at the split air solenoid will have ground on it when the shifter is in 5th gear.

 

my car has the same problem.... i never really paid much attention to it

 

Meh, that's a rumor. Those sources actually point out specific rare situations when cruise control gives worse mpg (steep hills), or they complain about the cruise control's teeny tiny fluctuation in throttle (when really variation improves mpg, it's just annoying). You get the same mpg either way. I know I do, or I might get better mpg with cruise control.

 

Yeah, my guess would be if my foot acted in such a way as to accomplish approximately the same speed result the mileage shouldn't differ by much, especially over a 10+ mile trip or tank of gas.

I just don't like the fact that my car isn't acting exactly as it should. I want to bring this machine to perfection eventually, so I'm doing all I can with what I have at the moment.