| Author | Message | ||
| Alex Vivaldi (Vivaldi)
New member Username: Vivaldi Post Number: 19 Registered: 8-2001 |
Same problem on an 87 Mondial. Intermittently works correctly, then reverts to 1/2 of actual RPM. It's not the $150 that Palo Alto wants that scares me, it's the potential damage of removing it from the dash when I don't know how it is held in place. | ||
| Jim E (Jimpo1)
Member Username: Jimpo1 Post Number: 548 Registered: 7-2001 |
This is one of the things I love about this site, now I know to be prepared for a tach fix. | ||
| Mark Rockcastle (Mrockcastle)
New member Username: Mrockcastle Post Number: 6 Registered: 5-2001 |
My 1987 is doing the same thing...however it seems to be getting better. I shift by ear anyway, so it is not vitally important to me. Palo Alto Speedometer will fix it for around $200, and it will take a mechanic about 2 hours to take it out and put it back in. Count on $350 low to $500 high. | ||
| Dave328GTB (Hardtop)
Junior Member Username: Hardtop Post Number: 184 Registered: 1-2002 |
Russ, It seems 328 tachs are problematic. I had an 87 where the tach was rebuilt 3 times. It was working when I sold it, don't know about now. My current 89 ran at about 1/2 speed when really cold. Now t seems to be about 10% low. I hit the governor at a reading of 7200. If someone has a good solution, I'll do it, otherwise, I'll leave it alone. New ones aren't very expensive, but they probably aren't any better. Dave | ||
| Russ Moore (Rem9)
Junior Member Username: Rem9 Post Number: 83 Registered: 6-2001 |
It appears from the schematic, there are two sensors, one a speed sensor on the right lower side of the transmission case, and the other a TDC sensor. Both these send input to the ECU then there is an output from the ECU to the tach itself. Seems simple enough. What am I missing? | ||
| Lawrence Coppari (Lawrence)
Junior Member Username: Lawrence Post Number: 106 Registered: 4-2002 |
This is just a wild shot but once the cruise control quit working on a German sedan of mine. The problem was the speed sensors in the wheels. The sensor is a magnet. Little teeth zoom by cutting the magnetic flux creating a signal. The metal particles from the brake pads coated the magnet making it look like a chia pet fouling up the signal. Once cleaned, the cruise worked. I wonder if the business end of the sensor is fouled. | ||
| Hans E. Hansen (4re_gt4)
Junior Member Username: 4re_gt4 Post Number: 55 Registered: 4-2002 |
One more observation: I saw an ill behaving tach on a '75 'GT4. (not mine) Since the 'GT4's tach gets its input from the distributor, it's probably not a sensor/input issue. Loose connection, or (more probable) the tach head itself? | ||
| Jerry H (Jerry)
Junior Member Username: Jerry Post Number: 117 Registered: 3-2001 |
Have the same "works doesn't work" situation. I have enquired but have gotten no real results (answers) Mine may be heat related but I am unsure. I agree this is a problem that we should be able to lick. | ||
| Russ Moore (Rem9)
Junior Member Username: Rem9 Post Number: 82 Registered: 6-2001 |
I would think someone has an awareness of what causes this. Hopefully we will find out. | ||
| M Grande (Grande)
New member Username: Grande Post Number: 49 Registered: 12-2001 |
I have the same thing. Everything worked fine. Car sat for 1 month, then tach goes at about 1/2 actual RPMs. Every now and then, it reverts to full scale. Thought it was the sending unit....no go. Seems the tachs just do their own thing ;) Could send off to Palo Alto speedo repair, but decided it wasn't worth it and I just live with it. BTW, asked a well known Ft Lauderdale mechanic about it and he said that if it's working at all, it's better than most  and he see's this fairly often. Sorry I couldn't be more help. Mike | ||
| Russ Moore (Rem9)
Junior Member Username: Rem9 Post Number: 81 Registered: 6-2001 |
I brought an '87 328 out of winter storage recently. When it was put into storage all components worked 100%. Now the tach lazily drifts between 800rpm and a max of 3000rpm even though I am running it at 6K+. I checked the connection and cleaned terminals to the speed sensor on the gearbox cover. No change! Anyone else have this type of problem? Suggestions? I have a hard time believing the tach went bad just sitting through the winter. Russ |