94rx7tt

iTrader: (1)

Here's the problem:

I take the car out on the highway to put break-in miles on the new motor. I go about 50-60 miles at highway speed (75-80mph) then get off the exit ramp and get back on to head home.
Everytime, without fail, the tach reads fine while on the highway but when I get of whichever ramp I choose that particular drive and turn around to head back home it fails. It will 'bounce' around from 2700 - 3000rpm (in 5th gear doing 80mph) for a mile or so then drop to 1500rmp then 1000rpm. Sometimes it drops to 1500- 1000rpm without bouncing around first. It never returns to reading correctly all the way home.

I put it in the garage until next time I'm going out. The next time I go out in the car, the tach reads fine until I get off the ramp and turn around again.
I have not driven it in the city to see what happens. I use hand controls to drive the car (due to not having use of my legs) and the stops and starts of city driving are a PITA! I try to get on the highway and just go for a cruise to put on the 2000 miles break-in. Then it's time to get it back on the track!

Background:

Instrument cluster was replaced with a used cluster (with 52,204 miles on the OD) out of a 95 to replace my original 94 cluster in which the tach was completely dead (did not move from zero ever) and the odometer did not function (no numbers what so ever. Just some nonsence dashes were numbers used to read).

Question:

What the hell is the problem?




Thanks in advance for any help.

7 POWER

For what is worth...I had a similar problem a long time ago. The dealer was at a loss so they changed the whole cluster. Still did the same thing on the way home. I ended up finding a loose harness socket in the passenger kick panel. Snapped it to lock and problem solved.

Aeka GSR

iTrader: (4)

last time I had a crazy tach was when the crank signals weren't clean.

94rx7tt

iTrader: (1)

Thanks. I'll check that out.

Thanks. I'll look into that as well.

94rx7tt

iTrader: (1)

Does the tach get it's signal from the trailing coil? If so, is it from the spark plug (and plug wire) or another wire that goes somewhere, from the coil itself?

I just put on a complete set of new factory plug wires (11/6-10). Had racing beat on before and the one never seemed very secure on the coil.

Unfortunately, the new wires had no effect on the problem.

blue87

iTrader: (2)

I had a tach that would offset after a few minutes of driving it would jump up and read about a 1000rpm high and eventually drop back down to the correct reading (compared to my pfc). Fixed it with a new cluster... but sounds different than your problem.

alexdimen

iTrader: (13)

Could be bad solder joints or surface mount components going bad on the PCB in the cluster.

I had a similar problem and fixed it for next to nothing while I was linearizing my stock temperature gauge. Haven't had a problem since I followed this write-up.

Here is the repair write up I used: http://www.wrex-racing.com/docs/fd/Tach_Repair.pdf

94rx7tt

iTrader: (1)

Yeah, sounds different than mine. I already replaced my completely dead one with a used one out of a 95.

This one has potential. I took a quick look at the write up and it seems simular to my situation and full of usefull info.
Since I still have my dead cluster, I'm going to practice on it. If I fix my old one, I'll try to fix the 95 one and sell it.
Thanks for the link!

RX7R1FD

Ive had the same issue it was connection at the passenger kick panel.

94rx7tt

iTrader: (1)

Do you mean the ECU or is there another connection at the passenger kick panel?

pyro_racer_0016

i had this problem then a month later tach went out completely i bought a new one then found out there are several shops that will fix them for about 50 to 100 $s one of which is fdnewbie imports i believe.

99spec_fd

iTrader: (4)

mine randomly goes out and none of the gauges work just once in a while , but i noticed my odometer is usualy out most of the time, during the week ive owned the car ive only seen its mileage twice

anotherfire

iTrader: (2)

Does anybody have a picture of the offending harness socket / connection at the passenger kick panel? In a right-hand drive car will this socket be at the cars' right, or left?