legokcen

iTrader: (8)

A strange phenomenon has started occurring now that morning here are getting pretty cold (well, relatively speaking of course). When the car first starts, for the first 5-10 minutes, I get no tach reading. Then as things warm up, it starts to work again. During the afternoons, when the sun is out, everything is ok when I get in the car after work. I checked my connections at the trailing coil to make sure things were tight. Anything else I should look at?

Thanks in advance.

ckm110789

Hey have the same problem. Once the car gets up to runing temp my tach works. It is wierd but i always tell myself that mazda made it do that so we know when its okay to drive

ray green

iTrader: (14)

It might be the connections to the trailing ignitor, try pulling them off and cleaning them up. When the trailing ignitor goes bad it shuts down the tach.

Ray

sweetege

Yea mine did that all the time, it is normal if you ask me, like he said, usually when it starts working it is ok to drive, I do not ever look at my tach anyway when she is warming up because I am inside warming up

sweetege

Oh yea but when I put my 2nd gen direct fire setup on her it fixed it, cause I had to either take off and clean or replace everything, so if it bothers you that much you could take the connections off and clean them

83rx7boy92

i think its actually the tach it self that is freezing....something about the grese mazda used on the needle will turn to a gel like subatance when its cold and as it warms up it turns back into a liquid making the tach work again

JSmith0101

iTrader: (6)

Define, "cold."

bugman1973

sounds like some one needs to park the rx7 in the garage to save you from doing this. if cold really does mean cold.

85 FB

Ditto on what The Doc said. Get some Electra-Motive spray for the eletrical connections. It comes in a red can with a white label. It's a metal spray can. Can't miss it. Should be by the Starter/Alternator spray. It does great work at cleaning the ends off. Then get some dielectric grease.

Rx-7Doctor

iTrader: (13)

The other thing that I researched that another member had mentioned in an old thread.
Our instrument clusters are basically circuit boards and contain many cold solder joints. It is possible that when the ambient temp drops below a certain temp that the solder joints are separating. Then when the temp rises they rejoin therefore completing the circuit.

This was a common problem on a lot of German cars and their A/C/Heater control boards.

To verify this you would need to pull the cluster and leave in the garage or other cold area. Then examine the solder joints on the back with a magnifying glass.
Any found broken/separated joints could be repaired by resoldering.

perfect_circle

what would explain a tach jumping when i go full throttle in 5th at like 25, or when its cold. i have the tach, but it measures way higher than it should.

trochoid

iTrader: (6)

Tach reading higher rpms than it should in relation to gear and speed often indicates the clutch is slipping. Flooring it at 25 mph in 5th gear is on of the best ways to check for a slipping clutch. If the engine sounds like it's increasing in rpms as indicated by the tach, clutch may be your problem.

glewsRx

iTrader: (1)

I thought this was a common thing. I seem to remember the Haynes manual talking about it and saying that it was just the nature of the beast.

ckm110789

i say we still go with when the tacs working the car is okay to drive : )

perfect_circle

okay well i know its not the clutch slipping for two reasons, one its a brand new xtd 6 puck disc, and two. it also does it in nuetral. i can try and get a video of it.

perfect_circle

http://www.youtube.com/watch?v=GrBQjmfeHcI

here it is, and as you can tell, the actual rpms arnt jumping. at one point you can actually here it stumble.

ray green

iTrader: (14)

That's looking electrical. I'd check those connections to the ignitor if you haven't already. Also check grounds, especially the chassis ground on the driver's side strut tower, I've seen that one affect some of the other gauges. The way the engine cuts out right when the tach jumps is suspicious.

FirebirdSlayer666

iTrader: (3)

This always happened to me when it started getting cold but mine would jump to 2 or 3000 when it first started and just stick there from it being cold but would start working as it warmed up

dantheman

iTrader: (4)

I have this same problem.

Happens what I see is that it deals alot with interior temps for me. The engine can be warm, but if I am driving around with the windows open it will hang for alot longer then if I run the heater.

Also, I find that if I keep the RPMS low, the tach will not jump untill the temps in the cab go up. If I rev the engine a bit, it will go up and then hang at a higher rpm. Like it will stick at 2k, and when it goes down to idle, it will drop down and sit there for a while.

Cab temps for me need to be in the 50s. Usually takes overnight for it to make this happen though. If the interior gets warm on the way to work, when I jump in it at lunch, even if it is cold out, it will work fine.

Just some more info for those who are trying to figure this out. I would love to fix it.

ray green

iTrader: (14)

Cold temps shrink metals and can break electrical contacts. Also lubricants will get more viscous so mechanical parts might start to stick. Likely to be the lube in the tach bushings and/or electrical connections to the tach, including grounds. Sometimes giving the dash a gentle well placed whack will work.

blwfly

iTrader: (4)

im with this guy^^^

Rx-7Doctor

iTrader: (13)

So you think it's jus becoming alittle "Tacky'?

MetaL-

Mine does this as well, and gives me the shift buzzer the whole time it's warming up. The first time it happened I was in a panic, thinking I was out of coolant or something. Once I realized that everything was in order, it stopped doing it. My tach will bounce off of 1500rpm if I rev it like this and the sound is annoying as hell. Only does it in extremely cold conditions though. I usually let the car warm up until it stops as well

j9fd3s

iTrader: (3)

this one is pretty simple, fault can be traced 2 ways.

1. trailing ignitor failure; tach isnt working, because the ignition isnt working, on a car with a fuel pump relay (84-85's), fuel pump will stop too.

2. ive had this on a couple of cars. car runs fine, ergo, it is a failure in the tach/instrument cluster/wire from the ecu. possible the tach is loose/bad connection, but more likely the tach unit itself is just bad. fixing the tach is possible, it would just take some time, and electronics knowledge