Hey all,

New to rotary,

I have a base model '83 RX-7 and have notced that when just starting the engine the Tach does not respond (reads zero rpm). After the car is driven 10 - 15 min. the Tach begins to work..... If you restart, it'll work fine all day. Next morning same thing (nothing for 15 min...then slowly starts to respond)?
Is this normal for an RX-7?

Thanks

P

 

No, it is absolutely not normal...but what is causing it really requires a person to be there to check for obvious stuff. Normally, when the tach starts acting weird and then dies, it never works again until you replace the trailing ignitor on the distributor. That's the ultimate source for the rpm count....the fact that you seem to have no problems with the engine behavior itself makes me think you've got a wire loose or totally oxidized, burned up somewhere in the harness between the tach in the dash and the feed off the ignitor. But where? I gotta be there...

Mario III

 

Thanks Mario,

It's weird because it almost seems like the Tach (or something in-line) has to "warm up" before it will start working. Once warmed up Tach works perfectly (ie. it's not erratic, doesn't cut in and out, and seems to give a pretty accurate reading). I would think if it's a loose wire or something burned up it tend to cut in and out?
Any help ill be appreciated.
Thanks
Pat
'83 base RX-7

 

Nope...I've got my '84 that does the same thing but with the oil pressure and water temperature gauge. I finally found the wire where the two get their "feed", fixed that but now they don't register correctly until they "warm up"...then they show correct pressure and temps that fluctuate and everything. The wire itself was down by the engine and thoroughly "work hardened" and caked with burned on oil and dirt. I cleaned all of it up and saw the connections were bad. Twisting wires together and then shrink wrapping it restored the previously missing water temperature gauge function but then it started the "warm up" nonsense.

OTH, it could very well be, it's the tach itself that is the problem... ....what's curious is that there are several critical electrical systems on an RX-7 that can work only "halfway"...you'd think with an ignitor, it's either working or not but that ain't true. It can be on/off/almost doing the job for a week or more before it dies for real.

 

I appreciate the input, although I don't understand the last comment? Are you suggesting the igniter may be ready to fail? The engine (seems) to run very strong especially for such an elderly car.
I'm new to the rotary thing, but I do understand (at least basics) of how things should work....just never saw anything like this and thought it might be "an RX-7 thing".

Thanks

 

No, it's not an RX-7 thing...my 1983 has all gauges working exactly as they should right from start-up. The '84 used to have all gauges except the water temperature gauge work right from start. Then I let a shop work on it to get it to pass emissions and he said he could fix it. He didn't. He "passed" the car as a "I'm sorry I screwed up your gauges" gesture and then both the oil and the water didn't work. I set about trying to figure out what he did and then did the stuff I described earlier.

Yes, the trailing ignitor can work for a week or more and then finally die for real...you'll just notice a slight loss of power and the tach won't work period once the trailing ignitor finally goes. I just cited it as an example that things on an RX-7 don't always follow the "it's working or it's not" school of thought. There IS gray...