I started my car this morning (started fine) but the tach was really slow to react. I had my normal startup routine and it seem like the tach was reading about 800rpm less that it should (where the engine is idling at 2000 rpm and the tach barely showed 1200). I revved the engine a bit but the tach hardly responded. Is this a tach coil issue? or a trailing ignition issue?

Thanks,

Alvin

 

did the engine actually sound like it was idling that high? what happened when you drove the car?

i'd just clean the connections to your coils and see if that helps any.

 

It ran just like usual, sounded just fine. I believe it is idling that high (it usually does when i pull out the choke to warm it up).

Alvin

 

How cold was it? I find my '83's tach does exactly the same thing if it's below 50F or so. It's not the input to the tach, I have standalone EFI and have good logs from that side of things, it's definitely the tach's improper response to a proper input.

-Mike

 

Holy crap!!! I thought I was the only person who had this problem. Weird isn't it???? I am running an aftermarket tach on the a-pillar off the trailing coil and it works just fine. I have had so many people say "It's your trailing ignition going out" enough times to make me sick.

 

Yeah, the tach in my '83 does funny things when the temp is below 50F, but once it warms up, it works fine.

 

same with mine too.

 

that's just weird, cauz it definitly wasn't the coldest morning we've had recently, but it's never done this before. Also, based on my shiftlight and my having my car at the dyno, my tach seems to be about 500-1000 rpm off at redline, where it's actually higher than it actually is... I might just go pick up a couple of extra ignitors and throw it in there and see what it does...

Alvin

 

I am thinking it is the tach. The ignitors are simple to swap and worth a try, though. Usually if it is the trailing ignitor, the tach won't read or it will be intermittent (bouncing up and down). Basically the ignitors either work or they don't. They shouldn't produce a signal that is too slow for instance. I think your tach is messed up being slow to respond and reading the incorect value. You can check the trailing signal with an aftermarket tach or an o-scope if you have access to one.

 

o crap **** we must have been drinking from the same cup!! I had the same problem untill I changed my ignitors.