Possessed Tachometer

[ahines]

If I crank my '84 and it doesn't start, the tach goes postal - maybe pegs, maybe flops, maybe just runs up to 6000 and sits. But as long as the motor is turning, it's right. What's my deal??? Hoping,

Albert

[biggo]

Do you wear glasses?

[Hen may possibly be a nut]

Hi, and welcome to AE86dc.

If you want to get a useful answer it might help to add a bit more information to your question, such as what car, what engine, what you've done to it, when it started happening, etc... (or even use the template provided for your convenience).

[--Redwork--]

The tacho in my 86 used to jump around like a retard all the time.. any eventually my car started to run real bad, miss and shit, and then wouldn't run at all... Was rooted contact points in the dissy..

[ahines]

Wow, let's see. Glasses? only during the day.
Type of car, that would be a Toyota Corolla, 1984 SR5 (4A engine), only mod is a newer stereo. I just bought it. And it does idle very rough when cold. But I figured such weird tach behavior would be a simple line answer.
The guy that sold it said it was a carb issue (hence a previous post), but the maintenance record shows a recent rebuild and I'm wondering if there might be a control problem that the wrong engine speed is getting fed back to the ECU or fuel controls.

[biggo]

by SR5 spec you mean 4AC motor?

If its just had a reco'd motor it could have been done by a bottom rung on the ladder trades man. And being carbed they probably have no idea. Get the service specs of the dizzy/points system and start their.

[Hen may possibly be a nut]

Bear in mind that the majority of this forum is Australian and so has little idea what an SR5 is.

But if you have an AE86 with a 4AC motor then there is no ECU or anything electronic about the whole engine. The tach works off a single wire from the negative side of the coil. Check your wiring is about all I could say, but Redwork sounds like he knows more.

And in general if you're new to AE86s, a repair manual, a good look under your car and a good read around the net does wonders for your understanding of them and troubleshooting skills.

[ahines]

Motor: The valve cover says 4A, but yeah the air filter cover says 4AC. It has the SOHC 1.59 liter engine.
Reco'd engine? No. It's never been opened or replaced. That's why I assumed this would not need a detailed description - it's exactly like it rolled out of the factory.
There are definiitely a number of ECU components feeding into the carb, all exactly as shown in the factory manual (that's the '84 Corolla FR manual showing the (correct) liftback on the cover (also see avatar)).
So, SR5 is what the logo on the liftgate says, Corolla is what the user manual and repair guide say. The VIN is JT2AE86C4E... whatever they call that down under.
SO, I am correct in gathering the Tach is electric? Is there a diagram in the OEM repair manual showing where that IIA wire routes?