Help! Lost tachometer, water t. gauge, alternator wont charg

[Saber]

I've got an AE86 with a AE101 4AGZE with removed a/c and power steering. It ran fine last summer, I drove it 2000+ kms (1240+ miles) and was stored in a garage through winter.

Now roughly two months ago I was going to put it back on plates and start driving it. In the first test drive, when I first floored the throttle, in the same instance, the tacho and water temp gauge died and the alternator charge light came on. A few kms/miles later it died because of no electric charge.

At first I just thought the alternator was dead (and thought that somehow affected the tacho and water temp gauge). But when I changed the alternator, the problem still persisted.

Then I thought it was bad grounding and checked that pretty much everywhere and the only place that didn't have proper grounding was the alternator body. Temporarily fixed that with some start cables, but the problem still persisted. (Is the alternator body/housing supposed to be grounded?)

(Yes the igniter has good grounding plus the head, block and transmission are grounded)

I tried finding a loose plug or burnt wiring, but since I did the wiring myself 2 years ago, I knew it should be solid and found nothing wrong with it.

What can possibly affect the tacho, water temp gauge and alternator charge at the same time? Anyone got any ideas? =(

[Ivan141]

Look at the common factor for the dash components: the main thing they share is the 12v feed coming from the gauge fuse. Have you checked that fuse already?
If other parts of the dash are still working (excluding the mechanical speedo) then take out the dash and inspect the flexible pcb on the back of the gauge cluster. Often, when something shorts out, the traces on this PCB will burn through, which is easy to spot (and fix).

The alternator is more or less unrelated, except for the fact that it supplies the voltage coming through the gauge fuse. The charge light is wired between the battery and the alternator, and will light up if there is enough of a difference between the 2 voltages.

Might be the alternator went bad, causing some sort of spike on the gauge cluster and blowing things up, but then again it could be anything.

[Saber]

Thanks Ivan. I haven't checked the back of the gauge cluster. Will do the next time I'm in the garage.

Let's say I wanted to check if the alternator is giving an electric charge, would you measure it with a volt meter and which terminals would you measure? (I have an idea, but I just want to be absolutely sure.)

EDIT: Of course I know that I can measure the battery while the car is running and should get around 14 volts if the alternator is working (which I don't). What I mean is, can I unplug the alternator from the wiring loom and simply measure the terminals on the alternator, to be able to rule everything else out?

[Ivan141]

Do not run the alternator disconnected from the battery, it needs some place to get rid of it's charge.

Start by checking your fuses before pulling the gauge cluster out..

[Saber]

Ivan141 Wrote:Do not run the alternator disconnected from the battery, it needs some place to get rid of it's charge.

Of course, that makes sense. Stupid me.

Ivan141 Wrote:Start by checking your fuses before pulling the gauge cluster out..

Checked the fuses already. All fine.

[Arima-kun]

Haven't you solved that problem?

[Saber]

Nope. Sort of gave up for a few months. Plan on taking a look at it again this weekend. Any thoughts?

[smackdownz]

just had this same problem, i also have 4agze in my 86 and alternator wasnt charging.....

rhs plug on the dash cluster was loose (i have a rhd car if that means anything)

pull dash out and wiggle plug around untill you get a good connection... once it gets a good connection alternator charges and gauges work.. as soon as its bad boom alternator stops charging and gauges die...

worst comes to work try a new dash... (mine old one worked)

cheers.

[Saber]

Thanks. After alot of measuring, thinking, looking at schematics and remeasuring, I finally found the culprit. It was just a fuse, ONE F*$KING FUSE! It looked fine, but when I measured it, it was open (burnt). I think it was the combination meter fuse. For some reason the car wouldn't charge without it.

Fixed it. Been driving the car since then. All was fine until last weekend, the battery came loose, fell infront of the engine, shorted to ground and literally cooked itself. Car died obviously and 1/4 of my engine bay was covered in battery acid. FUN FUN FUN!

Cleaned it up the best I could, swapped the battery and the car fired up like nothing ever happened. But now when I fire it up and the engine is cold, the car just stutters and chokes when under part throttle. Runs jittery when idle, bogges down/chokes under part throttle, but flys under full throttle. It's like the throttle position sensor only works under full throttle when the engine is cold.
But when the engine warms up, it gets better and better. When fully warmed, I hardly notice any bogging/choking/stuttering.

Weird...