AE86 Jolting, Jerking Issue (Frustrating) PLEASE IF ANYONE CAN HELP?

[Slydwayz86]

PROBLEM


When driving (at any speed) after maybe an hour the rev gauge goes crazy randomly and the car jolts and jerks as the gauge goes up and down then if i try to continue to drive after a minute or so it eventually stalls. I try to start the car and its pretty much impossible unless i wait at least 5 minutes and even then it really struggles to drive and the rev issue continues.


Felt the coil and module to see if they were overheating and they were fine.


Issue started before replacing alternator, coil and module.


Tested Battery at idle and reads normal at 14.6v
Tested Battery with car off reads normal at 12.6v
Tested Alternator to see if it was charging the battery and its charging.




"CHARGE" light on dash stays on with new alternator


Not sure if this would affect the issue but the radiator core is pretty bad and needs replacing


Car Details


AE86


- 16v Smallport 4AGE
- Side Draft Webers
- Facet Electric Fuel (Pump fairly new/filter clean)
- Crane Cams XR3000 ignition (Replaced last week)
- Crane Cams PS50 Coil (Replaced last week with XR3000)


New Rotor Button
New Dizzy Cap
New Spark plugs
New Leads
New Smallport 4AGE Aftermarket Alternator (Replaced 2 days ago)


Cant remember exactly when i replaced the battery but could be approx. 3 years old. It seems to be ok with multi meter but maybe could have some damage from being fully drained then using jumpstarter quite a few times. Will be replacing it this week anyway.


Here is the Youtube video Fqpkt0iooKY

If anyone here could help me out that would be much appreciated!


Cheers,
Logan

[Hen may possibly be a nut]

Firstly, fix the issue that is causing the charge light to stay on with the new alternator. May be unrelated, but definitely worth doing.

Your battery sounds like it could be on its way out (running them flat at all damages their life) but won't be causing the main issues.

The main problem seems like it could be an intermittent short somewhere. I'd be looking somewhere in the igntion system as the tacho dropping to zero, while the dash lights are rock solid suggests a missing signal. Check all the wiring on the ignition side. It could be a loose pin/plug, a wire with worn insulation that rubs shorts out randomly, or a bunch of other things. With the car idling try wiggling all connections and wires to see if you can recreate the problem.

Intermittent issues are a pain to track down, but work through it methodically and you will find it.

[zeus11]

G'day Logan

I had this issue for about 10 months. I found mine to be temperature related (after about 40min to and hours driving). It got to the point where I would only take small drives or drive during the cooler months only. I used those first couple of RPM blips as a signal to get of the road because when it would eventually stall it wouldn't restart until it had cooled down a little sometimes 10 minutes and sometimes 20. Although when I would pop the bonnet I could smell fuel a little.

I did all the simple things like plugs, rotor, rotor cap, leads and battery. None of these appeared to help although it is possible it was a combination of things.

The problem was fixed when I had the alternator rebuilt. I think with my situation the alternator winding's and or regulator would break down when it reached a certain temperature either from engine bay heat soak or bearing failure with in the alternator. Due to the breakdown the alternator was unable to provide enough juice to the dizzy and hence why the over fueling from lack of spark would occur and then eventually cause the car to stall.

My guess would be either a wiring issue with the alternator or the new alternator is unfortunately a dud, the dash charge light would support this. Before replacing my alternator it would check out fine at idle with a multimeter etc and there were not any real signs of voltage laziness.

Intermittent problems are the worst to try and fault find so I feel your pain.

Good luck with it

[Slimer86]

Depending on how ignition is setup using carbs, if using original distributor and electronic pick up it may be incirrectly set or worn out over time and heat cycling.

Sent from my GT-S7275Y using Tapatalk

[Matt]

The alternator is looking likely a cause, as the light should go out when it is charging.

Load it up with a carbon pile, but if u don’t have one you generally can test by having high beam on, heater fans etc in the car, stereo loud and measure voltage again.

Wiring is reasoanably simple, yellow wire to the light, thick and thin white to the battery and the other to ignition power.

If the car is overheating your idle will be hunting , but if the core is questionable replace the rad

[ZEROPILOT]

I agree that the alternator light should not be on. But right away I was thinking "fuel tank vacuum". A bad venting system and a vacuum forming inside the gas tank would cause those same symptoms and your engine would start again in a few minutes....
It would be SUPER easy to check. Make sure that your tank isn't completely full and drive around with the fuel cap on loosely.
Good luck. I'm sure at any rate it will be an easy fix.