Tachometer lagging/hanging/jumping?

Sub Zero

Junior Member

Posts: 17
#1

Tachometer lagging/hanging/jumping?

12-01-2015, 05:10 PM

I've got an 86 n/a with the analog gauges and am having a strange issue with the tach. The tach is working but seems to be "hanging" once I hit around 3k rpm while accelerating and will eventually jump up to around 5k rpm or so. It seems to do this at a few spots in the rpm band so I don't rev the car too hard since I'm not confident in the tach reading properly, don't want to damage the engine. I did a search and there doesn't seem to be anyone who has had this exact issue, usually it's the tach not working at all. I read about the resistor under the foot rest, I would think the tach would not be working at all if the resistor was bad. Any help would be greatly appreciated.
amreboot

Banned

Posts: 9875
#2

12-01-2015, 05:49 PM

Check the grounds near your coil. There should be 1-2 of them.
Also, check the grounds on the plenum, there should be 2 as well.

Lastly, make sure the CAS connector is good.
Sub Zero

Junior Member

Posts: 17
#3

12-01-2015, 06:47 PM

Thanks for the pointers. I'll give it a shot and see where I'm at.
Sub Zero

Junior Member

Posts: 17
#4

12-01-2015, 10:32 PM

Well, I couldn't see shit for ground wires around the coil. Not sure if I was looking low enough, but I possibly found the issue. I found the ground wire that attaches to the metal bracket on the right side of the plenum, the bracket is no longer attached to the plenum. The bolts for the bracket are broken off in the plenum, I guess I'll have to drill them out and see if I can use an easy-out.
amreboot

Banned

Posts: 9875
#5

12-02-2015, 12:38 AM

Originally posted by Sub Zero

Well, I couldn't see shit for ground wires around the coil. Not sure if I was looking low enough, but I possibly found the issue. I found the ground wire that attaches to the metal bracket on the right side of the plenum, the bracket is no longer attached to the plenum. The bolts for the bracket are broken off in the plenum, I guess I'll have to drill them out and see if I can use an easy-out.

Okay! Well, there are other areas to bolt the ground to on the plenum. Not a big deal to use another area.

The ground wire next to the coil runs along the fender well.
Sub Zero

Junior Member

Posts: 17
#6

12-02-2015, 12:42 AM

Alright, I'll look around tomorrow and hopefully I'll see the ground wires by the coil. I know I could ground in another location, I just like to try to fix it right the first time around. Thanks for the help
Z_Karma

Administrator

Posts: 3318
#7

12-02-2015, 02:23 PM

There is a ground wire that attaches from the engine harness to the drivers side strut tower, about midway down.

84 AE/Shiro #683/Shiro #820/84 Turbo
Sub Zero

Junior Member

Posts: 17
#8

12-02-2015, 08:57 PM

Originally posted by Z_Karma

There is a ground wire that attaches from the engine harness to the drivers side strut tower, about midway down.

Possibly why I missed it, I pretty much just looked around the coil itself. Haven't had very much time to give it a good look, currently working 12hr nightshifts.
Sub Zero

Junior Member

Posts: 17
#9

02-03-2016, 05:09 PM

Originally posted by amreboot

Check the grounds near your coil. There should be 1-2 of them.
Also, check the grounds on the plenum, there should be 2 as well.

Lastly, make sure the CAS connector is good.

Sorry to drag this thread back up. When you said the cas did you mean the cam angle sensor or the crank angle sensor?