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Tach oscillates when indicator is on by ReptilianRascal
Started on: 10-06-2021 01:07 AM
Replies: 11 (114 views)
Last post by: theogre on 10-10-2021 11:21 AM
ReptilianRascal
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Report this Post10-06-2021 01:07 AM Click Here to See the Profile for ReptilianRascalSend a Private Message to ReptilianRascalEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hi all.

New owner of an 88GT and new member of the forum here (first post).

I'm currently getting it ready for registration and I'm slowly working through all the niggling little problems I've found in the last few months since purchasing.

The main one I'm concerned might be a sign of something worse about to rear its head is the tach needle oscillates while the indicator is on. The volt meter needle does the same.

The battery is new and this happens when both at idle and while reving.

To give it more of a description, the tach and volt meter needles are steady when the indicator is off. When I switch it on (either left or right - happens the same with both sides), the needles start dropping and then coming back up to normal in time with the indicator light turning on and off respectively. The volt meter goes down to maybe 9V from the 13V when the indicator is off and the tach drops by about 600-800rpm when it's flashing on then back to normal when the light if off (I hope that description makes sense).

I'm wondering if this might be the tach filter that needs replacement (on the list of things to do anyway) or if it could be anything else.

Any help or suggestions would be appreciated.

Cheers
RR

Ps. Please let me know if this has been discussed anywhere else. I tried searching the forum for this but nothing I found was exactly the same situation.
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theogre
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Report this Post10-06-2021 01:54 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
volt meter etc bumps w/ turn lights On is covered here many times...

In short...
Have iffy grounds anywhere in the car.
Have iffy connectors etc for 12v side.
Have weak alt and/or "power pulley" crap causing weak alt output.

See my Cave, Wire Service and other cave pages.

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ReptilianRascal
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Report this Post10-06-2021 04:16 AM Click Here to See the Profile for ReptilianRascalSend a Private Message to ReptilianRascalEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for that. That's really helpful.

I think it might be the ground behind the radio as there has definitely been some work done there by previous owners and there were some other loose fittings in that area.

Really appreciate the help
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olejoedad
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Report this Post10-06-2021 07:34 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
Many Fiero owners have been known to run an extra ground strap from the engine block to the space frame to ensure good grounding.
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buddycraigg
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Report this Post10-08-2021 08:41 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
Every fiero I have ever owned has done that. Don't worry about it.
My 87 S-10 pickup does it too.
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ReptilianRascal
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Report this Post10-09-2021 01:46 AM Click Here to See the Profile for ReptilianRascalSend a Private Message to ReptilianRascalEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:

Every fiero I have ever owned has done that. Don't worry about it.
My 87 S-10 pickup does it too.


Thanks but unfortunately we've got pretty strict registration rules here (NSW, Australia) and sometimes, with the people who decide if a car can be registered or not, you'll get one who says "yeah, sure, no problem" and you'll get another who says "no, even if you get this fixed" and then there's a bunch of responses in between those 2 extremes.

I'd rather try to present it in as good a condition as I can to smooth out the red tape as it's already a little rough around the edges with the paint
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Mike in Sydney
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Report this Post10-09-2021 06:21 AM Click Here to See the Profile for Mike in SydneySend a Private Message to Mike in SydneyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hey, Rascal. Check your PMs. I'm in Meadow Flat near Tarana. Got two '86 GT's. Have owned Fieros since '91.

Mike
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theogre
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Report this Post10-09-2021 09:52 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by ReptilianRascal:
Thanks but unfortunately we've got pretty strict registration rules here (NSW, Australia) and sometimes, with the people who decide if a car can be registered or not, you'll get one who says "yeah, sure, no problem" and you'll get another who says "no, even if you get this fixed" and then there's a bunch of responses in between those 2 extremes.

I'd rather try to present it in as good a condition as I can to smooth out the red tape as it's already a little rough around the edges with the paint
I'm guessing your inspection is similar to MOT in UK that covers many things beyond most inspections in US including NY and maybe others that puts cars on a lift to look at bottom. MOT recent changes can fail you for having "Light Upgrades" for Headlights etc too because most "upgrades" are crap and illegal.

Ground behind radio and many more need to be looked at including everything bolted/screwed to frame or engine in back.
check 12v to + "box" under C500, battery and alt cables.
Clean/fix and coat w/ silicone or brake grease to keep out "water."
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buddycraigg
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Report this Post10-09-2021 01:04 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
Ah. I didn't realize that you were going to have an inspector getting all up in your business.
If you really HAVE to fix it, I would say checking the grounds sound like a good place to start.
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theogre
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Report this Post10-09-2021 03:10 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:
Ah. I didn't realize that you were going to have an inspector getting all up in your business.
If you really HAVE to fix it, I would say checking the grounds sound like a good place to start.
UK MOT and countries are way more strict... Far worse then most or all US states that have inspections.
Very old video aim at inspectors and shops... ~ 30 minutes https://www.youtube.com/watch?v=QcG-_w-he2Q
More recent to show the public a complete and passing MOT for a car. ~ 52 minutes https://www.youtube.com/watch?v=tBORGEXmlYU
More of same but shorter... ~ 18 min https://www.youtube.com/watch?v=YWNshqPS9Ys

If they see HID or LED "upgrades" in car came w/ Halogen HL recent changes can Fail you even if output pattern looks ok to you.
Even w/ Legal HL you can Fail just for bad alignment, dim bulbs, etc. because of the HL "machine" briefly shown in all above.
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ReptilianRascal
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Report this Post10-09-2021 05:30 PM Click Here to See the Profile for ReptilianRascalSend a Private Message to ReptilianRascalEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for all the replies everyone.

I'll get started checking all the ground cables.

From the look of it, a previous owner has already attracted an extra ground wire from the engine to the frame but it is a pretty poor job (wrong type of wire that's oxidised pretty badly), so I'll replace that and the factory ground to begin with.

I pulled out the centre console skeleton (need to replace it anyway as it's falling apart) and checked the ground wire back there. It's solid and in really good condition (looks almost new) but I think I'll clean it up anyway just to be sure.

Thanks again everyone. You've been a big help
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Report this Post10-10-2021 11:21 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Remove DIY grounds. Then clean/fix OE grounds.

Some OE grounds could be replace w/ heavier grounds when have a lot of stuff eating power like big sound systems.
Replace Braided ground(s) w/ same. This behave different and handle more power too. Braided ground(s) are Main Ground Path from Frame to Block and Alt Case.
If have crappy alt mounting hardware, clean that but do not lube most bolts. Only a bit of lube on the big bolt in the alt to stop "rusting" so can't replace a belt. Don't lube places where alt gets clamped by or hits brackets or will have belt problems.

Why Remove?
DIY Grounds themselves are often poorly done.
Even if best parts are used, often leave OE grounds there and they maybe iffy to bad.

Results?
In most cases, will have Too many grounds that can have Ground Loops causing problems.
Ground loops create they own circuits causing very high noise and other issues.
Or 1 bad ground wire act as antenna and noise out the system.
In Audio systems often hear this as a type of "Feedback" or Hum or 50 or 60Hz mains power buzzing that can be Very Hard to track down. In some cases can even hear AM radio from a station nearby. Can pick up FM etc too but sound like noise.
In "TV" cable and other systems w/ Coax Cable... Just one loose connection is enough to cause iffy ground even if the center wire make good connection. That iffy ground can slow down I-net to you to having problems for a whole neighborhood. (Many may see Cable Tech using an odd "wrench" to tighten cable ends. That is a Torque Wrench. Example: https://www.techtoolsupply....0lb-p/twaf-71620.htm )
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