Tach 0, fuel gauge full w/headlights on

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Tach 0, fuel gauge full w/headlights on

Postby 90Mark7 » Wed Jan 18, 2017 10:31 pm

Hey everyone. Proud owner of "Black Betty", my '90 LSC SE. Everything is stock on the car.

I believe this is a fairly common issue, that I may have asked many times but just want to be completely 100% certain before I shell out some $$$. When my parking/headlights come on, tach drops to 0 RPM and fuel gauge reads full. Adjusting the brightness dimmer switch alleviates, but doesn't solve, the issue. Turning on/off highbeams, or using turn signals, doesn't change issue. I hear a "buzzing" sound when I adjust the brightness. My DTE is also incorrect as well. Even when parking/headlights are off, fuel gauge moves around a bit.

Does this mean I need a new instrument cluster? 120-MPH analog 1990 LSC cluster, I mean. Or could it simply be that behind the instrument cluster and TripMinder just only needs a good cleaning? Or regrounding? Thanks so much.
"Black Betty" 1990 LSC SE all stock, black-on-black. Trac-Lok, JBL audio, power moonroof.
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Re: Tach 0, fuel gauge full w/headlights on

Postby 90Mark7 » Fri Jan 27, 2017 2:52 am

Bump. I know I asked before, but I just need to be absolutely certain.
"Black Betty" 1990 LSC SE all stock, black-on-black. Trac-Lok, JBL audio, power moonroof.
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Re: Tach 0, fuel gauge full w/headlights on

Postby robertbweltzien » Fri Jan 27, 2017 1:03 pm

It is a bad ground for the cluster. Is it the Orange wire? Someone chime in to correct me. I had the same problem when I got my '89 Mark and this solved the problem.

Bob
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Re: Tach 0, fuel gauge full w/headlights on

Postby 90Mark7 » Thu Feb 16, 2017 12:24 am

I'll be taking the instrument cluster out later this week, and checking the grounding. If it needs some cleaning behind it as well. I'm sure it does, being a 27 year old car. Heck, the car is older than me. I was born in October 1992, the car was made April 1990 according to the door sticker. :lol:

Wish me luck. I'll post my findings when I get the chance. The battery is good shape (relatively new), and does have new terminal end cables. I'll also be replacing the voltage regulator, and cleaning the TPS/IAC. Hopefully this all helps my Black Betty get fixed up.
"Black Betty" 1990 LSC SE all stock, black-on-black. Trac-Lok, JBL audio, power moonroof.
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Re: Tach 0, fuel gauge full w/headlights on

Postby 90Mark7 » Fri Mar 03, 2017 7:27 pm

UPDATE:

So after regrounding/cleaning behind the instrument cluster, it FIXED my issue. I can now adjust the dimmer switch w/o the buzzing sound, and have parking/headlights on and the tach/fuel gauge are fine...sort of.

Tach works, but fuel gauge remains incorrect. It "moves" around a bit, even when the car is idling parked, or I'm driving. How can I fix the gas gauge? Thanks.
"Black Betty" 1990 LSC SE all stock, black-on-black. Trac-Lok, JBL audio, power moonroof.
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Re: Tach 0, fuel gauge full w/headlights on

Postby 2manymarks » Sat Mar 04, 2017 8:57 am

90Mark7 wrote:UPDATE:

So after regrounding/cleaning behind the instrument cluster, it FIXED my issue. I can now adjust the dimmer switch w/o the buzzing sound, and have parking/headlights on and the tach/fuel gauge are fine...sort of.

Tach works, but fuel gauge remains incorrect. It "moves" around a bit, even when the car is idling parked, or I'm driving. How can I fix the gas gauge? Thanks.


Perhaps reground the gas tank? 8-)
Last edited by 2manymarks on Sat Mar 04, 2017 3:56 pm, edited 1 time in total.
As of July2017, 11 Mark[*] VII's, 3 licensed for the road:
1989 LSC Midnight/Current Red c/c (9G) mostly stock 99k.
1989 LSC Midnight/Current Red c/c (9G) 124k, stock, needs air suspension & bodywork.
1989 Light Titanium c/c (11) Bill Blass - stock. miles unk
1989 LSC Medium Sandalwood (62) Mass air+ 111k FOR SALE $900.
1986 BB (8T) stock 125k (wife'sDD)
1987 BB (4L) stock (miles unk)
1987 Base Model White (9L) 107k (2.73rear)
1984 Turbo Diesel Base model, Platinum (1Q), 131k+ FOR SALE $1000.
Parts cars: 88 LSC, 89 BB, 90 LSC - TLZ 5spd (complete conversion w/extras 4SALE)
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Re: Tach 0, fuel gauge full w/headlights on

Postby 90Mark7 » Sat Mar 04, 2017 2:23 pm

2manymarks wrote:
90Mark7 wrote:UPDATE:

So after regrounding/cleaning behind the instrument cluster, it FIXED my issue. I can now adjust the dimmer switch w/o the buzzing sound, and have parking/headlights on and the tach/fuel gauge are fine...sort of.

Tach works, but fuel gauge remains incorrect. It "moves" around a bit, even when the car is idling parked, or I'm driving. How can I fix the gas gauge? Thanks.


Perhaps regrouped the gas tank? 8-)


I attempted to, without success. I've followed some forums on here and elsewhere, but did not resolve it. Should the fuel pump be replaced then?
"Black Betty" 1990 LSC SE all stock, black-on-black. Trac-Lok, JBL audio, power moonroof.
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Re: Tach 0, fuel gauge full w/headlights on

Postby robertbweltzien » Sun Mar 05, 2017 4:30 pm

90MarkVII, If you are going to drop the gas tank, I would install a new sender and a new pump. This will also give you the opportunity to check for rust on the top of the tank. If the pump and sender gasket surfaces are very rusty and look iffy, I would also replace the tank. Always use new o-rings and make sure they are made of viton or some other fuel resistant rubber. Same goes for the rubber filler tube collar. I would also only purchase a Bosch pump, since they are OEM. New pumps have improvements in design so they are well worth the cost. Also try not to disturb the vapor return check valve grommet, as the aged rubber has a tendency to leak when reinstalled (it happened to me). If you can find an exact replacement, use it. Lastly, if the tank strap bolts are very rusty and difficult to remove, cut them out. When I removed them on my '89 Mark, it tore out part of the metal boss. Good luck and let us know how you make out.

Bob
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Re: Tach 0, fuel gauge full w/headlights on

Postby oldschool1 » Thu Mar 30, 2017 11:25 pm

90Mark7 wrote:... I attempted to, without success. I've followed some forums on here and elsewhere, but did not resolve it. Should the fuel pump be replaced then?

I so agree with Robert's post.
Cleaning and regrounding the existing strap is pretty easy as it's near the filler tube.
When you say you attempted to, exactly ~what~ did you attempt?
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