Tach Dies When Headlights Come on

[HRLMVII]

Can anyone help fix this problem, i have heard it may be a bad ground, and ive read in the tech section here about how to fix that. But i was wondering is there any way to do it Without the fuel guage acting funny

this is on a 1990 MARKVII LSC


Im new to the forums here so thanks for any help given

[Drake_tr7]

Whatcha got there sounds like the classic "orange ground wire fix" the fuel gauge will probably change but for the better and it will also make some other "head scratchers" go away as well. Might as well do it, you'll have to anyway in the long run ;)

[HRLMVII]

ok, but if i do the "orange Ground Wire Fix" will the fuel gauge always be screwed up or only when lights are on?

[JSev22]

The orange ground fix corrects the faulty fuel gauge problem, not causes it. Follow the tech article and you will be fine :D

[Drake_tr7]

When I said "change" I meant it "may" (or may not) change the way the fuel gauge maps the tank slightly. The orange gw fix solves a myriad of very wierd problems our cars are prone to develop. That's why I said you'll eventually have to do it anyway;)

[h r lincoln]

I did it recently and it fixed the tach prob and the fuel gage

[HRLMVII]

thanks for all the help guys, but now that i have done this, my fuel gage shows 1/2 tank when its empty, i guess ill just have to live with it eh?

[Drake_tr7]

For that, try putting a ground wire on the fuel tank, they're prone to the tank ground causing that. Use the screw that holds the filler neck brace to the tank and go to the chassis.

[HRLMVII]

do ya think a 8-gauge wire would be enough?

[Drake_tr7]

It should be

[Tony T]

thanks for all the help guys, but now that i have done this, my fuel gage shows 1/2 tank when its empty, i guess ill just have to live with it eh?

Just a reminder, the way the magnetic fuel gauge is wired on your LSC a poor or no ground will make the gauge err to the FULL side and the message center via the interface module on the cluster read on the low side. So maybe when you fixed the orange wire you really do have half a tank, unless there is somthing else going on.

[h r lincoln]

thanks for all the help guys, but now that i have done this, my fuel gage shows 1/2 tank when its empty, i guess ill just have to live with it eh?

that's what mine did before I did the orange ground fix,now it seems to be pretty accurate

[Tony T]

"Stop dave, my mind is going, I can feel it"

What I said above except if you didn't get the ground fixed it will read higher than actual amount of gas

[Hizhonor]

"Stop dave, my mind is going, I can feel it"

What I said above except if you didn't get the ground fixed it will read higher than actual amount of gas

+1 He also MUST disconnect the negative battery cable for a while and let the computer re-learn all the onboard electronics once he re-connects it and drives around for about 10 miles..

[JSev22]

+1 He also MUST disconnect the negative battery cable for a while and let the computer re-learn all the onboard electronics once he re-connects it and drives around for about 10 miles..


I don't think that is necessary, the ground only affects instrumentation as far as I know.....

[HRLMVII]

thanks for all the wonderful help, after un plugging the battery for an hour and then restarting and driving for about 19 minutes, everything is now in as close to perfect as i could want.

again, i cant say it enough, THANK YOU ALL

[Hizhonor]

I don't think that is necessary, the ground only affects instrumentation as far as I know.....

The PCM's in our cars are unique. They grab signals from everything. Whenever you do ANY work concerning gauges/instrumentation/sensors/tune-up (yes there's a new spark pattern with new plugs, wires and rotor-to-cap) the negative terminal on the batter must be disconnected for a while, re-connected and as stated, the PCM needs to re-learn the car's performance.