1999 Mercury Mystique Car jumped off now instrument acting

LSPORTS

MEMBER
1999 MERCURY MYSTIQUE
6 CYL
FWD
AUTOMATIC
131,000 MILES

Today I started smelling a rotten egg smell from car, 2 hours later my daughter comes to my work says car is acting strange. She cut if off and when she tried to crank car it acted like battery was dead it tried to turn over then started that clicking noise.I jumped it off and it cranked right up. Now when you stop at a light the mph gauge goes up to 90 then back down to 40 and up again. Just dial just plays back and forth. When you give it gas and start down the road gauge acts normal but starts acting crazy again when u stop. When I got the car home I cut it off. Waited a minute and tried to crank it again and it start right up. Any suggestion or ideas what I might need to have checked.

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

Hi lsports. Welcome to the forum. Sounds like you have either a defective battery or it is being over-charged. Use a cheap digital voltmeter to measure the voltage between the battery terminals when the engine is not running and again when it is running.

Not running, a fully charged battery will measure near 12.6 volts. If you find around 11 volts, the battery has a shorted cell and must be replaced. When the engine is running, the battery voltage must be between 13.75 and 14.75 volts. If it is too high, the battery will start to smell and produce excessive gas. You might see smoke coming from the vents and the sides of the case might be bulged out. The same thing can happen if the charging voltage is correct but the battery has a shorted cell. That's why it's important to measure the voltage with the engine off first.

Caradiodoc