Question about 1994 Mercury Grand Marquis

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1994 Grand marquis dash light 'CO'

Every few minutes the gas gauge lights on the dashboard for the fuel tank change from denoting the amount of fuel to two bars lit at the top and two at the bottom. At the same time, the display on the right, which can be toggled between fuel remaining, miles traveled, air temperature, etc. say 'CO'. Anyone know what the problem is?

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  • ragdollgirl Sep 26, 2008

    My '94 Marquis has done that for years. The problem is the sensor wires in the gas tank that detect the level of fuel. I was told that the top few wires are broken, so when I fill the tank, the broken wires are covered with gas, so the dash gauge shows 2 bars at the top and 2 at the bottom and the display says "CO". The CO stands for "Circuit Open". Once I use up some fuel and the broken wires are exposed down to the level where the wires are good, the gauge and display go back to normal (until the next time I fill the tank). I was also told that eventually more wires would break further down until I would have to have the sensor replaced. But this happened many years ago and it has never gotten worse, so I have not spent the bucks to repair it.



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SOURCE: fuel gauge not working all the time.

This is a normal concern.
The instrument cluster uses 4 different operating modes to calculate the fuel level:
Anti-slosh (default mode)
Key OFF fueling
Key ON fueling
After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.
The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from empty (E) to full (F).
The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The key must be in the OFF position throughout the entire refueling of the vehicle.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms.
If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.
The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The transmission is in PARK (P).
The key is in the RUN position.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
In key ON fueling mode, a 30-second timer activates after the transmission is put into the PARK (P) position (automatic transmissions). When the 30-second time has elapsed and at least 15% of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of PARK (P), the fuel gauge strategy reverts to the anti-slosh mode. The key on refueling mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.
Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level input during a refueling event. Missing fuel level inputs result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:
The instrument cluster is in the anti-slosh (default) mode.
The actual fuel level in the tank is greater than what is being displayed by the fuel gauge

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SOURCE: Odometer stopped working

output shaft speed sensor in the transmission

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SOURCE: 1994 Mercury Grand Marquis Check Engine Light Code 332

its the tube going from the egr valve to your exhaust it have carbon build up and you either have to replace it or get a metal coat hanger and clean it out.

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SOURCE: how can i change fuel filter in my grand marquis

you will need the proper Quick Disconnect tool, Look on the Frame rail for the filter, remove filter from the spring type retainer, remove the safety clips on the lines but not remove them completely, insert the disconnect tool & push into the fitting of the fuel line, push line & tool into eachother then pull filter away from line, if not done properly you will have a big problem putting the line back on

Posted on Oct 28, 2009

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SOURCE: 2003 mercury grand marquis headlights will cut out

My 2003 Mercury Grand Marquis has the same problem. We found out it was the headlight module located under the dash above the gas pedal. The black box has wire connectors coming out of the back. Hitting the box worked for a little while, then I had to reach in the back and wiggle the wire harness. The dealership wants 500.00 to replace the unit. I consider Highway Robbery! They have installed a faulty piece of equipment on my Luxury car that could easily be life threatening but we know it won't be recalled until someone dies because of it. My husband was able to remove the unit and looked it over it had two circuit boards and he was unable to visibly see any problem or loose wire. He cleaned the connectors and used some electrical terminal grease on the wires, this improved it for a short time. The problem still exsists. I have sat for 30 minutes or more waiting for them to go through the On/Off cycle till they stay on for the 45 minute ride home from work. I have beat the box with my flashlight (maglights handle the abuse, my fingers and nails don't) till it came loose from the brackets that hold it. I leave my car running while pumping gas, short shopping trips and start it 20 or 30 minutes early before leaving for work. It is frustrating and dangerous. If this is the kind of quality in our American made cars it's no wonder they needed a BailOut! The only thing we have found to "fix" it is to find a used part that could possibly have the same problem shortly down the road or pay the theives at the dealership to replace it.

Posted on Dec 31, 2009

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