Why does my Mercury Grand Marquis flash the check engine light and lose power?

Short answer: A flashing check engine light on a Grand Marquis means a misfire in progress. Owners saw cylinder codes like P0308 with power loss when warm. Do not keep driving—swap coils to test, check plugs, and fix it before you damage the catalytic converter.

Symptom: CEL flashes when warm, power drops, the car shakes, or it stalls after the misfire episode.

What to check first

1. Read and save the codes.
2. Do not keep driving on a flashing CEL.
3. Swap the coil from the misfiring cylinder with another and see if the code follows.
4. Inspect plugs and plug wells for oil or coolant.

Likely causes

1. Ignition coil or spark plug misfire. A flashing check engine light means an active misfire. Owners saw codes like P0308. Swapping coils between cylinders shows whether the misfire follows the coil.
2. Oil in a spark plug well. One Grand Marquis owner cleared a misfire after finding oil in a coil-on-plug well, cleaning it, and reseating the coil.
3. Internal engine problem (compression). If plugs and coils are good, a compression or leak-down test checks for a weak cylinder.

What it usually costs

Owners in these threads had not finished the repair; coils and plugs are the usual first parts.

Is it safe to keep driving?

No while the light is flashing. A hard misfire can overheat and destroy the catalytic converter and can make the car stall in traffic.

DIY or shop?

Coil and plug swaps are DIY. Internal engine work is a shop job.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists 19 recall(s) for the Mercury Grand Marquis in these years, and none match this problem. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 140 keyword-matched complaints for Mercury Grand Marquis 1998–2011 (of 2472 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-05; keywords: flash, misfire, blink, check engine, p030). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Flashing check engine light Mercury Grand Marquis on Car Talk, a 2000 Grand Marquis flashed the check engine light once warm, lost power, and stored P0308 (cylinder 8 misfire). Replies said a flashing CEL is a serious misfire—stop driving to protect the catalytic converter—and suggested swapping coils and checking plug threads.
• In Blinking check engine light on 2001 Mercury Grand Marquis LS on Car Talk, a 2001 Grand Marquis LS at about 215k miles flashed the CEL around 40 mph after warming up, lost power, shook, and sometimes stalled when stopping. The owner was deciding between O2 sensors and plugs/coils.

Quick tip

Treat a flashing CEL as pull-over-soon, not as a dashboard decoration.

Vehicle focus: Mercury Grand Marquis 1998-2011 with the 4.6L V8.

Safety / mechanic note

A stall in traffic can cause a crash. Verify with a mechanic.