2000 Ford Taurus P0303 Cylinder 3 Misfire: Diagnosis and Fixes After Spark Plug and Coil Replacement

Since the P0303 fault code indicates a misfire in cylinder 3, it's important to perform a fuel leakdown test to check for a clogged fuel injector and a compression test to verify engine integrity. If both tests show normal results, please post back with your findings so we can continue troubleshooting.

Check the electronic ignition module—though it's less common in older models, a faulty one could cause weak or inconsistent spark in that cylinder.

Does the vehicle actually have spark in cylinder 3? If not, that would point to an issue with the ignition system rather than fuel delivery.

Yes, spark is confirmed in cylinder 3.

Given that spark is present, what are the odds that a faulty ignition module is the root cause?

For a 2000 Ford Taurus, the ignition module is likely integrated into the ECM. I'm 75% confident it's not mounted under the hood like in some GM vehicles.

I’m not deeply familiar with Ford systems, but I don’t recall seeing an external ignition module on this model. It might be a confusion with GM-style coil packs—perhaps someone is assuming that setup applies here. Still, it's worth noting.

Most, if not all, 2000 Ford Taurus models use an integrated ignition module within the ECM. The ECM receives signals from the cam and crank sensors and uses them to control spark timing, fuel injection pulses, and other functions based on load, throttle position, temperature, etc. There’s no standalone ignition module in this model. However, older vehicles sometimes used a distributor-based hall effect sensor system with an external ignitor. Given that this is a 2000 model, it's highly unlikely to have a separate ignition module. Still, if the vehicle is very old or modified, there may be exceptions. The user hasn’t responded yet—so we can only speculate.

Hi—while the ECM likely contains an integrated ignition module, it's worth checking the ground wire for cylinder 3’s ignition coil. A broken or corroded ground connection could prevent proper spark. The wiring harness may have a middle connector that serves as a ground path—this could be faulty. Also, is there any chance the internal ignition module in the ECM is failing? Could this be the issue?

Ignition modules rarely fail, but if you're unsure, use an oscilloscope to test the injector driver circuit. If the signal shows proper peak voltage and pulse width, then the issue isn’t with the ECM or ignition driver.

A lot of discussion for a user who hasn't responded—maybe they're still working through it.

Well, it's satisfying to see such detailed technical discussions come together—even if the original poster doesn’t reply.

I own a 1998 Ford Taurus 12V 3.0L with P0303 and over 117,000 miles—expected fouled plugs, but found them clean and similar to other cylinders. The engine history suggests overheating prior to purchase. Cylinder 3 is furthest from the coolant pump and not exposed to airflow like cylinders 4–6. Additionally, there’s a lot of stop-leak in the system (likely due to a leaking freeze plug), which may reduce coolant flow around that area. I recently purchased this vehicle—engine light came on during test drive—and I’ve taken the risk. Has anyone else experienced burned exhaust valves or cracked cylinders in this engine? I don’t want to have bought a 'cash sink'.

A compression test is essential—this can reveal mechanical issues like valve damage or cylinder leaks.

The compression in cylinder 3 was about 35 psi lower than the others. During pressurization, a hissing sound indicated a leak into the intake manifold. Upon teardown, a burned intake valve was found—intake? Who would have thought.

Who would have thought? We did! This is a classic case of an intake valve failure causing misfire and P0303 in a 2000 Ford Taurus.