Having your car shake or run roughly after replacing the ignition coil can be frustrating and concerning. You replaced that bad part, so why does the engine still feel off?
Not to worry, This problem often stems from a few common causes aside from the coil itself. With some additional diagnostic tests and repairs, you can get your engine running smooth and proper again.
Below we’ll explore the top reasons a vehicle may still shake after an ignition coil replacement, along with tips to resolve the issue for good.
Table of Contents
- Key Reasons the Car Shakes After a New Coil
- Step-by-Step Diagnosis to Find Additional Issues
- Fixing Spark Plug Issues for a Smooth Idle
- Replacing Additional Bad Ignition Coils
- Repairing Vacuum Leaks
- Professional Help with Ongoing Engine Shakes
- Preventing Future Ignition and Misfire Problems
Key Reasons the Car Shakes After a New Coil
There are several possible causes why changing the coil didn’t cure a rough running engine:
1. Remaining Bad Coils
If you have a multi-cylinder engine, chances are that just one bad coil is not the only problem. It’s common for additional coils to fail around the same time. Replacing only one may not smooth things out if other coils are also faulty.
2. Spark Plug Issues
Faulty, worn or improperly gapped spark plugs can prevent proper ignition even with a new coil. Defective plug wires also impact spark delivery.
3. Low Fuel Pressure
Consistent fuel delivery is key for smooth operation. A failing fuel pump or clogged filter can cause low pressure and a misfiring shaking engine.
4. Vacuum Leaks
Any air leaks in the intake or vacuum hoses can allow additional, unmetered air into the cylinders. This leads to a rough run.
So while a bad coil often contributes to a shaky engine, it may not be the only factor. Read on for diagnostic tips and solutions.
Step-by-Step Diagnosis to Find Additional Issues
Methodically testing components and systems can isolate what else may be causing ongoing rough operation after an ignition coil replacement:
1. Check All Ignition Coils
Use a diagnostic scan tool to check for any misfire fault codes pointing to additional bad coils. Visually inspect coils for cracks or carbon tracks indicating a failure. Swap coils between cylinders and retest to pinpoint any faulty ones.
2. Inspect Spark Plugs
Remove each plug and check for worn, fouled, damaged, or improperly gapped electrodes. Replace any defective plugs, gap them to spec, and ensure plug wires are intact.
3. Test Fuel Pressure
Connect a fuel pressure gauge and verify pressure remains within specifications when idling and revved. If low, the fuel pump, filter or injectors may need repair.
4. Perform a Vacuum Test
Use a handheld vacuum pump and gauge to check for any intake or hose leaks. Spray sealant on any cracks and tighten loose clamps. Verify the PCV valve isn’t stuck open.
5. Scan for Engine Codes
Check for any other stored diagnostic trouble codes (DTCs) besides ignition misfires that could point to issues like low fuel pressure, vacuum leaks, or sensor failures.
By testing these other connected systems, you can determine what may be causing an ongoing rough run and shakes after replacing just one ignition coil. Then make further repairs until the engine runs smoothly again.
Fixing Spark Plug Issues for a Smooth Idle
If your spark plugs are found to be degraded, improperly gapped or defective, follow this process to fix them:
- Carefully remove each plug, inspecting for carbon buildup or damage. Look for a worn center electrode.
- Check the spark plug gap against the factory spec – usually around 0.6-1.0 mm. Re-gap any plugs outside that range.
- Replace severely worn or fouled plugs in pairs to prevent performance differences between cylinders.
- Inspect plug wires and boots for cracking or poor connections and replace any that are damaged.
- Reinstall each plug and wire, being careful not to overtighten or cross-thread them into the head.
- Perform a fresh engine scan to see if any ignition-related codes return, indicating further issues.
With good clean sparks, the engine should run smoother after this tune-up service.
Replacing Additional Bad Ignition Coils
If you find more coils are faulty through testing:
- Identify which specific cylinders have misfires and replace those coils first. Clear codes and retest.
- Visually check remaining coils for damage. Ensure coil tower o-rings are sealing properly against leakage.
- Consider replacing the entire set if they are high mileage or have unknown service history. Prevent future issues.
- Disconnect coils one at a time to isolate any additional bad ones signaling a misfire during testing.
By changing out all faulty coils, you restore strong spark to each cylinder for smoother everyday driving.
Repairing Vacuum Leaks
For any vacuum leaks found:
- Inspect intake tubing, hoses and clamps for cracks or detachments that allow unmetered air intake.
- Spray trouble areas with carburetor cleaner – the engine speed will rise if a leak is present.
- Replace degraded vacuum hoses and tighten loose clamps.
- Check for leaks around the intake manifold gasket – retorque bolts or reseal as needed.
- Make sure PCV valve,purge valve and fuel tank vapor vent valves seal and operate properly.
Sealing all vacuum leaks restores proper air-fuel ratios for clean combustion and engine operation.
Professional Help with Ongoing Engine Shakes
If the car still exhibits a rough idle or shaking after replacing the ignition coil and related repairs, have a professional technician conduct a complete diagnostic inspection to isolate the cause. They have advanced tools and expertise to inspect:
- Fuel injectors, pump and filter operation for proper fuel delivery.
- EGR valve and intake sensors function for vacuum/exhaust flow.
- Cylinder compression and valve seal integrity checking for leaks.
- Oxygen sensor readings and efficiency status.
- Early signs of engine mechanical issues causing misfires.
Sometimes the root cause of ongoing rough engine operation and shakes requires specialty tools and skills to uncover. Getting professional help can save time and ensure repairs are done properly when DIY efforts come up short.
Preventing Future Ignition and Misfire Problems
Here are some tips to maintain your ignition components and avoid those shakes coming back later on:
- Use only manufacturer approved replacement coils – cheap aftermarket ones often fail prematurely.
- Replace ignition coils at 60,000-100,000 mile intervals for preventative maintenance.
- Address any misfires codes promptly to avoid stressing the coils and plugs.
- Follow the spark plug replacement intervals – typically around 100,000 miles.
- Use dielectric grease on the plug terminals and boots for a strong connection.
- Check engine grounds are secure to provide a clean path for spark energy.
- Buy gas from busy stations and avoid low-quality fuels to reduce carbon buildup.
Staying vigilant with ignition system upkeep reduces misfire occurrences and the need for future coil replacements down the road.
While a faulty ignition coil is often the cause behind engine shakes, other issues like additional bad coils, spark plug faults, vacuum leaks or fuel system problems may still exist after only replacing one coil. Take time to fully diagnose the root cause, make necessary repairs, and seek professional help if needed to resolve those annoying engine shakes. Maintaining your ignition components will minimize misfires in the long run.