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Spark plugs light the fuel in each cylinder thousands of times a minute, and worn ones cause rough idle, hesitation and misfire codes. Route 66 Auto Repair in Upland replaces spark plugs with the type and gap your engine calls for, torques them to spec, and lays the old plugs out in cylinder order so you can see what each one says about the engine. ASE-certified technicians handle coil-on-plug engines, V6s with a hidden rear bank and older engines that still use plug wires.
When is it time for new spark plugs?
- Your owner's manual interval has arrived, by miles or years
- Rough idle at a light on Foothill Blvd that smooths out once moving
- Hesitation when you press the throttle to merge onto the I-10
- A flashing or steady check engine light with a misfire code
- Harder starts on cold mornings
What can old spark plugs tell us?
A plug is a small record of what happens in its cylinder. Wet black deposits point to rich running or a weak spark. Oily fouling on one plug can mean worn rings or valve seals on that cylinder. We lay the plugs out in order and photograph anything unusual.
If one plug looks very different from the rest, the plug is a symptom. We note it and suggest check engine light diagnostics or a compression test before you spend more.
Our spark plug replacement process
Step 1: Confirm the parts
We match plug type, heat range and gap to your engine.
Step 2: Clean before removal
Compressed air clears the plug wells so grit does not fall into the cylinder.
Step 3: Remove and inspect
Old plugs come out in order and get checked for fouling, wear and damage.
Step 4: Install to spec
New plugs are threaded by hand first, then torqued to the listed value.
Step 5: Verify
Coils and boots are reseated, codes are checked, and the car is road-tested.
What's included in a spark plug replacement
Included on the work order
- 01Plugs of the type and gap your engine specifies
- 02Plug well cleaning before removal
- 03Old plugs laid out in cylinder order for review
- 04Ignition coil boot inspection for cracks or carbon tracking
- 05Torque to the listed value
- 06Code scan and road test after the work
Need-now or need-later?
Need now: call
- A flashing check engine light, which can overheat the catalytic converter
- A misfire you can feel under load on the freeway
Need later: book
- Plugs at their interval with the engine still running smoothly
- Plug replacement bundled with other planned front-of-engine work
How pricing and timing work
Four-cylinder engines with plugs on top are the quickest. Many V6 engines hide three plugs under the intake plenum, which adds labor, and that shows as its own line on the written estimate. AAA members get 10% off parts and labor, up to $75, with the card at time of service. Most plug jobs are same-day when the board allows; call before you drive over.
Aftercare
The engine should idle smoother right away. If a misfire returns within a few days, the cause is usually a coil, injector or mechanical issue we flagged, and you should come back so it can be tested. See ignition coil replacement for that next step.
Frequently asked questions
How often should spark plugs be changed?
Follow the interval in your owner's manual. Many modern iridium and platinum plugs last a long time, while older copper plugs need changing sooner. Short trips, heavy idling and towing can wear them faster, so we also look at condition, not only mileage.
Can a bad spark plug damage anything else?
Yes. A misfiring cylinder sends unburned fuel into the exhaust, which can overheat and damage the catalytic converter. A weak spark also makes the ignition coil work harder. That is why a flashing light should not wait.
Do you use the plug brand my car came with?
We use the plug type, heat range and gap the manufacturer lists. Some engines are sensitive to brand, and when that is the case we match the original equipment plug. The estimate names what we will install.