Skip the auto shop - Our mechanics make house calls

Q: Car misfiring on cylinder three

asked by on

My car started missing on cylinder three. I figured it was about to drop a valve seat, so I pulled the head and had valve seats replaced, machined, and new seals -- an overall head job. I put the head back on and started the engine. It started right up but still had a misfire in cylinder #3. I checked the compression on all cylinders 120 PSI +/- a pound. I checked the pulse to injector with tester and could see pulse on tester. Then I swapped injector two and injector three. There was no change in the misfire in three. I got new spark plugs, swapped two and three plug. There was no change in misfire. I checked the rocker arm swing, which seems average to others, and there were no engine codes and no engine light. I checked that the spark was getting to plug, and it had a very strong spark. No CEL or Error Codes.

A: Hello! We will be happy to assist. You have...

Hello! We will be happy to assist. You have definitely been on the right path to finding the root of the misfire. However there are a few things left that I recommend checking. I suggest to check the spark at the spark plugs at each cylinder. There may be an issue with the coil pack causing the misfire. Also check the PCV valve because that is a known cause of a misfires on your particular vehicle. I suspect that the PCV valve and hose may be leaking and causing the misfire.

You may have the engine model which has the PCV valve located above the transmission next to the exhaust header. This engine model’s PCV valve is routinely looked over because most are unaware that there are two PCV valve systems and the first one is easily visible from the top. I also recommend checking the resistance and voltages at the coil packs with a multimeter. I have a friend whom worked as a technician at a Ford dealership once tell me of a problem with your generation of Focus in which the wiring to the coil packs were made too tight and the tension broke the wires overtime.

I would always recommend having a qualified mechanic, such as one from YourMechanic, assist you in diagnosing your engine misfire and assisting you in repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Muffler extremely loud

If your muffler has a hole or crack in it causing a leak, a patch is not a typical repair. If you are certain that the muffler is the cause of the problem, I would recommend having the muffler replaced...

Q: car truns over but wont start getting gas

You need to have the vehicle checked by scanning for codes that may point to the possible cause. It sounds like the crankshaft sensor may have been damaged when the pulley broke. If you need further assistance diagnosing your cars...

Q: I have a 2006 Ford Focus and want to know how do I turn on the auto lock on this model? And the auto unlock as well... thanks

To enable or disable the auto-lock function, do the following: NOTE that you have 30 seconds to complete the procedure or you must start over. Switch the ignition on. Press the power door lock button three times. Switch the...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...