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・Save up to 30%

Get a quote

What others are asking

Q: No Crank No Start, dashboard lightup with No Bus warning

Considering the problems at hand it may be best for an in person diagnosis of the situation. The problem could be as simple as a failed sensor or broken wire, or the power-train control module itself going faulty. Considering the...

Q: Error code P0139.

Hello, you are going to have to take your car to the dealer. There is a Technical Service Bulletin (TSB) 18 033 06. This TSB will refer you to having the software updated in the engine PCM and transmission control...

Q: Cruise control not working

Hi. There are quite a few things that could be causing this issue. The control switch position is sent to the steering angle sensor via the clockspring in the steering column. Then the steering angle sensor sends the cruise control...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.