Why am I losing compression on cylinder #4 on my 2006 Mazda 6

ANSWER : Hi there. If you are feeling air pressure coming out of the engine in this area then you have a problem with warpage or a crack that is not seen. Once everything is put together and torqued then you should not get any air. It is possible that you got a bad head or you may have a valve issue if the pressure is coming from the intake. You need to get some assistance from a certified mechanic, like one from YourMechanic, that can come to you to [diagnose why there is a loss of compression] https://www.yourmechanic.com/services/noise-from-engine-or-exhaust-inspection

ANSWER : Hello – unfortunately, this is not a service YourMechanic offers at this time. This task is best handled by a collision repair estimator at a reputable paint and body shop. S/he is trained to evaluate visible and not-so-visible damage, and the costs to repair. Contact a reputable paint and body shop in your area for an estimate and repair.

ANSWER : You need to check the PCV tube that goes behind the intake and connects into the back side. The hose can get a leak in it, causing a vacuum leak on the back side. This will create lean conditions that may be worse for cylinders 4 and 7 specifically on this engine.

If the hose is good then try and have the injectors replaced or cleaned for these two cylinders. You could swap them with different cylinders to see if the problem moves along to the other cylinder, doing so will help pinpoint the issue.

If you decide to get the car looked at, consider YourMechanic, as a certified technician can come to your location and diagnose your car’s misfire. An accurate repair can then be made once the problem has been pinpointed.

ANSWER : Hi there. What led you to the need to replace those mentioned parts? What were the diagnostic steps to determine the fault or faults? When a misfire code is stored, that means that the ECM detected a slow down on the combustion stroke of those cylinders specific to the codes stored. What caused the misfire? The ECM does not know why this occurred, only that it has detected the occurrence. There could be a whole host of causes from electrical to fuel to spark to a sensor to the ECM to an internal mechanical fault. The simple fact is that without a proper inspection using proper diagnostic tools and processes, the attempted repairs can become very expensive. I strongly suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a check engine light inspection.

ANSWER : The flexible hoses that go from the body to the calipers are frequently the cause of this problem. And your mileage is just about right. They have several layers and the layers separate internally leaving no apparent exterior damage. The broken lining acts as a one-way valve, allowing the brake pressure through, but not permitting it to bleed back when the brakes are released. The good news is that they are relatively inexpensive and not very hard to change. Proper bleeding procedure is important though. If you would like to have this or other jobs done for you, Contact Your Mechanic. They will send a technician to your home or office to check out your dragging brakes and replace the hydraulic hoses if necessary.

ANSWER : Hello – I would first ask for the basis of that diagnosis, including the problem codes which would confirm the sellers statement. Buying a vehicle under these circumstances is a very risky transaction in my experience. While everything represented to you may be accurate and legitimate, it suggests detailed technical knowledge on the part of the seller, but without making the repair. It may also not be a complete assessment of issues with the vehicle. I recommend a pre-purchase inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to vehicles location, diagnose any and all problems, and give you an accurate assessment of damage and cost estimate for repairs.

ANSWER : As you may know a knock sensor may fail for any of the following reasons:

The knock sensor is faulty and needs to be replaced
There is a wiring open/short/fault in the knock sensor circuit
The PCM/ECM has failed

Any of the above could potentially cause a misfire. The knock sensor should be located under the intake manifold between cylinders #1 and 2.

If you need assistance with this, consider YourMechanic, as one of our mobile technicians can come to your home to diagnose the misfire firsthand and help you fix it accordingly.

ANSWER : Hi there – unfortunately, pulling the plug on cylinder 6 is necessary for the next level of misfire diagnosis: is there actually spark at the plug while running? What is the compression on that cylinder (and any other – are they within 10% of each other)? Is that plug brown or black, or wet with fuel – signifying a leaking injector? You can get to a precise answer, but it will require a bit more effort. I would recommend an engine misfire inspection](https://www.yourmechanic.com/services/engine-is-misfiring-inspection) by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.