I’ve get a 2013 I’m working on for a family member and it keeps having a misfire on cylinder one no matter what gets changed out. I’ve done coil pack, plug, fuel pump, fuel sender, air filter and new battery just to clear the other codes it had as well. Cars got 200k on it. Next step is I’m gonna do a compression test to check the valves are covered in crap. Also I keep getting air at the high pressure fuel rail at the sensor. Any ideas on what it could be?

 

Welcome to the forum

 

Ok so first thing stop changing parts before you have physically verified. The suspected part has failed. Otherwise you may be adding problems to the existing one. You haven’t resolved yet.

next you need to clear the DTC‘s or basically turn off the check engine light. Let the car sit overnight restart the car and drive that will be one complete drive cycle. As soon as the engine check light comes in immediately go to your OBD two diagnostic connector with your scanner and retrieve the most current DTC make a note of them. Then look in the other two files predominantly check your monitors otherwise known as I/M monitors make note of all the ones that are not in green or what is called readiness. This will indicate certain emission controlled systems that are at fault which could add to the information to help resolve your problem.

you could do a compression test of the engine, but at this point, I can’t see any information that would warrant that however if you do a compression test, make sure that each cylinder does not rotate more than five crankshaft rotations. Otherwise, your results for comparison of your highest to lowest compression ratio will not be accurate.
if there isn’t extremely low compression compared to the highest compression, you can redo the test using the wet compression method testing and then re-compare your test results.
the last thing to follow, but not necessarily needed until you’ve done your dry and wet compression test is possibly a cylinder leak down test but I repeat I don’t see any information that you’ve given that warrants even a compression test at this point,.

One last thing I had to edit in, not sure where you get the idea about doing a compression test to indicate carbon unless you actually do a scope of the cylinder to physically see the carbon or if your compression is above the range from lowest to highest, whereas the highest is above even a new engine There may be some carbon on the combustion chamber or on top The piston, but not necessarily an indication of any or the amount of carbon buildup on the back of an intake valve.

 

it has a misfire on cylinder 1
thats the code it throws. It’s the last problem I’ve got out of the four things that were wrong.

its got 180 psi on all four cylinders btw

 

You have a new record …. A 200k mile engine with perfect 180 on all 4 .
This tells me that the tester, the compression gauge is faulty or the test was not done correctly.

So couple things you never posted the DTC? You did not suggest that you look in the ECU permanent DTC area also did not give any indication what your monitors are in state of. All this is important not just simply that you’re having a repeat of one single DTC on one single cylinder.

Just to save the thoughts going through your head right now about me not only in my long-term member, but I’m not a DIY.
Basically, so you can read between the lines if you were to bring your Mazda into my shop for service the info I am asking or would do would be some of the things that I would be looking at or having one of my Tech look at to determine what’s wrong with your car.


If you read your first response you indicated clearing codes as in plural not singular so while I hate to ask what were all the codes that you originally got?

 

it has P0301
the battery was weak and a different shop replaced it.
then they tried to fix the misfire by replacing one plug and one coil. When I got to it there was a low fuel pressure from sender and high fuel rail pressure code. Found air in the high pressure fuel rail and replaced the fuel sending unit cause it was only producing 24 psi to the pump. I’ll send you the report that I was given in a DM.

 

it’s always important before you start any kind of diagnostic on any OBD two or CANbus ECU operation system is to first low test the battery. So it’s a good thing they change the battery and hopefully they gave you one that was good? As for the misfire code, and the service shop replacing a spark plug, which is ridiculous unless it was broken or fouled and or replacing a coil pack based on the DTC tells me that whomever that person was that was working on your Mazda was not an automotive diagnostic technician and more than likely only General mechanic? As I indicated earlier, the worst thing anyone can do working on many cars that are ECU controlled is assuming that the DTC and what that DTC number is always relates to what the part is that may be wrong and then randomly replacing it. that’s not how not really how you properly solve problems relating to DTC‘s anyway I won’t go on that lecture any further. As far as replacing Any part on your fuel injection fuel supply system none of that relates to the DTC that you’re saying is the only DTC you are seeing when the ECU is scanned does not relate to that problem because you would have either the miscellaneous DTC which is a P zero 300 or you would randomly get various misfire codes on the different cylinders which you did not indicate you were getting.

Seeing the report may or may not give me a little information. We’ll have to see if you’d like to post it. But at this moment, it is 7:30 PM and I’m in Ireland 5000 miles away on vacation so I may or may not be able to respond too much more. Lol

 

It's not impossible for the fuel injector to go bad.

 

Thanks, Grim.
I haven't said anything just been reading but that was my first "thought/guess" (been there done that on a Ducati motorcycle) as without fuel it will not fire, and it is one of bunch of items the OP has not checked or replaced.

 

If a single fuel injection (or any number) goes bad or is not performing correctly there are several possible DTCs that will be activated and can easily then be determine using an oscilloscope to confirm a bad fuel injector. Also using a Dianostic scanner you can narrow down the question of a failing or failed F./I looking at the EGT, CAT TMP, I/M monitors just to name a few. It really not difficult nor is it guess work.
The funny thing is most engines that have over 150k miles are running on unbalanced and less efficient fuel injector performance then the owner realizes. Injector full service generally does not correct that but is often sold to customers when a better service would be to either replace them or the best is to have theirs service and balanced and reinstalled.

Motorcycles included...