2003 Protege5 running rough

Car has a serious miss. It started the other day so I changed the plugs and it was running fine until earlier. Cleaned MAF, no change. Different coils, no change. Not sure what code it’s throwing but the CEL is on. Any common things to check first?
 
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South Carolina
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12 MZ5 13 CX-5
First thing to check is obviously the CEL. That will tell you exactly where to start the diagnosis.
 
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South Carolina
:
12 MZ5 13 CX-5
If after you run the codes and you have two cylinders missing, and both are served by the same coil pack, that very well may be the issue.
 

pcb

The Diagram Dude
:
2002 MP5
^^^ What he said...

Coils for our car can be a real problem.
They can be bad, brand new, right out of the box.

Hitachi coils are a quality coil and worth the extra money.

I almost always buy the cheapest replacement parts for my car, but not for coils.



Screenshot_20210504-132246_Brave.jpg



Cylinders 1&4 are on one coil and cylinders 2&3 on the other.
 
L
^^^ What he said...

Coils for our car can be a real problem.
They can be bad, brand new, right out of the box.

Hitachi coils are a quality coil and worth the extra money.

I almost always buy the cheapest replacement parts for my car, but not for coils.



View attachment 298165


Cylinders 1&4 are on one coil and cylinders 2&3 on the other.
Last time it was scanned it said cyl2 had a misfire. The plugs fixed it for a little bit but I was thinking coils as well,until I swapped them out with mine and it didn’t fix it(I also have hitachi coils)
I’m about to just start digging into it,I mean the crank sensor looks like trash but wouldn’t that affect all 4 cylinders?
 

pcb

The Diagram Dude
:
2002 MP5
A cylinder specific misfire is a lot better to have than a random or multiple misfire.

There is a lot less possible causes.


Here's what the FSM says...


20210504_144132.jpg




If you've got the same code, I would check the condition of the plug to see if it's fouled or burnt, and check the plugs gap.
(NGK V-Power, regular copper plugs give the strongest spark and they are dirt cheap but they need gapped or replaced more often)

I forgot whether or not it's cylinder 2 or 3 that has the coil, but check the connection between the coil and the sparkplug.

Carefully inspect the electrical connector that plugs into the coil for corrosion or bent terminals and check the wiring harness for any kind of crack or broken/damaged wire.

If it were me, I'd put dielectric grease on all the connections, including the 12V connector on the coils.
It helps prevent corrosion and arching/sparking.

You may have a leaking or fouled injector.
A fuel system cleaner may fix it or a new injector may be needed.
(inspecting the injector is a bit of a chore.)

I can't see a vacuum leak affecting only one cylinder ?


You may have low compression on that cylinder due to age and wear, or high compression due to carbon deposit buildup reducing the volume of the combustion chamber.



The fact that new plugs fixed the problem for a while says to me that you are very close to fixing the problem.
 

pcb

The Diagram Dude
:
2002 MP5
I mean the crank sensor looks like trash but wouldn’t that affect all 4 cylinders?

I would think so, but perhaps if the sensor is missing a single tooth on the toothed ring, at every rotation, it could lead to a cylinder specific misfire.

(That's a complete guess though. The ECU may very well know that something is wrong?)
 
Last edited:
I would think so, but perhaps if the sensor is missing a single tooth on the toothed ring, at every rotation, it could lead to a cylinder specific misfire.

(That's a complete guess though. The ECU may very well know that something is wrong?)
I’m not sure,I’d love to go look but it’s monsoon season in Ohio apparently lol. My buddy forgot his scanner anyway so I guess it’s back to brainstorming
 

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