Misfiring after plugs and coils

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MeAndMyPenguin

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2002.5 Mazdaspeed Protege5
Okay, I have 2002 Protege5 with around 130,7XX miles. Its been running fine since around 120K miles and recently it started to misfire. The CEL came on and cylinder 4 was misfiring. After installing new spark plugs, the car still misfired, changed the PCV valve as well. Next was the coils. I just changed the coil for cylinder 3 and 4. Kept on misfiring and CEL came on again. Had it checked and got P0300 (random cylinder misfire). Ended up replacing the other coil as well and still misfires. Cleaned out the EGR valve and the MAF sensor and still misfires even after new plugs and coils. No CEL is coming up as of now. Also, I have a SRI and there are no cracks on the piping so air is not leaking out. I also put seafoam in the gas tank and oil hoping that something was clogged but that didn't work. Anything other suggestions on what to do next? This problem is very annoying.
 
Well mine had that problem as well but on cylinder number one. See the post that I just started I ended up having a burnt valve and exhaust port. Do a compression test and you will clearly see if something internal is wrong. Then put a tablespoon of oil in the cylinder and run a compression test again. If the number increases then your rings are likely bad if the number does not increase when you likely have a valve issue
 
Cleaning the EGR doesn't guarantee that its good.

Try to move the shaft inside the EGR, if it sticks or is hard to move, then its garbage. It is under pressure from a spring, it should close by the force of the spring every time you try to open it.
 
The_big_dill said:
Cleaning the EGR doesn't guarantee that its good.

Try to move the shaft inside the EGR, if it sticks or is hard to move, then its garbage. It is under pressure from a spring, it should close by the force of the spring every time you try to open it.
Click to expand...

this, plus where did you buy your coils? And what did you clean your MAF sensor with? What did you gap your plugs too?
 
The_big_dill said:
Cleaning the EGR doesn't guarantee that its good.

Try to move the shaft inside the EGR, if it sticks or is hard to move, then its garbage. It is under pressure from a spring, it should close by the force of the spring every time you try to open it.
Click to expand...

sorry for the extremely late reply, i can move the shaft inside the egr and the force from the spring closes it.

iracemine said:
this, plus where did you buy your coils? And what did you clean your MAF sensor with? What did you gap your plugs too?
Click to expand...

I bought my coils from autozone. I used MAF sensor cleaner. I have not touched or even looked at the gap of the plugs as I thought they were pre-gapped. I went and bought new plugs recently as one of the old plug threads broke off and was stuck in the motor. I bought Bosch plugs as that is all that they had in stock. Ill check the gap on them now.
 
If you search on this sit you will see that a lot of people have had bad experiences with the auto zone coils. It was worth it ti get the nicer coil packs form rock-auto.com, or in my case from mazda after I bought a pair from autozone that made my car miss much worse than the rusted out coils that were atop my motor.
 
Coils can be a Very Big PITA for our car,.. you would think "brand new" means they work but not always. They can even bench test as working and then start "misbehaving" once they're back on your car.

Sometimes they need to be hot to act up,.. sometimes they need to vibrate,... sometimes they arc (short out) to the valve cover,.. sometimes they need to provide a stronger spark but can't deliver,... and sometimes they are haunted (Gremlins)

I had no problems with my coils but replaced them before they started to fail and wreck my pre-cat. I got the BECK/ARNLEY from Rock Auto and they have been working fine,..

In fact,.. this might be the only part that I would recommend spending the big bucks for original Mazda OEM parts.
 
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Might wanna also change the 2 plug wires. Didn't see any mention of wires being replaced, just coils and plugs. If a wire is bad the coils and plugs will not make the code stay away.
 
Is it missing at idle or under load? Intermittent or regularly? Remember, three things needed for fire: fuel, oxygen, and ignition source. If it were the coil, both cylinders with the associated coil would have been missing. If it's just #4 cylinder, then it could be the spark plug (or plug wire), injector, or worse an issue with the valve. For "random", it could be an issue with the MAF. Try running with the MAF unplugged to see if it helps or hurts. If just at idle, possibly the IAC. EGR would also affect multiple cylinders.
 
Damn...I also have a thread with a 300 problem. I have the Napa echlin coils, which I'm pretty sure are what I used last time, but might try again with something else. Good luck
 
If you have P0300 and you have changed sensors, cleaned everything, changed coil packs and no difference you can try testing the coil wires in the harness between the ecu and the coils. Although this sounds far fetched and should be the last thing you check, I have heard of it happening before.
 
The_big_dill said:
If you have P0300 and you have changed sensors, cleaned everything, changed coil packs and no difference you can try testing the coil wires in the harness between the ecu and the coils. Although this sounds far fetched and should be the last thing you check, I have heard of it happening before.
Click to expand...

^^ What he said,..
Those wires leading to the coils get old and brittle and the pins in the connectors can get corroded.

Try not to bend the wiring harness more than necessary,... try not to pull on the wires themselves, just the connectors (that can be difficult if the connector has never been apart)

You could end up with one of those "intermittent" bad connections that can be really hard to find.

It helps if things are warm in the engine bay,... warmer wires bend easier.
 
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