my worst fear, might've finally happened...

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Mazda Protege5
hey mazda fam. looks like I might be down for a while. I had a sudden misfire happen to me like 3-4 days ago. the car threw a flashing cel and the code I got was P0302. I took it into the shop and they deducted that apiece of a valve is broken off. They said for the work to be done and thats not including misc part or other things they might find wrong along the way to an amount of $2k so at this point i think I might be looking at a new engine or is it something that I can fix on my own with some help? I do love the car and I've invested a lot of time on it and I don't have the money to buy another car atm the only one I would even replace it with would be a much newer subaru impreza. I just find a hatch so much more practical. Any info on where to start to look or maybe if you guys might have a spare engine laying about? thanks
 
I think you should do a compression test and see if number 2 cylinder is really low.

Getting a second opinion is a good idea at this point.

I haven't heard of a broken valve on our car in the 7 years I've been on this site.
 
Do I just go to another shop or is this something I can do on my own. Im assuming there's a tester?

Very true and I find that quite interesting.
 
It's easy..

You can do it yourself for cheap...
Just unscrew a sparkplug and screw in the gauge.





You may just have a bad coil or sparkplug and they're trying to sell you $2000 worth if labor.
 
A misfire is quite often a bad coil with our car.

Here's the list of possibilities for a cylinder specific misfire.

(it doesn't mention missing a chunk of valve. lol)

 
Is your cel still on and is it still flashing or did it just stay lit ??
 
I drove it from San Diego to home and it wasn't till I got home that it began to flash. That was about 80 miles or so.

According to the shop, they used diff coils and plugs to test the other cylinders and it was just the #2 that kept giving an error.
 
Apparently, if an engine misfire is detected the ECU goes into limp mode to stop the misfire.
It floods the engine with extra fuel and reduces the timing advance among other things to stop it.

As far as I know, once the misfiring has stopped the cel stops flashing and stays lit all the time.
 
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If you are missing a piece of your valve you will have very low compression on that cylinder.

A compression test will show that.

You may have a bad injector that isn't working right or is completely plugged/fouled. (if your compression is good)
 
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No, like you have to drive it a little before it does that otherwise the cel is just on but I do have codes p0140 and p0138
 
P0138 and P0140 are for the rear O2 sensor.
It looks like your sensor is bad.





However, it does mention that the code could be caused by low engine compression or an engine malfunction.

You should still do a compression test to verify the compression.

As far as I know, the cel only flashes while it's misfiring. If it just stays lit the ECU has stopped the misfiring. (or the other codes are keeping it lit)
I don't think the ECU can compensate for a broken valve but it may be able to compensate for a while to deal with low compression.
 
Check compression. Go go oreilly or advance or autozone and "rent" a compression gauge. You pay them up front, and they refund you when you return it. IT will take 10 minutes to do a compression test. IF a piece of the valve really did break off (which i've never heard of before) then you will have no compression in that cylinder. I haven't paid much attention but I think i'm at somewhere around 265-270k miles on my p5. I did a compression test a couple months ago and all 4 cylinders were between 200-210psi as a reference point.

I'd point more towards spark plugs or a bad coil.
 
I had a misfire suddenly and it turned out to be an arcing spark plug wire. Always try the easiest solution first. although I would assume the shop already checked those things first. you can also check injectors by holding a screwdriver to one and the other end to your ear and listen for a rhythmic "tick tick tick tick" sound.
 
Valves have been known to fail from time to time. Not very often, but it happens.

If you verify low compression, then you can often get in the cylinder with a borescope and confirm that the valve is busted.
 
although I would assume the shop already checked those things first.

Never assume anything. "the shop" is only as good as the guy that pulls the ticket and works on your car. I worked at a dealership and knew "master techs" that I wouldn't let work on my bicycle.

Also, a noid light is much better than listening through a stethoscope or screwdriver. most people don't know what to listen for. But anybody can watch a little light flash.

And agreed with Mr Giggles. While it is always a possibility for a valve to fail, it's extremely rare. I would really be surprised if this was your issue. Valve seats failing is much more likely, with wear and high mileage (especially if the engine is driven hard/high RPM) or valve adjustments are not done on schedule, the valves can beat the seat out of the head. Fix is a valve job or replace the head. I had a 4runner years ago that had this happen. $75 for a new head at a junk yard, adjust everything to spec and I never once had a problem with that truck.

And boroscopes are great. You can buy one on Amazon for around $25 that's wifi and use your smartphone or ipad as the display screen. Much cheaper than the $500 ones years ago from the snap-on guy because nobody else had them.
 
IMO, if there was a broken valve floating around inside the motor there'd be all kind of ruckus and something imploding or exploding before you drove any 80 miles. I'm trying to imagine that valve head bouncing around in the cylinder and just letting you keep driving along with nothing but a flashing light on the dash...........seems extremely farfetched. If any valvetrain item breaks the car isn't going anywhere except to the side of the road pretty much instantly.......................discuss
 
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