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Flashing check engine light

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I was driving tonight and accelerating up a hill at about 3/4 throttle when my check engine light began flashing for about 20 seconds then left. after everything seemed to be fine however my transmission has always shifted a little rough downshifting. As this is my first car I just assumed this was normal. I drove a little bit later and tried a little Italian tune up. When at full throttle or near jt when my car is at about 4 thousand rpm it starts to jitter a bit like a little shake that feels like it’s from the transmission And the rpm’s flutter a little bit. I just replaced the engine about 2 months ago so I know it isn’t an issue with that. from a cold start when you first drive at about 20 km per hour a little click wound comes from the transmission and I can feel it through the gas pedal, I am now wondering if this was an early sign of my transmission failing. Does anyone have any thoughts or ideas as to what this could be. im so done with this car I have had nothing but problems with it but I can’t get rid of it cause it was my grandparents car. Anyone have any ideas what this issue could be?
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I just replaced the engine about 2 months ago...
Seems very odd to me that there's no corresponding misfire information in the freeze-frame data; I'm not aware of any diagnostic that will cause a flashing MIL other than catalyst-damaging misfire detection. Regardless, did you do a CASE learn on the new engine? If not, that has been known to cause false misfire detection at high engine speeds.
 

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I’m not sure my mechanic put it in and did all the work he doesn’t speak great English so I didn’t ask many questions. If he didn’t do all he now could I do one my self?
If you don't have the appropriate scan tool, you can't. Even if you do, you might not do it right unless you know exactly how. I suggest taking it to a dealer.
 

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I have a high end snap on scan tool for the weekend I am borrowing but I don’t know how to do it.
With the tool hooked up, see if you can find a function called "Crankshaft Position Variation Learn". There are any number of descriptions of how it's done online, but none of them emphasize how quickly you have to get off the gas pedal when the fuel cuts off during the learn. You need to do it like cutting a really good light at the dragstrip, except that you're releasing the throttle.
 

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What happened if I’m not fast enough?
It's just part of making sure you get the best learn you can.

The misfire diagnostic works off of the crank position sensor signal. The CASE learn accounts for normal variations in the location of the crank teeth between different crankshafts. Since a different engine usually means a different crankshaft, you ought to do a learn to ensure the computer has the correct information.

The first one you'll probably let off the pedal too late, you'll know you were slow. Then you might get a couple of tries where you let off too early and you won't get the learn complete message. When you get one where you think you were too early but you get the learn complete message, that's the one you keep. Shut the car down and let the controller go to sleep, and you're good.

If you still see the flashing MIL, at least you'll know it's not this.
 

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I’m just going to send it off to my mechanic and sell it. I have had enough with This car. Idk if anyone else has had a terrible experience but I have just had problem after problem
I certainly understand your frustration, but if you have the right scan tool it won't cost anything but a little time to do the learn and it could solve the problem. Sure, it could be something else, but I've seen swapped cranks with no CASE learn cause false flashing MILs dozens of times. It needs to be warmed up, a/c off, in park, foot on the brake. Give it a try, you might be surprised.
 

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Went for a highway drive. Very few if any misfires until you out load on the engine. Did a test of 3/4 throttle up a hill. The bar began to buck and engine speed was all over the place. Got another big misfire with the flashing check engine light and p300 code
To me this is starting to sound less like CASE factors and more like fueling. Don't lose hope quite yet.

Gasoline is a mixture of molecules that have different vaporization temperatures. The distillation curve of the fuel is very important to proper engine function, and injector spray pattern and timing are all developed assuming a normal range of distillation curves. As fuel ages the light ends evaporate, and if it gets really old it can also start to oxidize and get gummy; both of these are bad for fuel prep in the cylinder, and the first place it shows up is high speed/high load operation. You've got fewer light ends to vaporize, higher in-cylinder pressure which slows vaporization and there's also less time for vaporization to occur, and you start getting poor ignition and misfires. Then there's higher than normal O2 in the exhaust which the O2 sensors pick up, closed-loop fueling thinks it's a lean mixture and starts chasing it with fuel trim... it's a mess. On top of it, whatever octane number was shown on the pump is bogus once the fuel degrades that much, you have no idea what it is now other than that there's no chance it went higher. And yeah, it can make the car buck around like crazy - it's happened to me in the past, and the exhaust smelled like crap too.

Since adding some fresh fuel seems to have helped, I suggest either draining the tank and getting rid of the fuel or else driving it like you're an old man until the tank's empty, and then get a load of good fuel in and see what happens.
 
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