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Discussion Starter · #1 ·
I attached a hondata datalog to this post for viewing purposes of the misfire on cold-starts only. The colder the weather, the bigger the misfire and rougher it sounds. (almost like a 2-stroke)

I do believe it is mechanical as Vit-Viper is doing my tune for my set-up.

K20z3, boosted.

I received a P0303 (cylinder 3 misfire) when cold start-up, code reads in less then 1 minute. I have also pulled other codes related to misfire on previous start-ups.(e.g.: random misfire)...

I have sent my injectors to be bench tested and cleaned, they were verified as ok. They are aftermarket injectors.

I have an aftermarket fuel pump, but my fuel gauge on the fuel rail reads a solid 50~ psi constant during idle.

I haven't replaced my CAS yet, because I'm not sure this $120~ replacement part is going to be the culprit?

I checked all my wire pigtails at the injectors to ensure they were in good working condition/connectivity.

I tried swapping around my coil packs, they all work.

New spark plugs, properly gapped.

I need ideas of what I am missing to check....

Any constructive help is welcome!:dance:

https://www.dropbox.com/s/fptjbom4bfuxn7f/datalog0004.fpdl
 

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compreesion test dry and wet.

wet test will represent the hot expanded piston. since you have a cold misfire compression test when cold.
 

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Discussion Starter · #3 ·
i've done compression test already.. cold only.. was 150+ on all cylinders
shouldnt need to do a hot compression test as the problem goes away when warm.
 

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Discussion Starter · #5 · (Edited)
Does it set a hard code or does the CEL go away? Is the car running like crap only on cold start?
only on cold start, after warming up the CEL will disappear all on its own. It will also start to idle properly and stop missing (slight misfire on idle). The misfire when driving gets retarded bad. So I don't drive it until its 100% warm and its done misfiring.

The CEL code still comes up with my datalog showing it happened though.

again, the problem goes away all on its own when its warm, runs like a champ and doesnt miss a beat. When its cold, its a different story.
 

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I'm having the same issue. Sometimes it'll start up just fine after sitting for 3 days in the teens, other it'll act up at 40 degrees. Runs super rich and misfires until it's warm, then purrs like a kitten. Boosted as well.
 

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Have you pulled your plugs to see what they look like? Just out of curiosity if you can see if cylinder 3 is running lean or rich?
 

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Not sure about him but I changed my plugs and did a compression and leak down test and everything is spot on, yet the issue still arises every so often. I'm thinking it might be an injector issue but no clue why it would be intermittent.
 

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Discussion Starter · #9 ·
I changed out all spark plugs. When misfiring all plugs get fouled badly. I have to reclean them to restart in some cases.
 

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Could coolant be seeping into plug #3, as the car cools down?

After starting the car and the misfire is over, because the possible coolant is gone (burnt off/evaporated), the car should run smoothly and the CEL will go away.

Try removing plug #3, when the engine is cold and look down there with a flash light.

Take a long cotton string/rope/candle makers wick and send one end (only) down the spark plug hole. Check the tip of the wick, to see if it has coolant.
 

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Discussion Starter · #13 ·
if this was the case wouldn't I be losing coolant and have bad compression? I did verify my compression at cold to be 150+psi all cylinders.
 

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I'm not saying there is enough, of a leak, to hydro lock the motor.
It only takes a couple of drops of coolant to cause a momentary (non-fire) misfire.
Those drops will quickly burn off.
This issue may not be common in Hondas, but the Caddy Northstar and Ford 3.8L motors routinely seep coolant and have misfire CELs
Anyway, if it is a coolant leak, it will only get worse and that will help you to diagnose it.
 

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Discussion Starter · #15 ·
I'm not saying there is enough, of a leak, to hydro lock the motor.
It only takes a couple of drops of coolant to cause a momentary (non-fire) misfire.
Those drops will quickly burn off.
This issue may not be common in Hondas, but the Caddy Northstar and Ford 3.8L motors routinely seep coolant and have misfire CELs
Anyway, if it is a coolant leak, it will only get worse and that will help you to diagnose it.
Its definitely worth looking into, especially if it has happened before.
Keep the suggestions rolling in. Need to trouble shoot this for good.

Thanks to all for the brain storming thus far!:vtec:
 

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im currently having the same exact issue on my co-workers 05 sentra. i haven't done a compression test yet so i gotta do that first. But it is very weird only happens every now and then on cold starts. Sometime i get a cel for multiple cylinder misfire and sometimes for cyl 3 only. cel stays in the memory but light goes away. I was think the same coolant issue because if the injector were bad it would be constant.... i will subscribe to this and any updates will be posted.
 

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Discussion Starter · #18 ·
I'm wondering if a almost gone o2 sensor would be the culprit? o2 sensors work off of heat to give off readings and adjust fuel/etc for the car. Now if the sensor is off, under cold weather until warm would this give bad readings? I know this is a stretch....

I was also thinking vacuum leak. But I bought carb cleaner and sprayed the crap out of the engine bay looking for any signs, I couldn't see any. The only other alternative now to be completely sure is a leak down test using a smoke machine.
 
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