p0300 gota love random missfire's

[Empyrials]

ok so i have a 2g talon tsi, and i've been geting this p0300 code on the highway. It only happens when i'm above 70ish MPH and i stay at a constant speed. I don't have to stay at the speed for very long but whenever it stays the same, say by use of cruise control, i throw the CEL. not cool when on the highway.

And i just blew my tranny before this, so i upgraded my clutch and tranny(just rebuilt). While i had plenty of downtime because of the tranny, i also installed a big 16g. It was only after this my problem occured.

What could cause this? and it's 1 2g engine so that rules the 1g engin in 2g thing out.

and the Speed limit is 70 so i was going close to the speed limit, .

 

[Pizzy]

I just read a tech article about this:

A "random misfire code" (P0300) is even harder to diagnose because there can be numerous causes. A random misfire usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty injectors, low fuel pressure, a weak ignition coil, bad plug wires or compression problems.

Perhaps the 16g is causing a lean condition...tune away, but I'd look into the rest of the suggestions as well. Good luck

 

[IHeartTurbo]

You're not boosting at cruise so it's not because of the turbo. I'd suggest running some fuel system cleaner through it and checking for vacuum leaks.

 

[Pizzy]

You're not boosting at cruise so it's not because of the turbo. I'd suggest running some fuel system cleaner through it and checking for vacuum leaks.

Yeah that's true, although even at cruise I would think that the 16g is still flowing a little more air than the T-25 even if not under boost...even at cruise, it might make a difference. :shrug:

Alas, it's just speculation. I think IHeartTurbo is on the right track though. You're more likely experiencing this from one of the other previously-mentioned symptoms. Try the easy stuff first: injector cleaner, check for leaks, check compression, check plugs, etc.

 

[verytalonted]

Any updates?????

 

[JLangevin]

I posted the same problem a few days ago. My post is a few below this one.. notice I am a stock car with mild mods, and also get it when crusing at 70mph. But I KNOW I have a valcume leak somewhere, just havent fixed it yet. This could be both of our problems.. I have been told that at Idle 18-20hg is normal, I have around 12hg.. so this tells me there is a vacume leak. When I get around to building a tester, I will find it.