Ok I will try to keep this as short as possible, So heres a cliff notes of what happened.

Scored a cylinder, Pulled motor and got it sleeved with darton sleeves, 11.5:1 CP pistons, Carillo rods. Running a stock head gasket with stock injectors/plugs/ecu.

I broke the new motor in by letting it run during the initial startup while running conventional oil, After 30 mins drained oil/changed filter. Went 500 miles with conventional oil, changed it again and went to mobil 1 synthetic. Engine ran great for about 750-1000 miles. Now its stumbling under load (But not all the time) Just about 75% of the time, And it just feels like it has no power. Still hits vtec but smokes like it is running lean. So I pulled the plugs and they have a white frosting like they are running lean. The car still starts and idles fine, Just feels like it is choking like its not getting the proper fuel or something, But that doesnt make sense to me because it was running great for a while with my new setup on the stock ecu. I reset the ecu after getting a knock sensor malfunction code after a coolant line leaked onto it, Also had a code for some kind of evaporatie something or other leak. But since I reset the ecu I havent had any check engine lights but the car is still breaking up and stumbling under load and feels like it has no power on the highway. I tried the map sensor whack but no luck. I know this is a very technical question and its pretty hard to explain over the internet so anyone local with extensive knowledge is welcome to try to drive it yourself and see what you think of the whole situation. Thanks for reading an wish me luck! Ohh and the new motor has almost 2000 miles on it.

 

Have you done compression/leakdown tests? Any datalogging to verify A/F ratios?

 

No and No. Dont have the tools for either one.

 

It doesnt feel like a problem that could be determined by doing a leakdown/compression test. It seems like a air/fuel problem and maybe a map sensor and something with the ecu and the timing. Doesnt seem like a mechanical problem if you get what im saying.

 

I am in kinda the same boat. I just need to install an A/F gauge now. They are like 350 bucks though so it could be a couple weeks.

 

you probably have to get it tuned since the motor is not stock any more, cant expect the stock ecu to run that modified motor

 

Thats what I figured but it doesnt make any sense to me that it was running great after I broke it in and after a week or two it starts acting up.

 

The stumbling problem has went away so far, But its still running very lean, What would explain the fat that the motor was running strong for about a week or two and now its running lean and feels like it doesnt have the power it had a week ago due to the lack of fuel.

 

I would put that on a dyno and make sure everything is ok.

Double check the install of the engine.

 

By the way strippermotorsports.com has AEM A/F gauges for 255 to your door. This is not a plug by the way, it is just the cheapest price I have found on a decent A/F meter.