OK guys, I need a little help, I just put a 2007 corvette LS2 engine in my 1971 GTO convertible. wire harness was rewired and the ECM reprogrammed for a standalone with a manual transmission. Engine starts right up and only has a P-300, Random miss fire, I am pulling a steady 21 in. of vacuum at idle. New wires and plugs have been installed. A new PCV hose, under the throttle body has been installed. The cars takes off with no power, builds up and power comes up, then around 3500 RPM engine shuts down, when it gets below 3000 RPM runs goods. I can't take off with a full thrittle. any ideas if where I should go?

 

I would be courious to know what the MAF sensor is reading.
Ive seen a bad or dirty MAF sensor cause some serious issues

 

 

I cleaned the MAF but will check it again, on my Chevy pick up if I was to unplug the MAF it would default to a factory setting and let the motor run on these setting, will the LS2 engine do the same?

 

Starts coughing and car starts to slow down, if I stay with a slow steady increase on the throttle it does not happen, just when I go to full throttle, I have a tech 2 system, the engine has the 58x cam sensor. I will plug in the tech 2 and check the "crankshaft variation relearn" Thanks

 

 

 

What fuel delivery system? Describe it please. How much fuel pressure do you have at the rails? Can you check FP throughout the RPM range?

 

 

Do not make the mistake of reading fuel pressure through the OBD port with a scan tool (tech II). There is no FP sensor on an LS engine. It will always read 58psi throughout the entire RPM range. You need to measure FP directly off the rail.

Slow down a little bit and do one thing at a time. Forget fuel trims, MAFS, crank sensors, etc. The basics are FUEL, AIR, IGNITION. Either lack of fuel (throughout the RPM range) or lack of ignition anywhere in the RPM range can cause P-03xx misfires. From post #1 it LOOKS like you have ignition confirmed? Next is fuel. If you can confirm fuel pressure is good through the RPM range, then you can look at more complex issues. In posts #1 and #5, you are describing classic weak fuel delivery to me.

You have an LS2 in a 1971 GTO...so what is the answer to my earlier question? - What fuel delivery system do you have? A 71 GTO with a 400 C.I. engine used a mechanical fuel pump mounted directly to the engine block, so it must not be that.

Put a fuel pressure gauge on the fuel rail. See if pressure is maintained with different RPMs. If you significantly lose pressure on acceleration then fix that first.

 

OK for those of you who gave ideas on things to try to get rid of the P300 code after I installed a 2007 Corvette LS2 engine in my 1971 GTO, I found the issue. I was talking with a friend who has a 2004 Corvette, he noticed the headers I put on my new installed, and told me to disconnect the O2 sensors on both sides. so I did, when I took the car for a test drive, it ran so much better. the engine no longer shut down and I can hit the full pedal without the engine shutting down, When I put on the headers, it moved the O2 sensors almost 3 feet from the original position, I am not running at full power but now know that I need to have the car put on a dyno to have the O2 sensors set to match the set up in the program. I was fighting the ECM all this time, program was trying to run with the O2's being a few inches away instead of 3 feet away, made a big different in the way to the car runs. Thank you all all who gave me advice and things to try.

 

I did put a gauge on the fuel rail, it maintained a 65 PSI all the way thru the 5000 RPM range, no drop, please read my new post about the position of the O2 sensors, thanks for the advice.