drabe

I have a 2005 C2S which needed a new engine so an X51 was installed. Since the install, the throttle responsiveness at part throttle has been jerk, with a flat spot at about 4000 rpm. My tech checked the throttle potentiometers and the throttle body potentiometers and they're in synch. At full throttle it runs fine. It's just at part throttle. Any ideas?

mrzoop

this might sound too simple but the ECU may need a reflash. that's the first place i would look especially if this was a simple mechanical swap. pop out the original engine and swap it with one that breaths and performs totally differently. the ECU is probably still expecting to find the standard 3.8.

kdurg

^^^^^ this...and are you running stock 3.8 headers and airbox or did you swap out to X51 equivalents ?

alexb76

You need to clarify what exactly have you done. Just engine replacement and adding X51 headers? or doing a complete X51 engine install? If the latter, ECU HAS TO change for X51 engine.

utkinpol

did you do it aftermarket or with a dealer? could you pls share what was the overall expense to get it installed?

I would not think that ECU was not replaced if car got new engine, it is just too obvious. did you run it on a dyno with air2fuel and timing graphs?

IF ECU is of right version - check your MAF sensor, unscrew it from airbox and give it a full bath, also - do you have X51 airbox or old airbox? But all those questions are pointless, you really need to put car on a dyno and get all required graphs under load to see what is going on where you have a hesitation or power loss.

drabe

Yes, X51 software. Stock airbox. Problem seems to have been solved with a new throttle body.