ziker

I am having an issue with my ap1 s2k as it hits around 6k rpm. It starts to buck and backfire like a fuel cut. I will give you the back history and mods then more description of the issue.
Im new to the forum and new to custom built turbo cars. The back history on this car is that it was built by a performance shop in my area. The previous owner only drove it a few hundred miles and sold it. That didnt leave much time for shakedown tuning
Here is a list of the mods.
6262 precision billet turbo
Twin 38mm tial wastegates
Custom header, downpipe and midpipe
Invidia catback
1000cc injectors
Fuel rail
Aeromotive regulator
Walbro 400 fuel pump
Competition clutch stage 2
Precision intercooler
Tial blow off valve
Custom piping
Bc racing coilovers
Ccw classics wheels
Nugent front lip
Aem v2 ecu
Aluminum radiator
Car made 400 @ 15 psi conservative tune

The first day I got the car it was cold (15 degrees Fahrenheit). It would not make boost (run over 5k rpm) for the first 15 minutes of run time without bucking and surging. I chalked this up to a cold engine mapping. The car would then run great but occasionally pop around 6k at full throttle, I coudl get it by 6k but I had to ease it through that rpm range. Almost like it was having trouble switching into vtec. It seemed better in first and second and got worse in the higher gears. As the weather got warmer it seemed to start running better with less issues. Today (50 degrees) the car will not run over 6k rpm. It starts bucking and backfiring regardless of how warm it is. Watching the AFR gauge the car idles at around 14.5-14.8. At partial throttle cruising its around 13.5-14.0 . At full throttle the afr is around 11-12 but I noticed it dropping to 10 at full throttle right before it surges and pops. I tried changing plugs and regapping around .028 but it did not help. Fuel pressure is around 49psi. The car seems ok in first gear, my guess is that because the tires start to spin its not enough load to cause the problem. Does this sound like a boost leak? spark blow out? major tuning issue? The car peaks at 15psi and seems to run good til I hit 10 psi. I appreciate any feedback. I am a fairly talented mechanic but limited in turbo issue diagnosis

jordannn93

Are you using the oem map sensor?

ziker

No it has an aftermarket map sensor

ziker

Another thing I noticed is that right before the vehicle would surge and buck it looked like it went from 15psi to 20. I cannot tell if its 20psi or 20 lbs of vaccuum. It spiked really fast the time i noticed it.

ziker

By speed sensor are you talking about a wheel speed sensor? My abs light is on, when I bought the car there was a harness that was torn off on the passenger side fenderwall. Looks like an abs wire. I soldered it back together but did not have a tool to shut the light off. It ran fine for a couple days after that. The bucking is severely violent.

ziker

I have not had a chance and may not be 100% sure what I am looking at. Does the aem ecu have a self diag ?

ziker

The car was built by M&S performance out of new york. Build looks great. My guess is this is going to turn out to be some sort of shake down related issue (incorrectly fastened couplers?) I am not sure who did the initial tuning. I am located in central CT. I have a pretty good vehicle diagnostic skill set so I am sure I can figure it out once I get to play with the software for a while.

ziker

That sounds good. PM me for contact info. I will go buy a new tuning laptop tomorrow and start playing around. I should also check wastegate fittings im guessing.

herecomesboost

I can take a look at the calibration if you'd like. My email address is: kyle.william.ritchie@gmail.com

riceball777

Sounds like it's hitting boost cut. You need to redyno and retune the car with a good tunnel that is familiar with the aem ems.