05 gto,ls3 head swap, cuts out at 4000 rpm

Attachment 90599Attachment 90600


hello all,
so I've been fighting this one for about 6 months now and just really getting my but kicked! was hoping somebody on here might have some experience with a similar situation. its an 05 gto automatic. under heavy load, tps above 50%, the engine cuts out, doesn't die, just wont accelerate any further. acts like its hitting a rev limiter. watching the log file, all airflow values gradually drop, and injector pulse drops with it when it hits about 4000rpm. I am even holding the throttle open at 90% but it will not move any air. however, this is where it gets tricky, it will run the rpm up if I keep throttle position below 50%, all the way to 6000. engine runs great, pulls good, doesn't skip a beat. even if I get above 4000 rpm and open up the throttle past 50%, it just stops revving drops back to 4000.

I have been calibrating the a/f ratio, and got it within a reasonable range, but still no effect to my problem. it was extremely rich reaching 9-1
I have talked to a few tuners and I am really leaning towards a mechanical problem. I have eliminated possibilities with restricted intake duct, or exhaust system. I have checked my lifter preload, and measured .030 on intake, .060 on exhaust. right now I am leaning towards the possibility of either lifters collapsing down at high rpm, or throttle blade closing without the sensor reading it (highly unlikely)

also, this all started when I swapped the heads, valve springs, and intake. the car originally had this cam installed along with headers and never had a problem. everything else is stock and original to the car. I am in the process of installing a procharger, haven't installed it yet though.

my mods are:
comp GRIND # LS1 3727R /3731R HR114 +4
DURATION @ .050 INTAKE 234 ROCKER
ARM RATIO
VALVE ADJ INTAKE .000 DURATION @ .050 EXHAUST 242
INTAKE 1.70
VALVE ADJ EXHAUST .000 LOBE LIFT INTAKE .3530
EXHAUST 1.70
VALVE LIFT INTAKE .601 LOBE LIFT EXHAUST .3590
VALVE LIFT EXHAUST .609 LOBE SEPARATION 114.0
DURATION .006 INTAKE C/L 110.0

headers
comp 7.4 pushrods intake, 7.350 exhaust
unknown stall converter

installed 12/10/18
ls3 intake
ls3 heads, hand ported, with ls9 exhaust valves installed
patriot dual gold springs,
btr ls9 dual spring retainers (to compensate for installed height)
gm 2 bar map

I can't open your tune, a dialog box says "Translating Tune unknown source" But besides the Map dropping at WOT, your Bank 1 O2 MV is dropping. Looks like there is a misfire on Bank 1.

Russ Kemp

Attachment 90615

how about this one? I couldn't open the other one directly either, but can through the editor, strange. but this one worked for me

funny you say that, I thought for a little while I might have a misfire, was searching for it, but only felt like I was chasing my tail. under load and driving I don't feel it at all. but at idle, and especially in gear it really sounds like something misfiring, there is a pop every once in awhile in the exhaust. the misfire counter would go up on cylinder 3 mainly, but a few randoms on all others. I just kinda thought it was my cam slobering around, and I adjusted the table for misfire detection. this car already had a tune on it before I got it so I wasn't sure what they did or did not do. , and my neighbor even commented on it one time, sounds like its misfiring a little!

will the computer cut fuel or take action like this in case of a misfire? even if I turn the sensitivity down for the misfire counter?

It has new plugs, I pulled them all out, they all are dry, clean all looked the same. I swapped the coil to the other side, never did move the injector though. I did a compression test, results were around 130 psi, never did check running compression though.....

I got a gto with ls3 heads...so I'll try to help. In your log when the maf drops out, with you still wot. Your map also drops out...wondering if the intake tube is collapsing, or filter is. For both map and maf to fall out...something is closing or restricting it alot. even the wot run at the 3467rpm point..the maf lb/min is high (almost 29 lb/min). Mine at that rpm is only at 20 lb/min...it will hit 45+ at redline. Are you still running the ls2 style maf or have you converted to the ls3 style? It looks like you have the 2bar settings in the map functions, but can't tell if you have applied the 2bar OS.

i have verified no restrictions on the intake side. I have all the duct and intercooler for the procharger hooked up. disconnected the air duct at the maf sensor and tried to run it open without any duct, same results. i did run it with the maf failed, thinking that would eliminate the sensor from being a problem, such as going out of its range, maybe i'm wrong on this one?

I don't have cats on the exhaust so there really shouldn't be any restrictions on the exhaust side.

I did switch over to the 2 bar os when I changed the sensor out. I changed the map sensor trying to fix this problem, so it was there after the head swap, even with the old map sensor.

I am still running the stock ls2 maf

it does look like the throttle blade just closes, is it possible for the blade to close but the sensor still be reading 90%? I wouldn't think so as it always moves progressively and theres never a sudden drop. I did take the duct off with the engine off, and I could see it go to wot when you push the peddle down

well, after almost a year of trying to figure this one out, I finally got it! just wanted to make a post and share my findings. so, I had done all the work to the engine and hooked all the piping up for the procharger. I wanted to make sure everything worked ok before I gave it boost. the only thing I didn't have bolted on was the head unit itself, I just put an air filter at the very end.
I disconnected the air duct at the maf, and the engine ran absolutely great! no issues! just for the fun of it, I hooked the air duct back up again, and removed the air filter. problem came back again just like before. lesson learned, cant suck an n/a motor through an intercooler, had no idea!

could have sworn up and down it was one of the first things I tried, but it had been so long ago, so many times on and off, that I forgot about it. I knew this one would make me feel like an idiot once I found it!

anyhow, bolted the procharger up, did a little tuning, had it running good, until my first wot pull. I think it was trying to make an upshift 2-3, and it flared up real bad, bounced the rev limiter. after that, no more 3rd or overdrive! so looks like the trans will be coming out, I guess that's how it goes...?.

heres a log of what I will someday build and maybe drive again

Attachment 91071

oh and by the way, yes I also had a misfire. cylinder 3 was fouling the spark plug to the point it wouldn't fire anymore. it kept getting worse the more I drove it. I think it was from running it too rich, too many times. finally tracked it down, put a new spark plug in it, ran great!
strange part, it didn't look extremely wet, or extremely black. it was clean, and it just looked wetter than all the others, they were very dry