05 GTO Misfire, Hesitation, Lack Of Power

**MM Alexander** · 01-23-2014, 07:47 AM

Hello and THANK YOU for taking the time to read my thread and possibly offer me some advice/expertise on my issue(s).
This will be a long read but I will attempt to make it condensed as possible.
Back Story on the car/motor:
05 GTO LS2 E40 computer that I've owned since 06 82K on car currently. In 07, I put a cam with 918 springs, LT's and Svede CAI on to car and had it tuned.
Car ran great no issues at all - outside of a 918 spring breaking one day (luckily it did not drop the valve) and a C6 clutch kit not being up to the task (put a Monster Level 3 in). Replaced springs with some Tooley racing units and all was well again ... which is where this story should of ended ... Late 2010 / Early 2011 the "upgrade bug bit and I added a set of TSP CNC'd LS3 heads, intake and LS3 injectors. Not "impressed" with the power (idiotic, I know) I decided to go back to my tried and true favorite from my Mustang Days of yester year and put a pair of hair dryers on the car. Built a rear mount (just to try something different) ... drove it for 2 months like that and quickly realized why I must build a front mount.
Moved them up front and about 3 months in, I while driving to work one day, had a smoke show as I cruised in the parking garage. Got it homed thinking I had lost the motor but it turned out I had only lost one of the Chinese turbos. Now it all goes down hill, LOL!
I upgraded EVERYTHING: Schwanke forged short Block, Turbonetics Hurricane Erin units, Ed C. custom Spec'd cam, 3" exhaust from turbos to bumper yada, yada.
So I get it running and I take it to the internet famous local 3 letter shop for a tune ... what a forking mistake that was. Car ran better before I took there (where it sat for over 2 weeks) for that crap they vomited into my ECM. Upon start up car had "Service Engine Soon" literally soon as I started the car up! It bucked, hesitated, back fired and got a whole 8.1 mpg for the trip back home (5 miles) awesome sauce! After a lot of trial and error, self tuning it over the course of a few months. I got it much better but far from being "right". I could never clear the car of a misfire and slight "shake" upon throttle transitions in lower RPM.
Frustrated and not happy with the car (less than 2K miles it had on the new stuff), I decided to upgrade again ... But this time the upgrade would be to a another car -

2013 Corvette Grand Sport

GTO parts were sold and I put the stock LS2 long block back into the car (LS2 heads/Intake) along with the original Cam upgrade I had done several years back. Got a new set of Long Tubes (sold the old set when I went turbo) Put in new plugs and brand new wires along with the Svede.
When I did the TT kit, I had my stock LS2 injectors upgraded to 60's by FIC which I included in the sell of the TT kit. I'm currently using a set of LS3 injectors (with spacers and the proper data put into the ECM).
The only carry over items from the TT build would be LS7 lifters, timing chain and fuel rails.
So the car is pretty much exactly as it was when it ran like a dream NA with no issues ... Yet the damn car has issues ... similar to what it had when boosted.

Rough idle
Very rough under slight load at low rpms (shakes shifter all over when releasing clutch from stop)
Weak top end and rough low end, still pulls strong in the 3,000 - 4,000 RPM range
Smells rich, there's a fuel smell when cold
Backfires out exhaust under load at low rpms.

My courses of action(s) thus far have been:
Tested all coils with a coil test light by placing the tester between the plug and the coil. Light flashed steadily on all the coils.
Noid light on all injector circuits. All are getting a signal from ECM
Ohm'd the Spark Wires and got 450 on all of them.
Ran a compression check even though I doubted anything being odd and got 190 - 192 on all holes.
Car pulls a steady 18 inches of Mercury with no mechanical problems/noises.
Perplexed and not having any codes present, I've been driving it to work for the past 2 days. While it drives like pure dog crap but it never cuts off/leaves me stranded and averaged close to 16 in traffic and a 21.9 on the expressway at 70. Not great but much better than when it was originally tuned by the 3 letter local shop.

I have gotten the check engine light

Symptoms:
-p0300 - Random/Multiple Misfires P0300 - Engine Misfire Detected (SES) (Old) (History) (Immature)
-P0305 - Cylinder 5 Misfire Detected

SES light blinks under load stays solid most of the time.

I had the Vette in the garage doing brakes (stock brakes throw way too much dust ... much too much) and decided to put the coil packs from it onto the GTO. Drove it and issues still persist.
Swapped Plugs from Vette to the GTO after that ... Same exact issue. I actually get a misfire code at times from cylinder 6 as well. It also seems to be down on power a lot for just one cylinder misfiring.

So if it's not coil packs, plug wires, plugs the only thing I can see being an issue would be the injectors???? I have an ECS kit going on the Vette and it comes with new injectors. I'm going to swap the injectors from the Vette to the GTO once I start on the install. Not sure how soon that will commence and I'm also not convinced the injectors are the problem.
Any idea/thoughts/opinions on what else to check and what I could have missed are all appreciated greatly.

***SMWS6TA*** · 01-23-2014, 08:16 AM

I was going to say have you check the injectors? wiring for them and the coils (not the plug wires the wire harness part)?

You could move the cyl 5 injector and see if your codes move to new cyl.

How do the plugs look? wet, dry, burnt?

are you running on stock fuel pump?

**35th-ANV-SS** · 01-23-2014, 11:32 AM

So, according to you, you picked the car up from getting it tuned at a shop and it immediately ran like shit, had a check engine light....but you drove it home?

Can I ask why?

**cammed goat** · 01-23-2014, 08:14 PM

I agree with Jon. I would have taken the car back and had the necessary adjustments made. I was going to ask if all the spark plug wires were tight, as in clicking onto the plugs and coils because if any of the wires DO NOT snap onto the plugs/coils, you WILL have a misfire code. Speaking from experience as my #4 wire was actually dangling next to the plug and not on the plug. I ALSO began to think your car was in "limp" mode since it's an LS2/drive-by-wire. The throttle body shits the bed and only allows for a certain RPM to get the car home. OR, I'm thinking it may be a wiring issue. Possibly a broken/burned wire somewhere in the engine compartment.