Car - 2008 Cobalt SS
Mods - GMS1
23k miles

Issue - Had car on a dyno today. Started a 4th gear pull @ 2500 rpm, and as soon as turbo spooled it starting pinging very loud. I could hear it, everyone around the car could hear it. Let off immediately, and upon checking the dyno graph it was registering a 14.5 afr at the time. So, it sounds like it's starving for fuel...problem is from what? Haven't some people had issues with the CDFP?

This isn't the first time I've heard the ping, however it's not consistent and the dealership has never been able to duplicate it. Got it on video this time though...hopefully it comes through clear enough. Worst case I just drive the **** out of it until it pops.

 

did you disable the ESC? and at that low of an RPM, sounds about normal with GMS1. it richens up later in the rpms

 

ah you did 4th gear pulls no wonder matt dynos so much higher than you I knew there was a reason

/threadjack lol

 

the first pull was a 3rd gear pull then he did a 4th i heard it too also a big puff of black smoke came out of the exhaust when that happened i dont know if you noticed it tom?

 

Actually the clean pulls were in 3rd.

I'm sure my car being 20 ponies shy of other GMS1 cars has something to do with the issue at hand. What did he put down today anyway?

 

I'm sure it is, he put down 286 and 314

 

Hmm...my numbers may not be that far off by comparison, though. He does have CAI, pipes and an i/c, and got me by 27 hp and 20 tq. Still, need to figure out why my car is doing what it's doing.

 

Bump...here's the dyno video with the knocking clearly audible. Any thoughts from the resident experts?

http://s85.photobucket.com/albums/k6...ipt2all007.flv

 

It is definitely pinging. Are you running 93 or 91 octane?

 

91 - it's the best available out here. It has done this while stock as well, albeit very rarely. When it happens, it's always happens at high boost / low-mid rpm.

It's almost as though the fuel pump can't supply enough fuel pressure at lower rpms.

 

do you have a dashhawk or something to datalog this? you can see if you are getting knock and what your afr's are then. maybe its **** gas as well?

 

If it's **** gas, then all the gas in the east valley is ****. This isn't a new issue, just the first time I've been able to get it on video. It has happened with every brand of gas I've tried.

No monitoring to speak of, however the dyno read a 14.5 afr when it started pinging.

 

Getting some real logging would help alot. I wonder what lambda is actually being commanded when it is pinging.

 

sccobaltss has hptuners and can log you shoot him a pm

 

i think the car hits 14 afr stock a lot...

 

Should be whatever lambda that GMS1 commands? There is no custom tuning or any mechanical changes done to the car, so I have problems understanding why this one is having issues when at least two other guys near me have GMS1 with no issues.

I will try to get some HP tuners logs - Cameron only lives a mile away from me...hopefully he's not too busy.

If I recall right, the stock tune commands .95 lambda in the midrange? That's ~13.95, so right around 14. I haven't seen a GMS1 tune yet, so I have no idea if it's supposed to be richened up or not.

 

well I can go log with my dash hawk, but I saw 14's on a dyno at the CED meet. theres so many variables and it depends on sea level and location in the US everyone will experience different stuff. In certain situations id have KR and 14's on my ms3. I just never looked on the ss yet.

 

bump, update?

 

Dropped the car off at Thoroughbred this morning with dyno graphs and video. They better be able to duplicate and tell me what's going on...

Well, the shop guy was able to duplicate the issue while taking it for a drive, so that's a good sign. Now at least I know I won't get the car back till it's fixed.

 

good to hear tom!

 

Ok, so on further review the shop guy said all he could hear was what he called 'mild spark knock'. I went on a 10 mile drive with the guy after work and couldn't replicate it. **** it...just going to drive it till it pops.

 

I have to ask what did they use to get your RPM lead? If they put the little spark plug boot on it... then that is what is causing it...

The gas isn't the issue... you were getting massive misfires... But the 14.5 AFR (at the tailpipe I presume or by the gauge you never clairified) If it's 14.5 at the tailpipe then you are more like a 14.8-9 (which is about normal).... and it richens up as it goes up to about a 12.8 or so at WOT.

The reason I ask is the last time I dyno'd they used a little plug boot (basically sat inbetween the coilpack and the plug and my car did the same thing... untill I noticed it and we pulled it out...

Then make sure you turn off the ESC

 

I wish I could say the dyno was the first time it happened, but this has been an ongoing issue for over a year. And you're saying the car should be running 14.9 under 20 pounds of boost? Even the stock tune only commands 14.0. That said, perhaps it could be a coilpack issue?

Adding fuel to the fire (no pun intended) - last night noticed e-brake level was adjusted. Only took about 1/2 the distance to engage. I'm thinking, 'Cool, maybe they check and adjust this as part of their service routine.'

This morning on my way to work, I notice a grinding noise coming from the rear brakes at parking lot speeds that was definitely not there before. WTF!!!

So far the rotors look clean, but we'll see what happens. Going to lift the car up tonight and look at the rotors / pads to make sure they're not worn(they shouldn't be...looked great last time I rotated the tires), and bring it back tomorrow morning.

 

Well, while my outer rears have maybe a little under half the material left, apparently my inners are pretty much gone. I'm at 24k miles, so for my pads to be worn isn't too surprising, but I'm a little concerned at how uneven the wear is. I know it's a sliding calpier - could it be due to the fact that I don't drive the car very hard? I imagine under harder braking both sides would grip fairly even, but if I do mostly light braking, so perhaps only the inside pads are really working...not enough brake pressure to bring the outsides in fully? Maybe an expert can chime in here and let me know...

Engine ping has yet to resurface, although all they did on Monday was replace my serpent belt because it has some abnormal scoring on it. (may have been like that since day 1...couldn't see anything that would have caused it)

 

There is actually a thread on the site about the rear brakes wearing prematurely. It seems to happen to ALOT of the SS/TCs.