Stamina

I'm so excited about this that I couldn't wait until tomorrow to report it...

Summary:
Had random erratic AFRs at idle and cruise, causing engine to not idle very well and to stumble while cruising. Unplugged electrical connection to my Evap Purge Solenoid and all AFR and driveability issues went away. Car runs like new compared to what it was. I am very excited.

The background:
I had been having some random erratic AFRs through light to moderate throttle (<800 PSI or so fuel pressure). The car would hold good AFRs and then suddenly swing rich, followed by swinging lean. When it swung lean, you could feel the car lose some power, and in some cases would sometimes stumble. I couldn't tell any rhime or reason to it. At moderate throttle and above (>800PSI fuel pressure), the car would stick around stoich like glue.

I took it in to the dealer and they said that it wasn't anything they hadn't seen before. I wasn't convinced, so I had them write up a report on it to have on file anyway.

I had been in touch with Gettinausernamesucks and More_Torque_More_HP, exchanging ideas on possibilities. I had changed the wideband O2 sensor in the exhaust housing of the turbo and still had the issue.

Finally More_Torque_More_HP mentioned the possibility of the Evap Purge Solenoid having an issue, as they had some field problems with them going bad. Well after troubleshooting other things first and not finding any solutions, I flipped back and found that PM and tried disconnecting the electrical connection to the solenoid tonight.

The results:
The car now runs like it did when it was new. Driveability is much improved. Gobs of power and response are back. AFRs are spot-on in idle, cruise, and WOT (found out that the tune I've got is actually a ~12.2 tune... sorry BYT/T2...guess I better get to asking for a revision).

I can't believe the problem is gone. I have been stressing over it for so long now.

So now with that said, I'm faced with where to go from here. I'm guessing my purge solenoid went bad at some point, but it never tripped a CEL. Speaking of which, since disconnecting it, I still haven't gotten a CEL like I thought I would. Perhaps it'll take more key cycles or me filling up the tank again.

06_ion2

Interesting, maybe you have a clog in the evap line?

mongorat427

iTrader: (82)

Where is the connector located ?

BYT*SS*TURBO

iTrader: (6)

Do you have an intake on the car?

And no sweat on the AFR, that line gave me a chuckle tho LOL!

Stamina

The solenoid is on the front edge of the intake manifold, in the middle.

I marked it in this picture. I simply disconnected the electrical connector on the backside of it.



Nope. No intake. Just a K&N drop-in.

The pic above is my engine bay currently. Maybe I'll fill out the backside of the bay a little more in the future.

The interesting thing about this was that when logging with HPT, it would show up as crazy STFTs, randomly and suddenly going up to 25% one way and then another and looking like a reducing sine wave as the ECU found its mark again.

Iam Broke

iTrader: (10)

Might be why I get a random LTFT shift that I could never attribute to anything else after about 30 mins of driving. If I see it happen again, I'll try it.

BYT*SS*TURBO

iTrader: (6)

Hmm. Ive never seen it do anything like that with the STFT's, thanks for the tip tho if I come across it

Iam Broke

iTrader: (10)

Never 25 %, but I've seen 4-5% for no good reason steady state. Could be the purge sol. hanging up I guess.

Terminator2

I tried disconnecting mine to see if it makes in difference in the idle on my car. It is rough at idle sometimes for no apparent reason.

buellfooll

THIS is why I like Cobalt SS Forum!

HHRSSouth

Interesting, so what were you suppose to be originally tuned for, 12.8?

Terminator2

He thought it was 12.8 A/F.

Stamina

Update:
On the cold start this morning, the CEL for it being disconnected finally popped up. Low and mid throttle are much more responsive and have better kick to them.

When I disconnected the power to the solenoid, I basically made it to where it stays closed. The ECU sends power to the solenoid to open the valve inside it. Although it fixed the problem, it doesn't necessarily mean that the solenoid itself is the issue. I basically just eliminated the whole Evap System variable. What is wrong with the system exactly is what I need to troubleshoot now. It's probably the charcoal canister is clogged somehow or the solenoid isn't opening/closing correctly. I'll continue looking into it as I have time and will post up any findings.

It's just interesting that the GM Engineer mentioned that there were sometimes field problems with the solenoids.

Yeah, I had a 12.2, and thought my new one was 12.8, but verified it last night as being 12.2. Now that my AFR needle is steadier it's much easier to read a consistant AFR.

I may try and see if Vince can't whip me up something custom. With the car running the way it is and feeling as strong as it does now, I'm much more confident about everything.

Terminator2

I can diable the code if necessary. If it makes the car runs smoother it will make me happy.

Stamina

It runs much smoother. Cold starts are a little weird though as I found out this morning.

It kept the fuel pressure at normal pressures and instead raised RPM to ~1500 RPM or so to get through the cat warm up as opposed to keeping it around say ~1300 RPM. I still heard the turbo make the typical cold start sounds and everything else seemed normal. Once the cat warm up was completed, it was is a happy camper.

Another Update:
I contacted my dealer. I'm going to be getting it in to be looked at next week. They said that GM tends to not let them fix things without a CEL of some sort, but when I mentioned the stumbling/possible knock when it swings lean, that seemed to be much more receptive to getting it in. I may take my coorespondence from More_Torque_More_HP with me to help make my case.

pantherqs

Bad idea is bad, check your long term fuel trims with that unhooked.

Stamina

Have you done this on this car and experienced LTFT issues?

I've researched the topic and have been told by both the GM Engineer involved in the development of this vehicle and engine, and a service advisor that it'd be perfectly fine to drive with it like that for an indefinite amount of time and actually advised separately by both to do it (the advisor even started to offer to turn off the code off the record ). I've seen no adverse fuel trims yet either. If anything, the trims should be much better as I've been told the ECU does not take purges into account (the whole reason for my problem to begin with in a way).

That being said, I'd like to be able to remain "emissions friendly", and I'm looking into getting whatever it is in the system corrected so I can have everything hooked back up as normal. Thanks for the input. If anything turns up, I'll post it up.

Berto09ss

does anyone else have these issues??
i never had

does anyone else have these issues??

Stamina

Apparently not too many, as I've asked around for some time and never found anybody that had noticed anything similar until just recently. That's why I went to the engineers to begin with.

A couple weeks ago we got an RPD installed on a friend of mine's TC. He started noticing the same swings with his AFRs and then an Evap CEL followed not too long after. That was the last clue along with what the engineers told me that brought everything full circle.

He also tried disconnecting his solenoid today and the random erratic AFR deviations went away. His is probably the solenoid, due to the CEL backing that up. I'm not sure what mine could be yet. It's going into the dealer next week probably so we'll see what comes of it.

pantherqs

As a matter of fact, I did just that a short bit ago. I also had most of the issues you described, but mine ended up being the HPFP crapping out and purge solenoid as well. A few tuners and myself are trying to diagnose the cause of our rpd wideband data shitting itself and our trims automagically disappearing while throwing a phantom p2237 code over on the HPT forums. The same thing happens when the evap plug is pulled, ltft's are reset to 0, however on my 07 ecu they will not go back to normal until evap is hooked back up and code is reset. You're essentially leaning the car out if your ltft's hovered in the positives, which would account for the "extra power" you're feeling. So basically, if your ecu is the same as mine, and your trim's do reset to 0 and no longer adjust, the dealer and whoever else told you that it's perfectly fine to drive around like that should probably get into a new line of work. Just some food for thought

efactor

iTrader: (2)

thanks for the post, I needed that. I posted a forum with the error code P0497. It happened to me, when me and two other guys were aiming the HID's on the Gen4's. I heard this loud funny noise like something sounded like a loud blending machine like if it was scratching on something, then it went away. It kind of freaked me out, so I took it to AdvanceAutoParts to get a code reader to see if I had any error codes and its popped up with "P0497" which had something related to do with EVAP solenoid being at fault. The guy at the dealer said its not a big issue, it won't harm the car or affect its performance just you won't pass inspection. So they looked at it and said the error for it went away 200 cycles ago and its acting normal. They order me an insulator which I haven't heard anything yet, which it suppose to stop the engine from rattling.

1Rare4Door

Don't know if I am having the same issue but when I first start up in the morning and the car runs through its warmup cycle and the engine reaches only 85 degrees or so the idle is kind of rough until it reaches normal operating temp. Once warm it still seems to idle a little rougher than when I first got the car. Don't have any codes. Also tach doesn't just around any more than usual it like the idle vibrates the car harder.

Terminator2

My car does the same exact thing.

Tofu

Mine also. So much so that it's my daily routine to simply let it reach near normal operating temp before I drive it. If I cold start the car and immediately drive off, she gets angry.

Stamina

That's what was happening to me too.