I have a 2009 Cobalt SS with around 44K miles on it. Over the winter the battery went dead, so I replaced it with a Die Hard Platinum and thought all was well. It takes a couple of days after I reconnect the battery and it starts acting weird (stumbling at highway speed(RPD shows the HP and TQ all over the place +/- 20), ECU seems like its giving a lot of extra gas when I let off the clutch resulting in 2K engine RPM when starting in first among weird feeling shifts.

I originally got:
P0300 Random Misfire
P0301 Cylinder 1 misfire
P0303 Cylinder 3 misfire
P2261 Bypass valve stuck open (I have a Forge BPV I haven't greased I 3 years, coincidence?)

I replaced the plugs, no change (they looked normal, no damage, and all looked uniform), I swapped cylinder 3 and 4 coil pack, no change, changed the Evap purge solenoid, no change. I finally disconnected the battery and the random misfires mostly went away on cylinder 1 and 3 on my Solus Pro. I thought everything was good until a couple days of driving and it goes back to being weird.

I just replaced yesterday the Evap Purge and Vent Solenoids. I thought it ran better, but it still does the same thing. After changing them I got a couple of codes but didn't write them down (one was about the throttle body). I just pulled the positive battery cable again, figuring the ECU needs to relearn again. After disconnecting the battery and reconnecting it, it took like 10 seconds of cranking for the car to start, that seems odd(this happened when I put in the new battery, but not when I disconnected the battery for the misfire after the spark plug change)?

I found, by chance the incoming fuel line to the regulator or HPFP turned 180 degrees and bent at 90 degrees. I have absolutely no idea how the motor ran. I was able to strong arm the fuel hose the way it should be, it appears its been like this since I purchased it new off the showroom floor, it was starting to wear through the outside jacket. Maybe it ran lean and i have engine damage?



Do I need to just buy a boroscope and see if my valves are all coked? I pulled my charge pipe from the turbo going to the intercooler and it was clean as a whistle.

Mods list since it might help:
K&N SRI
Forge BPV
ZZP Charge Pipes/Intercooler(might be worth while to test for leaks?)
GM Stage 1 with crimped connectors installed by a local stealership
Purchased the Powell PCV oil separator but have not installed yet

I am out of ideas and I have spent hours looking though threads. I thought I had something with the Evap Purge/vent solenoid but apparently not.

I am not even bothering with the local stealership, when I took it in for P0236 and told them they needed to solder my crimped on connectors for the MAP sensors they replaced for GM Stage 1, they told me to pound sand and my SRI was causing the issue.

Any insight would be greatly appreciated.

 

just wow! I would borescope the valves to be sure they are okay. Get the pcv Upgrade on asap. I would solder those crimped connections asap. And really a tech 2 scan would save you a lot of time with diagnostics. good luck.

 

What makes the tech 2 scan so great (besides it being a proprietary GM scan tool)? The Snap On Solus Pro seems like it has a lot of options.

I have been planning on soldering the MAP sensors for a while now. The one on the intake seems easy. How would you do the one that connects to the intercooler piping? I had a hard enough time trying to get my arm in to remove the MAP sensor much less trying to solder.

 

Agreed. And don't forget to buy a new PCV to replace the old one while youre there.

I doubt it would run any leaner than the stock and GM Stage 1 tune from that, now if you tried running e85 you probably couldnt supply it with enough fuel.

Also get a leak down test performed.

 

Tripping the bypass code and having the bypass stuck open or closed would easily cause this. I would address that first.

 

I hear the bypass valve opening and closing normally, when the car starts acting weird, I hear it open every second or I hear the famous flutter. I'll have to grease it regardless.

Keep the ideas coming.

 

It threw a code for the bypass valve sticking. LISTEN to what people have to say. Take off your intake and grease it, it's obviously dry and sticking after three years WHICH will throw a bpv code and resulting misfires as your ecu is saying "Maintain your car, I don't know wtf is happening"

Then once that is done, disconnect battery for a 30 minutes and restart. Then go for a drive and see if any other codes come up.

Good luck.

 

If ur bypass valve is opening and closing at highway speed then the most likely culprit is ur vacuum tank. Mine did this sometimes at higher gear boosting up to 15 psi the bpv would open and car would stumble and not go past 15 psi. I bypassed vacuum tank and it was fixed. Plug ur bpv solinoid bottom port directly to manifold. Unplugging the line that now goes to manifold, which is the line to the vacuum tank, and bottom of solinoid is also to vacuum tank. So ya unhook line that plugs into manifold and plug bottom of bpv solinoid directly to manifold. If all works, ur vacuum tank is bad, if it still does it, plug bpv directly to manifold, if that fixes it, ur solinoid is bad. Hope u understand that lol

 

Say that again in USA English lol

 

im Canadian. me no speak usa English. he will figure it out

 

I have the stock BPV...............and I've never had to grease it.

 

Took the Forge BPV valve out, moved freely and wasn't binding, greased it anyways. Reinstalled it without disconnecting the battery drove it around and it just fluttered and the car made no boost. Took it out again and checked it over... all gaskets were in place so reinstalled it and disconnected the battery. Car now runs normal until it reaches 195 and then acts weird for about 5 seconds. The car will act normal the rest of my 30 mile commute.

I have noticed that each trip I make with the car, the car acts weirder longer. Yesterday was the worst were it acted up multiple times. This would be its 8th drive cycle since reconnecting the battery.

I wish this was completely random, so then I would be like it has to be coked intake valves and I would have to clean them.

No CEL yet. I'll have to borrow a boroscope from work to look at the valves next or maybe just bite the bullet and do it.

 

did u bypass the bpv solenoid and vacuum tank to see if they caused this?

 

I have not, but this isn't only isolated to highway speed anymore, if that makes a difference. Yesterday I started the car, drove a mile and got stopped by a train, turned the car off since it took around 20 minutes. Upon restarting it, car didn't want to do anything when I pressed on the gas.

 

weird. well try that anyway and see if ur bpv issue is fixed, at least u can get that out of the way. mine behaved just like urs did with the bpv when my vac tank was bad.