I posted previously that a battery replacement got rid of them, but they're back! The misfires range from a few hiccups to many misfires followed by a huge cloud of black smoke out the exhaust when wot through a gear at 15+ psi.

Getting random misfire, and cylinder 1,3,4 misfire codes (p0300, p0301,3,4)

Changed the plugs, switched around the coil packs, changed the front o2 sensor, cleaned maf and maps, cleaned cam position sensor(oil was leaking), ran two gallons of boiling distilled water through intake at 2000 rpm, ran sensor tests in torque android app and all is well, watched sensor outputs with torque log function and they look good. Haven't done compression test. Ruled out the tune by installing an old tune (that worked flawlessly prior to dealership engine rebuild) and get the misfires.

Only happens at 15+ psi and wot. Idle, part throttle boosting is good!

The weird pattern: They go away for a while by disconnecting the negative on battery and resetting ecu.
[/B] Disconnected leads to put in new battery and no misfires for a while, disconnected negative after installing o2 sensor and no misfires for a while...runs great and pulls hard when no misfires!

What is going on? My best guess is some sort of grounding issue.

 

Spark dwell insufficient, plug gap too large.

Also clarify the boiling water thru intake manifold comment?

 

Yeah I've never heard of putting boiling water through an intake, let alone 2 gallons

 

Grounding issue wouldn't go away and come back like, but do check and make sure your ground strap to the valve cover is attached.

I'd suggest having the car re-tuned, you need to log the car and see at what point it's starting to misfire. It may be as the fuel trims come back in line it's having problems, and when you reset them by disconnecting the battery they are ok for a bit. Impossible to guess without seeing the data though. Find someone with HPT who can log the car for you at least.

 

Only time i ever saw water through the intake was a very old school way of cleaning/decarbonizing a combustion chamber. Most ever put through though was a small 6oz coke bottle full and that was on a v8. Not sure I'd try it on a modern 4 cylinder. Might also be that he was hoping to remove any oil deposits in the intake.

 

But at 2k rpm?

 

As another stated, old school method of cleaning carbon; boiling water more likely to turn to steam/more energy and cleans better. Sucked through vacuum line on im, lots of bluish smoke out exhaust. Previously would run a gallon room temperature as a pre-cleaning prior to seafoam. Never danger to teh manifold.

I understand trims wacky or plug gap, but last night when they first began to reappear after a reset, I pulled from first to fourth to a few hiccups in first and then the rest of pull clean. I know it far fetched, but I can't help but imagine some kind of charge building up that skews sensor readings, or loose connection, maybe something grounding. I'm gonna clean grounds and zip tie the harness a bit, God willing...

I was so happy yesterday when i installed o2, reset ecu, and they were gone! To celebrate I finally did the side exit I always wanted (catless dp to big oval tip-glasspack combo). Drove around all day no probs, then when going home it starts misfiring.

 

We need to see your fuel rail pressure and you need to run that compression test.

 

Sounds like similar symptoms to the ones my car had... after having all ignition coils, maf sensor, and all plugs (that one out of pocket) replaced under warranty, they ended up doing a compression/leakdown test and it failed miserably.

Ended up being a cracked piston ring, it's in the shop for the issue right now under warranty (which you should still have)...

And it all started with a misfire while shifting at WOT...

 

Yes, I need to do compression test.

I have trifecta e47 tune, only way to datalog fuel pressure is via torque. I tried to share file once and couldn't get it to work. Advice

I grounded the engine in five additional places, zip tied a bunch of harness, tightened my freakin subframe bolts due to creakin noise(Midway Chevy is garbage, never get service/ warranty work from them). I reset ecu again today and no misfires. Shut car off for a 4-5 hours and wot misfires again, but they seem to be more consistent and not as random: I get two brief misfires at wot throttle between 3k-4k rpms and then it pulls nice. I'm beginning to think it's the tune.

 

Here is screenshot of fuel pressure from torque, wot roll on in 2nd gear from 2k-redline:



Car wants to misfire like crazy for first 10-20 minutes of driving; ogged a few misfires on cylinders 1-3, but 26 on cylinder 4. Then once car is good and warm give a couple of misfires while boost ramping up and pulls clean. Both short and long term fuel trims 0.78%.

 

Fuel rail pressure is there, so now for the compression test. That will tell you if you have a broken piston ringland or possibly coked-up valves. Considering it is multiple cylinders, I'd guess coked-up valves.

 

Trifecta got back to me on logs, Steve said: "I took a look at your logs. It looks like injector misfire, but not due to incorrect fueling. Your injectors just cut out completely (all the way down to 0ms/closed) for a single frame then resume normal operation as if nothing happened."

I remember getting 2 misfires as boost was climbing in the torque screenshot, you can see two flat spots as the boost is ramping.

I reset ecu, starting getting misfires again and all were logged on cylinder #4. Me thinks #4 injector is bad!

 

Could be a rail pressure sensor, if you had an injector failing the pressure would be rising not falling.

Or an HPFP problem, not uncommon.

 

This is true, pressure would rise

Last driving cycle 11 misfires on #4, 0 on others makes me think the injector.

Please advise if you know of a way to pinpoint the problem.

Thanks

 

Compression test now. Then I I'd say failing fuel pump or injectors. Btw, what model is your car and have you ever replaced your injector seals with e85 compatible ones?

 

Need to buy a compression tester.

I have an '08 SS/TC. I'm replacing #4 injector and new black seals on all injectors this weekend.

 

Being an 08 you should be still under power train warranty for a month or two... I'd have the dealer do it for free...

 

What was the outcome of this? Im having 2nd gear misfire through rpm at wot. 2009 SS Sedan stock with GMS1

 

Took off intake manifold, cleaned valves, replaced injector #4 and problem solved!

 

Hmmm because I've cleaned my valves and swapped coils and plugs and still get a misfire at WOT in third gear. The dealer ran compression and said it was fine and that they couldn't find anything wrong. Only cylinder 1 will misfire so that leaves the injector like you had or a magic random valve problem. I'm guessing the former.

 

Just bought my SS a few days ago and dealership (Not a GM dealership) said they replaced the plugs. \

Well i pulled the plugs and checked the gap they were at .60 WTH!!! I changed the gapping to .32 like ive seen all over this site. I also noticed the bottom MAP sensor was not flush with the cold side CP so I fixed that issue as well. Started the car and took her for a drive and no more misfire!

So glad I got this fixed!

 

Congrats! Good to hear you got her fixed!

 

actually today I went out for drive out what it still had a slight misfireso I went and bought a can of seafoam and ran it through the vacuum line and now the misfire is gone

 

Think you are calling it to soon. Give it about a week then say its gone