spooneralmighty

Well guys I have an 06 gto that if your cruising it will start to miss and at WOT it will clear up and run perfectly.... almost like it is loading up at low RPM

Car has kind of always done it since i got it.

The car has long tube headers, catless extensions, SLP Predator diablo tuner, and vararam.and 02 extenders

So far I seafoamed the motor, replaced the upper o2 sensors, replaced the spark plugs, replaced the spark plug wires, sprayed the injectors down with carb cleaner, and cleaned the fuel rail, sprayed the MAF sensor with cleaner, and took the intake off and cleaned it and put new seals on it.

The car was sitting for a while before i bought it.

I also had to plug the 02 extenders in backwards to make them fit on the car. They wouldn't slide into the groves if you tried to plug them in correctly. But they were for the 4 wire sensors. (plugs were zip tied together so they wouldn't come loose)...just dont want to leave out any details

Could the 02 extenders being too long cause this? could it be a bad MAF sensor? Like i said under WOT it doesn't skip a beat. HIgh RPM it runs awesome. Could it be the predator diablo?

The only other thing i was thinking is to move the breather hose that hoes to the cold air intake. Maybe it is somehow sucking air through there? I sprayed the port where it goes into the coupler with carb cleaner and the rpm's didn't jump at all. I'm thinking about removing it from that coupler to the actual vararam tray and venting it to atmosphere, and then replacing that coupler with one that doesn't have a hole.

Last night I removed the Predator and returned the orginal back up to the car. I also unhooked the neg battery terminal for about a min to try to reset the computer.

Just very nerve racking because I cant seem to figure this miss out and I feel like I have tried everything

When I changed the o2 sensors the misfire went away for about a week. then progressively got worse again. Thinking of maybe pulling the extensions off and just adding 6'' of wire to my o2 sensor.

Youngblood16

Sounds like a bad maf sensor to me. You can try cleaning a maf with that spray **** all you want but it usually wont do much. Imagine trying to clean a window by spraying windex on it and not wiping it off... that's whats happening. Yet you cant touch the maf sensors "strings" so wiping it clean isn't an option. I would say try a new maf.

spooneralmighty

Had it plugged in and looked at data. A few misfires across the boards. Saved in the computer. 2957 misfires number 7 cylinder. All other cylinders weren't even 50. Seems fuel related.

At least I got it kind of narrowed down.

Leaning towards a bad injector. Reading up it seems like a bad coil would be a more consistent miss. And an injector would be more random. The car did sit for 4 years.

Might be time for a set of injectors

joecar

Try swapping injectors between #7 and #1 and see if the misfire counts follow the injector or not.

if not, then swap coils and see if misfire follows or not.

Ed Wright

iTrader: (1)

Don't go out and buy a MAF. it won't cause a misfire. Dirty will cause high fuel trim numbers. Spray it until those tiny wires are shiney again, shake out the excess (do NOT blow it dry with compressed air?) is all it takes. That is all K&N air filters are good for. Don't run one bit faster. Just dirty MAFs.
#7 could have a broken valve spring or a leaky valve also. If you have no other way to test parts, swapping them between that cylinder with a good cylinder as already mentioned is a good method.

ctd

iTrader: (1)

Is it possible to have an intermittent leaky valve? I understand the broken valve spring & that can come & go but you can see it if you take it apart. How would you diagnose an intermittent leaky valve if compression & leak down tests don't show a problem?

joecar

Were compresssion and leakdown tests done...?

Ed Wright

iTrader: (1)

Could not be leaking enough to miss bad enough every time for the misfire monitor to show it up. If you have a sensitive vacuum gauge, if you do this enough you can recognize a leaky valve there. The needle will fluctuate some with any misfire on a sensitive gauge, but more so and look different with a leaky valve. Hope you find it.

ctd

iTrader: (1)

That makes perfect sense....... is it possible for a leaking valve to be intermittent in this condition?

Ed Wright

iTrader: (1)

The valve could not be leaking bad enough for the PCM to catch every misfire everytime.

Youngblood16

Ive had a maf cause misses before, yet it was so extreme it barely ran. he never originially stated cylinder 7 had that many more misses than the other, I was just going off of a random miss. These injectors dont usually go bad, but they can.

Youngblood16

Just pointing it out, a leaky intake/exhaust valve would not be altered by changing the o2 sensors which was stated in the original post

Youngblood16

Should be something on the electronical/ computer controlled side

Ed Wright

iTrader: (1)

Here is what he said: "Had it plugged in and looked at data. A few misfires across the boards. Saved in the computer. 2957 misfires number 7 cylinder. All other cylinders weren't even 50. Seems fuel related."

Looks like #7 is missing to me. Not sure why it "seems fuel related", but I wasn't there. I have never personally seen an injector cause a misfire unless it was extremenly dirty. Heard of it, just never had one come in my shop that had actually failed.

gagliano7

I had a similar problem on my truck and it ended up being a bad coil. Part throttle was rough but wot was fine. Should be pretty easy to check. The way I found it was using an infrared temp gun and I checked the temp of each exhaust primary and found cylinder 8 was running quite a bit cooler than the rest.

Justhereforinfo

iTrader: (2)

My tuner fixed my p0300 in seconds.

joecar

Did he disable the misfires, or did he adjust the limit counts...?

You make no reference to your mods (cam, valvetrain, etc...) so we don't know what you got.

Ed Wright

iTrader: (1)

Getting rid of the code, and fixing #7 cylinder are two different things. LOL

Youngblood16

I understand that he says it is the number 7 cylinder missing. HOWEVER. if you notice he put that in post #3, after my post, which was number 2. In the 1st post of this thread, which was all the info i had to go on for my first post(aka #2 of the thread), It was a random miss.

SUMMARY: I know its not a maf if its a single cylinder miss. ***THAT WAS NOT ORIGINALLY MENTIONED IN THE FIRST POST THOUGH***.
I dont mean to sound aggressive im just clarifying.

Free bump any new info OP?

I would try a coil swap and see if the misfire moves.

Ed Wright

iTrader: (1)

The random misfire code (P0300) means that misfire (in this case #7) is random ie: it does not misfire every time. It does not neccessarily mean random cylinders are misfiring. The misfire is random. When you see misfires as high as #7, that cylinder has a problem.
P0307 would mean that #7 is dead, misfires every time.