Well for the past like 8k miles, I have been misfiring in 4th or 5th gear when lightly accelerating to catch up to traffic. Couldnt figure out what it was, I replaced spark plugs, checked gaps, everything. Never threw a check engine light as it only did it for a few seconds, when i let off the throttle, got back on it, it usually went away. One day it did it real bad however and I threw 3 codes, misfire cylinder 2, 4, and random all cylinder misfire codes.

On the way to carquest today for unrelated stuff, I had an appiffony (cant spell that one) and thought maybe its my throttle body sticking. Maybe it just needs to be cleaned. SS/SC cobalts have alot of problems with throttle bodies getting dirty, I did have a Dejon Intake on my car in the past and charge pipes, and a BOV and all.

That would explain the misfires at only low acceleration. under WOT, it performs fine, but at 10% throttle it occasionaly misfires. Maybe it gets stuck at idle position, i hit the gas, it adds more fuel, but cant get more oxygen causing an all cylinder misfire untill i get off the gas, and hit it again where it breaks free and opens all the way and performs normally. I believe the gearing of the misfires is unrelated b/c light acceleration in 2nd and 3rd you usually give more gas then you would in 5th when your just barely accelerating, where I run into my problems. I ran countless fuel injector cleaner through my car, still having problems. Dealer replaced my ECU, still problems. What do you think as this being the issue? I felt like House from the TV show

 

I noticed this too but it seems to happen only after a reflash for me.

What gas are you using also? If I run Sunoco, I get a lot of cruise KR where with Shell I get 0KR at all times!!

 

I like Shell in my car as well. To the OP you can get rid of those part throttle misfires by carefully tuning your MAF tables and sometimes adding a little spark advance in the part throttle areas helps as long as you are seeing no knock. Misfires are caused by either running too lean or too rich, depending on timing as well. I get a few misfires for a while after I reflash my car but they go away as my car relearns.

 

but how would this expain me misfiring like this with all of my stock parts back on, stock intake, CP, DP, ECU. everything

 

why did u put every thing back on???

 

cause i was having all sorts of problems and took it to 2 different dealers. was just easier for them this way. dealers near me are a pain in the ass about mods. one popped my hood when i was back to stock, saw wiring for my gen 2 headlights and went "wow this thing is modified"

 

Stock airfilter? I know it sounds funny but the drop in K&Ns cause about as much MAF skew as most intakes do. Stock plugs? Have you checked them lately?

 

When you returned to stock parts I assume you flashed back to stock? Did you do a write entire?

 

He has two different ECMs one tuned, one with the stock tune.

 

stock air filter, only thing i am missing is the snorkel that goes behind the passenger headlight. i left that off for ease of install.

^correct. havent had the hp tuned one in, in god i cant even remember how long

 

Any WOT misfires, smoking, and have you checked all your plugs for oil?

 

2nd set of OEM plugs and they have been in for about 2k miles. no smoke, no funny smells, no oil on plugs. cleaned with brake parts cleaner and reinstalled, misfires continued. Checked gap, gap was fine. like i said i ran fuel injector cleaner through the car, recently had my high pressure fuel pump replaced so thats not an issue

 

Wow that is a tough one. I would say log the injector pulse widths for all 4 cylinders and see if one is not spraying as long as the others or sticking open.

 

im tellin ya lol. im hoping its the throttle body

 

Are you getting anything other than misfire codes?

 

rear O2 sensor low voltage/stuck lean. thats getting looked at today. believe its from my catless Downpipe with no O2 bung i ordered, didnt know i could easily disconnect the O2 sensor so i taped it up under the car against the frame. imagine that caused it to go bad and need replacing

 

It is from the catless DP. Rear O2 does not matter as it determines only whether the cat is functioning properly or not.

 

when i said its getting looked at i mean there gonna replace the rear O2 sensor since i need an inspection adn i need the CEL off

 

Ok. Should not cause those misfires though. These cars misfire so easily even the slightest disruption in air or fuel delivery will cause misfires. Too rich for a second, too lean for a second, and cam angle changes (especially in the mid load range) can often produce misfires as well. Has the car had a cold compression test done yet?

 

no not yet. explain please

 

Taping it up there is what caused the code. It wouldn't cause it to go bad. The rear o2 sensor needs something other than pure air, or it triggers a code - thats why most of the catless downpipes move it out of the air stream but don't seal it off.. Positioned like that, it still reads a bit other than pure air, which fools it into thinking the cat is functioning. When its in open air, it reads super lean, which triggers the code.

 

got car back today and CEL's are gone and after the long drive home nothing popped back up. Thank god. feels good to have my car back and not need to make any more service appointments. They replaced both O2 sensors, pre cat and post cat. they said there was ALOT of carbon buildup on both the sensors, including the wideband sensor. Now i just gotta drive this bitch and hope misfires are gone. they also said to just get gas at shell for awhile and see if the misfires go away. they said shell is the only "GM approved" gas in my area

 

Well it sounds like the Front O2 sensor was causing your issues. It was improperly reading the A/F mixture so the car was probably running richer than the ECM thought. Either that or the excess carbon buildup is from being tuned too rich at WOT. What does your A/F read at WOT on your interceptor? Stock tune and other tune. Should be 14.0-12.9 stock and I dunno tuned.

 

I was hoping our cars won't have throttle sensors going out. Because that happend in my 03 Neon SRT-4 that drove me insane with misfires and causing my car to accelerate up and down without putting the foot on the gas pedal. I'm glad you got your car fixed Gestople007. Too bad I can't make it for the meet this upcoming Wednesday because of an event going on at work. Last Wednesday was a crappy, weather storm, and I didn't want to take the risk of wrecking my car. Saving my money on that Stage 1 from GM.

 

I think I just lost my front O2 as well. Reading really irratic during cruise but seems ok WOT.