check your connection at the throttle body, they can be finicky and that could be causing those codes.

the ls4 (not lq4, big difference) is worth it on a highly modded car, on something like yours it will just make the throttle real touchy. it also requires tuning to make it work.

the air intake is typical. basicly the mass air flow sensor is calibrated to the size of the tube its in, so they try to make the tube the same diameter so it wont mess with the calibration too much. unfortunately no aftermarket intake works 100% proper on these cars without a tune. that being said, generally it causes the fuel trims to go positive (meaning the pcm is adding fuel), not negative.

the intercooler system having no coolant in it is a big deal. it really needs to function on these cars because the charge temps can get high quite easy (in excess of 200*f). the problem is they arent tuned even from factory to be able to deal with such high charge temps because it has an intercooler system and should almost never exceed 160*f (and thats on a real hot day), and the end result is a lot of knock. now if its out of coolant, it had to go somewhere. the system uses 50/50 mixed dexcool, the stuff leaves white/pink trails, so if its leaking outside the manifold you should be able to spot it. if you find nothing, its likely in the manifold. you may not see it just looking down into the manifold, when i had the o-ring leaking i had to take it off and dump it over before the coolant would come out.

now onto the scan data you have there. o2 sensors, are they moving around fairly rapid? what about when cruising, they should be moving above and below .450v fairly quickly. another thing im interested in is when you get into boost, they should be go rich (above .750 volts). id also be interested to know if it has black smoke out the back when you get into boost. and if you can, let us know what your ltft and stft are doing when cruising.

i have a theory but id like to know a little more info before i toss it out there

 

This is going to cause you a lot of problems.

Your fuel trims are really high but that also is prob from the misfire.

I would figure out the misfire and make sure it holds coolant before driving it any further. Before it causes some permanent damage to the car if it hasn't already. If it were me I would run a compression and leak down check across the board before I went any further. That way I know I have something to work with.

Not trying to come across harsh but if you are only take parts off and cleaning them and then bolting them back on that is really going to do nothing for you.

 

Got treed lol

 

Over 70k has been put on the car with the misfire issue. Compression is a touch over 190 on all cylinders and injectors are flowing good.

The car feels completely fine unless I make it over 8lbs once it reaches 8lbs or so it looses all boost (or shows it at least) and the car begins to rapid misfire.

Car seems a little rich to me, noticeable gas smell, however there is no black smoke when the throttle is blipped. I'm replacing the map sensor near cylinder 1 first. I'm almost positive it's toast, it's also really old, date on it is 2008.

I didn't take stuf apart to just clean it, I took it apart to figure out the issue and didn't find anything that would cause issue besides a dirty sensor.

 

map sensors arent really a failure item, most people are still running their original. generally when they go bad they set a code for open circuit or you will get a maf/map correlation code. the way to tell if its toast would be to drive it with the scan data on and see what its reading. if its eratic or all the sudden drops out when you go past 8psi then it might be worth it to change it.

 

I mean the sensor inside the plastic cone is completely corroded, the plastic is corroded and the o ring gasket is flat and completely solid. It needs to be replaced and seeing as it was already replaced once back when the car was two years old makes me think the sensors do suck. As of now my car is just throwing random codes, I'm nearly positive it has no idea.

 

Also what would make me read such high boost. Nearly positive that 17 psi is a little much for a 3.1" pulley.

 

Is it going into power reduced mode when that happens?
Your issues sound very similar to what I experienced when my TB first started going.
If your scanner can see it, what are the "expected" and "actual" throttle positions doing? In the end mine were drastically different.

If I'd known then what I know now, I would of bought the LS4 TB. Now that I'm better educated about the LS4 swap, I just can't justify replacing a part that's practically brand new now.

Oh, and is your boost gauge glitchy or does it stick? Mine does that so I can never accurately tell what kind of boost I'm making.

 

Boost gauge seems to move fine.

From what I can tell with the cheap scanner I'm borrowing is that throttle position is 18% at idle.

02 voltage jumps around from .2 to .8

Highest IAT so far has been 95*

Seems that a certain point in the throttle triggers the misfire. However I've been codeless for two days now.

 

Also it is not going into power reduced mode.

 

Probably not the same as mine then. I was seeing differences of 5-15% between the expected throttle position and actual throttle position on my friends TechII scanner

 

I still can't get the car to throw a code even going into boost a few times. Only code is p0420, pretty sure this would not effect anything.

 

the p0420 wont cause any issues.

is the car still stumbling/missing? on that scan tool does it show misfire data?

 

Still no codes.

Short term fuel trim looks okay, long term fuel trim looks screwed up, it's -20.7.

Best way to describe my issue is like a dead coil pack, however I can't get it to throw a code and it does misfire under partial throttle.

It does seem to have a point in the throttle that it seems to have this issue, to me it seems that it starts this issue at a certain point, that point is nearly identical every time too.

 

No misfire data. It's just a cheap scanner. I might scoop up a better one tomorrow or something. Car seems fine if I'm just daily driving, getting good gas mileage and everything. Once I reach that certain point I'm doomed from there.

 

if its always happening at the same point, watch the scan data that you have and try and duplicate the problem. see what happens to the o2 sensor, maf, map, etc when it happens. make sure the sensors are moving smoothly (not erratic) and dont drop out or spike. also watch the ltft as your driving. the fuel trim isnt just one value that acts over the whole fuel map, there are seperate trim cells for the whole fuel map. one area (such as idle) might show one value but cruising or light or medium acceleration might be completely different. at heavy throttle the fuel trims wont move around very quickly as the ecm goes into "power enrichment mode". basicly, it in open loop and doesnt refference the o2 sensor for fueling calculations.

-20 is the farthest the ecm can compensate on fuel trims. its trying to remove 20% fuel from its programmed value. im starting to wonder if your car doesnt have the stage 2 tune in it. the stage 2 injectors are roughly 25% larger than stock, now with the ecm being able to pull 20% fuel out you likely wouldnt notice the slight rich condition, and the car would drive fine. however once you go into power enrichment and the o2 sensor and fuel trims arent used for fueling calculations the engine is running 25% more fuel than it should be, and that would cause the misfire/stumbling.

 

It definitely has a tune because it revs 7000 or more. The o2 sensor bank 1 sensor 1 is all over the place from .1 to .9 volts all the time. It's far from steady.

 

as it should be.




Your IAT reading sounds like IAT 1 which is not the one you want to watch. IAT 2 is the reading you want to pay more attention to.

 

I'm about to the point of just buying a coil pack and going down the line until I find the faulty one.

I can't really see it being much, over 125 miles driven, no cel but problem persists.

Like I said it feels like a certain point in the throttle it cuts out. Probably like 1/3 of the way down it starts missing hard. How bad it misses depends on how far past that point I go.

 

Ecotec Parts ZZP High Voltage Coil Packs-LSJ

put those in then. cheaper than a set of stockers and way better

 

I have as set of good working stock coil packs that had 45k on them if you are looking for a cheaper option also. Just throwing that out there.

 

I was looking at the ZZP packs. I noticed them being cheaper as well.

My first guess is cylinder 4 because I can hardly get the thing to clip in on that one, then cylinder 2 has a ACDelco and the rest are no name.

My very best guess right now is a bad TB (less likely, it's only a year old and clean) or a bad coil.

One thing I noticed was for the two days it was running fine it got "31.0" mpg now it says "24.2" and I reset the car both times, so something failed since I've owned it I would say.

 

On a small side note, intercooler pump seems to be working and there is coolant in the lines. I guess it was a little low because the pump was replaced and no one rechecked the level? I barely put any in before it filled up. I'm guessing the best thing to do is keep checking level until the air is out of the system? Either way it seems to be working, so we'll see on that one.

 

I can't wait to get this car fixed so I can start playing with it. The Cobalt is about 20x cheaper than a Focus to mod. Planning on doing a dual pass upgrade at minimum.

 

I've done a little research on MAF readings and believe my MAF is reading much more air than it should be. I'm going to replace the MAF today and see how that goes. If that doesn't work I'll pull the coils and check the resistance.