Sputtering/missing under load, hesitation...WTF?

[dbtk2]

So, I completed my topend swap and proceded to break in my cam.  I know the computer will need some work for the car to run properly, and I plan on getting this done, however what its doing now doesn't seem like a computer tuning problem.  After I got done with breaking in the cam I took the car for a drive, but I have a problem.  When I step on the gas, the car hesistates, sometimes the revs even drop, and then its starts going.  Sometimes from a stop or from idle in park/neutral it will stall.  If I press on the gas hard enough to get boost in gear it just sputters and has a hard time accelerating.  I also noticed this evening that when this happens black smoke is pouring out the back, so obviously the car is running rich...very rich.  The computer sees the problem, whatever it is, because it has pulled all the boost and now I see a whopping 3psi under WOT.  The car runs smooth at idle and doesn't miss, and at 75mph highway crusing I don't feel a miss either.

So I know the problem is that the car is running rich...thats mostlikely why it hesitates and misses, however what is causing it to do so.  I am thinking of 3 things.  It hasn't thrown any codes at all (not even the EGR code, and there is no EGR on the car anymroe, so that worries me a little).

Maybe the 02 sensor is bad?  I unplugged the 02 sensor and it made absolutely no difference at all, so I don't know if that means it is good or bad.  I was told when you unplug it the computer will run off "default values", but if its bad will it do the same thing?  I would think that with it as rich as it is, the 02 sensor would set off a rich exhaust code at least.  

Maybe the TPS is bad or something.  I know it works somewhat, because I unplugged it and the car revved up a lot more, the SES light came on, etc....  So its working a little, but maybe its not reading completely accurate or something?

The last thing is the fuel injectors.  They are stock LT1 fuel injectors, which I was told are 24lb/hr (not sure if its true, but thats what I was told by numerous people).  They looked identical to what was already on the car, but I was told they could be a different kind of injectors, like multec or something, and those don't work right with our computers.  Maybe thats the problem?  Would that cause it to run like that?

Any ideas or suggestions would be appreciated.

Thanks,

Shawn

[skalor]

I would check the vacuum line to the MAP sensor as what your describing is kinda what my turbo lumina did when I did the swap.  Turns out the hard plastic line was cracked.  I don't know what kind line the 3X00 topend uses for the MAP so I could be wrong.

It could also be the injectors, but I would find out exactly how many lb/hr they are.  I thought there were guys here running 24 lb Accel injectors with no problems?!?

[dbtk2]

All of the vacuum lines look good.  That was the first thing I checked because it kind of acts like a vacuum leak.  It has 21 in. of vacuum at idle, so I'm thinking there isn't a leak.  It only had 18 in. of vacuum before the swap...  I will check again, thanks for the suggestion, but I don't think thats it.

Shawn

[RareGMFan]

All of the vacuum lines look good.  That was the first thing I checked because it kind of acts like a vacuum leak.  It has 21 in. of vacuum at idle, so I'm thinking there isn't a leak.  It only had 18 in. of vacuum before the swap...  I will check again, thanks for the suggestion, but I don't think thats it.

Stupid question, but I need to know (because I need to check this on my own car).  How did you check the ammount of vacuum at idle?  I know you need a pressure gauge, but what do you hook it up to to get the reading?

[sleeperred90tgp]

All of the vacuum lines look good.  That was the first thing I checked because it kind of acts like a vacuum leak.  It has 21 in. of vacuum at idle, so I'm thinking there isn't a leak.  It only had 18 in. of vacuum before the swap...  I will check again, thanks for the suggestion, but I don't think thats it.

Stupid question, but I need to know (because I need to check this on my own car).  How did you check the ammount of vacuum at idle?  I know you need a pressure gauge, but what do you hook it up to to get the reading?

Use the line that comes off the manifold for the modulator as a base line. Then check each line seperatly where they terminate. They should match.

Jud

[dbtk2]

Well I fabbed up a new EGR block off plate, as I found that to be the culprit of my hesitation when I pulled in the driveway today and heard a high pitch squealing noise coming from the plate that was there.  So I put the new EGR plate on and put my stock injectors back in the car.  Started her up and no hesitation anymore.  Didn't notice any more vacuum at idle.  It seemed to run a lot smoother through the RPM band, but I couldn't tell if it was running as rich as it was before because its dark out now.  (before black smoke would pour out)  I noticed a slight miss between 1-2k but that might be fouled plugs.  Well anyhow, the car is running smoothly now, but still is only getting 3psi boost.  I don't understand that.  Does the computer go into some sort of limp mode if a sensor is unplugged?  Would the unplugged EGR cause it to do this?  I'm still really confused.

Shawn

[skalor]

The stock wastegate actuator is supposedly ~4 psi, but it could be lower as the spring in the actuator will fatigue over time.  I would look into the wastegate control solenoid.  It would seem that the wastegate actuator is getting full manifold vacuum all of the time, which would keep the wastegate open so that you only get ~4 psi (or less like I stated above).  Do you have the vacuum lines for the wastegate actuator hooked up correctly?

I don't know if the EGR being disconnected could limit the boost.  I have not seen anything on the chip that would leave me to believe that it could limit boost, but I don't know how the chip incorporates the 'limp home' mode, or even when it's enabled.