2019 1.5L sputterin

[offtheglass21]

This is at idle. Everywhere I have read it states it should be at around 440 psi

 

[PoManNox]

This is at idle. Everywhere I have read it states it should be at around 440 psi

Is your problem at idle or at speed?

 

[offtheglass21]

Is your problem at idle or at speed?

At speed if it happens it is not very perceivable, and the fuel trim shows it because it stays at basically zero. If I slightly press the gas pedal then I will see the trim varies to around -6 to -8. At idle is when you really notice it and feel the stuttering. Last read I did she is hovering around -5.48 on the long term and short term jumps between -3 to 0.

Things that have been done:
One injector replaced by dealership
Cleaning of intake by dealership for carbon buildup
Spark Plugs
Injector harness because one wire was chewed by a mouse
MAF sensor cleaned (it was not reading at proper level, after cleaning it is operating at proper metric)
EVAP purge canister
PCV valves (outside ones not the one in the valve cover)

 

[offtheglass21]

Went back under the hood and it seems my MAP sensor is not reading properly, it shows with key on/engine off a pressure of 16 inHg and Barometric is actually 29. Should I replace the MAP sensor?

 

[offtheglass21]

WELP... Swapped the MAP and still get the same reading even though the car is idling better at start up. My reading is 16 inHg when key on engine off. When running it will be somewhere around 4 inHg. During rev up to get to speed I am reading -0.748. Like I mentioned upon start up she is idling just fine, after I got to work, a 40 minute drive at around 50-60 mph it shows me it is idling at -10 and slowly climbs down (a span of som 10-15 minutes). So, my issues are the following:

Is my MAP reading normal? (Everything I find it seems to not be) This was swapped and tested what it would read if I just unplugged it and it said 74 inHg.
Upon load it is fine but hen lightly pressing the throttle she gets into the -7 to -8 on long term

I have videos of the scanner data during idle after drive and when lightly pressing gas pedal I can send to you if you want.

Any ideas or information is appreciated.

Thanks!

 

[PoManNox]

I don't have access to GM data, alldata, identifix, etc, to know what a key on, engine off MAP reading should be. I'd verify that first. The only other thing I could think of is some scan tools can give erroneous numeric values for certain sensors.

 

[offtheglass21]

I am back at it again. The sputtering has not gone away. I decided to get a XTool bidirectional scanner. It seems I have a misfire on cylinder 3 but it is minimal and happens mostly at idling. Shows me between 2-6 misfires. Worse case was at startup which had around 24 and even showed misfires on cylinder 1&4 but those never misfired afterwards. Please give me ideas on anything else I could check into with this more in-depth scanner to narrow down. Already swapped coils and misfire did not travel with coil. The injector in cylinder 3 is supposed to be new, double checking today, as well as double checking the spark plugs which are supposed to be new.

 

[Big Papi]

Misfire on startup can sometimes mean a very slight to moderate coolant leak into the cylinder from a head gasket when cold. A bore-scope AKA Mr. Wiggles (IYKYK) can give you a good view of it when other detection methods have failed. Good luck!

 

[PoManNox]

Again, I'm a total novice shade tree hammer mechanic, but a single digit amount of misfire counts in the midst of a cold start sounds normal to me and should be basically non-detectable. I'm just saying this so you don't go off into the weeds.

I like the idea of pressure testing the cooling system while sending an endoscope cam down the spark plug holes. Problem is, if you have zero coolant loss, all should be well with the HG. If you had broken hard parts in one of the holes, such as a pitted valve seat or a chunk missing from a piston, the problem would present all the time. Not intermittently. Either way, it's worth a look.

 

[offtheglass21]

Yeah I have no loss of coolant or oil. I might need to give up and take it to a mechanic I guess. I thank you for all your inputs.