2007 lacrosse 3.8 shutter/miss issues

[inline300]

Went through some flood water last weekend, no choice really, next day, car ran fine, drove it quite a bit. Second day, noticed a slipping/missing symptom, lack of power, when going uphill, as the trans downshifts, or, if I push the go pedal to engage passing gear.
No codes.
Internet suggested pressure solenoid. Symptom being shuttering or hard shifts. Six months ago the car was shifting hard, but that only lasted a week. I cleared the code and it stopped.
Not sure if either are related to the problem now but thought I'd mention it.
Typically, symptoms are limited to hill ascent or downshift under acceleration. However, one day, it did it all the way home, 5 miles, regardless of conditions. Yet the next day, it went back to the previous scenario.
What I've done.
Disconnect battery to reset solenoids/controller of, no change.
Replaced 4 quarts of fluid, added a shutter treatment (see if it might be a fluid issue). No change.
Cleaned maf and throttle body. No change.
Next I used an obd adapter to watch the TCC. 4-500 rpm under acceleration. 19 ish rpm under cruise or lock up. Seems acceptable?
Transmission does downshift when the shutter/miss symptom occurs, I can see the command and feel it but the get up and go, just isn't there.
Last time I checked for codes, noticed a pending PO300 code.
So set up my display to show real time cylinder misfires.
Easy driving, no misfire.
As soon as I push the pedal down, it downshifts, and it begins the slipping/miss no power symptom.
Cylinder 3 and 6, show one misfire respectively.
Cylinder 2, shows 124 misfires.
Other cylinders, 0.
So now I'm thinking bad coil pack, next step seems to be, change plugs or swap coil.packs, see if the misfires move with the coil.pack.
Thoughts?

 

[Zeroboostbuick]

I know with older f-150's with the same issues was due to a faulty MAP sensor that would work ok under normal load.

 

[richardnewton]

This is an excellent video on a poor running Buick 3800 with 0300 code, includes some testing and coil pack & input (!) investigation:

With potential water ingress, I have no idea. Was it salt or fresh water?

We had similar issues on our 3800 Regal 2001. Tested coil packs in dark with no issues. Changed wires and plugs and good to go. Ran much smoother, nearly like new.

If you need to change the back plugs there are some ways to do that without rolling the motor forward. There are a few videos on this. Not sure if this applies to your lacrosse

 

[Zeroboostbuick]

This is an excellent video on a poor running Buick 3800 with 0300 code, includes some testing and coil pack & input (!) investigation:

With potential water ingress, I have no idea. Was it salt or fresh water?

We had similar issues on our 3800 Regal 2001. Tested coil packs in dark with no issues. Changed wires and plugs and good to go. Ran much smoother, nearly like new.

If you need to change the back plugs there are some ways to do that without rolling the motor forward. There are a few videos on this. Not sure if this applies to your lacrosse

South Main Auto videos are awesome. My favorite channel to watch.

 

[Zeroboostbuick]

To zeroboost's comment above, mechanic diagnosed bad MAF on our 3800 Buick. By disconnecting the MAF plug car ran perfectly.

Our MAF completely failed and car would not start for more than a second or two. Cleaned MAF with no success. Purchased used OEM MAF from junkyard for <$20, cleaned it, and car runs fine now.

I was taking about the MAP (Manifold Absolute Pressure ) and not the MAF 😉

 

[richardnewton]

I was taking about the MAP (Manifold Absolute Pressure ) and not the MAF 😉

Reading too fast! Deleted message.