2014 Cadillac CTS (LF3 3.6L twin turbo) -MAF Low?

tiride62 wrote: Two questions, did you get this fixed yet? I feel like I'm reading a mystery novel and I'm waiting to find out who did it. My other question is the long term fuel trims in the Global data showed -18 both banks but also showed -5 and -7 I think "without purge". Does that mean the goofy fuel trim numbers where with the evap system purging and if so wouldn't that be expected since the engine is being fed fuel vapors from the canister? I'm new to this stuff so if I've asked a dumb question I apologize. For what it's worth my thought was blockage in the air intake system, I pictured a shop rag in the air intake tube.

Thanks for interest and while nothing has been fixed I do have some new information and interestingly at least one of the issues may be related to the evap system (though I don't know the answer to your second question).

1. The MAF rate is likely twice as high as suggested by the OBDII PID. The car's ECU is likely getting the correct MAF rate reading.

• The LF3 has two MAFs that the ECU is either summing or taking into account independently, according to a Cadillac propulsion spokesperson
• I test drove another 2014 CTS LF3 3.6L twin turbo and plugged in the scanner -- it had the same MAF as my car. Of the handful of other PID's I pulled the only significant difference is that my car had way more misfires.

2. Subsequently two issues either started (or became noticeable):
(a.) rattling noise upon acceleration and (b.) humming noise for 10-20 or so seconds upon shutdown

Neither results in a check engine light. Here is a sound clip link instaud.io/1jSf (you can hear the rattle in 0-26 seconds; and the humming noise start at about 0.30)

• (a.)Rattling noise: Dealer has a muffler on order.
• (b.). Humming noise on shutdown: According to other owners of the car this is related to a malfunctioning vacuum actuated wastegate solenoid valves. Dealer has solenoid valves on order.

So I'm not sure if these two items are related to the original performance issues but since they are audible at least it can't be ignored as "no code no problem!"

I think an engine as complicated as this really demonstrates the value of what Paul is teaching in his class.

Hi all,

Wondering if you've had any luck determining the cause of this. I'm far from an expert but probably know just enough to be dangerous.

I've got the exact same car with the exact same problem. I absolutely love this car... when it works as intended. There are days when I want to drive this over to GM Headquarters and set the damned thing on fire in front of their building.
2 trips to the dealer resulted in "Cannot duplicate" so I've given up on them and tried to solve this on my own and with the gentlemen that normally work on the car.

In my case, it appears to have had a number of small problems possibly contributing to the overall frustration/discomfort.

- I put the summer tires on (freshly balanced) and the vibration wasn't as harsh but still present. (One of the winter tires was wildly unbalanced)

- The OBDII was showing a horrendous amount of misfires on 2 cylinders (one of them went over 80) so I replaced all coils and plugs. No more misfires. Even when the engine exhibits these vibrations.

- I noticed that the driver rear tire pressure would get noticeably higher than the others (one time as high as 12 kpa) when the vibration was most evident. Placing my hand near the rotors after stopping, the driver rear was hotter than the passenger rear. It turns out the driver rear caliper was getting stuck. Rotor was beginning to discolor and inside pad was scorched with some white, ashy remnants. Rotors machined to give a "clean" surface, pads were sanded down to remove the ashy, glazed sections (since they are only a couple of months old) and both rear calipers replaced.

After all of this, the vibration is nowhere near as violent but is still present under the same conditions described as the original poster.

Here are a couple of my theories:

1. I've recently discovered an alarming amount of oil in my air filter box. It seems that under boost, I'm getting a fair bit of blow by. I suspect that one of the MAF sensors is getting coated with oil just enough to confuse the computer with an incorrect reading (but not so bad as to throw a code)?
I'm looking into the addition of a catch can and will get the walnut shell blasting and throttle body cleaning done at the same time.
- I'm also wondering if this problem is the result of the intake beingcoked up due to the fact that it's a GDI AND has the oil blow-by issue.

2. A problem with one of the sensors in the "Weather Station" but that should throw a code, shouldn't it?

www.motor.com/magazine-summary/gm-3-6l-e...onics-november-2013/

"In addition to the new hardware, there are also new sensors and actuators that are unique to this engine. One is a multisensor setup GM calls its “weather station.” This is much more than a MAF sensor and it’s included to deal with some issues directly related to the twin-turbo setup.

The weather station includes a sensor to measure mass airflow, two temperature sensors, a humidity sensor and a barometric pressure sensor. The burning of fuel and air is pretty much a science experiment that can be predicted by a formula that calculates the amount of oxygen and fuel to be burned. The problem is that the amount of oxygen in a particular sample of air is not a constant, fixed value. The hotter the air, the less dense it is. When the barometric pressure changes, that changes both the air density and the flow rate into the engine. The weather station measures these changes and affects the engine calibrations accordingly."

3. Magnetic ride control malfunction. I wonder if one or more of the magnetic struts are malfunctioning to cause a vibration...