stratosteve

iTrader: (1)

My buddy owns a 2008 cts 3.6l DI awd. The car has been nothing but problems and I am becoming a full time mechanic on it. Current problem is a p0101 code which is a mass air problem code and a bank 2 cat efficiency code. We replaced the mass air and reset the code and it came back on after a few cycles.

I have viewed the data while driving and the ltft's are maxed out at +25 on bank 2. Since only the bank 2 side has high fuel trims, i dont believe there is a pre TB leak. I am thinking the problem is a leak in the exhaust before the upstream o2 sensor, causing an artificial lean reading and a corresponding max out of fuel trims. Thoughts?

2ndGearRubber

With trim THAT high, you need to reference short trim. If it's in the 7-8% or more at idle range, you have a weak/clogged injector.

With the MAF code, you need to check all the things that reference MAF signal to the computer. TPS is a big one. Did you use a GM part?

IIRC: there isn't a whole lot of distance between the head and the first oxygen sensor. After the manifold, it's 10 inches or so down. If you had enough of a leak to skew an O2 sensor, you'd hear it. Even if it has a slight leak at the manifold gasket, it will not change that much.


Also, check the wheel bearings. They aren't well built cars. What's the mileage? Rarely do those cars escape needing both cats.


EDIT: If a cat is truly fucked throughout the honeycomb, it can skew O2 readings.

stratosteve

iTrader: (1)

Will check the stft's and see where they fall.

The new mass air is an oem part for cadillac dealer. I will check the tps in the data area of the scanner.

Originally there were two cat efficiency codes (bank 1 & 2). The bank 1 hasnt come back on in thousands of miles.

I believe he has 150-160k on it. Maintenance is nonexistent and i dont really want to even touch it. The car drinks and leaks oil like the Valdez. At one point, I was chasing down random missfires on bank 1. I had replaced the coolant temp sensor as there was a CEL for it. I replaced it and it still had the problem. I was baffled and on a whim, I checked the oil level. No oil registered on the dip stick. Apparently, these engines are sensitive to oil levels due to the cam chain tensioners. Low oil pressure results in the cam timing to be off and viola, random misfires.

You think it is possible that a clogged cat could trigger both codes we are seeing? The cat skews the o2 sensor causing the cat code and because the o2 is reading wrong, the ecu dumps more fuel causing maf code?

stratosteve

iTrader: (1)

Understanding Fuel Trims - Long Island Catalytic

The above site has some decent information. So a clogged cat can cause both codes and the high fuel trims. I will run their tests for confirmation of clogged cat.