Code after new exhaust

[ScottS4050]

So some of you may have read my post in the Intake/Exhaust section.
I got my exhaust done Friday, hi flow magna cat, 3" piping and magna muffler.

Saturday the car popped a "DTC P0174 Fuel Trim System Lean Bank 2" code on me.
I have one of those cheapy ebay code readers. I didn't think too much about it,
and figured it was the computer getting used to the new flow rates, or something.
I cleared the code and drove the car around town doing misc errands and stuff.
The SES didn't come back on. Today (Sunday) I got in the car and started it up and within one minute
the SES light came back on. So I drove to the store and came back home and checked the code.
The same P0174 code is back. I searched this site a bit and found a couple of
threads saying that high flow cats can throw this code.

So do you guys think this is what's happening? Or could it be something else?
It can't be coincidence that I got the exhaust done the day before the code showed up. Or could it?
The car seems to run perfect. More power than its ever had before.
Last weekend I put new NGK TR-55 plugs in, and MSD 8.5mm wires, but I don't see how that could be the prob.
If that were it, I should be getting a misfire code, or something like that.

What seems wierd to me is - Why is it only bank 2 that is running lean?
If it is the hi flow cat causing the code, wouldn't the pcm think both banks are running lean?

I await your expert advice...............

[Docta]

Re: Code after new exhaust

The way I was told, the more amount of airflow from the new exhaust is throwing it off. But thats just what I was told.. oddly, my magnaflow system only pulls o2 sensor codes, with no cat.

[ScottS4050]

Re: Code after new exhaust

The way I was told, the more amount of airflow from the new exhaust is throwing it off. But thats just what I was told.. oddly, my magnaflow system only pulls o2 sensor codes, with no cat.

Do you have a stock or hi flow cat?

[Docta]

Re: Code after new exhaust

I have no cat. None. Period.

[ScottS4050]

Re: Code after new exhaust

I have no cat. None. Period.

Did you get an O2 Emulator, or have the code deleted? Or do you just deal with the SES light being on?

[Bobd1001]

Re: Code after new exhaust

Just get the O2 emulator from ZZP. works great to kill CAT related codes from being thrown

[Docta]

Re: Code after new exhaust

Just the code atm. Getting the emulator next paycheck.

[whitdog54]

Re: Code after new exhaust

You can try moving the 02 sensor farther down stream. Its worked for a couple ppl

[ScottS4050]

Re: Code after new exhaust

You can try moving the 02 sensor farther down stream. Its worked for a couple ppl

It would be a whole lot easier to just get an emulator, rather than take it back to the exhaust shop and have them relocate the bung.

[bigbrian442]

Re: Code after new exhaust

And none of this will fix your problem. The post cat sensor doesn't set this code. This code is set when your long term fuel trims call for 15% more fuel to keep the AFR at 14.7:1. Some of the first things to do is hook a good scanner to it where you can read fuel trims and see if bank one and two are close to each other. If they are not the bank 2 sensor might be starting to go south. If they are close, Then it would be a good idea to clean the MAF. You may even find that with your new exhaust you need to tune your MAF table in the PCM to correct this.

[ScottS4050]

Re: Code after new exhaust

And none of this will fix your problem. The post cat sensor doesn't set this code. This code is set when your long term fuel trims call for 15% more fuel to keep the AFR at 14.7:1. Some of the first things to do is hook a good scanner to it where you can read fuel trims and see if bank one and two are close to each other. If they are not the bank 2 sensor might be starting to go south. If they are close, Then it would be a good idea to clean the MAF. You may even find that with your new exhaust you need to tune your MAF table in the PCM to correct this.

That's what I was really afraid of. It didn't make any sense that only bank 2 would be running lean, and not bank 1. My code reader does allow me to see long and short term fuel trims, but I really don't know much about it. When you say bank 1 and 2 should be close, how close? I just cleaned my MAF about a month ago with seafoam (not too happy about the sefoam results in general, will probably be the last time I use it.) Previous owner removed the MAF screen, should I get a new one and put it back?

[bigbrian442]

Re: Code after new exhaust

Yes, put the MAF screen back in and get a spray can of MAF cleaner and clean the MAF. Close would be 3-4 %.

[ScottS4050]

Re: Code after new exhaust

UPDATE:
After my last post I reset the pcm and didn't see the ses light for almost 2 weeks. Today it came back. This time I have the same P0174 code and P0171 = Lean Bank 1. I had just stopped for gas and filled the tank with 89 oct. Light came on within 30 seconds of leaving the gas station. I did some research and then came home and took the MAF out and cleaned it with MAF/Electronics cleaner. I also replaced the fuel filter. The MAF does not appear to be the original - no GM, Delco, Remy, Delphi, etc printing on it (not sure who made the OE.) All I found is a stamp in the metal that says "Japan." I'm guessing it has been replaced before I got the car. I hooked my laptop up, reset the pcm, and watched the polling for a bit, and I noticed that the long term fuel trims are very erratic and fluctuate between about 4% and 19% just idling (ltft2 being worse than ltft1.) I am not familiar with reading these numbers, so I really don't know what I'm looking at.

I doubt both O2 sensors went bad, and I've read that is a very common misdiagnosis. The pcm does a self diagnostic on the O2 sensors prior to setting the DTCs.
More research has led me to think the MAF sensor may be bad, but if that were true, wouldn't I get one of these? :
DTC P0101 Mass Air Flow (MAF) Sensor Performance
DTC P0102 Mass Air Flow (MAF) Sensor Circuit Low Frequency
DTC P0103 Mass Air Flow (MAF) Sensor Circuit High Frequency
DTC P0104 Mass Air Flow Circuit Intermittent
The cheapest autozone MAF is $109us and is non-returnable.

This all started the day after I had my new catback installed.
Zlexiss is supposed to do a pcm tune for me this weekend, but I'm not sure if it should be done until I know for sure the DTCs are gone (should I wait and see if replacing the fuel filter and cleaning the MAF worked?)

I still need to check for vac leaks using the carb cleaner method. There doesn't seem to be any obvious audible leaks. Engine idles smooth, and there is no performance loss, no knocks, seems to run perfect.
Tonight, however, when I was holding the engine at about 3000 rpm, the ses light started to flash, then stopped when I returned to idle. This happened a couple of months ago while I was driving (in the pedal a bit) and then stopped about 10 seconds later. I have since replaced the plugs and wires. Old plugs looked good.

One other thing I forgot to mention before - I was getting an EGR code a couple of months back (don't remember the exact code.) I did some research here and decided to Seafoam the car (did half in the tank and half in the intake, and cleaned the EGR/tubes with the Seafoam Deep Creep) That didn't fix it so I bought a new EGR valve. That code hasn't reappeared since then.

[bigbrian442]

Re: Code after new exhaust

Not having the MAF screen in place will cause the MAF to have erratic readings. I would put that back before i bought a new MAF sensor.

[WarShrike]

Re: Code after new exhaust

I own a '00 car that's heads/cam/intake and I run the maf screen. I watched the MAF readings with and without the screen and there's a marked difference. You want smooth flow over that little wire, not erratic.

Get it scanned and maybe look into some denso O2 sensors. Run a can of seafoam through the gas tank first before you do it and install a new fuel filter after the first tank if you haven't done that in awhile.