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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 10-02-2015, 12:25 PM   #1
BUDGET76
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Join Date: Mar 2015
Location: Hartford
Posts: 117
My Ride: 03' M3 & 95' 330TI
Car going to Open Loop Under Deceleration & Hard Accel?

Trying to track down this issue, any help would be appreciated.

For the past couple months I had been getting the P0420 "catalyst system efficiency below threshold (bank 1)" code randomly. It started where it would pop maybe once a month. Then it progressed to once every 500 miles, which with it being the cat efficiency check I just cleared and figured I'd track it down when I had more time.

Recently with the cold weather it has been popping more often, as in once every 100 miles or so, and I'd REALLY like to track it down. Been watching more info on Torque and I have been seeing something suspect. The Fuel System Readiness switches from closed loop to "open loop due to system error" when decelerating or accelerating hard.

Everything I've read is the post-cat sensors have no effect on the fueling system and only report on cat efficiency, so I'm thinking something else may be triggering the cat code & causing the open loop.

Things I've done/info:
-New OEM thermostat this spring. Car consistently at ~180*F (82C). Warms up very quick as it should. Don't remember how hot it got during summer temps.
-Cleaned MAF last night, no effect. code popped this morning
-Air filter is OEM BMW
-Checked for vacuum leaks by spraying starting fluid around the engine bay with it running, no effect
-O2 sensors voltage appears normal: haven't seen a sensor stick at 0, they all consistently move from .0v to .8v or so in Torque
-Long Term Fuel Trim 1 is ~9%, LTFT2 is around 6.5% if I remember correct
-Occasionally get a hard-start where the engine cranks strong but doesn't fire. Turn key off and back on and it fires first crank. Don't believe it to be related to the cat efficiency code
-Occasionally get a P1434 code (once every 1000 miles or so) which I have read could either be the gas cap (going to replace soon in case) or the secondary air injection pump (either pump or relay, also going to order soon)

My first step is to swap the post-cat O2 sensors from bank 1 to bank 2 and see if the code follows, I just haven't had time to previously. What else should I be checking/watching with Torque?

Thanks for all the help. Will post up anything else I figure out.
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'03 M3. Titanium Silver/Black. Bilstein PSS10, 19" VMR 710, UUC SSK, UUC LWT clutch/flywheel, UUC catback, ///Avin Avant2.
'02 330XI daily
SOLD'95 S50 TI, bad weather beater, tow rig

Last edited by BUDGET76; 10-02-2015 at 12:26 PM.
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Old 10-02-2015, 07:54 PM   #2
Commando
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Join Date: Sep 2011
Location: Western Australia
Posts: 643
My Ride: '02 325Ci MT '04 M3
I don't think you should be concerned about the open loop messages. During acceleration and over-run the air/fuel mixture is far away from the stoichiometric ratio that the closed-loop mode of operation endeavours to achieve. At these times I assume the DME will switch to some pre-defined fueling tables. These mixtures are outside the range of the narrow band lambda sensors in our cars so the system is open-loop. When the motor and cats are warming up a similar situation exists. I'm not sure if the fuel trims have any bearing at these times.
I've also experienced the crank but no start on the first attempt once or twice. Maybe thats the DME having an internal dispute and hanging?

Swapping the sensors is a good idea - maybe the cats are the problem. There is a temp sensor back there on my Euro system too.
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Old 10-04-2015, 11:16 AM   #3
BUDGET76
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Join Date: Mar 2015
Location: Hartford
Posts: 117
My Ride: 03' M3 & 95' 330TI
Quote:
Originally Posted by Commando View Post
I don't think you should be concerned about the open loop messages. During acceleration and over-run the air/fuel mixture is far away from the stoichiometric ratio that the closed-loop mode of operation endeavours to achieve. At these times I assume the DME will switch to some pre-defined fueling tables. These mixtures are outside the range of the narrow band lambda sensors in our cars so the system is open-loop. When the motor and cats are warming up a similar situation exists. I'm not sure if the fuel trims have any bearing at these times.
I've also experienced the crank but no start on the first attempt once or twice. Maybe thats the DME having an internal dispute and hanging?

Swapping the sensors is a good idea - maybe the cats are the problem. There is a temp sensor back there on my Euro system too.
This make sense and I thought may be the case, but didn't know enough to be sure. Thanks for the info.

Still haven't had time to swap the sensors. I just picked up a 330xi that needed some thorough cleaning and some other maintenance, so that kept me busy yesterday.
__________________
'03 M3. Titanium Silver/Black. Bilstein PSS10, 19" VMR 710, UUC SSK, UUC LWT clutch/flywheel, UUC catback, ///Avin Avant2.
'02 330XI daily
SOLD'95 S50 TI, bad weather beater, tow rig
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