help me diagnose this misfire code

[windeye]

Hi, It's the 2000 Mazda MPV, over 200K miles now. Temp dropped to below 30 in the morning, drove to work, no problem. Car was parked for the morning, and at noon, went to start the car to drive to lunch, when the misfire happened.

Code is P0301, Cyl #1 misfire. I took a close look at the freeze frame, here is what I see:

Fuel Sys 1: CL
Fuel Sys 2: OL-Fault
...
STFT B1: -25.0
LTFT B1" -1.5
STFT B2: 0
LTFT B2: -0.7
Eng RPM: 1493
Veh Speed: 0

See picture of the definition of the engine (Duratec V6 2.5L) below. Questions I have:
1. why is bank1 in close loop while bank 2 in open loop?
2. if bank2 has fault on O2 sensor, why is cyl#1 (which is on bank1) misfiring?

Thanks,

 

[Trav]

Because bank 1 is pulling fuel at a greater rate than it was designed to. The injector on that cylinder is continuing to pump fuel in, possibly a failed plug or coil assuming it has COP.

STFT B1: -25.0
LTFT B1" -1.5
STFT B2: 0
LTFT B2: -0.7

The issue is clearly on bank 1. Repair this now before you loose a cat. Are you seeing a large amount of white/grey smoke? It would be rare but a stuck/sticking injector is another possibility.

 

[irad]

Your short term fuel trim is at the min -25. This means the computer thought too much gas was going into the cylinder. Could be at bad oxygen sensor for bank 1 or a bad fuel injector. Clean the oxygen sensor. I have used non-clorinated brake fluid cleaner. You can use mass air flow cleaner or fuel injector cleaner. Make sure whatever you use is non-chlorinated.

 

[Trav]

A dirty or failed O2 would not cause this, this is cylinder specific P301 not a P300 which would be generated if anything common to all cylinders on that bank were at fault.

 

[windeye]

Maybe bank 1 fuel system is the culprit... for a car that sat 4 hours in cold, and upon 1st crank, the fuel system should not go to close-loop. What make it go to CL?

 

[irad]

Trav,
A no spark condition, as you suggest, would cause a high fuel trim, O2 sensor seeing a lot of O2. OP has a negative trim. Oxygen sensor is seeing less oxygen. I also expected p0300 but maybe the computer is not seeing other misfires, it is a 2000 car? OP has 200,000 is this the original O2 sensor?

 

[windeye]

Hi, irad, bank 1 O2 sensor (upstream of CAT) was replaced a few years ago with a Denso one, due to heating circuit failure. Bank 2 has original O2 sensor, which I harped on bank2 OL-Fault initially. All plugs were replaced with the bank 1 O2 sensor, wires and ignition module (not COP) are original. The P0301 misfire lasted for about 5 seconds (MIL blinking), and then went steady.

All fuel injectors are original as well, maybe they are leaking and due for replacement. but I am still puzzled by bank 1 goes to CL immediately...

 

[Trav]

It should not be in closed loop until a certain temperature is reached (around 120f iirc). What is the misfire count on the other cylinders on that bank.

With a failed sensor it should not go into closed loop, I have not seen one bank going into closed loop and the other not,
The fact it is showing fuel trim fluctuation on both banks shows it is in closed loop. What scan tool are you using?

 

[anndel]

Most likely the coil pack or the spark plug in cylinder #1 is bad. If you can, move the coil pack in cyl #1 to #2 or #3 (same bank) and see if the problem moves to either cylinder you switched it with. If coil pack is bad, you should see P0302 or P0303.

Bank 1 STFT of -25 means it's running super rich and not burning fuel properly.

 

[irad]

Windeye,
I would but a can of Beryman's b12 in the gas tank. You can get it at walmart for $3.17. Has the problem occurred again? A blinking mil light is worse than a steady mil. Blinking means stop the engine immediately or the catalytic converter will be destroyed.

 

[eljefino]

So how did it "feel" as a misfire?

I bought an olds silhouette for cheap that was missing real bad at idle but drove okay on the highway. Had a leaky/ stuck open injector. One injector to the hole OBD pointed me to and she purred like a kitten.

OTOH my wife's HHR threw a misfire code when it was idled in severe cold, like below +5'F. Wasn't programmed to ignore the normal ones you get in the cold. Didn't feel a thing.

I am leaning to the injector thing, like perhaps it leaked down while parked. A bad coil usually poops itself when you suddenly gun the gas and give it a load.

 

[Trav]

Originally Posted by anndel
Most likely the coil pack or the spark plug in cylinder #1 is bad. If you can, move the coil pack in cyl #1 to #2 or #3 (same bank) and see if the problem moves to either cylinder you switched it with. If coil pack is bad, you should see P0302 or P0303.

^ This. Its simple and easy. If it doesn't move then look deeper into it.

 

[windeye]

Originally Posted by Trav
.... What scan tool are you using?


Hi, Trav, Tool is Invova 3130.

 

[windeye]

Originally Posted by Trav
Originally Posted by anndel
Most likely the coil pack or the spark plug in cylinder #1 is bad. If you can, move the coil pack in cyl #1 to #2 or #3 (same bank) and see if the problem moves to either cylinder you switched it with. If coil pack is bad, you should see P0302 or P0303.

^ This. Its simple and easy. If it doesn't move then look deeper into it.

Sorry but this engine does not have Coil on Plug. It is the 2.5liter, with a single ignition module.

 

[windeye]

Originally Posted by eljefino
So how did it "feel" as a misfire?

.

Hi, there is more vibration that can be felt thru steering and seats.

 

[StevieC]

Could be a bad wire or a bad spark plug. Pull the plug from the cylinder and see if you have spark on the plug with it grounded / cranking.

Or given the miles it might have a valve sticking open from a bent valve or dropped seat. Possible to do a compression test if it's not the spark plug / wire?

-25 is a lot of fuel going out the exhaust if the O2 sensor isn't lying, which I don't think it is in the presence of a cylinder misfire.

 

[windeye]

Thanks for all the comments and suggestions. I checked my records, plug change was done in 2015 at 177,000 miles. So less than 30k on the plugs. I should note that the misfire (cylinder specific, not random misfire) happened earlier of the year. All the occurrences were at cold start, and they only lasted a few seconds. After that all driving is normal. I am leaning toward leaky injectors.

 

[StevieC]

The plug can still be bad. I've seen plugs with less miles than that have weak spark or no spark at all. Visual inspection is always best. Take the plug out connected to the wire and have someone crank while you watch. Make sure it's grounded and your fingers are away from it.

 

[Trav]

Originally Posted by windeye
Originally Posted by Trav
.... What scan tool are you using?


Hi, Trav, Tool is Invova 3130.


Okay I looked at it, check the wire with a DVOM it should have about 10K ohms per foot, compare it to a similar length wire also to double check. Move the wire around while testing it to see if the readings drop out.
Change the plug, its probably fouled now anyway..

 

[windeye]

Originally Posted by Trav
Originally Posted by windeye
Originally Posted by Trav
.... What scan tool are you using?


Hi, Trav, Tool is Invova 3130.


Okay I looked at it, check the wire with a DVOM it should have about 10K ohms per foot, compare it to a similar length wire also to double check. Move the wire around while testing it to see if the readings drop out.
Change the plug, its probably fouled now anyway..


I will pull the plug and take a look, also check the resistance on the wire.... To answer a question earlier on tail pipe, I don't know, but did not notice any blue or white puffs as I backed out right after it stopped misfiring. Normal cold start does not have either blue (oil) or white (coolant) smoke coming out from tail pipe.

In thinking of injectors, what brand do you guys recommend?