What's Up Folks ?? I am a newbie so forgive the rookie !!! I would like to say thanks for any help that may occur. Also, forgive my long-windedness......
I appreciate any help in advance. I recently purchased a 2006 Dakota ST 4x4 quad-cab 3.7 v6 automatic. When the P300 event happens, it is on starts where the engine is not warmed up. After idling for a few seconds, I can feel the engine acting funny. It hesitates, burps and feels like it is about to die.

Usually the MIL Error Light flashes for a while. Sometimes the issue clears and the error light ceases flashing and the Error Light does not stay on solid. Other times the MIL error light flashes, then the problem clears and the Error Light comes on solid with a P300 Random Miss-fire.

At any rate, either I stop and start the engine, which clears the problem, or the problem clears on its own. Either way, I am then on my merry way. The issue wil not reappear until usually the next time the engine cools totally down.

I have a Pro model scanner and have spent quite a bit of time researching all aspects to this issue. I need some fresh eyes to review my data and hopefully provide some guidance. Any help would greatly be appreciated.

Facts:
--> This situation ONLY occurs on Bank-1
--> The problem only occurs at about 14 to 15 seconds from the time the engine is started. In fact it is exactly at the moment the system cycles from Fuel Status 'Open Loop' to 'Closed Loop'. Which means that at that moment, the STFT (Short Term Fuel Trim) comes into play and it is always showing a big negative number from around '-15' all the way to '-32'. Like I mentioned earlier, when STFT comes into play when it cycles to Closed Loop, if STFT is not on '-32' it quickly gets there. I suspect when the '-32' is reached, this is when the Error Light starts flashing.
--> At the end of the event, if the Error Light ends up coming on solid, the P300 Error Code with Freeze-Frame data are set. If at the end of the event the Error Light does not come on solid, the Pending Code is set to P300 but no Freeze-Frame data is established.
--> The Scanner's "$06" ODB results reflect that only Bank-1 cylinders miss-fire. (the 'odd' numberd cylinders on the 3.7 v6)
--> The Short Term Fuel Trim for Bank-1 either begins at "-32" or quickly migrates there and stays there for the duration of the event.

Repairs that have been accomplished:
-- Replaced the S1S2 O2 Sensor
-- Replaced the S2S2 O2 Sensor
-- New Plugs
-- replaced stock breather element with a K&N breather element
-- running strictly on Premium Gas

Other Scanner Results:
-- No Leaks detected
-- No Errors detected in the Oxygen Heater Sensors
-- No other ODB Error Codes than the P300
-- One exception -- I do receive the P0457 Code referring to the Gas Cap being loose. My research shows this is a common issue for this model truck and most likely has no effect on the P300 issue.

Here is my overall theory as to what may be happening:
(I actually do have much experience in this area but I have learned enough about it to offer an opinion/suspicion)

Something appears to be falsely telling the S1-O2 sensor the system is way RICH. Then it adjusts for the false Rich Condition by Leaning out the mixture which because the mixture was probably OK, the Leaning effect takes the mixture to a deadly level which starves the Bank-1 cylinders (the Odd ones) which results in the miss-fires.

Supporting Comments:
Because the STFT Bank 1 in Closed Loop is showing the -32.8, it causes the system to decrease the injector pulse width.
It thinks there is a RICH condition and attempts to LEAN out the mixture.
Because it is a false positive, the resulting Leaning takes the Bank 1 so low that Miss-Fires occur.
As to why it is getting the -32.8, that is the $100 question.
Possibly the Bank-1 pre-cat O2 sensor is bad and producing the false Rich condition, hence the “problem” (P300).

Scanner Stats:

View Freeze Frame
DTCFRZF() P0300
FUELSYS1() CL
FUELSYS2() CL
LOAD_PCT(%) 87.8
ECT(¡£F) 150
SHRTFT1(%) -32.8
LONGFT1(%) 1.6
SHRTFT2(%) -0.8
LONGFT2(%) 2.3
MAP(psi) 1.5
RPM(rpm) 404
VSS(mph) 13
SPARKADV(¡£) 15.0
IAT(¡£F) 127
TP(%) 20.0
RUNTM(sec) 44
EVAP_PCT(%) 0.0
FLI(%) 80.0
BARO(psi) 2.1
VPWR(V) 14.051
LOAD_ABS(%) 61.6
EQ_RAT () 0.999
TP_R(%) 7.5
AAT(¡£F) 122

Cylinder #1
EWMA (Exponential Weighted Moving Average)
TEST() 154
MIN() 0
MAX() 65535
STS() OK

Cylinder #2
EWMA (Exponential Weighted Moving Average)
TEST() 1
MIN() 0
MAX() 65535
STS() OK

Cylinder #3
EWMA (Exponential Weighted Moving Average)
TEST() 158
MIN() 0
MAX() 65535
STS() OK

Cylinder #4
EWMA (Exponential Weighted Moving Average)
TEST() 0
MIN() 0
MAX() 65535
STS() OK

Cylinder #5
EWMA (Exponential Weighted Moving Average)
TEST() 168
MIN() 0
MAX() 65535
STS() OK


Cylinder #6
EWMA (Exponential Weighted Moving Average)
TEST() 2
MIN() 0
MAX() 65535
STS() OK
Help – Please !!!!!!

 

When you have a high short term adaptive on ONE bank and/or a P0300 basically all by itself, you need to start by looking at a mechanical issue with timing, compression, etc. All that data is just a fog for now until you rule out the simple things.

 

Thanks for your time. I obviously am a rookie. My background is in Corvettes but I have put that aside for a while. At any rate, I am now, again obviously, driving a Dodge Dakota truck. Forgive me but help me understaqnd a term you used: "adaptive"


Also, thanks for the Keep It Simple Stupid reminder (KISS method). I really need to rule out the obvious/simple stuff first. Although the scanner leak tests did not report any problems, But, to me, hands-on is always better than a computer test. Tomorrow I intend to use a can of brake cleaner and spray around some obvious vaccum areas watching to see if the idle changes. I was told this was s simple way to find obvious vaccum isses. I will report back on my findings.


Thanks again, Bill

 

I forgot to mention, I was talking to one guy at the parts house and he suggested looking at the Crank-Shaft Sensor and the Cam-Shaft sensor. He seemed to think since this is a P300 all by itself, the above mentioned sensors may be good suspects. I am not clear on hot to go about 'testing' for these two sensors.

 

one thing that our engines are known for is carbon buildup in the intake manifold. When i took the TB off my 2011 i found that there was a buildup of "stuff". I used a spray can of seafoam (half a can as per direction, through the TB) and it made a huge difference. My intermittent misfire that i was getting back then was gone, until recently when i had some bad gas. i have to do another application of seafoam to clean the top of the valves, the O2 sensors and the cats. you can hear the difference after the seafoam is put through. i noticed my exhaust seemed to flow better. I had that low rumble at idle that i havn't heard in a while.
I prefer the spray that is done through the TB vs the bottle that you suck through a vacuum line. The spray you know is getting to all cylinders vs trying to find the right vacuum line.

 

@TNTech --> I answered my own question about the usage of the word "adaptive". The STFT is 'adapting' to the ever-changing environment via data from the O2 sensors by adjusting the air/fuel mixture. Hence the term "adaptive". Sorry, I did not catch-on at first...... The 'rookie' strikes again...


@pierrejoly --> the things we learn as we go along thru life. Just Friday I had a tune-up shop do an upper-end clean job on my truck. I was watching them and they definitely sucked a bottle of cleaner/stuff thru some vaccum lines. Hmmmmmmm. Ohh well. At any rate, thanks for the advice. I will know better next time.
@pierrejoly --> do you know if our 3.7 engine has a traditional fuel filter ?? The only one I could find is a device that is placed into the fuel tank that acts as a 'fuel-filter'.


@Everyone --> I am trying to think thru in my mind what all could possibly involved in order to have only the "left-side" effected by the Miss-Fire. Also in the mix I am thinking that since the "problem" only occurs when the engine is not up to normal operating temperature. Not 'cold' per-se but but definitely 'not hot'. Anyone care to throw anything on the table here for discussion ??
List of left-side suspects:
* Bank-1 pre-cat O2 sensor: although I would think I would be seeing other O2 sensor related error codes
* Could there possibly be something that is allowing the gas to drain out of the Bank-1 fuel rails resulting in very low STFT (short-term fuel trim)


As always, thanks for everyone's help/guidance.

 

I was reviewing my research material on the topic of Fuel Trim Values and something interesting caught my attention. Negative Numbers reflect the Bank is runing "rich" so the system reduces the amount of gas being sprayed by the injectors on that bank. I was thinking backwards (surprise surprise). So now the question becomes, what can happen that causes too much gas ??

 

SHRTFT1(%) -32.8
LONGFT1(%) 1.6
SHRTFT2(%) -0.8
LONGFT2(%) 2.3


Short term and long term "adaptive numerators"




Loss of compression for starters. There are a number of things that will cause that such as a valve stuck open/closed or timing being off. I've seen 3.7 and 4.7 break a chain on the non-cam sensor side and never make a noise. One cylinder can affect the whole bank because the O2 only sees the total condition for that side. being that it's practically maxed out at 32, it should be easier to find.

 

I am not an expert but it seems to me if it were something mechanical, it would be occurring all the time. Literally this problem only happens once the truck has set for a period of time and is started.


Like I said, the problem does not happen every start. Interestingly, the truck always start easily, idles normally and runs fine. But on occasion after it has set for a while (I am thinking the minimum setting time of at least an hour is required) and is started then about 15 seconds later when the system cycles from Open Loop to Closed Loop, this is when the problem surfaces. The Error Light starts flashing and it feels like it has no power.


Correct me if I am wrong but once it cycles from Open to Closed, isn't that when the Short-Term-Fuel-Trim takes control of the air-fuel mixture ?? So because the -32.8 is telling the system it is totally rich, it would then try to lean-out the mixture. In doing so, if the mixture was somewhere normal and the system totally leans it out, wouldn't that create a dangerously lean condition resulting in miss-fires, but only on Bank-1 ??


I also suspect that because when the engine is first started the system is running on the numbers from the Long-Term-Fuel-Trim because it is in Open Loop which the LTFT numbers are within normal range. Therefore, the engine would run fine and it does.


I am starting wonder that based on the evidence and the pattern to the problem, maybe the Bank-1 pre-cat O2 sensor has gone flaky. Maybe it is old like me and needs a few minutes to warm up before doing any work.


Thoughts ??

 

Injector leaking down while sitting? Small amount of coolant squeezing into a cylinder while sitting.