My F- 150 was manufactured in Nov. of 2005 , it currently has 168,700 miles , for the last year it has thrown P 0315 code but always ran normal , I would have
the code cleared and it always returned after about 80 to 120 miles , never did
figure out why , then about two weeks ago it started to run very rough when I
was on the freeway at 65 mph , long story short I replaced the crankshaft sensor
and now it will run smooth as glass for 4 to about 8 miles then really rough for
about the same distance , then it will start to " clean up " and run perfect again
for about the same distance , then rough again , this condition has been fairly
consistent for about 250 miles now . anybody have any idea as to what the
problem could be ?

 

Are you still getting the P0315 code after changing the crank sensor?

 

Yes the code will pop up after about 60 or 70 miles ( the dash lite ) however when
I went to town yesterday I had the the at guy oriley's check it and it showed up on his
scanner and not on my dash lite till 20 miles later .

 

I can tell you what is going on. The PCM tries to learn any variations in the crankshaft position sensor tooth wheel spacing. It uses this information to minimize erroneous reporting of misfires. If it can’t learn this profile the PCM will set the P0315 DTC. And if this profile can’t be learned the misfire monitor will not run.

This profile is best learned by decelerating from 60+ mph down to <40 mph with out using the brake or downshifting. This will eliminate any power pulse on the crankshaft while the PCM learns the tooth profile. If it fails to learn the profile within 3 attempts it will set the P0315.

Is there any history of work being done to the timing chains/components?

 

^^^^ 100% correct and clear crisp description. Including the follow on question.


With the stated miles, a likely possibility is the chain has stretched and broken a guide - with a piece of guide catching on and bending the tone ring, effecting the CKP sensor ability to read the tooth profile.

 

I bought the truck second hand , as far as I know the timing chains/ gears are
original , I'll try the deceleration procedure , question on that ; should I do that
3 times in a row , and with overdrive on ? , as far as replacing the timing chains/
gears and components , from what I have read in my Haynes manual it is a major
job and I'll have to wait till I have a second vehicle l to get around in , now I know
this next question is kinda stupid but with a worn timing train will it all of a sudden
fail to the point of being stranded or slowly deteriorate to the point of not running ?

 

I would like to hear @pdqford's comment on this - but my view is if you have worn chains (and slack in them) to the extent of broken guides, you would be approaching the ( uncertain ) point where a misfire or backfire could result in timing chain jumping a link or two on the gears - and leave you stranded.


I'm not positive it matters that all three decelerations @pdqford mentioned be done in one drive cycle or not. But certainly it would have to be within some time frame or distance. That's the reason you are seeing the condition repeat after some number of miles - it's retrying. I would probably do it very deliberately within one drive cycle - and on a nice smooth road. NOTE: it calls for "de-fueled decelerations". You need to get _completely OFF the accelerator and coast a good distance _ where the PCM will literally 'cut fuel' (Fuel trims go to Zero) for an extended period of time. I would try to continue decel even below 40. The following description is from the Motorcraft OBDII Theory of Operation Manual:

Page 9 of 98
" "Profile correction" software is used to "learn" and correct for mechanical inaccuracies in the crankshaft position wheel tooth spacing. Since the sum of all the angles between crankshaft teeth must equal 360 degrees, a correction factor can be calculated for each misfire sample interval that makes all the angles between individual teeth equal. To prevent any fueling or combustion differences from affecting the correction factors, learning is done during decelfuel cutout. The correction factors are learned during closed-throttle, non-braking, de-fueled decelerations in the 60 to 40 mph range after exceeding 60 mph (likely to correspond to a freeway exit condition). In order to minimize the learning
time for the correction factors, a more aggressive decel-fuel cutout strategy may be employed when the conditions for learning are present. The corrections are typically learned in a single deceleration, but can be learned during up to 3 such decelerations. The "mature" correction factors are the average of a selected number of samples. A low data rate misfire system will typically learn 4 such corrections in this interval, while a high data rate system will learn 36 or 40 in the same interval (data is actually processed in the AICE chip). In order to assure the accuracy of these corrections, a tolerance is placed on the incoming values such that an individual correction factor must be repeatable within the tolerance during learning This is to reduce the possibility of learning corrections on rough road conditions which could limit misfire detection capability. Since inaccuracies in the wheel tooth spacing can produce a false indication of misfire, the misfire monitor is not active until the corrections are learned. In the event of battery disconnection or loss of Keep Alive Memory the correction factors are lost and must be relearned. If the software is unable to learn a profile after three 60 to 40 mph decels, a P0315 DTC is set."

 

I live in a area ( wheat country ) were we have some 20 mile long flat roads
with basically zero traffic , so I'll try the 3 decel procedure , maybe from
65 mph down to 30 mph ? , the check engine lite is still on ( I assume it
still is a P0315 ) should I disconnect the battery or not before I try this ?

 

Would be great conditions for it.

I probably wouldn't clear DTCs. It is a subject some might disagree with me on. But, while many despise a DTC and get overly anxious to make it 'go the heck away', they actually can be your friend under many situations. AND, clearing DTCs does a lot more than just make the 'wrench light' go out. Some can be useful for diagnosis. The PCM will clear any DTC if it determines whatever caused the DTC has gone away. To me, there is some subtle diagnostics value in just THAT.

If there are multiple codes, you can read them again (without clearing them) and see if a particular one is still present.

Certain ones take multiple drive cycles to SET a DTC - so understandably those would also take multiple drive cycles to clear. (I do not know about P0315). But you can check for it again later or your symptoms might go away too.

When you reset DTC, it clears all emissions test flags (Evap, CatStat, HO2sStat, I/M Readiness -(Inferred Mass air flow - EGR), and other stuff. Reading codes shortly after clearing will give you a P1000. I certainly read and monitor codes, but I do not hardly ever clear them anymore. /// If you clear them and they don't come back ----- the PCM would have cleared them anyway, sooner or later ///.

 

Well no luck with the deceleration procedure , still the same symptoms ,
so think I'll switch out the plugs and get new boots for the cops .

 

It is generally ALWAYS a mistake to ignore the literal definition of a DTC code. It is the only way the ECU has of communicating with us.


In this case - (as pointed out by @pdqford in post #4, this thread) the ECU is saying "it cannot correct for mechanical inaccuracies in the crankshaft position wheel tooth spacing". You have already replaced the CPS. Concentrate on WHAT else could prevent it from successfully doing this. All it is trying to do is "sum of all the angles between crankshaft teeth to be equal 360 degrees, and calculate a correction factor for each tooth for a misfire sample interval that makes all the angles between individual teeth equal.


I think it is time to consider the possibility SOMETHING has bent or distorted the tone ring on the front of the crankshaft. ie: a piece of broken chain guide. I think the poor running cycles you experience has to do with the ECU resorting to default values while trying to recalculate the profile - and something in those settings results in more misfires, poor fuel/air mixture or something.

 

If its a tone ring I'm done for ..., I'll have to live with it as is , just not in the cards
for me to pull it apart to replace all the timing train components , the pickup is
my only transportation I have at this time , I thought it would be worth the gamble
to replace the spark plugs , and perhaps the cops as well , and hope for the best.
If that doesn't pan out and it not something like a sensor , it will be time to look for
different truck

 

Sorry.


Would almost never hurt to change spark plugs. But do not waste your hard earned money replacing COPs. 99.9999% of them that are replaced do not need to be. Boots, YES. But a good - clean room style - plug change without greasy finger prints on plug ceramic, with a dab of dielectric grease on plug end of 'NEW' boots is all you would need - unless you have one of the 'specific' codes indicating coil primary or secondary circuit problems or cracked broken COP electrical connectors. (Again - trust literal meanings of DTCs).

 

Going to change out the boots and plugs , is part # SP 432
a OEM Motocraft spark plug ? and would that be my best
plug choice ?

 

I was hoping someone (one of the 1,000s) who know more than I do would hop in here and give you some 1st hand advice based on experience, as mine is a 5.4l and a different handful of problems with plugs.


Best I can do is go to RockAuto - *where I come up with a different number* - SP493


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