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2005 f 150 4.6 has -20% LTFT's revisited/ over reporting MAF/ (FINALLY FIXED)

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3 years 6 months ago - 3 years 5 months ago #43434 by Patrickreaves
2005 f 150 with 4.6 with -20% fuel trims on both banks although they are not always identical. (this was the name of a post i made about a year ago.) my exhaust would blow out white smoke after idling for a few minutes . I thought that it was raw fuel since my fuel trims were -20% and more. i changed the valve seals with the engine in the truck without removing the camshafts. ( took me 4 days. lol ) it was a hell of a job by myself. but thankfully it no longer smokes or goes through oil. however my fuel trims remain -20% to -24% on both banks and rpm has no effect on trims.
here is what i am thinking at this point. ive read that at idle (700 rpm) that the MAF g/s should be about what ever the engine size in liters is, in my case it should be about 4.6. how ever my MAF at idle is .02 lb/s which converts to 9.07 g/s this number is 2 times higher than what it should be. so now i do a volumetric efficiency test .
MAF 258 g/s
IAT 118 degrees
RPM 4925
ENGINE 4.6 liters using a V.E. calculator shows a volumetric efficiency of 124% with these numbers. ( tested 3 times with similar results)
yet 80%to 90% V.E. is the normal range for N/A engines. so now im thinking my MAF is over reporting air intake by about 25% which i think correlates to the -25% fuel trims. since i have 2 different f150s, one with a 4.2 and one 4.6, i do some comparison.

4.6 liter
baro=14.9 psi
baro=160.04 hz
V.E.=124%

4.2 liter
Baro=14.4
Baro=156.97hz
V.E.=80%
I believe my MAF /baro reading on the 4.6 f150 is higher than normal which tricks the ECM into thinking that more air is entering the engine than it really is, with the fuel to match that air. hence the -24% FT.
it is said that a clogged CAT will lower the MAF reading due to restriction which causes the baro to be lower than expected, would the opposite be true if the cats were empty/hollow? that the MAF would read higher and air flow easier due to the less restrictive exhaust, i would think that it would alter the air flow and thus be skewed from the original air flow charts that ford programmed . but im not 100% sure of anything.


any advice and help is appreciated and if you need any info just let me know. i have a cheep scantool with live data and a vantage pro osscilascope.
thanks again
Last edit: 3 years 5 months ago by Patrickreaves.

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3 years 6 months ago #43445 by Matt T

Patrickreaves wrote: its said that a clogged CAT will lower the MAF reading due to restriction which causes the baro to be lower than expected, would the opposite be true if the cats were empty/hollow? that the MAF would be higher and air flow easier due to the less restrictive exhaust, i would think that it would alter the air flow and thus be skewed from the original air flow charts that ford programmed . but im not 100% sure of anything.


Removing the cats might improve VE slightly but it isn't going to bump a N/A motor up to 124%. Sounds like your MAF is over-reporting for some reason. Does the truck still have the stock air intake?
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3 years 6 months ago #43447 by Patrickreaves
thanks for the reply, and yes i believe the air duct is factory, but im not 100% positive as i bought the truck 3 years ago with this condition being there from the start. let me back up.

I bought the (2005 4.6 f150) with an anti theft issue that was disabling fuel, starter,injection pulse and spark. I then went to a junk yard and found a (2006 4.6 f150) that had everything i needed to swap the PATS (passive anti theft) components, ( ECM- key w/chip- antenna coil that reads the key-and also the instrument cluster) as research says they are all programmed together. I put all the used parts into the 2005 f150 and it fired right up but with -20% LTFT on B1and B2. I have been trying to find the issue for about 3 years now. didnt want to be a parts changer but want this issue resolved so have replaced all kinds of components relative to the fuel trims in hopes of getting lucky , nothing has worked yet. yesterday i changed out 5 different MAF's that i got from the junkyard and reset KAM every time, with no changes
research says that changing the diameter of the duct that the MAF lives in will change your MAF reading. ex. a larger than factory intake duct will slow down air velocity and read less air, and that a smaller than factory intake duct will speed up air velocity and read more air. an expert said changing the bore size by 1 mm will effect the MAF reading.
With that, i believe i understand what you are getting to when asking if I have e changed my air box. and the answer is no i have not changed it, but bought the truck used and the previous guy could have. but from my trips to the junk yard it looks like its the one that belongs to the truck. i have even seen 5.4s from 97-2003 with the exact same air duct.
im going to measure the diameter of the MAF housing and compare it to other 4.6's at the junk yard. because your question is exactly what i was thinking, that maybe its the air duct thats skewing the readings.

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3 years 6 months ago - 3 years 6 months ago #43448 by Patrickreaves
thank you Mondo, I understand what your saying ,that the Baro value is inferred from the MAF. ive just seen videos where a clogged cat will lower the baro reading and cause a lean condition. so was wondering if a less restrictive exhaust would do the opposite and raise the baro reading causing a rich condition.
Last edit: 3 years 6 months ago by Patrickreaves.

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3 years 6 months ago #43449 by Matt T
I was thinking aftermarket, "go faster", crap not incorrect factory looking ductwork. Your answer has provided some direction though. Took a quick look on rock auto and they show a different MAF for the '06. So your '06 PCM may not be reading your '05 MAF correctly. First link is '05, second '06.

www.rockauto.com/en/moreinfo.php?pk=3469422&cc=1431301&jsn=519

www.rockauto.com/en/moreinfo.php?pk=4436106&cc=1432397&jsn=630

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3 years 6 months ago - 3 years 6 months ago #43452 by Patrickreaves
thanks Matt ,no after market box of any kind.
but i believe that ford uses the same MAF sensor for the 4.2, 4.6,and 5.4 engines, (not 100%) so was thinking maybe the air box got switched out with a different factory box from a different engine. so i just went to the junk yard to look. The 5.4 ,2 valve and 4.6 have the same breather box and duct work from 97 to 2003. my 2005 4.6 has the exact same breather and duct as the years mentioned above. the 3v 5.4 is the only engine with a different breather box, duct, and a MAF (like the 2006 version you shared in the link in the above comment.)
Last edit: 3 years 6 months ago by Patrickreaves.

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3 years 5 months ago - 3 years 5 months ago #43473 by Patrickreaves
Ok here are some captures with engine warmed up at idle (650rpm)
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Last edit: 3 years 5 months ago by Patrickreaves.

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3 years 5 months ago - 3 years 5 months ago #43474 by Patrickreaves
This is a 1st gear pull to 4,700 rpm.
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Last edit: 3 years 5 months ago by Patrickreaves.

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3 years 5 months ago #43477 by Matt T

Patrickreaves wrote: thanks Matt ,no after market box of any kind.
but i believe that ford uses the same MAF sensor for the 4.2, 4.6,and 5.4 engines, (not 100%) so was thinking maybe the air box got switched out with a different factory box from a different engine. so i just went to the junk yard to look. The 5.4 ,2 valve and 4.6 have the same breather box and duct work from 97 to 2003. my 2005 4.6 has the exact same breather and duct as the years mentioned above. the 3v 5.4 is the only engine with a different breather box, duct, and a MAF (like the 2006 version you shared in the link in the above comment.)


You really need to either find an '06 4.6 truck or hit the O.E. parts catalog to find out what that '06 PCM will be programmed to work with. Pretty sure it will be different to the '05 and will require either an '06 intake system or a PCM reflash to fix this.
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3 years 5 months ago #43481 by Matt T

Monde wrote: The MAF specs with key on, engine running is 0.46- 2.44v. Your MAF voltage is within specs. It seems to be reporting accurately. Something else is causing the rich condition. Can you find the maf voltage specifications to compare it with mine? I got mine from mitchell.


The '05 MAF appears to be working properly but the '06 PCM isn't interpreting it correctly. VEs over 100 means the PCM is seeing more airflow than the engine can physically pump.
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3 years 5 months ago #43484 by BetterCallBrody
If you had access to HP Tuners or SCT you could download the file and compare the table to a known good stock one to see if its stock, maybe the '06 had a tune on it.
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3 years 5 months ago #43485 by Patrickreaves
i appreciate the input from every one , and now that i think about it, i worked on a 2006 f150 4.6 a few years ago that had a misfire from coolant entering the the spark plug hole and was shorting out the spark. it had a( black plastic manifold with short/low runners). I changed the manifold and actually kept the intake and just stored it with other junk.
how ever my intake is all aluminum and is probably twice as high as the plastic one. i remember trying to research when ford revised the intake and was unsuccessful as it wasn't that important at the time. i will now resume that research . below are pictures of the two intake manifolds

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3 years 5 months ago - 3 years 5 months ago #43486 by Patrickreaves
Here's the different manifolds. The little black plastic one is for the 07-08 f150 4.6
And the aluminum one is the one I currently have on my 2005( manufactured in 2004) f150 4.6.
As suggested above maybe there is a difference in the transfer function table in the micro processor between the two different engine computers, and thus causing the issue of the over reporting MAF sensor.
but at the same time, i am in mustang and f150 groups on face book , and there are a lot of people opting to swap out there intake manifolds with that of a ford windstar as it supposedly has the best intake. i wonder if they had issues like this. what about people that put the P.I. heads on non P.I. engines, surely doing any changes would cause air flow velocity issues.
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Last edit: 3 years 5 months ago by Patrickreaves.

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3 years 5 months ago #43490 by Patrickreaves

Monde wrote:

Patrickreaves wrote: Ok here are some captures with engine warmed up at idle (650rpm)




The MAF specs with key on, engine running is 0.46- 2.44v. Your MAF voltage is within specs. It seems to be reporting accurately. Something else is causing the rich condition. Can you find the maf voltage specifications to compare it with mine? I got mine from mitchell.


I watch a lot of "ford tech makuloco channel" as he is a ford tech works on these fords and provides lots of content like scanner danner does. But he says that the maf spec should be .75 volts at idle and up to 4 volts WOT. but have not confirmed this spec with any other source.

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3 years 5 months ago #43491 by Patrickreaves

BetterCallBrody wrote: If you had access to HP Tuners or SCT you could download the file and compare the table to a known good stock one to see if its stock, maybe the '06 had a tune on it.


as far as a tune on the 2006 ecm, any thing is possible. I dont know how i could tell if it has one or not. My cruise control does not work because the 2006 ECM was on a plain Jane XL model that doesn't have cruise control, while my truck is an XLT and does have cruise control. with my scan tool if i put the original ecm in i can actually test the buttons functions on my steering wheel, and they all work. they do not with the 2006 f150 XL ecm installed.

i have got some quotes from lock smiths to try to fix the anti theft issue, $180 just to make a chipped key. and i have to have 2 keys to program it.
But then im also worried that its the ecm that is bad and not the key. it just sounds like a $1000 repair that i cant do myself. even worst would be getting the anti theft issue fixed only to find -20% fuel trims in the end lol . what i can do is find a junk yard ecm from 2005 with the same configuration as my truck.

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3 years 5 months ago - 3 years 5 months ago #43501 by Patrickreaves
i have great news, i went to the junkyard and found another ECM and key out of a 2005. The part numbers were a little bit different but it was a 4.6 xlt with the same trans code. my truck now has the correct throttle response, matter of fact that was the main issue, that some times i would apply part throttle to get moving and it would do nothing for about 4 seconds, i would then floor it , and that would eventually get it going. this meant i could not pull out into traffic like normal, more like a semi truck.
My fuel trims are now

STFTB1 = +/- 5%
STFTB2 = +/- 5%
LTFTB1 = 0%
LTFTB2 = 0%

my MAF voltages are still the same , however my new grams /second reading at 4800 rpm = 177. V.E is now 85% and the old readings were = 254. grams/second @ 4800 rpm. V.E.=124%. It must just be the way its interpreted by the ECM that was different, just as Matt suggested. So great call on his part. I have literally been chasing this issue off and on for 3 years. so just want to say thank you to Matt, and Mondo and everyone who made comments and suggestions. I am very happy to have this issue resolved. And my cruise control works for the first time also.
Last edit: 3 years 5 months ago by Patrickreaves.
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