Hi! I have a 2003 ford f250 w/ a 5.4 and a 6 sp. Recently been diagnoising a missfire. After doing all the typical ford 5.4 fixes and it not fixing the problem, I Finally just took it to ford to be diagnosed. Has two bad spark plugs (just put new autolites in about 3500 miles ago). Also, the mechanic said that my truck is running lean. He told me that the MAF sets the fueling for the truck. Don't the o2 sensors play a role in fueling too????
My truck doesn't have the cat (not my choice, previous owner took it off) and doesn't have any restriction in the exhaust so I was not suprised when he said it was a little lean.

First question, Can anyone tell me if what he said was 100% true about the MAF???

Second question, other than having the injectors cleaned or buying a new MAF, what all can I do to richen up the fueling (leaning twords x3 tuner from mike @ 5 star...any suggestions welcomed).

Third question, how much of a difference does the ethanol in the fuel make w/ my 2003 truck????
Thanks,
robert

 

What all did you replace already? How many miles on the truck? Did you change the COP boots with the plug change?

The MAF, O2s, intake air temp sensor among other things are used to try and run and keep the programed a/f ratio. The program in the ECM/PCM sets the A/F ratio, the sensors help the computer calculate how much fuel is needed to maintain the programmed a/f ratio throughout the rpm range. How many O2 sensors do you have? If you only have two, one on each bank of the y-pipe right after the exhaust manifolds your ok. If you have an O2 downstream behind where the cat used to be you will have issues if the O2 is not shut off. That said you can expect the plugs to look a little white with some lite ash deposits. Your not going to see a light brown color on the ceramic like in some other applications.

I would get some CRC MAF cleaner and clean your MAF sensor. Replace the fuel filter if you didn't replace it recently and maybe change the COP boots due to the age. Maybe run a couple tanks of Marine Stabil and/or Chevron with Techron fuel system cleaner through the truck to help clean the injectors. The Chevron w/ Techron is the same as the Motorcraft stuff but cheaper. I would also check for any air leaks around the intake, intake manifold and hoses leading to either. Make sure the rubber plug that the MAF wires go through at the air cleaner didn't come out and let in unmetered air. Check for exhaust leaks at the exhaust manifolds.

These trucks from factory do not use WOT fuel enrichment. They basically run stoich (14.7:1) all the time. E10 fuel leans out the a/f fuel ratio because the 10% ethanol in the gas now gives it a stoich of 14.2:1. The 5 star tuner will add fuel at WOT and when needed and I highly recommend his tunes BUT I would make sure you have no other issues before installing the tuner.

 

just to answer your questions:

I changed/fixed/or cleaned the following:
new fuel filter
cleaned maf
cleaned iac
checked hoses for leaks
cleaned the throttle body
changed the crank pos sen
checked the cam pos sen
checked the tps
checked the injector ohms (11-14 normal mine all were 13.2 ohms)
changed all 8 cops (new cops come with the new boots)
put in new plugs (the autolite plugs had about 3500 miles)
ran 1 tank of mid grade fuel w/ techron fuel cleaner (had to buy 2 bottles for the 33 gal tank)
and I'm sure I forgot something

gave up after everything and took it to the ford dealer. Here, two of my 3500 mile old autolite plugs had gone bad. One was creating a pretty steady miss, and another one was more sporatic miss. Also they said that the truck was running lean.

I have an o2 sensor on each pipe, none after the cat. The cat has been removed and has two thrush (staight through, only has baffles) mufflers. So, due to the lack of back pressure I'm not suprised that it's running a little lean.

Thanks,
Robert

 

I always wonder when someone says a free flowing exhaust system causes you to run lean.

Since your engine becomes more efficient at expelling exhaust, wouldn't it run at the same air fuel ratio? Your 14:1 ratio (or what ever your PCM determines is correct) remains 14:1. That ratio is set upstream from the combustion chamber.

If exhaust remains, less fuel charge enters the combustion chamber. When mixed with the exhaust, your 14:1 ratio becomes diluted to something like 15:1.

To say free flowing exhaust makes you run lean would be true only if your fuel system would not be able to supply the additional fuel required. If that were the case, you have issues far beyond running a little lean.

 

O2 sensors only effects closed loop A/F. The MAP sensor along with pcm programming handles open loop. Too free flowing of an exhaust will cause a slight lean condition. Reason being is the lack of back pressure hurts the scavenging effect.

 

Very true. I can't see why an EFI system wouldn't compensate for the less restrictive exhaust, but with carbed engines, lots of people that add exhausts only to their vehicles find it usually runs worse. The reason I think an EFI should be able to tune itself is that lots of EFI cars run "dry" nitrous systems which only add nitrous rather than also adding gas as non-EFI cars would. The O2 sensor sees the lean condition and calls for more fuel, therefore tuning itself rather quickly. Seems like it should see the exhaust flow the same way.

 

It would be nice if our trucks or any EFI system could self tune. But i don't see the manufactures doing it any time soon. The only two manufactures that i can think of that will warranty a tuner is victory and HD. But then again you will melt any air cooled motor adding mods without tunning it. The closest thing i can think of to what your talking about is in the V twin world called power commander 5. It only took fuel injection about 30 years to be the norm so maybe there is hope to see self tuning in another 20 years.

 

Which the 2V SDs run over 95% of the time. Runs open loop for about 15-30 seconds after startup, during engine braking, and when the catylist and/or engine is over temp.

Sounds like you went over thing very well. IF your misfire is gone just get a tuner from 5 Star. Your truck will run better and you will notice more power and the a/f ratio will be corrected. His performance and tow tunes are great.

People usually have good results with autolites, I use them myself. On my modulars I use MC SP479 plugs though because I like the nickel plating. What number autolites did you use?

I've seen dyno charts before and after aftermarket intakes, exhausts and headers were installed and they usually do lean out the A/F ratio. Add the leaning of the aftermarket parts and then add the ethanol and it makes it even worse. The stock tune is made with all OE components in mind. The pcm is even programmed to recognize the timing between when the cylinder fires and when the expended exhaust gases from that cylinder reach the O2, so I've been told. A complex system for sure.

 

The EFI doesn't actually "tune", it's more like an "adjustment" and they will do it right now and have been able to for 20+ years. Look up how dry nitrous systems work and you'll see what I mean. EFI systems actually make many thousands of adjustments everytime you drive it. They read the outgoing gas content, the water temp, throttle position, engine load and many other factors and adjust the A/F mix accordingly. I also suspect that with the huge number of bolt on, cat-back systems out there right now in use that any modern EFI system can and will compensate for the increase in flow immediately. Also, I'm not aware of any air-cooled trucks, so I'm not sure what you're talking about there, either.

 

Thats good to know. Do you know if the 3v motors are the same?

I understand how EFI works making small changes to keep the A/F due to temp, humidity, air density ect. The OP is missing a CAT and a large amount of back pressure because of it. The stock programming can't make major adjustments to A/F. Which is why i brought up tuners. Sorry if I confused you. I wrench on motorcycles so its easier for me to use them as an example. That is why i used the air cooled motor comment as harley and victory use air cooled motors and will warrenty tuners. As for self tuning thats what i meant. If you add CAI and CAT back exhaust it will run slightly lean but the pcm's programming can adjust for it. But say you add a cam and throttle body with them. The pcm wont be able to comensate. With self tuning the pcm would be able to make the changes to keep the A/F within the stock programming.

 

[quote=dkf;10944779]
People usually have good results with autolites, I use them myself. On my modulars I use MC SP479 plugs though because I like the nickel plating. What number autolites did you use?
quote]


If I remember correctly they were ap-103's??? They were what crossed over from the stock plugs. I don't think that the mcsp 479's were what was what I removed from the truck when I changed them. If this sounds wrong, I will gladly go and look @ one of the factory plugs(I still have them).

Also, with out the cat there is now where near the back pressure that what comes from the factory. The computer can make small adjustments, but I can not adjust completely to the needed fuel when you combine the lack of cat and the ethanol in the fuel.

So, on a side note, does this mean that I'll prolly get worse milage after I get the tuner and install the 87 tune?? I am pretty consistant in driving habbits and I average about 13.5 beating around between farms/backroads. The best that I've got was 15.5!!!
Thanks,
Robert

 

I got another question: How can my dealer sell mcsp 479 spark plugs for $8 a piece(not installed, just the plug)?? I asked their parts dept. how much plugs were for my truck.

 

The Autolite AP-103 plugs are good plugs. I've installed quite a few of them over the years and never had any issues at all.

The dealer gouges A LOT on parts prices to make money no doubt about it. I bought 10 SP479 Motorcraft plugs the other month for under $34 to my door from Rock Auto.

Under normal driving conditions you probably will not notice an mpg difference. The major fuel use difference will be at WOT because the A/F ratio will go from 14.7:1 down to between 12.5:1 - 13:1.


The 3V are tuned differently. They have WOT fuel enrichment. The stock tuning still leaves some power on the table though.

 

I had always heard that Autolites were good plugs, but had the same problem happen to me. It was #7, and they had less than 700 miles on them. I changed the one plug, the problem went away. Eventually, I changed them all out again to Motorcraft's.

 

I just don't underderstand because autolite makes motorcraft????? But, it's fixed for now and I need to call mike @ five star tomorrow (b/c I was supposed to follow up today and got stuck in the woods trying to cut firewood).