back to the issue at hand...

[tedennis]

OK... Upstream o2 sensors are the ones that impact fuel. They will fluctuate from about .100 to .900 volts or 100 to 900 millivolts. Depends on scanner being used. 500 is the middle. It should not stay there though. It should swing from 100 to 900 and back constantly. That is normal operation. If it is staying over 500 it is running rich. Because of this, the fuel trims will go negative. This means the computer is reducing the injector on time to cut fuel.

If the o2 sensor is reading less then 500 more often then it is running lean. The fuel trims will go positive which means computer is adding fuel by increasing injector on time.

Perfect fuel trims are 0. The goal of the short-term is to keep the long term at 0. The short term will change constantly. The long term more slowly. The short term fuel trim will increase and decrease to try to get the long term to 0. The "total fuel trim" is the short term and long term added together.

I will add more later. Got to run.

 

[tedennis]

A little more. Temperature sensors can play a large part of driveability issues. If the sensor is reading hotter or colder than actual ambient temp, the computer will change the amount of fuel sent to engine. Colder air is denser air, more air molecules in same volume. So the computer will send more fuel to compensate for denser air. Same for barometric pressure. The higher the elevation, the less dense the air. If the computer does not cut back on fuel it will flood it out and it will either run very bad or not at all.

The mass air flow sensor measures the amount of incoming air to help determine amount of fuel injector on time. If it is higher or lower than actual, fuel will reflect it and cause it to run too rich or too lean. Both will cause a lack of power.

The egr opens up at cruising speeds only. It allows exhaust gases to enter cylinder which cannot contribute to combustion and just take up space. In doing so, it reduces the cylinder temperature which reduces the oxides of nitrogen produced by combustion. This will be referred to as NOX emissions. It is one of 4 monitored in states that require annual inspections.

If the valve sticks closed, you will not feel it. You should get a CEL and a code but no other ill effects. However, if it sticks open, it will reduce power, run like crap and if bad enough, stall at an idle.

Vacuum leak can cause similar issue but would be obvious. Fuel trims would be way positive at idle. Normal range is +/- 7. More than that and i get suspicious.

Personally, the way you describe it, i think you may have a mass air flow issue. But hard to say without having a scanner hooked up and chdcking. The only way to find it other than throwing parts at it is to take it to a shop that has a good driveability tech. I say good because the bad ones just throw parts at it too and charge you for them. I good tech will be able to figure it out in an hour or two with a scanner. most shops around here charge $70-90 per hour and guarantee their work.

My recommendation as a guy that does this for a living is find a good shop and let them look at it. You have already spent more than the diagnostic would have chasing it.

Good luck and please post when you get it fixed.

 

[sitruc_btb]

The dealer is always an option. They have scan tools specifically for Ford systems, which aids in diagnosis.

 

[jlo82585]

yeah I printed off the no CEL power loss/ surge troubleshooting guide from fords tech. website. I wont really be able to use it due to needing special diagnostic software to read ford PIDs and my $300 mac tools scanner wont do it.... essentially it want me to test the following

EGR valve
DPFE sensor
injectors
plugs
fuel filter
fuel pump
COP's
IAT sensor
MAF sensor

since fuel filter, pump and plugs have been replaced I can cross those off. I tested the IAT sensor with my scanner and its what I would call close enough ( =/- 5F ) so thats okay, COP's in my mind should create a hard miss or CEL if they were bad, so im left with MAF, EGR, injectors, and DPFE sensor. I am going to record data from the drive home from work tomorrow and see if I can find an over or under fueling situation going on. anyone know how to test a MAF sensor? They are $70-90 and I don't want to throw that kind of money at it.

 

[tedennis]

Hard to test a Maf without a scanner. One way is to have truck sitting warmed up at idle and tap on it. If the engine stutters at all, is a sign it is bad.

Also, i know you dont have this symptom, but have had cars come in that would crank, no start. Unplug the maf and would fire right up. Doesnt help you much though.

A general rule of thumb i was always taught was at a warm idle, the grams per second should be close to the displacement in cc's. So a 5.4 l equals 5400 cc's of displacement. So grams per second should be close to 5400. Ive always seen that actual was a little lower than cc's. Hope this helps some.

And i have also seen brand new fuel pumps be weak. Will supply enogh fuel at idle and low rpms but lack at higher rpm. Can cause lean condition. You can check by dead heading the pump. You need a minimum of 70 psi fuel pressure. May be able to find example of test on youtube.

 

[98EXPnSRQ]

Have you checked the exhaust back pressure?

 

[jlo82585]

nice I will have to try the dead head test. I am certain that there is an issue with the fuel pump as since I replaced it I have an issue with the engine cutting out on left hand turns when the tank is 1/2 full or less. also with regards to exhaust back pressure, one ore more of the cats would have to collapse in order for that to happen as I removed the muffler and resonator last summer. I am also running 3" pipe from the cats back so I dont think that could be an issue

 

[jlo82585]

okay so I finally got my buddies code reader and recorded a short 5 mile trip and actually, I didnt see any problems, the fuel trims were where I would expect them to be all +/- 7%. o2's all looked good for the most part but they were changing too quickly for me to gather a really good reading. the power loss is still there but like I said, after the plugs its not nearly as bad as it used to be. and after the plugs the fuel mileage is around 11-12 in town and 13-15 on the highway so perhaps the plugs were the main issue. 2-3 of the 8 plugs were pretty much gone where as the others looked pretty good so im thinking COP's may be in order soon. now I just have to diagnose the issue with engine cutout on left hand turns... still looking for any information on this issue...

 

[lunchboxlust]

I ran my tank almost empty one time and after that the rig ran like crap some times. wouldn't always throw a code. IF I remember right it got worse on hills and fast turning. It ended up being the fuel filter. I had just put one on it not to long before that tho so I dicked around and changed all sorts of stuff first. When I change the filter again I cut it apart and it looked like it was completely full of coffee grounds.