It's been ~1wk since my last post on this issue. My CEL has remained off and I've logged a few miles going to & from work (80mi/day), but my MPG is still poor. I'm not sure where to look next. Below is a summary of the work done.

- New Fuel Filter
- New Air Filter
- New PCV
- Cleaned MAF
- Cleaned IACV
- Cleaned Throttle Body (on vehicle)
- Removed PCV line & inspected for leaks. Rear elbow swapped out with used one.
- Upper vac line from TB elbow to DR firewall replaced.
- O2 sensors validate with carb cleaner (above 0.8V with rich condition
- I checked the vac lines on the engine and most are pulling 20in at idle.
- The brake booster can hold a vacuum

After the truck has warmed up and is driving around my LT Fuel Trims are between 0 & +10% consistently. At idle they have occasionally spiked over +10%.

Is it possible for my MAF to be bad? How can I check this?

 

Yea, you should specify which PCV valve your using and O2 sensors. It matters. For the most part, only use a Motorcraft PCV valve. Other DO NOT have the correct margins. For the O2's, you need to run louvered that spin exhaust gases around the sensor. The worst sensor that I've seen is BW's (Borg Warner's). The best I've seen is Motorcraft on the graph. You can use Bosch or even those skinny NTK's, but definitely don't use the BW's.

Also, I pull the emissions harness completely and bench test it with vac tool. You disconnect at the trunk connection over by the battery box and the entire harness is easily removed. I can't tell you the number of times that the elbows were pushed onto the tube ends to far cutting off vac completely.

You also need to dip the elbow/boots in MEK when reconnecting. Specially if they've been exposed CC and have lost integrity lol. This shrinks boot ends or rubber connections onto it's fitting leaving them leak free. Always use MEK on most rubber connects. Unless of course the line is under a lot of pressure, to where you would need a metal/rigid fastener. This eliminates the need for clamps on old rubber hoses. In some instances, it's standard with new installs for the perfect fit. Besides, clamps are tacky lol.

 

Yeah, I thought Ford had one of these. -Here's a Ford factory write up and how-to. It's generated for repair, but apply this procedure as standard practice and you won't have leakage problems, as long as there's no damaged or badly worn parts. It really does work well, better than you might think, -

 

Also, make sure that the boot and hose ends are set right. Over time and I'm not sure how this happens, just that it can, the 90 degree boots get pushed on to far and cut vac to 0hg. They may eventually leak vs making it to intention.

The emissions harness has bulb markers that are used as a guide and preventative. These don't always work over time and can get pushed onto to the line to far.

Here's what I mean about the bulb markers or limit, the boots aren't to exceed bulb, -





The reason for such an explanation. It can make a major difference with the way she runs and has been the root cause of many issues troubleshooted in the past.

 

I just resolved these codes TWICE. I had been offroading and got stuck and was trying to work my way out of it for quite some while and got my truck hot, and my PCV elbows and fittings got very pliable. They didn't LOOK to be bad, but when I tried to pull them off they ripped. So make sure and inspect those very well. My other isse was my brake booster but you probably wouldn't have the same issue. Somehow, it cracked around the area where it is bulged by where the master cylinder seats. Crazy stuff. Honestly, what sucks about these codes is there's tons of different possible culprits.

 

[QUOTE=jbrew;4960827]Yea, you should specify which PCV valve your using and O2 sensors. It matters. For the most part, only use a Motorcraft PCV valve. QUOTE]

I replaced the PCV with one from Autozone, but do have a used Motorcraft one to swap in.

Also, I didn't replace the O2, they are factory original. I just validated their function by inducing a rich condition and watching the voltage exceed 0.8V.

I will check the emissions harness tonight and see what I can find. Nice tip regarding the MEK.

 

Drove truck home in 4HI last night and got better mpg, I think it might be a leak in 2WD component by battery. Will check tonight

 

Yea, that's where they fracture and break. The pink and blue vacuum lines become real brittle,- between the battery box and firewall. The exhaust manifold heat traps a little right there and dries them out over time. They can snap like a twig when touched. Just at that location.

 

So I checked vacuum. The actuator on axle is moving when switched from 2WD to 4WD. I have 20in vac at the pink in 2wd and 20in at blue in 4wd. At the solenoids I have 20in at both black and white vac supply lines. My vac in the pink line in 4wd when I plug the black line is 12in. Is that right, or a leak in the diaphragm on actuator? I'm going to junk yard tomorrow to pull a few spares to mess with.

 

I ruled out the 4wd actuator since it can hold vac in both pink and blue line. Couple short lines in vac system showed deterioration, so I replaced. Drove it around last night for a while and fuel trims were near zero. Idled at around 5%. Now today I'm idling with lt trims at 14%. The 4wd solenoids appear to be functioning.

 

That's not how you rule out the actuator. You ruled out the lines tho.

 

How are too checking for vacuum? With a hand pump or when the engine is running with a gauge? Also you don't have any exhaust manifold leaks right?(cracks)
Does your reader show you freeze frame data for a set code?
Also it seems odd that your setting those codes, I think 18% roughly on LT trim is what triggers lean. What I do to look for leans is set my code reader to o2 sensor voltage, then spray your choice of flammable not rubber eating fluid around all aspects of intake. Even exhaust... lol be very careful with exhaust as its hot obvs can catch fire.

 

call me crazy but did you check and make sure your cat converters weren't clogged up?

 

An update. I haven't thrown the P0171 & P0174 codes for a couple of weeks. Since I last looked at the truck and reset the battery. I am still getting ~10% LT fuel trim at idle. My mpg is horrible, probably ~10 mpg. Occasionally when I check LT trims they are around 15%. I have not seen my lt trims go negative. That would mean that it is always adding fuel right? Also, my LT trims are not very stable even after 500mi of driving. They seem to bounce around. At 55mph they are around 3% or so.
I have a mity-vac pump with gage.
How would I check the 4WD actuator for vacuum? I put 20in to both blue and pink after the solenoid.
Since this issue first came up and I was setting codes I have replaced a few of the deteriorated vac lines and have seen s slight improvement.

 

I checked my LT Trims again on the way to work. Driving ~1600RPM im getting between +3 & +7%. When I arrived at work, hot idle was +17%, which is the highest I have seen it lately. This morning was unusually cold (15F), how would temperature affect the LT fuel trims? Does the denser colder air register more with a O2 sensor?