white89gt

To get the proper reading, the vacuum line should be disconnected from the regulator, and plugged off.

SpartanSV

Pressure with the vacuum line disconnected and plugged was 41 psi. I thought the issue of being rich at idle may be related to injectors hanging open, but the fuel system held pressure after shutting the truck off.

I had an egr insuffictiant flow code at some point and the throttle stuck once so I know the throttle body is full of nasty. I'll be pulling it off for a cleaning and inspection.

Still looking for ideas on what else could cause a rich condition at idle and a lean condition under load.

akdoggie

This is one of the most covered question on this site. There is at least 100 of these threads.

Almost always there are 2-3 reasons this happens. Since it is lean reading, most likely (1) dirty or defective MAF, (2) vacuum leak after the MAF, (3) bad PCV valve and or the PCV connector. A weak fuel pump can affect this code, as Brew pointed out. There are a couple others, but these are the very most common with our truck models. Use of any PCV other than Motorcraft, can and will in a lot cases, throw these codes. Check the simple things first, then if they check out, go for the pump.

SpartanSV

I'm aware that these are common codes for these trucks, but the codes almost always relate to a vacuum leak. My measured fuel trims indicate that a vacuum leak isn't the issue. My LTFT's show rich at idle and lean under load. A vacuum leak would give fuel trims that show lean at idle with less adjustment needed under load.

I have cleaned my MAF with MAF specific cleaner, and I'm confident that it is giving accurate readings. 50 cfm at idle about 150 cfm at 1500 rpm.

For the sake of being thorough, I have made a smoke machine using a glowplug from a 7.3 diesel and a live bait aerator (I'll post pics if anyone is interested). I'm very confident that a vacuum leak isn't the issue. I've also given measurements for fuel pressure, and I am confident that is not the issue.

I'm not one to ask for help without thoroughly researching first. My issue seems to be more unique than the traditional lean code problems.

akdoggie

Are you running a K & N element by any chance? Have you changed the fuel filter recently?

SpartanSV

Standard paper filter. Fuel filter was replaced about 5k miles ago.

SpartanSV

How would a bad fuel pump cause a rich condition at idle? Pressure is staying in spec when the truck is driven under different loads.

akdoggie

I'm still leaning to the MAF.

Here is a decent write up on checking the MAF. I realize you research things, but this might be something you haven't seen. It is Ford specific to the 4.2, 4.6 and 5.4's. It you can't use it, maybe someone else can.

http://easyautodiagnostics.com/ford/...sensor-tests-1

SpartanSV

Thanks for the link. I had seen that article but hadn't done the test. I have an OBDII bluetooth adapter and torque pro which allows me to see what the MAF is reading. The readings seem stable and accurate, but I'll be doing the test anyway in case there is some irregularity that isn't showing up on my graphs.

Fordfan2006

Do you have ticking exhaust manifolds? If they are bad enough you'll run lean too.