A week ago I bought a 98 F150 4x4 with the 4.6. I'm a lifelong Ford owner and this is my 3rd vehicle with the 4.6 engine. My other current car is a 4.6 Town Car with which I am very happy. In the week I've owned this truck however, I've been futzing with the EGR system due to a recurring P0401 code. (I am also experiencing slightly rough idle and HORRIBLE fuel economy).

When it first came on, I knew I would want to clean the EGR ports in the throttle body....I had to do this in the past on my other cars with this same motor. So I took the throttle body off and cleaned the whole thing including the EGR passages (one of which was completely clogged). The problem persisted, so I tested the EGR valve with a vacuum pump. I was able to achieve a small change in idle but not a near-stall condition. So I replaced the EGR valve, and while I was at it, I threw on a new DPFE sensor to see if it would do the trick. So far none of these has solved the issue. The DPFE hoses are fine and the EGR tube is also clear.

Today I checked the EGR solenoid voltage....it is receiving 12v from the battery. I disconnected the supply vacuum hose from the solenoid and with the engine idling I was not able to observe any vacuum present at the tip of that hose where it would connect to the solenoid (I felt for vacuum with my finger as well as hooking up a mityvac pump and seeing if the pump's dial would read any vacuum at idle). I'm not sure if this means I'm lacking vacuum there or if there is just normally no vacuum there at idle.

So, at this point here are the knowns:

-EGR is brand new and works. I even tested the new EGR and it damn near stalled when I applied vacuum to the nipple.
-DPFE is new.
-EGR tube is clear and dpfe hoses are also clear and not leaking.
- EGR ports and throttle body are clean.

So what gives? What I'm mainly after is advice on the procedural part of this whole thing - what steps to try next after the most common fixes (cleaning ports, checking EGR, DPFE and EGR tube). I fear we're entering into the realm of major vacuum and electrical system inspections which I dread.

Thanks in advance, I hope to fix this issue soon and be able to enjoy my new truck a lot more than I am now.

 

Carefully trace out the EGR vacuum lines stating from the manifold.
There may be one that goes into the wheel well to a canister that is causing the test fault.
The EGR never has vacuum at idle or any other time except under specific conditions in OD or third gear at light throttle above 45 mph.
Look for codes with a reader or Scanner because there may be others your missing after the 401 clears and the CEL is still on for some other code.
Fuel mileage is enhanced and is related to the EGR system during the specific time it operates. With a EGR code set, the EGR system operation is disabled.
Vacuum leaks that shift the fuel tables rich also have a huge effect on fuel mileage.
Restricted cats have a large effect on mileage and power.
Lazy Ox sensors also contribute to reduced fuel mileage.
Good luck.

 

Thanks for the info....gives me somewhere to start anyhow.

So are you saying that the supply line to the EGR solenoid will not have vacuum at idle, or are you saying that the green hose going from the solenoid to the egr itself will have no vacuum at idle? I figured the green EGR vacuum line wouldn't at idle since to do so would open the valve and cause the engine to stumble.

 

Solenoid (EVR) to EGR has little to no vacuum at idle.
The EVR is actually a 3 port device.
At rest is closes off engine vacuum and opens the EGR to outside air.
When operated it passes vacuum to the EGR and closes off outside air.
It needs to operate this way so the EGR will close again once it is operated or it will hang open and cause drivability issues.
Good luck.