Healthy engine vacuum and DTC question

[shadow460]

TL;dr What's the vacuum supposed to be on a healthy 4.6 engine. Are there any serious DTC codes the truck might throw?

The old truck threw me a P0401 yesterday which I traced back to either a faulty DFPE (sp) sensor or clogged ports. I replaced the sensor last year, which cleared that code for a good long while. Voltage changes from 1.1 to 1.25 while pulling a vacuum on the EGR valve, so I think the ports are clogged.
However, the troubleshooting process left me with a couple of questions:
First, what's the normal vacuum reading on a healthy engine? Mine sits at 18 and does not move until I hit the throttle. I think it went up when I hit the gas, but it slowly returned (took a few seconds) to 18 and set up shop there.
Second, are there any truly serious DTC codes? I carry a code scanner as part of my emergency equipment (jumper cables, jack, etc.). Anytime I get a code I read it ASAP. So far I've had (and successfully repaired) p0171, p0174, and p0403 (IIRC anyway... see above).
Gonna open up the engine a bit when three of four new gaskets arrive. I might change out the EGR valve itself for $60 just to get a lifetime warranty on that. While open I plan to clean the ports on the throttle body elbow and try to clean out or replace the hoses and the tube going to my exhaust.

 

[98eb5.4]

dealt with p0401 recently, brand new dpfe was bad so i wouldn't assume yours is good,

seen a test on u tube for clogged ports, u pull a vacuum off the top of the egr, u can do that by sucking on a tube, engine should slow down & run ruff, if not quit,

check easy stuff first like vac lines for leaks, loose lines/faulty gas cap, etc..

i ended up checking vac at the egr solenoid & doesn't take much for it to work at that point, there's alot more vac from the main line

do you mean serious codes involving p0401? 401 can mean big dough if it involves exhaust egr tubes that can turn into an ex manifold job, cleaning clogged intake ports ain't cheap,

yes, some codes can be very serious, at the same time, a code can be either or cos they often don't tell the whole story

p0401 in itself is mainly a fuel mileage hit, but can involve money to fix if emission testing is in the picture

a misfire code could be a spark plug or coil, but could also mean a head gasket ..etc, u don't wanna ignore a minor sensor code, if it results in plugged cats (converters) ..4 of those on a expy

lotsa minor stuff can trigger p0401 that all needs to be ruled out first, and it can be a real pia figuring out what exactly is causing the p0401

u read alot about clogging but i didn't have the issue with ~ 477k clicks and cleaning the intake ports alone can get into some dough,

might be cheaper to spend money for a full diagnostic of p0401 systems/parts, even tho can easely cost 100+ bux but then can point directly to a problem or faulty part

the 3 main ~ cheap, easy to fix parts are dpfe sensor, egr solenoid, egr, shop wanted ~ 45 bux to do the solenoid that came off easy by 2 small bolts & a wire connection,

u can check alota stuff on your own but then also not know for sure if what u are checking is ok or not

Part 1 -How to Test the Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor

 

[Bedrck47]

The bad thing with the 4.6 is the exhaust ports thru the throttle body. On the 4.6 there are two small ports that tend to get clogged whereas the 5.4 has one larger port which will over time clog but not as bad as the 4.6.

Also the two rubber hoses from the DFPE sensor to the Exhaust tube riser tend to dry rot over time and should be replaced

 

[shadow460]

Most of that stuff is now under lifetime warranty. The Check Engine light went out but the code is still set. I will watch it to see if the light comes back on and if it does, I'll clean the ports here at home.
I did some research on the exhaust tube. If that's clogged I can blow the carbon back down into the exhaust system with compressed air. If I stopped up the ports going to the sensor and shot air down the fitting where the EGR valve is it would force everything back into the exhaust system where it came from, then all I'd have to do is unstop the small ports and hook 'em back up.
Replacing those rubber hoses makes a lot of sense.
BTW, the other day while troubleshooting it was as if the computer was simply turning off the EGR system. I didn't have the valve hooked up during that test; instead the vacuum line was hooked to my vacuum pump so I could monitor the vacuum "signal" to the valve.
As for bad head gaskets... that's easy to spot if you know what you're looking for. IT took me all of five minutes to explain to a friend of mine why he was losing oil in a half ton Chevy. The coolant looked like coffee, which is a pretty big sign. So is white smoke or an obvious leak from that mating surface. ODdly enough he drove the old Chevy for about six more months before oil contamination killed one of the crankshaft bearings.
In my Expy the coolant and oil are the right colors.

 

[shadow460]

So how about the vacuum reading on a healthy engine? 18? 21? More?

 

[Bedrck47]

check the attached link

http://www.expeditionforum.com/f42/about-egr-pcv-dpff-evap-iat-tps-maf-23583/#post191356