Multiple vacuum problems. Now receiving P0401 and P0308 codes.

The emission hose routing diagram should be on a 3" x 5" sticker either on the underside of the hood or on the top of the radiator support or on the air cleaner housing cover. It's kind of a symbolic diagram but will indicate what goes where. There are very few vacuum lines on one of these so it should be pretty straight forward.

I have your vehicle as a 97 Ford Expedition...Is this correct? Reason I ask is that Ford uses Coil-On-Plug and you said "I changed the wires"...Which would mean all eight coils were changed...P0308 is telling you the ECM is seeing a fault on cylinder #8...I would strongly suspect a bad coil for that cylinder...Question; Did you change all eight coils? If not change #8...saailer


I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

The EGR valve is in a very difficult spot to work on. If the EGR is bad it will set off the check engine light and make the vehicle run rough or stall at idle. It really doesn't make it run rough while driving or accelerating. What are the conditions when the car runs rough?

OBD-II Trouble Code P0401 - Insufficient EGR Flow

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR. You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.

A code P0401 most likely means one or more of the following has happened:
The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

Check it and keep us updated. Hope this helps (remember to rating this free answer).

If you have a manifold leak that will cause a MASSIVE vacuum leak and make it run rough at idle only. Look at your short term fuel trims with a scanner, if they are way negative you have a vacuum leak. Fix the intake manifold leak and that will fix your problem.

Could be a EGR vacuum issue or temp sensor issue

Common Problems That Trigger the P0401 Code

• Restriction in the EGR passages, usually caused by carbon buildup
• Lack of a proper vacuum signal to the EGR Valve from EGR Vacuum Solenoid
  
• EGR Vacuum Modulator is defective
• EGR Temperature Sensor is defective
• EGR Valve is defective

This is from:
http://repairpal.com/OBD-II-Code-P0401-Ford

This code is an EGR code for insufficient amount of egr. It could be that the egr tube is clogged or the egr itself is bad or there is not enough vacuum to open the egr properly. There is also a sensor called the DPFE(differential pressure feedback egr) is faulty.

This blinking light indicates a problem. You will have to have it scanned for trouble codes to find out
what it is.

the light may have nothing to do with the previous fault
run the fault codes again

try to clean out the tubes, it is very common for the tubes to get clogged up with carbon, also check for any breaks in the vacuum lines