Multiple vacuum problems. Now receiving P0401 and P0308 codes.
1998 Ford Expedition 5.4 Triton. I have replaced numerous vacuum lines, such as the PCV line, and others due to holes or tears. Now the engine runs rough again. Codes indicated are P0401 and P0308. Any suggestions?
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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
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?
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
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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.
I have several ideas. The code 401 is about EGR flow. While it can be an Electric switch like the DPFE that you replaced, the diagnostics do not included the source of the EGR flow or the Backpressure pipe which the vacuum lines from the DPFE operate from.
In short, it is about plain old low tech plumbing. The EGR passage gets its flow from a groove under the Airhorn. If the groove is plugged you need to remove the Airhorn and its gasket and scrape the groove clean. It has about 8 bolts, a $10 gasket and you need to disconnect the Air Intake and a few Electric wires.
Connected to the DPFE are 2 high temperature Vacuum lines. If the tip above does not help, then you need to check this plumbing pipe out for holes. In particular, there is a irregular joint on this pipe which can separate and vent. It should not vent. This will throw off the closed system and generate Error Codes. One end goes towards the exhaust and the other to the EGR.
Finally, do not forget to clear the computer. Old problems stay in the system for 25-35 Startups. I hope my solution has been very helpful to you.
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.