Can not get this check engine light off!

[LubeMan]

Here's the deal, I have a '96 Explorer 5.0 AWD that has a constant check engine light on. I had the vehicle scanned at my buddies garage and these are the codes that I received.

P1400 EVP EGR Sensor Circuit Low Input
P0402 Excessive EGR Flow Detected
P0446 EVAP Canister Vent System Range/Performance


I have already replaced the EGR Valve Position Sensor and the EGR Vacuum Solenoid, with no luck. The check engine light comes back on after about 2 miles of driving after being reset.

The only other possibility I can think of is the actual EGR Valve is bad, but other than that neither I nor any mechanic I have asked has a clue as to what is causing these codes to trip.

If anybody has any idea what might be causing my problem I would greatly appreciate your input. I gotta get this CEL off so I can pass my inspection at the end of the month! Thanks!!!!!

 

[BradE.]

DPFE sensor. Clean the MAF sensor while your at it.

 

[LubeMan]

Already got an aftermarket MAF sensor on it

Where is the DPFE sensor located at if I was standing at the front of the engine bay looking at the engine? I know what the DPFE sensor looks like so a general explanation would work.

 

[pmcmaster]

If yours is fitted with a DPFE sensor (rather than a PFE sensor) it is mounted on engine beside oil dip stick. If an EGR error is thrown there are several causes, as BradE says MAF sensor also Throttle position sensor (TPS), Engine coolant sensor (ECT) and Trasmission Control Control i.e. the control that controls the controls (only Ford could come up with that one!!!) (TCC). EGR tests Disconnect harness to EGR vacuum regulator, with ignition on there should be voltage at the harness end. With ohmmeter check resistance of regulator - for DPFE systems should be 26-40ohms (PFE systems should be 20-70ohms). Voltage at the harness end of the DPFE terminal VREF should be 4-6 volts (ignition on engine not running). DPFE test, at the DPFE connector identify the SIG and GND wires that run to the PCM. backprobe these wires with voltmeter, with engine running COLD (No EGR) there should be 0.75 - 1.25 volts (black plastic DPFE) or 0.35 - 0.8 volts (aluminium DPFE). As engine warms and EGR is called the voltage should increase to 4.0 - 6.0 volts. If tests values are incorrect - check the vacuum source to the DPFE if ok the DPFE is probably faulty.

Pat McMaster

 

[LubeMan]

Ok, I checked my engine bay and other resources and I think I might not have a DPFE sensor. What is the PFE sensor and how can I tell if I have this typ eof system?

Btw, thanks BradE and pmcmaster for that very helpful information.

 

[pmcmaster]

I'm not sure as mine is fitted with a DPFE but acoording to Haynes your model is fitted with the earlier PFE sensor. The difference is that the PFE only monitors downstream exhaust pressure (it will only have 1 pipe to the EGR valve tube) while the DPFE monitors downstream & upstream pressure (it has 2 pipes from the EGR valve tube). With a PFE system the PCM has to estimate the pressure diff to determine the flow rate but a DPFE system can measure the actual pressure diff between upstream & downstream (not that this helps you much!). Some bits out of Haynes that may help;
Too much EGR flow can cause engine to stop after cold start, stop at idle after deceleration, surge at cruising speed or idle may be very rough. Too little EGR flow can cause high combustion temp during acceleration and load conditions causing knocking, engine overheat or emmision test failure (have you had emmisions tested?). The PCM energises the EVR to turn on the EGR valve. The PCM controls EVR when three conditions are present; the coolant temp is above 113-degrees F (hence my prev comment on the ECT), the throttle position sensor (TPS) is at part throttle and the MAF sensor is in mid range. These conditions should NOT be met when the vehicle is in Park or Neutral or Idle or Wide Open Throttle. You can do a simple test on the EGR valve diaphragm by connecting a plastic tube to the vacuum connection on top, suck on the tube and you should feel resistance as the diaphragm lifts the EGR valve up (no resistance means a hole in the diaphragm). Release the vacuum quickly and you should hear a clonk as the EGR valve drops back into its seating. Check that the vacuum pipe to the EGR valve is good. As you can see you need to be sure that the MAF, ECT and TPS are all working correctly. NOTE if replacing EGR valve you must check/match the code stamped on top of valve.
Pat McMaster.

 

[LubeMan]

I finally got the check engine light off! It turns out you where right pmcmaster by saying I have an older PFE system. It turned out that by shaving down the shaft of the EGR Position Sensor so that its output was within spec fixed my problem. Apparently the new EGR position sensor that I had installed was reading slight high when the EGR valve was closed. So rather then mess with that sensor I just bought a new one and tested it. It also testing high when the EGR valve was closed. So I just used a file to shorten the metal shaft of the EGR Position sensor until it read the correct reading. Reset the computer, took the truck for a 50 mile drive and still no CEL. Interesting fix but it worked.

 

[pmcmaster]

Well done Lubeman - nice to see that someone has beaten the maniac's at Ford design!
Pat McMaster.