97 F150 P402 code going insane
Hi All, I'm hoping that some of the experts here can help me resolve an issue that I'm having with my 97 4.6 F150. I'm at my wits end trying to figure out what part is causing the P402 "excessive EGR flow" code. My truck idles fine but it misses during midrange or normal driving.
After reading the forums I started out by replacing my DFPE sensor (Duralast from Autozone) and cleaning out the EGR ports in the throttle body (were clogged shut) . After resetting the code the check engine light reappeared and the engine still ran awful.
I'm starting to think that the new sensor is faulty because I have checked all of the other parts related to the EGR valve system. This is what I have done so far...
1) pulled vac on EGR valve during idle and idle speed drops considerably. EGR valve seems to be working.
2) checked EGR vac solenoid resistance (ok). Solenoid opens when 12 volts are applied and vac reaches the EGR valve.
3) Checked the DFPE hoses for leaks or damage. Hoses look great and they were not clogged.
4) checked all EGR vac lines on engine and replaced PCV valve elbows. Solid vac at EGR solenoid and EGR valve when solenoid valve is powered. After these changes truck still runs awful.
I started to think that the EGR valve was stuck open so I disconnected the egr valve, blocked off the EGR valve port and started the engine. Engine still ran rough. During this test I checked the EGR valve for leaking exhaust and noticed no leaks. When vac was applied to the EGR valve exhaust flowed freely thru the EGR and stopped when vac was removed.
So now I'm back to square one. The egr valve, solenoid valve and vac lines seem to be ok. Is it possible that this brand new Duralast DFPE sensor is bad? I'm clueless as to where to go from here.
I thought I read here that someone suggestted that the TPS sensor is bad or that the MAF sensor is dirty. Does it make sense that one of these sensors may be bad and causing the missing and P402 code??
What the heck should I check now?? Should I check the battery area for other vac leaks or does this sound like a sensor problem? Damn I hate driveability problems
Any tips or clues as to what to check would really be appreciated.
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