Time to get serious...
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Time to get serious...
OK guys, I really need your help here as I've got to pass my MA emissions test in 2 weeks. Truck is a '97 F-150 4x4 with 5.4. I've had a CEL for awhile now and have done a number of things to clear the dreaded PO401. What I have done so far: New EGR, IAC, DPFE. Removed and checked ports (remember this is a 5.4, not 4.6) and they were clear. I checked vacuum supply to the EGR control solonoid and it's at 5.7"w.c., I ran the truck down the road with vacuum gauge on line to EGR and at idle it is at about 3", WOT it drops to 0" and loafing down the road at speed it runs as high as 5.4". I've checked voltage to the DPFE in park at idle and get 5.1VDC at both outside terminals, the middle one shows 0. Where do I go next? 
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Anyone? Anyone? Bueller? I found the Tomco Techtips that someone posted awhile ago and will be working my way through with them. Is there a more current trobleshooting guide available? Is my net vacuum enough to satisfy this system? I read that EGR full open is 8" W.C. and I max out at about 5.7... DAMN! I think I found it, the charts are in inches of mercury and I've been reading inches of water... I've got no vacuum to the EVR! I was reading the techtips to make sure I had my terms right as I typed. Update coming...
I found the Tomco Techtips that someone posted awhile ago and will be working my way through with them. Is there a more current trobleshooting guide available? Is my net vacuum enough to satisfy this system? I read that EGR full open is 8" W.C. and I max out at about 5.7... DAMN! I think I found it, the charts are in inches of mercury and I've been reading inches of water... I've got no vacuum to the EVR! I was reading the techtips to make sure I had my terms right as I typed. Update coming...
Last edited by hugepettyfan; Oct 17, 2005 at 04:21 PM.
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So, this leads to more questions... It looks like the vacuum source for the EVR is the large vacuum tank inside the passenger front fender, there is a manifold vacuum line that runs to the tank from the TB manifold pass. side rear. There are two white lines from the tank and one black. One of the white lines I assume goes to the EVR. I don't see any solonoids between the TB manifold and the EVR, only the lines and tank. I don't have a large vacuum leak because the truck idles and runs fine and I disconnected the line at the TB and the truck immediately died. I'm thinking plugged line or vacuum tank... anyone see or hear of this before or have any suggestions? I really don't want to pull the fender to fuss with the tank. :-(
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I ran mine through the emissions test with a 401 code. It passed. Where bouts are you located. Im in Missouri. Emissions here are tuff. Did you try going through the emissions test after you did all the work?I would try that if you havent.
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CEL on is automatic failure here in Massachusetts. I found a vacuum line diagram for my truck that Racerguy posted back in '03 which will really help. It looks like the vac tank inside the fender is for the 4x4 stuff so I've eliminated it as a problem, the 4x4 works fine. I got to the two tanks behind the battery, one of which is for the EVR. It's looking like a broken line somewhere, I just have to find it in the mass of lines back there. Thanks for your reply.
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So, I got to the root of the problem... I traced out the lines and found that the line to the EVR does come from the tank inside the fender... I removed the fender liner and the tank drops right out, thank goodness I didn't have to remove the fender... The tank has a huge chunk cracked out of the front lower corner! The tank is giant and looks like this:
And is cracked bad!
I know why it is like this too, 1.5 years ago I wrecked my truck by plowing into a concrete post in a parking lot... buried the truck on it too... I got a CEL right after the wreck but believed the body shop when they said the CEL wasn't because of the wreck. I've ordered a new tank and it will be in Thursday, I didn't want to try and patch up this one because I'm afraid it will leak again down the road. Lesson learned is: test for vacuum first, these trucks are getting old enough now that age (and accidents) are a factor!
And is cracked bad!
I know why it is like this too, 1.5 years ago I wrecked my truck by plowing into a concrete post in a parking lot... buried the truck on it too... I got a CEL right after the wreck but believed the body shop when they said the CEL wasn't because of the wreck. I've ordered a new tank and it will be in Thursday, I didn't want to try and patch up this one because I'm afraid it will leak again down the road. Lesson learned is: test for vacuum first, these trucks are getting old enough now that age (and accidents) are a factor!
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Originally Posted by code_red
Cool detective work. Glad to see you found the issue. Hopefully this will resolve your CEL.
Yep, it did! The new tank will take a few days to arrive so i glued the chunk back in with black rtv and no code so far... it used to come back within a few miles of driving. I'm relieved to have this behind me, especially after throwing all those parts at it!