Originally posted by lkinley:
Why are you suspecting the tube?
I have an elusive P0401 (insufficient EGR flow). So far, I have replaced:
- EGR valve
- EVR (EGR vacuum regulator)
- DPFE (differential pressure feedback EGR).
I took apart the throttle body yesterday (see below), and have also checked most of the plastic/rubber vacuum hoses and they all seem fine.
I don't see much left. I'm trying to assess what to do next.
I ran Vehicle Explorer on the car yesterday. I started the engine, and then slowly raised the RPM to 3000 (while in Park), in increments of 500. The EGRVR reading went up to 90%, but the DPFE reading did not go above .8 volts.
This tells me that the EGR valve is being commanded open, but there is still no flow through the EGR tube. I can only think that there is either a leak somewhere (which I haven't found), or there is something impeding EGR flow.
Originally posted by lkinley:
What usually plugs up is the passages in the upper manifold, right behind the throttle body.
I took the TB (throttle body) off yesterday and looked behind it (into the UIM (upper intake manifold). I did not see much buildup and did not see any "EGR passage" that people talk about.
There were three small passages that enter behind the throttle body, but none of them were for the EGR system. There was a passage that came from the bottom of the UIM which seems to come from the evap hose. There were another two passages that came from the top of the UIM that seemed to come from the two black vacuum lines on top of the UIM. All of theses passages looked fine and were not clogged up.
I stuck my fingers into the UIM and felt around and could not find any "EGR passage". I even stuck a mechanics mirror into the UIM to see if I could find the elusive "EGR passage", to no avail.
Originally posted by F111D F:
You're not still chasing that P0420??
Actually, it's a P0401 (insufficient EGR flow), but I have been chasing it down for quite a while.
