I hopped in my '98 4.2L truck yesterday to go home for lunch and it was running very rough. Never noticed any problems until then. I drove it home 1.2 miles and I knew I had a problem. On the way back to work it was still running rough and the check engine light came on. Same situation on the way home last night. This morning I drove it to Advance and he pulled a code. There are 2 on the printout he gave me.

DTC P0402 EGR Flow Excessive
DTC P1000 OBD Systems Readiness Test Not Complete

Seems like I have a problem with my EGR Valve, or the Module that is inline with the tube on the exhaust port. The guy at the parts place told me to find out what is was before throwing parts at it as there were several components that could be the culprit.

I have checked the two hose that connected to the DPFE. There is a lot of White Crud built up on both ports. I scrapped the crap off and tood a small screwdriver and scraped what little was actually inside of it and the 2 small hoses. I've got them back on and they seem to be snug. I looked at the line running from the EGR valve to the port on the bottom of the intake and it does not appear to be cracked or leaking. The red hose that I supposed feed the vacuum switch I can only see about 2 inches of, but it isn't cracked from what I can tell.

I've searched and read the many thread on these forums about this code. No one has mentioned the white crud. What would cause this crud to build up on the DPFE ports and what kind of problem would that cause or be cause by? I had a Jasper put in there last Janruary and only have 6200 miles on the new motor. Could this be from the Hydrolock.

Anyway, I guess I'll pull the EGR and see if it is stuck. I read in one thread about using water to see if it is leaking? How would you do that?

Thanks!

 

I pulled the EGR Valve off. There is nothing there which appears plugged, in the valve itself or the tube or what little of the inlet into the intake I can see. I have not taken the tube off to of the exhaust manifold to check all the way through. I wouldn't think it to be a problem.

If the Flow is Excessive wouldn't this mean that it is not a Vacuum problem? If there was no vacuum the valve would remain closed and I would think it would give a P0401.

If the flow were Excessive I'm guessing the valve would have to be stuck open (bad Valve), the valve would have to have vacuum holding it open (bad Regulator), or the PCM giving the wrong signal to the Regulator (BAD DPFE?)

I can pull the valve open with vacuum. It is a bit dirty, but I see nothing that could be considered plugged. Did not seem to be stuck open either. I'm probably goign to just clean the egr valve up with carb cleaner and put it back on. I dont' want to throw money at the problem if it seems it isn't the problem.

The problem I'm having is at an idle. When I accelerate the truck doesn't seem to misfire. Should I be looking for a leak now? Guess it is a good thing I have all day tomorrow to try to figure it out. I only know enough about tearing this stuff up to be dangerous. I'm up for any suggestions those of you in the know might have to help me find the problem and save me from buying a bunch of parts I don't need.

Thanks..

 

Dude, I'll write something here so you don't feel ignored. But I don't know much about 4.2's. However, get some pipe cleaner (that fuzzy stuff at walmart) and ruun through the ports. That'll help you figure out if the passages that you can't see are plugged.

 

Thanks for not letting me feel ignored

I threw it back together and started it up. Still idles rough. I removed the vacuum line to the EGR while it was running and plugged it with my finger. It does have ample vacuum, and the truck idles smoothly when it is not connected to the EGR valve, when I connect it back up to the ERG valve it idles rough again.

Anyway, enough fun for one night. The entire basement smells like gas now I think I'm going to go watch some Sci Fi and mess around with it tomorrow.

 

You just found your problem by doing that.
The line to the EGR is not supposed to have any vacuum on it. As of now it is holding the EGR open and causing the rough idle.
The EVR is the problem. The PCM normally opens it while in light throttle cruise, then when out of this routine, the EVR lets air into the EGR line to allow it to close. (Once the EGR is opened by vacuum the process has to be reversed by letting air in thru the EVR). It it a 3 port device.
If this 'gate' valve is stuck open, full vacuum would be applied to the EGR all the time the engine is running.
Good luck.

 

Thanks Bluegrass

I didn't have a way to check to see if the PCM was signaling the EVR to remain open, so I figured I would replace it. I couldnt' find one at the local parts stores and hate buying from the dealerships so I figured I'd get one at a used parts place. I knocked on it with a hammer though and it does seems to be cooperating for now.