I have been told by a ford tech that it is a good idea to start the truck for a moment when you disconnect the exhaust line to the EGR, to blow rust chips, etc out.

If you run out of ideas, stick the old EVP back on to make sure you can duplicate your results.

My EVP did not test within the specified range of resistances and I replaced it, it had no effect. That is all I tried so far.

 

hey eds72, i had this problem for ages with my 1988. the code was a 31 or may be a 32 that read "below minimum voltage" or whatever. the egr was relatively new so i replaced the sensor - that didn't work. believe it or not what did work was this: my good friend (a gifted mechanic) figured out that the little rod that comes out of the sensor onto the the egr diaphram was not quite the right tolerance. This is really important, the tolerance has to be perfect or it doesn't push quite enough on the diaphram and thus you get the error. so what he did was "added" a wee little bit onto the end of the rod and no more problem! he just used a braise rod or something and tacked it on and then ground it down so it was just a bee's dick longer than original and that was enough to make the code go away. i know it may sound crazy but trust me it works.
give that a try.
good luck.

 

After work today, I decided to take another crack at this. The first thing I did was to apply vacuum to the EGR in order to measure the resistance of the new EVP. Much to my surprise, the EGR would not hold any vacuum. I removed the EVP and quickly found my mistake. The new EVP did not have the little rubber gasket on the bottom of it. I did not notice this when installing it in minimal light last night. I pulled the gasket from the old EVP and reinstalled (I later found the new gasket mostly concealed by a cardboard flap in the box).

I cleared my codes and took it for a drive. My CEL light did not come on! I drove the truck for over twice as long as it had been taking to see the light. My joy was not long lived, however, when I pulled my codes. Although my stored codes were clear, I got a 328, "EVP below closed limit", from KOEO. At this point, I decided to call it a night and pulled the negative battery cable to reset the computer and force it to relearn it's operating parameters.

Well, I couldn't leave well enough alone, so I returned to the truck after 45 minutes or so, reconnected the negative battery cable, and pulled the codes. This time, I got 328 from KOEO, and 328 AND 512 (Keep Alive Memory test failure) from the stored codes. Since I got stored codes, I'm thinking I didn't leave the cable disconnected for long enough to clear the memory. I'm hoping the 512 might have been a fluke related to this. Anyone have experience with this one?

As for the 328, I'm thinking rusty's theory may be correct. I did visually compare the 2 EVPs, and the the rods looked to be the same length. However, it sounds like even a tiny difference could have an impact. As soon as I locate a bee's d!ck, I'll give this suggestion a try.

 

Did you measure this value? It would be useful to compare before and after values.

 

I went through this experience with the EGR system about 2 months ago. My truck would buck under load at low RPM's. The CEL didn't come on but I had the same codes. Problem was the EVP. I had the same problem with AC coming out the defrost, to the point where I disconnected the control arm from the vacuum controller under the dash and manually flipped the arm between floor and vent.

Here was my test procedure. I took the EVP off the EGR valve and checked resistance manually. It was within the specs so I knew it was good. I stuck it back on the EGR then applied vacuum to the EGR right at the valve and again checked the resistance on the EVP, starting with no vacuum then to full vacuum. Again the EVP showed the correct resistance. I held the vaccum for a period of time to make sure the EGR valve had no leaks. Since the guage did not work properly on my pump, I kept the meter attached to the EVP. It held constant until I manually relieved the vacuum. Then I reconnected the vacuum line to the EGR valve and repeated the procedure by installing the pump to the line at the EVR. Since this line runs behind the engine, I couldn't tell if it was broken. Again the EVR showed correct resistance when I applied the vacuum so I knew this vacuum line was good.

I didn't quite understand how to test the EVR, so I took a leap of faith and purchased a new one. I had taken the old one apart but couldn't find anything manaully wrong. When I put the new EVR on, the truck quit bucking. I reconnected the control arm to the vacuum controller under the dash and found that I had also solved the problem with the AC. It no longer reverts to the defrost when the engine is under load.

When the engine is under load, you have less vacuum available. In my case, the EVR was leaking the vacuum, so that is why AC went to the defrost (default or no vacuum position). If your EVR is good, then I would check the system for leaks. The EVR not functioning properly could be the cause of the vacuum leak or it could be the symptom from a leak ocurring elsewhere in the system. Hope this helps and good luck. I also spent quite a few nights testing and thinking until I got it solved with some good advice from this website.

Quick addition. Get the parts from the Ford dealer and make sure you tell them your emissions code if you need to replace the EVR. Same might be true for the EVP, but not sure. There are different EVR's and you could get the wrong one.