I have two questions regarding EGR/EVP trouble shooting. I have a 90 f250 7.5l. The fordfuelinjection site gives voltages at EVP pin for various states of open. I assume this is measured in reference to ground? Without a breakout box, how is one typically to tie into the this circuit? I could also check the EVP by unplugging it completely and checking the resistance across the pins but I don't have the allowable values. Anyone have any additional information on this? It would be greatly appreciated.

 

EDIT: Never mind the original post. A quick test would be to check that there is a resistance sweep as you depress the sensor rod. It should never be completely open or shorted. If that checks out okay then I wouldn't look at the other parts of the system.

 

I did that this evening, plus a whole host of other checks. I checked the vacuum at the little X-mas tree thing: strong, idle increased when unplugged, (cold engine). I did a leak test on the vacuum canister: no issues. I did a leak check on the black line leading from the canister to the EGR vacuum solenoid, no issues; though I was not impressed by the volume of vac available at the solenoind end of the line. I pulled the EVP out of the EGR, hooked it up to a Multimeter, the sweep was smooth with no issues though I would like to know what resistance value is expected across the two non-sweeping ends of the potentiometer. I measured about 3.9K. I don't want to just start replacing parts. I have searched other threads, guys have replaced everthing under the sun and still no resolution. Since I mentioned previously I found the vacuum at the EGR solenoid a little weak, I bought a piece of vac tubing and am going to bypass the OEM line just as a test. At idle, what kind of vac should I be getting at the end of the black OEM vac tubing at the solenoid? What has started this whole thing is my persistant pinging problem (YEARS) and the fact I have be throwing code 32 lately.

 

A code 32 has nothing to do with vacuum or the EGR solenoid.
It is a low voltage problem coming from the EVP sensor.

Possible causes:

Poor continuity in EVP sensor harness or connectors.

Damaged EGR valve. (Valve more closed than the normal closed position, stem to low).
Could try unhooking the battery for 15 minutes to get a new closed voltage value in the computer.

Damaged EVP sensor. (It may have too high a resistance when the valve is closed)

Damaged processor.

 

Yea, I have been focused on the EVP and just ruling out other possibly related causes. Nobody yet has answered my real original question; what resistance value should I be getting across the EVP unplugged. I have no way of tapping voltages because short of poking a hole in the wire insulation, how do I tap a reading. I don't have a breakout box. My vacuum pump took a dump on me (made in china) so I'll need to pick up a new one tonight for further troubleshooting.
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Thanks again for all replies!!

 

The input side should get the same vacuum as you see at the tree on the intake. The output side will be whatever is commanded by the PCM. According to the specs the EGR will open 50% at 4inHg & 100% at 8inHg so it doesn't take much. You can force the EVR regulator to full open by grounding the left terminal inside the connector. You should be able to reach inside the back of the electrical connector with a probe while it's still hooked up. If you do that at idle the truck should almost die because that is supposed to pull the EGR wide open.

 

Here is what I get on the bench (no vacuum) with EVP still and has never been unmounted from the EGR valve.



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Thank you for the diagram and the values, that's percisely what I was after.

 

Hi: I just wanted to update on what I discovered. I checked out the EVP with a multimeter and found no electrical issues with it so I just reinstalled it. Having just bought a new hand vacuum pump I decided to check the available vacuum at the EGR regulator/solenoid. I was getting only about 2 or 3 in Hg at the end of the tiny little vac line. I check what was available at the little tree fitting thing on the intake manifold and found it was running about 20 in. Hg. I had done a leak test earlier on the whole EOM vacuum harness and found no issues so I was a little suprised. Further investigation found that the vacuum canister was too only getting a couple inches of Hg vacuum. Pullin an the vac harness in a certain maner would raise the reading, a lot. To make a long story short, I know too late, I replaced all the vac lines associated with the EGR with new rubber lines and now have no more code 32 problems. Unfortunatly, the pinging problem still exists, the whole reason I pulled the codes, but I'll start a new thread on that.

Thanks for all the help!