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I was noticing my engine seemed to have less power than usual and it would die once when the idle dropped on cold start-up. I initially guessed that maybe my ECT Sensor was possibly out of range showing warm causing the engine to idle down when not fully warmed up. So I decided to check for Diagnostic Trouble Codes to see what was up.

Using my Equus 3145 Ford OBD-I Code Reader, I received the following DTC Memory Codes:

DTC 327 – EGR valve position circuit below minimum voltage
DTC 334 – EGR closed valve voltage high





Mmmm… Maybe not the ECT, but possibly a dirty EGR or bad EVP. Interesting, both the EGR and EVP are newer Motorcraft parts. :scratchhe



First, I checked the mechanical operation of the EGR Valve. I placed a screw driver under the diaphragm on the metal tab attached to the center pintle shaft being careful not to damage the diaphragm. Pushing upward, the valve opened and closed freely.





Then I pulled the bottom vacuum line off of the EGR Vacuum Regulator (EVR). Using my handy dandy hand held vacuum tester, I applied vacuum and noted the EGR Valve freely opening, holding vacuum and then closing when vacuum was released.





To be sure, I started up the engine and manually operated the EGR Valve finding the engine idle decreased as it should. Then I used my vacuum tester to operate the EGR and again found a normal decreased idle. Finally I ran a KOER test and visually saw the valve operate. Mmmm… If the EGR Valve was old, sticky or showed signs of excess carbon build-up, I would definitely remove it for cleaning. Yet the mechanical function of the valve is fine, so I ruled that out. I moved on to the EVP Sensor...




So, what the heck is an EVP Sensor anyway? The EVP is a Linear Potentiometer which uses variable resistance to provide the EEC with a voltage signal indicating the position of the EGR Valve Pintle. It is attached to the top of the EGR with three nuts and has a gasket or O-ring which seals the vacuum chamber of the EGR. Under warm, no-load cruise conditions, the EEC commands the EVR to direct vacuum to the EGR causing it to open a calibrated amount which bypasses exhaust gas back into the intake. The EVP then provides feedback to the EEC allowing it to calculate spark timing, air/fuel ratio, EGR flow adjustment and service code notification.







With that being said, time to electrically test the EVP with a DVOM. Note that the EVP has a three terminal connector and the specific location of the terminal pins.




The terminal pins are as follows:

• Voltage Reference (5v from the EEC)
• Signal Return (Sensor Ground)
• EVP Signal (Varying voltage to the EEC)


Testing parameters are as follows:

• Reference Voltage (5v at pins VREF and SIG RTN)
• EVP Sensor Resistance (< 5000 ohms at pins VREF and EVP)
• EVP Sensor Resistance (> 100 ohms at pins SIG RTN and EVP)




I started by testing for approximately 5v Voltage Reference at the harness connector. Remember this is a Sensor that operates on 5v EEC Reference Voltage, as opposed to an Actuator which operates on 12v Battery Voltage. Unplug the EVP connector. With ignition Key On/Engine Off, place your DVOM on DC Volts and probe the connector at the VREF and EVP terminals. My 4.78v is good.





Next I tested for Sensor Resistance at the unplugged EVP Sensor. With your DVOM on Ohms, probe EVP Sensor pins VREF and EVP. You should have less than 5k ohms (5,000 ohms). Note that my test shows 32.6K ohms (32,600 ohms). :shocked





Finally I tested for additional Sensor Resistance at the unplugged EVP Sensor. With your DVOM on Ohms, probe EVP Sensor pins SIG RTN and EVP. You should have greater than 100 ohms. Note that my test shows 23.1K ohms (23,100 ohms) which is not even close to 100 ohms.





So, off to the parts store for a new Motorcraft CX-1464 (F2ZZ-9G428-B) EVP Sensor. You can find one online for about $66.00-$75.00 or the Ford Parts Desk for $98.00. O-Reilly had one for $137.00!!! :shocked Just make sure that the gasket is in the box.







Now to test the new sensor before installing. You don’t have to, but it is always a smart move to test new parts whenever you can. ;)



Lets see… Sensor Resistance between pins VREF and EVP is 4.26K ohms (4,260 ohms). Less than 5K ohms (5,000 ohms) is good!





Sensor Resistance between pins SIG RTN and EVP is 126.7 ohms. Greater than 100 ohms is great!!!





Now we remove the bad sensor and install the good one. To remove the unplugged sensor from the EGR, start by removing the three lock nuts. Be careful that you do not drop or misplace them or they will be gone. :banghead





Carefully pry up and remove the EVP sensor from the EGR.







Remove the old gasket. If you cannot find one, that may be the source of your problem! :doh0715:





Your new EVP Sensor should come with a new gasket. Before installing it, coat both sides with Dielectric Grease to ensure pliability and a tight vacuum seal.







Clean the top of the EGR and install the new EVP Sensor, once again being careful not to drop the lock nuts. :banghead







After it is installed, use a Q-tip to lightly coat the weatherproof sensor gasket and the barrel of the connector. This will help keep out moisture and make it easy to remove the connector in the future.







Finally, plug in the harness connector and delete any diagnostic Trouble Codes. I drove around for a while and returned home for a retest.





All seems to be driving good now, no more dying once during the cold start. I know this is a simple service but for some a detailed explanation goes a long way. The hardest part is the simple testing which allows you to confirm the problem and avoid replacing good parts. Good Luck! :thumbup

 

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Discussion Starter #2
Just a question...my 1986 threw code 31 and so I went through the testing procedures you outlined...first volts on the wire came out to 3.82. Is that too low??
You may have resistance in the wiring, but more likely in the harness connector. Attempt to isolate and correct it.



Second I could not get any ohm readings from any of the posts on the sensor...I'm assuming its toast! I have yet to check vacuum. The ohm meter stayed at 1 at all ohm level readings ( 200, 2000, etc,)

Any advice?
Assuming that your DVOM is working correctly and you are making good contact with the proper sensor terminals, replace the sensor!
 

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Thank you for this, helped with replacing my EVP. I am now looking for the part number to order a new EGR Valve for my 94 Bronco 5.8, any idea the part number for that? I am seeing a bunch online and want to make sure I get the correct one.
 

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Discussion Starter #6
Motorcraft CX-1302A (fits 90-95 Ford Bronco 5.8L).

First test your EGR Valve to see if it will hold open with vacuum and look for carbon deposits that may be blocking the valve when closed. If you find that it works well, I would then test the EVR and associated vacuum lines.
 

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I am only reading .5 DCV. What do I do for this problem?
Did you have ignition on?

Thanks for the writeup! Here are my results:

Voltage on connector: 3.80V (although the first time I checked it was 5.98V)
Resistance between VREF and EVP: 3.68k ohms
Resistance between SIG RTN and EVP: 547 ohms

It's unclear if these are out of spec enough. Can anyone confirm?

I'm getting intermittent CEL with all EGR codes coming up: 558, 558, 1, 327, 328, 332, 327, 328, 332.

UPDATE: Took the sensor off and re-measured:
SIG RTN - EVP measures 30 ohms. If you push the pin in, it'll go all the way up to 3.7k ohms. This means with it installed the pin gets slightly pushed in and reads ~500ohms. Not sure what all this means, I'm starting to think the sensor is just fine.
 

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US, 89, 5.8,C6, 1356 BW (manual), 5 Bolt Hub (automatic) No modes like to keep it or
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Seattle FSB,

I read your post on EVP testing from Feb 21, 2013. It had a lot of good information and the pictures made it easy to follow. The area I have a question on was with your parameters for testing the EVP. When you tested the EVP Sensor pins SIG RTN and EVP, where did you get the value of 100 ohms? The reason why I ask is because I can't find that test or value in the Engine/Emission Shop Diagnosis Manual Vol H. The only thing I could find close to that is Pin Point Tests DD5 (pg 17-48), which has you measure resistance on the Breakout Box Test Pin 27 (EVP), 26 (VREF), 46(SIG RTN) and 40/60 (Power Ground) for resistance greater than 10 ohms?
I do have a breakout box, for clarification.
 
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