This would be my first post to this forum, and I think this forum is great. From my subject line, you can see that this is the problem that I am having. I will provide a little background into the symtoms of my problem. On and off, it is very random, I will be driving at highway speeds, and my whole truck seems to buck/vibrate. This can come and go. It also seems to be mostly in Overdrive at 65 mph and above. After the normal items, tire rotation, alignment, etc. I have come to conclude that the engine is leaning out. It seems to be very dependant on atmospheric conditions, as it doesn't happen all of the time. In addition to this symtom, I hear alittle bit of knocking sometimes on acceleration. After looking through literature that I have--Ford Fuel Injection & Electronic Engine Control, Haynes Manual, Chilton Manual--for my truck, and checking a few items, I decided to change the EGR valve. I did this because it was original, and I figured that it certainly couldn't hurt. As soon as I did this, I got a Check Engine Light, which when I read the codes, translated into a Code 31 EVP Below Minimum Voltage. I thought that maybe the EGR sensor was bad, so I put a new one one. Same thing. So looked in the manuals to try and see how to diagnose this problem. The following are the results that I got.

KOEO Test
On Demand Codes = 31
Continuous Memory Codes = 31,29

EVP Sensor Tests
Resistances @ different vacuums
0 inHg = 4.57k ohms
5 inHg = 786 ohms
10 inHg = 240 ohms
VREF @ EVP = 5.00 VDC

EVR
EVR Resistance = 46.7 ohms
EVR Volts = 10.85 VDC
In the Haynes Manual it gives a procedure on how to check operation. In short hook Vacuum gauge to EVR outlet port, then hook hand vacuum pump to supply inlet port and apply vacuum. "Vacuum should hold and no vacuum should be indicated on gauge." I did this, and could not build vacuum. It also sounded as if it was leaking. By this it should be bad, should I replace??

ISC-BPA
Resistance = 10.8 ohms
VPWR Voltage = 11.93 VDC
Engine RPM dropped when unplugged @ idle, didn't stall.

Engine Vacuum
@ Idle = Steady @ about 15-16 inHg
"Goose" throttle = Drops to a little below 5 inHg about 3, then comes back
Reving Engine = Steady @ about 18 inHg

Fuel Pressure
@ Idle = Steady @ 32 psi
Reving = Steady @ 34 psi
w/ Vacuum line off = about 42 psi

Timing @ Idle
Spout Out = 8° BTDC
Spout In = 12° BTDC

EGR Valve
Vacuum @ = less than 1 inHg
When I hook vacuum pump to the EGR valve and start to pull vacuum the engine idle roughens and the check engine light goes out.

Based on all of these measurements, it appears that everything should be fine, except for the EVR valve. I am very interested in hearing from anyone that might help me solve this problem--both the bucking/vibrating and the knocking. I am not sure if they are the part of the same problem or different. Other than this, my truck runs great!! And I plan on keeping it for a long time.
Thanks!!!

 

You should work from the lowest number code when repairing codes. Fix the code 29, clear the codes and see if it returns. 29 is insufficient input from vehicle speed sensor, that could be causing the bucking/vibrating(doesn't know how fast you're going).

 

Watch out here. The Haynes is not clear on the testing of this component. See these threads: EVR thread #1 and EVR thread #2

Just make sure that the EGR you replaced is exactly the same- there are several different styles. Also, you need to make sure the EVP is the same. There are two different ones (white and black) and they give different signals.

 

I'd say that your EVR solenoid is bad. I've recently changed EVRs on two trucks (out of two trucks that use this part). Truck #1 the EVR was open circuit. Truck #2 the EVR tested just like yours. However I observed with a "scan tool" that the computer was commanding EGR but the EGR valve wasn't moving. Manually applying vacuum to the EGR moved it. I swapped EVRs and the problem was fixed.

BTW, vacuum testing the EVR is pointless. Both ports of even a new solenoid will leak.

 

Well, I have an update on what I have found. I went and got a new EVP valve. I wish I had seen the post by billman before I went. Thanks for the information. Anyway, I got the new valve and it checked out the same way as the old one by the procedure in the Haynes book. Still have the Code 31. So I decided to check the new EGR valve and compare it to the old one again. However, I must say first that this one was purchased at NAPA not Ford. The nearest dealer is 15 miles away. Anyway, I remember reading a post by someone that they had found EVP was not touching the EGR valve. So I broke out the calipers and measured the EGR depth with the EVP valve removed on both the old and new one. New one 1.597" old one 1.557". The new one is 0.040" deeper. The sensors appear to be the same length of about 1.625". This would mean that sensor would be compressed more on the original EGR valve then the new one. With the old sensor on the old EGR I measused 3.28 k ohms and 3.34 k ohms with it off of the EGR. With the new sensor on the old EGR I measured 4.43k ohms and 4.62k ohms with it off. When I put the new sensor on the new EGR I measured 4.62k ohms. Does this explain the Code 31?? If so, I guess this means I should have bought a Ford part. This brings up a question, if I can measure the voltage at the EVP SIG line while the engine is idling, what kind of a value should I see?? I would guess a couple of tens of a volt. Anyone know?? Thanks for the help.

 

That is what I tried to convey in my previous post about the several different styles of the EGR.

It is possible that the Code 31 EVP below minimum voltage exists because the EVP sensor (built in variable resistor) is too extended. With the numbers you gave ("The old sensor on the old EGR I measused 3.28 k ohms and 3.34 k ohms with it off of the EGR. With the new sensor on the old EGR I measured 4.43k ohms and 4.62k ohms with it off. When I put the new sensor on the new EGR I measured 4.62k ohms"), I am not sure how much of a difference that could make- maybe a Ford Tech would know. The Code 31 problem could be answered (albeit extra effort) by reinstalling the old EGR with the new sensor, clear the codes, and see if the Code 31 returns. If not, the EGR is likely the culprit. You can get stock Motorcraft from www.fordpartsonline.com
or O'Reilly Auto Parts.

Hopefully the one you introduced (31) will go away. The Code 29 may be that you just need to R&R the RABS in the differential. If you pull it, take a good look at it. You may be able to clean and reinstall it- but it is not that expensive to replace. By the way, when your truck "bucks" what does the spedometer do??

Keep us posted.

 

EVP sensor voltages observed on an 89 E150 5.0:

Idle: 0.31 volts (ie EGR closed)
Moderate throttle: 1, 2, or more volts

On a test drive, the EVP occasionally jumped to over 4 volts.

 

A quick update on where I'm at. I put the old EGR valve back in with the new sensor, and cleared the codes. The Code 31 went away. So, the part I got from NAPA has something not right with it. I will get a Ford part and put it on. As far as what the speedometer does when the truck bucks, it stays steady. It wasn't jumping up or down or anything. As I said earlier, I am pretty sure that it is leaning out, and from the measurements that I took so far, it appears that nothing is low. So where to go from here?? I am going to replace the EGR valve with a Ford part. I keep your posted.