Victim: 1986 E-250 van w/302 V8 fuel injected 150k miles
Recently had the TFI battle whereupon I changed the TFI module,
Ignition coil, rotor, cap, pcv valve and breather filter. Vehicle now
starts where it was dead before. HOWEVER, after running my diagnostic
tester I get a #34. Removed the electronic EGR/EVP assembly and found
it plugged with carbon. Cleaned to the point where I can apply a vacuum
and the plunger/popett will move smoothly up and down. While there I
cleaned (as best I could the matching inlet hole in the manifold with
carb cleaner, round wire brush and paper towels). Reinstalled. Ran the
diagnostics (did a clr before to be sure NOT reading the same/leftover
code again). Still get a #34. Following the vacuum routing diagram
vacuum comes from the vacuum canister to the EGR vacuum control
selenoids assembly(2 small selenoids side by side). It appears only one
controls the vacuum to the EGR valve. I started the vehicle and
measured the voltage on the two electrical leads 12 volts +/-. Ran a
'run' test and the voltage never disappeared (remained 12 volts -
normal??) Upon completion still get a #34. Manually energized the egr
selenoid valve and could hear a hissing noise and felt small amount of
vacuum at the egr fitting. Started vehicle again, at idle attached a
manual vacuum pump and when it got to about 10in vacuum the engine
dropped rpm and started to stumble. This tells me the valve is working
and while there may still be some residual carbon in the intake there
is still enough open area to allow the EGR system to work. My questions
then are: is it normal for 12 to be constantly ON at the controling egr
vacuum control selenoid? if not what is keeping it on? While the egr
selenoid valve was letting some vacuum through can/could the valve be
blocking the vacuum needed to move the valve? Would a defective EVP
valve cause these problems (selenoid energized, no stem movement)? AS
you can see I am stumped by contradictions to evidence. I don't like
NOT being able to solve a problem therefore ANY and ALL help and
suggestions will be greatly appreciated....... Look forward to your
The Definition for DTC 34 on your van is " EGR Valve Position/Pressure
Voltage Above Closed Limit"
What this is telling you is that the PCM is "seeing" the EGR valve open when
isn't supposed to be.
At the EGR vacuum line, at idle, it is not uncommon to feel a slight vacuum. I
believe it is usually 1-2"hg. At the EVR solenoid there should be 12 volts at
times, the PCM controls the "ground".
You can do a quick check of the EGR valve and solenoid by connecting a test
Battery - and back probing the connector with the engine running. On one side
should be bright. This is 12v (VBAT). Back probe the other (ground) side of the
connector. This will slightly energize the solenoid and partially open the
will tell you that the solenoid and valve are able to operate.
With code 34, like I said, the PCM thinks the egr valve is open when it
be. The valve may or may not actually be open. There are 3 things that come to
that can cause this:
1. EGR valve has a layer of carbon keeping the pintle up slightly, fooling the
EVP.(Or a chunk holding it open, along with poor idle).
2. EVR filter clogged allowing vacuum to the EGR valve at idle
3. EVP sensor shorted internally sending a false signal to the PCM
There could also be a high resistance short in the wiring to the EVP sensor or
wiring concerns but these are uncommon. At 150K it could be any or all of the
First, check the filter in the EVR. It's under the round cap on the solenoid.
it with hot soapy water. You can just remove it for testing but be sure to clean
reinstall it. If this is not the cause of your code 32 then look at the EGR\EVP
You mentioned that you had to clean the valve due to carbon fouling. In my
experience, although you can free up the valve so that it will move smoothly, it
difficult to de-carbon the pintle area so that it can fully seat. Even though
valve may seal, the pintle is up a few thousandths of an inch causing a false
at the EVP sensor.
Speaking of the EVP, these were a high failure item on EEC-IV vehicles. You
it with an ohm meter if you care to, but after 19 years and 150K
you get the idea.
If this were my vehicle, I would just replace the EGR and EVP and call it
yours I would suggest at least a new EVP. If the code is still present, grind
1/32" off of the EVP shaft so that it is sending the proper "EGR closed" signal
PCM. I've had to do this a few times even with new parts due to manufacturing
If you happen to have the factory Emissions Manual (Volume H) for your truck,
will tell you what the feedback voltage from the EVP should be when the valve is
closed and how to test the EVP resistance. You won't likely find it in Chilton
Haynes. The info is also available on Alldata for a fee.
Fully concur with Tom's elaborate and accurate response. I would like to
stress one point from my experience of many years maintaining two vehicles
of that vintage (one is still in service). The EVP sensing potentiometer is
designed very close to the limit of the tolerance. Unless the pintle is
perfectly seated, it will throw the the 34 code. Many a time I was tempted
to 'adjust' the EVP tolerance by grinding a bit off the shaft, like Tom
suggested, but with a bit of patience always found it unnecessary. If you
don't want to throw out the otherwise perfectly functional EGR valve each
time this happens, take it off (no need to separate the EVP), keep it open
with a handheld vacuum pump attached, and carefully scrape both the pintle
and the seat. A curved scraper is ideal; a small screwdriver will do. When
you can't see any more carbon falling off when you tap it, scrape some more
anyway. And then a bit more... To test, just release the vacuum, temporarily
reconnect the harness to the EVP and re-run KOEO test. If it does not throw
the code, you are done. If it does, scrape some more. Patience is a
I remember actually determining the exact tripping point for the code and
figuring out the exact EVP resistance at which the code is set, then using
an ohmmeter attached to the EVP as I was scraping the valve on the bench,
instead of going through the slow KOEO routine. No, I don't remember the
number - you are on your own with that one... And it's probably different
from one valve to another anyway, due to manufacturing tolerances.
BTW: Rumor has it that at some point Ford came up with a screen-type filter
that was supposed to be installed on the exhaust port of the EGR valve
adapter, and that reduced the carbon deposits. I have never seen it.
And I too agree with you.
My only argument is that I've spent a lot of time cleaning egr valves as
described. It can be done. I'm a little older now and prefer to spend the ~$60
than spend ~2 hours cleaning a 15 year old EGR valve (If on my personal vehicle,
Murphy dictates that the diaphragm fill fail exactly 8 days, 4 hours and 12
after reassembly). If the vehicle were newer and had 75K fewer miles, I'd do it
way for sure. You say tomato....
IIRC the code will set at .8-.9 volts on the signal return, it's been a while.
I believe the filter you're talking about is called a carbon trap. It was
for carb'd and CFI vehicles that had the EGR in the spacer plate. These had
carbon problems. It replaced the EGR cooler used on many early to mid 80s cars.
won't help with carbon buildup in the valve, it filtered out the boulders that
in the spacer plate then lodged the EGR valve open. I've never heard of one for
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