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Discussion Starter · #1 · (Edited)
When 12 VDC is applied to the EGR valve solenoid, should it open or close? And are any inbetween voltages applied to it, or is it ever pulsed, to open the solenoid variably (if that's even possible for it) instead of just open or closed?

I'm getting a 33 code (OBD 1) on my 94 Taurus with a 3.8 engine, which means "EGR valve opening not detected", or "EGR valve not closing fully". I tested the EGR valve by disconnecting its hose that runs to the solenoid, substituting a length of rubber hose that I plugged into the EGR valve, and sucking on it while the car was at idle. The engine stalled, and picked back up when I stopped sucking on the hose. So apparently the EGR valve is OK (though I'll be removing it anyway to check for carbon deposits in the cavity it's connected to, since I've read this test won't necessarily indicate the presence of such deposits which can interfere with the EGR valve).

Then I checked the EGR valve solenoid. I measured 33 ohms through it--the allowable range for this model is supposedly 30-90 ohms, so its wiring appears to be OK. It's getting a full 12 volts at idle, which I at first assumed meant 12 volts should close the solenoid since it should be closed at idle, or else it will gate vacuum to the EGR valve, causing the car to stall. But then I read another thread here (http://www.taurusclub.com/forum/82-maintenance-repair/79791-need-help-ses-code-401-a.html) in which "sundarpn" stated that the solenoid should be closed (can't blow air through it) when there's no voltage applied, which would be just the opposite of my assumption. I was able to blow air through it, with no power connected to it. Then I attached a power supply to it, set to 12 VDC, and though I saw a tiny spark at the solenoid's positive voltage contact when I touched the power supply's plus volts output to it, I heard and saw no change in the solenoid's behavior, and I was still able to blow air through it to the same degree as when no power was applied to it. So it appears to be stuck half-open (or half-closed, depending on your point of view), which to my way of thinking, might generate a code indicating "EGR valve opening not detected", or "EGR valve not closing fully".

So: what should 12VDC do to the EGR valve solenoid--open it, or close it?
 

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12V applied = solenoid open (vac flow thru it). Note that the solenoid has a third port (with a filter element) on it that vents vac to the EGR valve when the solenoid closes.
 

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The ECM does pulse these EGR solenoids to control EGR valve position. While it's certainly possible you could have a bad solenoid, it's much more likely that you have a bad PFE sensor. Those things go bad all the time.
 

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The EGR valve & it's controlling vacuum switching valve are normally closed, until directed to open by the computer. The computer sends the VSV a pulsed/duty cycled timed electrical signal to open it's vacuum port & thus apply timed vacuum pulses to the EGR valves vacuum diaphragm, which causes the EGR valve to open & close in time with the pulses. The computer gets operating clues from various sensors who's PID output to the computer must not be corrupt, lest the computer will make a bad decision about when & how much timed EGR vacuum to have the VSV apply to the EGR's vacuum diaphragm to open it. The vacuum lines to the VSV & to the EGR valve & the EGR valves vacuum diaphragm have to be in good shape & not leaking vacuum, All a vicious circle.

All that said, from your posted code & from the test results you've posted, it sounds like the VSV is defective.

From the vintage of your system, I agree it's probably a good idea to pull the EGR valve while your in there & inspect it for carbon deposits, rust/corrosion & it's gasket too. If the engine isn't using oil because of wear & you've been using the right service grade engine oil over it's lifetime & using a good grade of fuel, it'll likely be clean.

More thoughts for consideration,let us know what you find.
 

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I believe the EGR solenoid is called the EVR = Exhaust Valve Regulator.

That part is no longer available, as far as I know.

The EVR got corroded up on my '87 MT-5 and the EGR never opened, thus giving a code (messed up the fuel economy, too)

I found an almost new 12V vacuum solenoid from an '80 Bobcat. Wired it in, connected the hoses and it worked. Had to mount it differently, though.
 

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Discussion Starter · #6 · (Edited)
Thanks for the replies, everyone. I'll be going to Pick N Pull later today, with a 12 volt battery, to test some of the EGR valve solenoids I find in the Tauruses there, to compare their behavior to mine and try to find a good one. I had a hunch that solenoid might be receiving something other than a straight 12 volts, or nothing. That makes me wonder if an EGR valve could pass the simple vacuum test (stalling the car), but be fouled in a way that doesn't let it respond quickly enough to the vacuum pulses going through it.

Note that the solenoid has a third port (with a filter element) on it that vents vac to the EGR valve when the solenoid closes.
I noticed that, and wondered what it was for. On mine (same as on others?), that port is the entire top of the solenoid, with a pop-off cap that contains a foam rubber filter. Once removed, you can see the solenoid. When you say this port vents vacuum to the EGR valve when the solenoid is closed, do you mean it vents vacuum that would otherwise go to the EGR valve if the solenoid were open, so that the vacuum starts pulling air in through this filtered port instead?

While it's certainly possible you could have a bad solenoid, it's much more likely that you have a bad PFE sensor. Those things go bad all the time.
I've been wondering about the condition of my PFE sensor for some time. When I got the car in 2006, this sensor was no longer on its bracket (which was missing), but instead it was hanging loosely by its two hoses, upside down over some other parts and cables. I replaced the bracket last night with one from the local PNP, and installed the PFE sensor onto it, right-side up. I'd read a few months ago that it can get filled with water from the exhaust that enters it, and sure enough, when I pulled the hoses off of it at that time, water came out. Last night the same thing happened--the whole thing seemed to be filled with water. I wonder if that's because it was upside down, and the water couldn't drain back out as it can if it's mounted upright. I also wonder if water can damage it. I'll be testing it with info at http://www.tomco-inc.com/Tech_Tips/ttt36.pdf, and replace it if it's bad.

The computer sends the VSV a pulsed/duty cycled timed electrical signal to open it's vacuum port & thus apply timed vacuum pulses to the EGR valves vacuum diaphragm, which causes the EGR valve to open & close in time with the pulses.
Interesting. More complicated than I first thought!

The vacuum lines to the VSV & to the EGR valve & the EGR valves vacuum diaphragm have to be in good shape & not leaking vacuum
Speaking of which, in addition to the potential solenoid problem I discovered last night, I also discovered that the thin plastic vacuum line running from the EGR valve solenoid to the EGR valve had two breaks in it, one near each end of the line, which someone (before I got the car) tried to fix by pushing the broken ends into rubber hosing, and topping it off with some rubbery conformal tape. That might have worked at the time, but now it was leaking, which I discovered when I removed this line and blew and sucked through it while covering one end--air passed through the breaks. I replaced the line with a piece of rubber vacuum hose of the same length and inner diameter, in case these factors are important in regulating the amount of vacuum reaching the EGR valve.

From the vintage of your system, I agree it's probably a good idea to pull the EGR valve while your in there & inspect it for carbon deposits, rust/corrosion & it's gasket too. If the engine isn't using oil because of wear & you've been using the right service grade engine oil over it's lifetime & using a good grade of fuel, it'll likely be clean.
My Dad owned the car (from new) before I got it, and though I think he probably maintained it well, I don't know the details (while he was an aircraft and car mechanic, I was a computer repairman). I've been topping off the oil (a slow leak I'll be dealing with soon) since 2006 with conventional 10W30, and I've completely changed the oil and filter only twice (lately with synthetic 5W30), based on the relatively small number of miles I've driven it (only about 13,000 since 2006). A couple months ago I looked at the throttle body intake, and it was almost completely clean, with so little goo at the bottom of the opening, I was able to wipe it away with my finger. I don't know if that means I might not be seeing carbon when I remove the EGR valve, but I'm hoping, so I can spend the time doing something else.
 

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Discussion Starter · #7 ·
At Pick N Pull yesterday, I tested two EGR vacuum regulator (EVR) solenoids identical to mine. Sucking and blowing through the top and bottom vacuum hose connections, seemed to be nearly identical to mine--a small bit of air flow in both directions through both connections, instead of the supposed none that "sundarpn" said one should find, so I'm going to assume for the time being that sundarpn wasn't correct since it's unlikely three different solenoids would behave the same (not impossible, but unlikely). I applied a fixed 12 VDC to the inputs of these two PNP solenoids, and as with mine, there was no discernable activity inside the solenoid--no movement, no sound, and no difference in how much air could be sucked or blown through their vacuum hose connections while power was applied. So, maybe my solenoid is working properly. I left both solenoids at PNP, in a place where I can find them if I decide to buy them to compare their behavior to mine when installed in my Taurus.

At home, I removed my Taurus's EGR valve. There was some carbon lining the cavity that the valve fits over, and inside the EGR valve's metal fitting and actuator pin (for lack of the correct term), and less inside the pipe that connects the EGR valve to the exhaust manifold, but not enough to block air/vacuum flow. I cleaned some of it out using starter fluid (one of the more toxic chemicals we work with on cars?), but stopped for now because I decided there probably isn't enough of it there to be causing the 33 code. I'll be cleaning out all this carbon after I troubleshoot other parts. If there's enough carbon somewhere to cause trouble for the EGR valve, it'll be behind the throttle body, visible when I remove the TB's gasket.

I didn't get a chance to test my DPFE sensor yet.

More later on some interesting things I found when I did some in-car testing of my EVR solenoid.
 

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The vacuum line between the VSV/EVR & EGR valve diaphragm that you found spliced & leaking & replaced, may have fixed the problem, as that vacuum leak would have been applying a weak vacuum to the EGR's diaphragm, causing it to not open, open partially, or it operation to be sluggish. SO, since the vacuum hose replacement, have you cleared the code & driven the vehicle to see if the code resets????
 

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If the PFE was filled with water, my guess is it has failed. PFE and DPFE are mounted so hose(s) come out the bottom for a reason.
 
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