I have had an intermittent CEL for much of the past year - getting worse over time and definitely related to a warmed up vehicle and and ambient temps. Finally got a code reader - pointed to the EGR and position sensor - sorry I can't find my notes this afternoon.

I pulled the EGR - looks clean and moves freely. Research indicated this can also be related to the DPFE sensor. Despite some excellent pictures, I can't seem to find this device - and the online parts stores don't list the thing for my truck. I did find a listing for the EGR control solenoid - and I find this thing in the engine compartment.

Two questions - can this be the culprit and how can I test it other than a parts exchange?

Second, one of the codes indicated an EGR position issue. when I look at this, I see no way it would be bad - other than electrically - how would I test this?

OK - three questions - when I check the vacuum lines, I can get a sustained vacuum from the manifold connection, through the solenoid, and to the EGR connection - but I can not maintain a vacuum at the EGR itself. Looking at the position sensor, I find no gasket or any indication of a seal - although the assembly looks like it should have a sealing o-ring. Am I missing something here?

Thanks for any advice or guidance - I've got emissions due next month and they won't check it with a CEL on.

Jeff Rees
'91 2.3 4 speed

 

Hello from Hotlanta. The EGR has a diaphragm inside that is operated by engine vacuum. The vacuum comes from the apply and dithering valves. If you apply engine vacuum to the diaphragm, the EGR valve should open. If you do this while the engine is idling, as in grab vacuum from the 'tree' on the firewall and apply it to the EGR, the engine should die.
To get an error code for the EGR means that the computer told the vacuum valve to apply vacuum, and the dithering valve to let the vacuum through. The sensor on the EGR itself reports position by varying resistance as the valve moves in its travel. If the command works. If the valve doesn't change the resistance, the computer will throw a code.
The two solenoids operate valves. One is the apply to provide vacuum and the other is used to 'keep' the vacuum once applied, or release some of it, or all of it. Either way, I think the valves are pretty stable operators, and most problems come from the EGR valve itself.
tom

 

Tom,

Thanks for the input. Near as i can figure, the '91 doesn't have the DPFE that most threads address. Inspection of the system leads me to the conclusion that the system operates as you describe. As the valve moves freely and I can get vacuum, I was at a bit of a loss. Now that I've discovered that the diaphragm chamber "leaks" with the position sensor in place and while it appears there should be a sealing O-ring, I have nothing in the way of a seal, I'm headed to the hardware store to see if I can find a reasonable match for the "missing O-ring to see if that improves things.

If not, it looks like the old "change parts till the problem goes away" approach.

Atlanta here also!

Jeff

 

If you have the "hard plastic" hoses with the rubber tips going from the EGR valve to the switch change this plastic hose to a good rubber hose - or at least inspect it very carefully. You do not get vacuum at the hose all the time - only when computer calls for it - so you will not know if no vac if you just check it at idle for instance. Mine had two of the four plastic lines in the system cracked and I made the mistake of buying and changing EGR and it's sensor when all it was was the plastic hoses had cracked.

 

I do have the hard plastic lines. While I can pull and sustain a vacuum with these lines, they would be simple and inexpensive to replace - I'll try that.

I did install an O-ring of close to the correct size yesterday afternoon - this morning, on the way to work, I got an almost immediate CEL that stayed on the whole way in. Truck runs fine - just need to clear the CEL so I can get the emissions inspection done.

Back to the original question - should there be an O-ring or other seal between the EGR assembly and the position sensor enclosure?

Jeff

 

If there were an O-ring, it would have nothing to do with maintaining vacuum internal to the EGR valve. The diaphragm is inside the flattish disk, stretched from side to side. It is flexible and rubbery, and moves when vacuum is applied on one side. When that happens, it moves the pintle inside the valve part to allow EGR flow.
As the valve parts move, they also move a sliding resistor pickup, varying the resistance reported to the computer.
Now that I think about it, I don't remember an O-ring, but I don't remember what it looks like inside either. I would have thought that the white plastic part would have a gasket at its base where it rides on the diaphragm body, or the diaphragm would have an internal seal. I just don't remember. It seems to me there was a 'button' that was on the diaphragm that pushed on the probe from the electrical part of the EGR valve. The probe, being spring loaded, followed the EGR as the vacuum moved it within its range. But I may have made up this memory.. too long ago.
The O-ring you installed may have displaced the plastic, changing the position reported to the ECM, and thus set off the CEL. It may have made the computer think that the EGR valve could not be closed, such as at idle, but for sure was not responding properly to commands. If there had been an O-ring, it would still be there unless you have a 'helping hand' that works on your engine while you are not around...
tom
No need to replace the lines if they hold vacuum.

 

Tom,

The vacuum connection from the control valve connects to a small metal "spigot" that opens to the EGR valve proper. When I try to pull a vacuum on that port, I get nothing. Opening the assembly I find the spring and EGR valve assembly "open" to the atmosphere - and as the following sensor appears to have an O-ring groove in it, I made the assumption that the missing "seal" was the cause. From what you are saying, it would seem that the EGR should NOT be open at the sensor end? If this is the case, i have a completely failed EGR valve as there is NO diaphragm at the sensor.vacuum connection end. I can clearly see the return spring and the metal plate at the end of the EGR assembly. If this is not correct, you have helped me find my problem!

Jeff

 

I think that is right. I just finished complete rebuild / install of crate engine on my big Bronco before winter and it is a 5.0 but EGR is probably similar. I think the EGR is sealed. When the computer controlled vac switch gets turned on it lets controlled amount of vac pressure go to EGR via the hated plastic hoses. The vac causes EGR to move and the amount it moves is measured by the electric sensor on top of it and tells the computer. It is tiny amount of movement the sensor is looking for so if you put a ring on and it raised the sensor up a 1/16th of an inch even I think you will get a engine code. When computer turns off vac port I think port vents the vac. I remember the manual showed tests for these things. Will look when I have a minute and see what it shows. For now go to Advance or Autozone websites and look up your EGR and the sensor on top and look close at any pics they show of the parts to see if they have something on them you are missing. I know I had constant engine light and had replaced EGR, sensor on top, and found someone had run vac straight to engine and thing ran just awful. Then I found cracked plastic hose and put new hoses back the way they were supposed to be (via computer controlled port) and engine was fine.

 

If you apply vacuum to the small tube sticking out of the diaphragm housing, the valve should open. If it doesn't it is defective or has had some 'adjustment' of parts content, i.e., removal or loss of a sealing O-ring.
I have dealt with EGR since it first came out in 1974. I had it on my first new car, and dutifully took it to the dealer for its first oil change to insure that the warranty (12mo/12k) stayed in effect. I watched as the mechanic went about his business, and noticed that he removed the rubber tubing to the EGR valve, and seemed to be stuffing something inside. After I got home, I discovered he had pushed a small ball bearing into the tube to block the vacuum from ever opening the EGR valve.
Today, that would not work. The engine would ping, the CEL would be lit, and if your locale demands emissions tests, you would fail from the get-go. That car was my 240-Z, well as much of one as I could afford. I don't think I ever removed the ball bearing.

 

Tom,

Vacuum at the spigot on the EGR does nothing - and can't even be generated. You can hear the air being drawn into the center of the EGR - and if you reach in and put your finger on the interior opening, you can feel the suction. So - looks like I'll get a replacement valve and see where that gets me.

Thanks for the input and guidance.

Jeff

 

Tom - I worked at a Nissan shop back in the late 70's (was Datsun then) and some of them back fired under the right conditions with the EGR valves. Had a 210 that blew open mufflers because of the issue. Still have in my parts bin some clamps and adapter pipes from that car because the exhaust diameter was 1 1/4 in spots and have not seen any that small since - even my kids Quads have bigger exhaust (and more HP than that car) but EGR in those early cars were pretty bad.

Jeff - I looked through all my books and I think you are right on the money about your EGR being bad. It does not open at idle, or when cold, usually about 1500 RPM or so and if you pull vac at bung and it does not move you are correct that it is a leaker. Good Luck..

 

Just to close out this issue:

First, thanks for all who made suggestions.

It took me a while to locate a replacement EGR - when I went to pick it up, it too was open to the metal spigot, with no way to pull a vacuum to move the valve. With that information, I went back to the truck, removed the EGR position sensor - the one I suspected should have an O-ring - or at leas some sort of seal - to allow the vacuum to position the valve. I ended up coating the face of the sensor with gasket sealer and reassembled the sensor. After allowing a few minutes to set, I found I could generate vacuum and hear the EGR valve moving and reseating. I left it to cure and when starting the truck, no longer had an immediate - or even short time CEL.

After two days of Atlanta heat and traffic - no more CEL! - so it looks like the whole problem was a failure of the position sensor to seal, preventing the valve from responding to commands and thus not reporting the proper position.

Again, thanks for everyone's input!