Ok. 1983 Ford F250 4x4 gas ... 4180 carb. After driving and then coming to a stop it idles like crap. I was able to ascertain that the EGR valve was not closing thus causing the crappy idle. However .... when I disconnect the vacuum hose to the egr and then reconnect its all fine .... so the valve is not sticking .... its just not getting the drop in vacuum required to let it close. So I investigated further .... on this truck the egr is run off carb vacuum port near the top of the carb that runs to a temperature vacuum switch on the thermostat housing. This only effects things when the temp is low before the truck warms up so that is not the issue as far as I can tell. I hooked up vacuum gauge and tested various things and the port off the carb running the egr produces vacuum when its supposed to and then drops to zero at idle like its supposed to .... so now I am clueless as to what the issue is. My question is this : when the truck returns to idle is the egr supposed to bleed off the vacuum that it had built up to open it so that it can close? Because as soon as I release that vacuum build up (by pulling the hose off and on real quick) the egr closes like its supposed to. It seems to me that the vacuum applied to open the egr valve is still there at idle even though its not being produced by the carb so I would assume it is supposed to bleed off in order to close the egr valve. And if that is the case, why is it not doing so right now? Its a mess of vacuum hoses under the hood in this CA emissions model so that's the best I can figure out. Any help would be extremely appreciated because I need to smog this old beast next week ! HELP

 

You might have the hoses hooked up backwards on the temp sensor switch. Swap them around and see if it fixes it.

Also take a look at the diagram, make sure there are no components missing in the EGR line. Sometimes there are valves or other gizmos that relieve the vacuum when the vacuum drops to zero. In other words, it lets air into the line to let the egr close. Try swapping the lines first. Or after the engine warms up you could take a small piece of pipe and take the lines off the coolant switch and splice them together direct and see how it acts. All the switch does is lock it out till the engine warms up. If it works ok and shuts, then you know it's something with the switch.

 

Already tried pretty much all that before I resorted to posting here. I ran a hose directly from the ported vacuum on the carb to the egr valve thereby totally eliminating the temp switch and all the purge / valve crap on the rest of the emissions T. Problem still persisted. Which is what brought me to the confusing conclusion that perhaps the EGR spring is too lose (OLD) so that it can't close when the vacuum is shut down at idle and the little remaining vacuum buildup still holds it open ? ? ? make any sense to anyone? Because again, when I pull the hose and release that little bit of vacuum buildup the EGR valve closes fine and when I reconnect the same hose a second later there's no issues. So the carb is not pulling vacuum at idle either .... it just seems that the little vacuum buildup left behind after going from cruise speed down to idle remains and is enough to hold the EGR open. So .... when all else has failed I post here in the hopes someone who knows more than me can help ..... because this ones got me stumped

 

This also led me to believe that there might be some part of the egr valve I don't understand or am not able to see that is responsible for bleeding off the vacuum when it goes down to idle and the carb stops pulling vacuum .... but the egr valve is a fairly simple device and I can't see anything that would be responsible for this function

 

There is the possibility you have the wrong egr valve, or there is a problem inside it. Most of the egr valves ford used have a fuzzy strip around the bottom edge of the egr valve diaphragm.

These valves are throttled by exhaust backpressure. There are two diaphragms inside, the rubber one that the vacuum pulls on, and a metal one that the exhaust pushes against. When there is exhaust pressure pushing on the metal diaphragm, that diaphragm throttles the vacuum going to the rubber diaphragm. The rest of the vacuum sucks air through that felt filter strip around the underneath part of the valve. This is how they give the engine max egr during different engine conditions. Generally, the more engine rpms the more egr the engine can take. More engine rpms means more back pressure, which closes the metal diaphragm more.

The above is why you cannot test most Ford egr valves on the bench with a hand vacuum pump.

 

Try connecting your vacuum gauge inline with a tee, as close to the valve as possible. This will show what's in the line at idle under actual operating conditions. Could be that disconnecting the lines while testing is venting the pressure as you'd hope to see, but it's not happening when everything is connected. A teed gauge will show what's really happening. If vacuum is still present, then at least you'd know you should determine why it isn't bleeding off.

 

If you reach around the EGR valve there should be some holes on the back side that allow you to manually push the valve open a bit with your fingertips.

With the engine idling, push on this (careful of moving parts!) enough to just crack open the valve. Your idle should roughen a lot, maybe even threaten to stall. Let go and the valve should close, and idle return to normal.

This test might show if the return spring is working, and if the valve closes at idle vacuum.

It does make sense to me that the EGR failing to close all the way due to a weak return spring could cause the problem you are describing.

 

Well this thread is a little over a year old but doesn't have an end or final outcome, did it get fixed what was the problem ?

 

Does anyone know the resolution to TKC432's EGR issue? I'm having the same issue.

 

I know the resolution, the proper shop manual giving the diagnostic routine rather than taking wild guesses and throwing parts at something.

Either that or defeating it...

EDIT-

I'm sorry for that emotional outburst. It is just frustrating (to me) to see head beating against the wall and not being able to get to the source of problem such as this.

If you do not have the appropriate year shop manual (not CHILTON-HAYNES) you are most likely going to be lost with a whole bunch of guesswork and $$$ involved.

Systems such as this can change drastically from model year to year.

 

EGR System diagnosis (brief) for this time period vehicle-

 

KULTULZ - May I use the above on my web site? If so, do you have it in pdf? And, what happened to pages 2 & 3?

Thanks!

 

Of course you can use them (remember to credit FORD). We all exchange info and your site is a plethora (college word) of needed info.

Pages 2 and 3 in this publication discusses other types of valves and this page is most relevant to the time period and applications being discussed here (IMO).

I need to learn how to convert .jpg to .pdf.

1984 CAR SHOP MANUAL- EMISSIONS DIAGNOSIS VOL HC

 

I did the conversion to pdf, so don't worry about it. I just thought you might have it. No problemo. But by doing it in a pdf and then doing an optical character recognition pass on it there are actually words and numbers in the document instead of pictures of words and numbers. So eventually, when Google and scanned my web site thoroughly, you should be able to search for those words and find them.

EGR System Description & Testing - ???Gary's Garagemahal

 

KULTULZ, thanks for the edit and the additional troubleshooting documentation. Between your information and other links on this site I have learned a lot about the EGR circuit.


I finally got some time to troubleshoot my EGR issue. With a hand vacuum pump/ gauge I confirmed the thermal vacuum switch, venturi vacuum amplifier (VVA) and EGR value were all working correctly. I found that the manifold vacuum line going from the carb to the VVA so connected to the incorrect vacuum port on the carb. So the manifold vacuum line on the carb was not providing variable vacuum (based on the throttle position) to the VVA so the VVA was not providing vacuum to the EGR valve. I connected the manifold vacuum line to the correct the vacuum port on the carb. After a test drive the EGR valve is functioning correctly.