So glad I found this vacuum leak.

[Colt45ws]

Ive noticed over the past month or so poorer fuel economy, even worse than usual and I started noticing the HVAC losing vacuum (going to defrost) During heavy throttle uphill climbs in OD.
I scrolled over to long term fuel trim readouts on my Scangauge and saw around +10% at idle. That isnt enough to cause a code, but when I tuned the car it was around 3% at idle. So I knew there was a leak, albeit a small one.
I went over everything yesterday. Plugged this line, and that line. Finally ended up pulling the whole engine vacuum harness off while the engine was running and plugging the barb into the intake.
Pretty quickly short term trim went -7% to -10%, essentially eliminating the highish long term trim that was in effect.
Except that only lasted about a minute and it was right back to where it was.

Shelved it and got some brake cleaner today. Got home from work and started hosing all the connections and hoses down. Noticed I would reliably get the short term trims to blip if I sprayed in certain areas around the intake plenum. I tightened hose barb fittings. Put clamps on hoses. But still registering it occasionally.

Finally figured out I was hitting the egr valve when I got those little blips. So I concentrated on that and I found the issue.


$37 later, I have a new motorcraft EGR valve coming from Amazon. Should be here Thursday.

 

[AVB]

I need to do the same thing on my old Towncar. It is just a toy that I use to run around on the farm with, so I haven't looked into it. It is a 1992 with the EGR at the firewall and I just haven't felt like messing with it.

 

[3800Series]

I have one somewhere on my spare car. I haven't really bothered to find it yet as its nothing major but last year I pretty much replaced all the lines and hoses when I had the upper radiator hose blow out.

Funny thing is the hose was in really good condition..

 

[Merkava_4]

Is that a vacuum operated EGR ? It has that mushroom shape like a vacuum EGR would have.

That hole you were putting the straw into was probably the vent hole. When those rubber vacuum diaphragms rupture, they let unmetered air into the engine through the vent hole. That vent hole is there to vent the housing that contains the rubber diaphragm so that you have atmospheric on one side of the diaphragm; atmospheric being on the bottom side.

 

[Colt45ws]

Yes, vacuum operated.
But it still works, so I think the diaphragm is intact. Not only that, but the EGR valve was closed at the time; I was monitoring it along with my fuel trims. Ive also pulled the vacuum line off the top and plugged it with no change.
I believe its leaking around the shaft where it goes into the body of the EGR.

 

[Merkava_4]

Originally Posted By: Colt45ws
Not only that, but the EGR valve was closed at the time


It was closed by its spring return. The vacuum diaphragm is opposed by spring pressure.

 

[Colt45ws]

Originally Posted By: Merkava_4
Originally Posted By: Colt45ws
Not only that, but the EGR valve was closed at the time


It was closed by its spring return. The vacuum diaphragm is opposed by spring pressure.


Im aware of that. Since there was no vacuum going to the EGR, the spring would indeed keep it closed.

 

[Colt45ws]

Got the part in today. Took a few tools home from work to do the swap. It didnt go smoothly.
My issue is Im using a Trick flow plenum intended for a mustang. One of the 1/8NPT taps on it for vacuum lines comes out right where the EGR is. My OE EGR was sitting against the 5/16 90* hose barb I have in that position.
The new part interferes with said hose barb fitting so bad that I couldnt tighten it down.
Optimally (if I wasnt time limited) I wouldve liked to remove the plenum, drill and tap a new vacuum point and plug the original hole. But being time limited, I chose to make a spacer out of some steel.
Using the gasket as a guide, I cut and drilled some 3/16"x3" flat stock. 3/16" ended up being perfect, with just a smidge of clearance.
I used copper high temp RTV to seal both sides of the spacer.
Unfortunately I wasnt able to test drive it like I had planned, since it got so late, so I will find out for sure tomorrow.. Due for an oil change tomorrow too.

 

[Colt45ws]

While this did improve my fuel trim numbers, I was still losing vacuum to my HVAC on acceleration.
Earlier this year, I converted my car from manual HVAC controls to the Electronic Automatic controls. When I did that I was aware of the fact that the electric vacuum solenoids suffer from dry-rot of their rubber o-rings and eventually fail. It has been particularly hot here that past couple weeks that Ive noticed this. So at this point Im thinking thats what is happening.
In order to ensure that I was right, and it wasnt a fault with some other part I disconnected the HVAC vacuum harness under the dash, and connected a mityvac to the supply line, to use as a gauge.
It showed about 20"Hg vacuum at idle.
I proceeded to drive the car around my area briskly accelerating, and going up a long, steep hill at 60mph. It never went below 20". So the check valve is good, and there are no appreciable leaks after it.
I then hooked the mityvac to each of the HVAC vacuum cans and pumped them down to 20". They all seem to leak a little vacuum, but at similar rates, so I wasnt too concerned about them.
Just to verify, I reconnected the HVAC controls to vacuum. The can that switches the system from fresh air to recirculate is fairly accessible, so I disconnected it and ran a line from there to my mityvac.
By switching the controls to "Max A/C" it opened that valve, permitting me to see the system vacuum once more.
It was barely 10" at idle. When I drove the car around, it hung out between 7 and 10" typically. Going up the same hill resulted in the vacuum depleting to under 5" at which point it switched to defrost.

I ordered some silicone o-rings to replace the dry rotted ones in my HVAC controls.

 

[Colt45ws]

The deterioration of my HVAC gets worse each day, and I will not be able to fix it until next week and Im planning on going on a trip this weekend.
I have setup a work around using the original manual controls. Their function is merely to control where the air goes. My digital controller will still be handling temperature control and blower speed.