Vacuum lines and leaks
 

I have a '78 300 which almost runs great. A while back I replaced all the vacuum lines, replacing them one at a a time to be sure they did not get mixed up, but over time it has become apparent that the emissions controls are just not right. The smog pump fell off years ago, and the bottom pipe off the front of the EGR is been cut and folded over so I question if the EGR is even a factor other than having a vacuum port. So:

1. 1) The closest I can find to a vacuum diagram is the one for calibration number 9-51-RO - it is published at various spots as the correct diagram for a '78 or '79. Based on what I can find, looking at my (partially destroyed) calibration sticker my calibration number should be 8-52G-R0. First question: are the vacuum diagrams the same? If not, anyone have access to the correct one?
2. I seem to have a major vacuum leak at the base of the carb or top of the EGR. Given that in Texas the EGR is unnecessary, what is needed to just eliminate the EGR - just disconnect and plug the vacuum line to it? Or do I need to physically remove it and source shorter studs to mount the carb?
3. I have a box-stock 300, but the vacuum lines on it were wildly different than what the drawing shows, to wit:

• I checked that the lines from the purge valve on the carbon canister are all routed as shown, and that I have manifold vac to the AT, brake booster, and bi-metallic valve under the air cleaner. The vacuum advance is hooked to the S port, the Bowl Vent to the carbon canister port, Wide Open Throttle port T'ed into the E-port line which goes to the vacuum valve by the thermostat, and that the VCV's other line goes back to the carbon canister and EGR port.
• My problem areas: There is a combination valve/T on the line to the coffee-can vacuum canister. The T'ed line goes through the firewall to the dash (probably for AC/heater controls)- I'm OK with that. BUT - since I got the truck that line is a manifold vacuum line direct to the tree on the manifold, and it terminates at the canister. On this drawing there is an air bypass valve after the canister and the line routes via the TVS in the side of the air cleaner. Do I need to change that to run via the TVS? Or leave it manifold vacuum? What is the air bypass valve on the drawing?
  
• At the top left you see a line goes from the carbon canister to the PCV where it terminates... on mine there are TWO lines to the PCV in the valve cover, not one. I routed the second line to manifold vacuum on the theory that the charcoal canister/PCV valve would need vacuum - is that correct or does the carbon canister work best using ported vacuum via the VCV?
  

I strongly suspect that the drawings for my calibration number is different than the generic one I show...anyone have any input on that?

And in a minor note, the carb number is hard to read - 7350S, possibly 7650S or 7550S. Any hints to make that number easier to read? It's already clean.

On a 1984 and 1986 F150 with 4.9L engines, a vacuum leak was found to be an unused port on the vacuum tree which screws into the intake manifold under the carburetor. This "tree" has 5 or six ports and some were unused "from the factory" depending on options, etc. There is one port nearest the engine block and pointing towards the cab. On one of these trucks, this port pointed slightly downward placing it nearest the exhaust manifold [heat] and away from sight as it was hidden by all the vacuum lines, wiring harness, etc. On both of these trucks, there was a hole in the center of the rubber cap, which may have been the original [31-33 years old!]. It was amazing the difference in state of tune when this issue was discovered. I will attach a link to the thread where this was discovered and I hope it will help.

https://www.ford-trucks.com/forums/1...expensive.html

Think mine has five manifold vacuum ports on that tree, all of which are gainfully employed at present - BUT I'll get in there with a mirror as soon as I get home today and check! My previous "find" was the S port on the carb which is pretty much hidden from any reasonable sight.

I am however getting a strong stumble when I spray carb cleaner at the EGR top surface. Not when I spray at the base of the carb, above it, though.

Time to light up a cigar! :)

well, checked that vacuum tree - indeed the 5 ports I remembered are the only ones. I am tempted to try and finish setting the vacuum lines exactly as shown in the drawing above, which would require buying a PCV made for a single vacuum line - but every pic I can find of any PCV of my pruck shows that same 2-vacuum line PCV. I feel like I am missing something basic somehow!

Side note - found a listing of '77 Ford emissions items which appeared identical to the '78s - and the initial idle setting was 6 degrees, not 10. On mine the idle really starts to climb when I go past 6 toward 10, which is what all the specs for 78 say. What started this was a high-idle and dieseling confdition which forced me to back off the 10 degree setting. Keep coming back to thinking maybe I gotta break down and rebuild the carb...

In the hope of making someone else's life easier - I finally found what I think is the right diagram (at least it ends in the right 5 numbers/letters). (Looks the same to me!)
An ancient on-line Chilton's in the Houston library gets credit for having it.

I still have one major problem - all '78 Ford PCVs including what is in the truck have TWO lines connecting to them and this diagram also shows only one.

CAN SOMEONE WITH A '78 PLEASE TELL ME WHERE THE TWO LINES FROM THEIR PCV GO???

Update - google-fu said the PCV second line should go to manifold vacuum. So that is where I did it. Also replaced the gasket under the EGR and the carb flange gasket yesterday. My vacuum hoses EXACTLY match the vacuum diagram now - a bit messy but at least they are hooked to the right places, I think. Truck was idling about 500 rpm yesterday and pulling 18" on the vacuum gauge. Timing got to 10 degrees at idle, too (before as soon as I hit 6 degrees the idle started skyrocketing.) Then today when I drove to work it was idling at 15" and running poorly; back under the hood tonight! Think if it refuses to tune in I will just start capping off ports - I figure I need vacuum to the transmission, distributor, carbon canister (for fuel fumes), vacuum reservoir (for AC) brakes, PCV and EGR for crankcase venting... hell, there is almost nothing left after that but the air cleaner stuff!

Don't rule out an intake manifold leak. Re-tighten everything.

agree, have a fresh can of carb cleaner on hand. Have not had isues there in the past yet, it has all been vacuum lines and the bad flange gasket.

Just as verification - there are 4 ports on a YFA, right?
S - Spark - to distributor advance. On the base to the rear of the idle mixture screw
E- EGR - on the base in front of the idle mixture screw
BV - bowl vent - on the front side of the carb even with the fuel line
WOT - passenger side of the carb above and somewhat to the rear of the S vent.

And there is one high on the passenger side of the carb at the extreme top - think that connects to an EGR port?

One thing I do notice - just forward of the standard throttle linkage on the carb is an electrically connected throttle adjust which keeps the idle high unless I push the plunger - then it clicks into a close position and my idle drops significantly. I am guessing this is an emissions related throttle positioner...which could fall off with no ill effects?

Friday update
 

well, it ran even worse on the way home...to the point where I popped the hood in the bank parking lot and, lo and behold, the #2 plug wire was dangling! Makes a WHOLE lotta difference... when it ran poor on the way to work the wire must have been making intermittent contact.

Did notice that the vacuum operated stuff on the air filter is not functioning, will check it for leaks this weekend.

Fallback plan:
Manifold vac:
1) to the PCV and thence to the vacuum reservoir.
2) to the carbon cannister, thence to carb bowl and gas tank port only.
3) to the EGR port.
4) to the AT and brakes
Ported vac:
1) Distributor advance
Cap everything else and I should still run mostly clean with a very simple system. (Also castrate that electric throttle positioner, whatever it is.)

YFA vacuum ports
 

Well, after bugging folks at Mike's, Carbs Unlimited, and finally Daytona Parts, I am told the following applies: The vacuum advance is by the idle adjustment screw in the base. The EGR is the single port in the middle section of the carb. The 3/8" bowl vent (BV) port on the carb top goes to the charcoal canister, and the 1/4" port is the clean air port for the choke. I think the attached is correct in that case. (note that this makes my post above WRONG for the location of WOT and E (EGR) ports!) The label locations kinda ran onto each other; the vacuum port in the EGR spacer I have running to the PCV.

If you don't have the metal line going to the EGR, cut and folded over if I remember right and don't need a vacuum line to it.
Either way I would remove the line and cap it.


Have you replaced the gaskets between intake & EGR plate and the EGR plate & carb?
Could be leaking there. Also if the EGR valve is stuck open a little it will cause a vacuum leak.
Also if the EGR valve diaphragm is cracked it can cause a vacuum leak.


I only see a need for vacuum to dist advance, Brake boost if you have it, PCV system, Trany vacuum, and AC/Heat system.
Dave ----

Dave- yes, the metal pipe from the PCV is cut and folded. Should it be sealed? And yes, I replaced the carb flange gasket and EGR to manifold gasket. Have not replaced the little gasket under the EGR itself. I used a good chunk of a can of carb cleaner and found some minor leakage but nothing extreme; was able to pull 18" on the vacuum gauge at a very low (ca 450 rpm) idle. My hoses are all hooked to the right ports with the exception of the air cleaner's; since it is not functioning I am leaving it disconnected. We'll see when I top off the tank next month if this has any effect...last tank I got less than 8mpg in town, and I expect with the 300 in good tune I should getting half again that. I'm not asking for Kia mileage, just healthy mileage.

Thanks for your help.i had removed the actuator from the blend door and seems to be working when i hit the control button the motor guide rotates as which it's supposed to move. So i manually moved the blend door and it plays around so I believe blend door and actuator are working. when i hit the control button on the heater and move the blend door you can feel blend door gets suck in but no heat is coming out with or without the actuator