No Ported Vacuum

I'll bet the port is blocked. Most likely gasket 61 is missing a hole, or is wrong and blocking the passage. Or, is wrong and is bleeding off the vacuum. Take a piece of vacuum hose, connect one end to the ported vacuum nipple, and blow in the other end. I'll bet you can't blow through it. If you can blow through it , you need to find where the air is escaping.

There is a nipple on the base, next to the left idle mixture screw, just above screw 59. It's usually capped from the factory. That is also ported, but is calibrated differently than the one on the side. That may cause hesitation, or not enough EGR.

Note in that picture that gasket 61 is not facing the same direction the carb is. It's backwards. Maybe somebody actually managed to put yours together like that. :-)

Also note that venturi vacuum has been mentioned in this thread. Ported vacuum is not the same as venturi vacuum. Venturi vacuum is much lower than ported, and would not be enough to actuate the EGR valve. Your carb has no nipples for venturi vacuum.

The port above #60 is a ported vacuum port. Not venturi vacuum. That port originates in the carb base, just above the throttle plate, in the throttle bore. There is no external port supplying venturi vacuum on a BBD carb.

The port Steve refers to is pointing to the right in this photo:

Ford did use venturi vacuum to control EGR via a vacuum amplifier on some models in the 70s as I recall.

Venturi vacuum comes from the venturi in the carb. Ported vacuum comes from just above the throttle plate.

The port Steve is referring to is the port that supplies vacuum to the EGR valve through a CTO valve. The CTO only prevents vacuum from being routed to the EGR valve until the engine is warm. The Jeep system doesn't use anything like the valve in your picture, nor does it need one, as it doesn't use venturi vacuum to control EGR.

Hi All,

So I changed every inch of vacuum hose in the Jeep this weekend and connected everything to factory specs and guess what - still no ported vacuum. I did find the other port referred to in this discussion and checked it too - also no vacuum. I tried blowing into the port and it is not blocked and I can hear the air entering the carb somewhere down below the chock plate. Anybody have any ideas. I have not gone for the smog test yet since the EGR obviously has no vacuum and don't want to risk failing another test.

I think the next step is to take the carburetor apart. You may have a damaged or wrong gasket in there. Just because air is entering the carburetor, that doesn't mean it is entering in the right place.

Earle

I can't see how you can have 0 vacuum on the ported and still have manifold vacuum.....

I would be guessing the carb is loose or the base gasket has blown out or the intake manifold is loose.

How is the idle? Can you make it idle at 650 rpm?

How are the brakes? What happens to the idle if you pump the brake pedal?

Any oil puking into the air filter?

Mike

On some vehicles, ported vacuum only works above a certain rpm, some distributors use ported vacuum, which only opens at certain point, like an EGR valve.

Don't know about yours, but you might try raising the engine speed and see.

Spdloader

Here are some more answers/clues: The idle is very good and smooth even down to 600rmp. I do have manifold vacuum. I did have oil puking into the air cleaner but I took care of that a long time ago by venting the crankcase out the back of the Jeep via a long hose...and yes, a lot of blow by does come out. I also went for the smog test today and failed. The hydrocarbons were good, CO was 0 at both 15 and 25 mph but the NO was 1100 at 15mph (max is 750) and was 690 at 25mph. I also failed because the timing was 0 btdc. The guy told me that the timing might be causing the high NO but I am woried that it is the EGR not getting any ported vac. I know the egr is not strong at 15 but I am sure a bit of egr would help. It seems to work at higher speed. Any thoughts? Also, anybody have the link to that trick to adjust timing without a timing light?

Thanks again for all the help...glad you guts are sticking with me here!

What grade of gasoline are you using for the test? The lower the octane the faster it will burn, might be enough to get you a passing grade.

Steve, put the timing where it should be and it will help the NOx readings some. The CO might go up a little, but obviously you're ok there now. The EGR more than likely does not function at 15 and 25 MPH even when things are working properly. The main design function of the EGR was to reduce HC emissions, but it might also help NOx somewhat. Like I said though, at the vehicle speed they are testing, I'm pretty sure the EGR is not doing anything. They are designed to open at higher speeds. If your EGR opens at low speed, your drivability will suffer dramatically. The other thing that causes many people to fail emissions testing is a catalytic converter that is too cold. If you can, take the vehicle for a good highway run right before you get to the test station and I would venture a guess that you will pass your test even with a non-functioning EGR.

Chris

hydrocarbons

Now we are getting closer I think....

You have to address the blowby first. That is the main symptom of a blown out charcoal canister. This will kill your ported vacuum (EGR) and make your manifold vacuum too low. It also will mess up the timing advance big time. This was already mentioned by someone as a possible cause.

What have you done with the canister and the small vacuum line to it that comes from the EGR circuit or from the CTO valve?

What have you done with the large vacuum line that comes from the PCV line at the solenoid at the rear of the carb and goes to the canister?

Does your PCV valve still rattle when you shake it?

The PCV line runs along the valve cover and makes a right angle turn at the back of the carb. Is that rubber right angle fitting still in one piece or has it gone soft and collapsed?

The trick to adjust the timing depends on you having manifold vacuum. You don't have proper manifold vacuum if the canister is blown. But basically you adjust the timing with a vacuum gauge on manifold vacuum and adjust until you hit the maximum vacuum, then back it off 1" of vacuum and tighten it up. This will have it close.

Can you address the above questions, then I can come back with maybe some more answers or fixes.

Mike

Mike,

The canister is blown. I have blocked the vacum signal to it from the CTO but the manifold vacum is not blocked (should I). Also, the hose to the PCV is blocked - otherwise it would be sucking in blowby and clog the carb.

The reason the crankcase 'intake' line from the air filter to the engine is puking out oil is because the PCV isn't working. The PCV sucks air out of the valve cover into the intake manifold. This air comes from the air filter to the back of the valve cover and circulates through the PCV.

The reason the PCV isn't working is because there isn't enough manifold vacuum due to a blown charcoal canister purge valve or a dead solenoid switch or line (see below for explanation).

The reason the ported vacuum and EGR isn't working right is because of low manifold vacuum.

Your timing advance also isn't working right which will blow your emissions readings.

Lets start with some basics and see if you can get it purring again.

You can 'temporarily' disconnect the canister, but it 'is' the gas tank and carb float bowl vent so if you block the wrong things, the Jeep will act like it wants to run out of gas. A vacuum will build up on the gas tank.

This also will happen as the charcoal gets saturated with fumes because of no purge and as the air filter on the bottom of the canister gets plugged. The air filter is only a couple bucks but is a real SOB to get the first one out of the canister. Ya gotta dig it out.

The PCV valve should rattle when shaken. If not, it is cheap and needs to be replaced.

Then follow the PCV line along the valve cover making sure the 90 degree elbow is still good. I replaced that part with a copper tube bent to a

Then the PCV line comes to a solenoid thing at the back of the carb. This solenoid never worked properly and the factory fix is to toss it away and replace it with a normal T fitting.

Off this T fitting, one line goes to the base of the carb and the other line goes to the canister top. This is the vacuum purge line from the canister to the PCV system. This large line to the top of the canister needs to be blocked at the carb end. It is letting out the manifold vacuum.

For 'temporary' use this line to the canister can be unplugged at the carb end and the PCV line just put directly onto the carb base nipple. That gives the PCV direct manifold vacuum and shuts off the canister.

You then need to unplug one of the other large lines going to the top of the canister. I usually unplug the one leading to the carb float bowl. The other goes to the gas tank. This will relieve pressure on the canister so you don't act like you run out of gas but will allow gas fumes to escape when it sits. No real getting around the gas fumes, that is what the canister is for anyway.

The 'best' fix is to replace the canister.... Anything up to a 91 will work.

As to the timing, the computer controls it according to how much vacuum it sees. The vacuum switches sit on top of the valve cover or on the center firewall. There are two of them side by side. If these are electrically unplugged for any reason, the timing will jump about 8 degrees or back to 0 like you see and the idle will drop. This also happens when you unplug the computer.

Mike

steve wrote:

Mike,

I will try plugging the manifold vac from the canister but do not want to hook up the PCV system. The engine has 185,000 miles on it and the blow by forces oil through the pcv into the carb and clogs everything up. I will try the other fixes, buy a timing light and hopefuly go for another test today. will let you know what happens.

The PCV is the one emissions control, that is actually good for your engine. If you like a sump full of goo, water, and acid, then by all means leave it unhooked. Like Mike says, you have to fix whatever it is, that is preventing the PCV from working properly. Otherwise you probably will never pass emissions either.

Earle

GOOD NEWS everyone,

I past the smog test! I took mikes suggestions and plugged the manifold vacum going to the canister and that got the ported vacum back. I adjusted the timing and went for the test and past easily. Mystery solved. Thanks everyone for all the help!

-Steve

Thanks for the update.

Now that you have manifold vacuum working, that PCV system might actually work properly again.

I only blow oil into my air filter now after a sustained 75-80 mph run. I had to put a new canister in to get my vacuum back also. I tried running without it but the gas fumes became too bad so my wife insisted on fixing it.

I might stuff some steel wool into the intake line from the air filter to catch the high speed spits and let them drip back into the valve cover like Volvo used to do.

Mike