I am struggling with my truck failing emissions. I found that my vacuum booster for the brakes was leaking. I've plugged the hose and at idle I do not have enough vacuum to move my vacuum advance distributor. The vacuum advance module holds a vacuum and advances with my vacuum pump. My question is how much vacuum should my 1985 22R engine be producing where? I'm getting around 4- 6 PSI vacuum at the distributor, anyone know what it is supposed to be? BTW I have done a compression test and my compression is good.

Thanks for the help,

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It should have a dual diaphragm vacuum advance can if the distributor is factory original. The inner diaphragm (closest tot he engine) is full vacuum at idle. The other is ported vacuum which received vacuum off idle. Manifold vacuum should be a steady 20 inches at idle. Check for vacuum leaks at carb and intake gaskets, vacuum hoses, and verify all vacuum motors are functioning properly. I had an EGR valve hang open once and caused a low vacuum/crappy idle scenario. That took a bit of diag to find that one.

 

Thanks for getting back to me, the intake manifold seal is good. I understand about the vacuum lines o the distributor. Now the EGR valve, is it supposed to hold a vacuum? If so which lines? As it seem to me it has three vacuum hoses going to it...

I saw another post about their choke vacuum module leaking causing problems, I'll be checking there also. I have checked most of the vacuum modules/motors and everything I checked has held a vacuum except the EGR valve, but the diagram in my manual looks like the line across the top is a pass through to something else... It was kind of confusing. I have a factory srvice manual for the truck.

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Well... I know where the vacuum leak is, just don't know what it is yet. I took my can of starting fluid and sparingly sprayed around vacuum systems. If I spray the back side of the carburetor, where all of the linkage is, the engine speeds up. So what is leaking? Any ideas?

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A worn throttle shaft bushing on the carburetor creates an unmetered vacuum leak and will cause running issues, especially at idle. Spraying the throttle shaft with carb cleaner is a quick and reliable test. If the idle rises when the shaft is sprayed, the throttle shaft bushing is worn. There are some places that will still rebush a throttle shaft but they're getting harder to find.

The EGR valve itself should hold vacuum. If it doesn't, it's trash. The 3 vacuum lines leading to the ports on top of the EGR modulator will bleed off vacuum, this is normal. There is a diaphragm in the EGR modulator that goes bad after a while since it's operated by and exposed to exhaust gasses that trigger to pintle to open and closed the 3 ports on top of the valve. A burned out diaphram will cause cause a vacuum leak. You can test it pulling a vacuum on the port directly under the modulator valve.

The factory service manual has test procedures for the EGR system.

 

Okay, got the gauges on the EGR and from what the book is showing me, it looks like it is working like it is supposed to be. I've finally replaced the Vacuum booster for the brakes (I had the line plugged off and still had problems.) I also went through the carburetor and the truck is running a lot better, passed emissions, YEA!!! It passed emission but the idle HC was high, just under the legal limit, but better than last year's readings... The loaded HC readings is less than 5-8% of legal limit. With the timing set at TDC with vacuum lines plugged, the vacuum pulls timing to about 8 degrees at idle, at the distributor gauges say the vacuum is about 14 inches at idle...

I have not got the carb-cleaner back out yet to look for more leaks or to test the butterfly bushings, it's been really hot here for this late in the year, last two days were 109 in the shade... so I haven't been to active out side...

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14" at idle and steady needle is good. The 14" will possibly increase and HC drop if you lean the mixture with the idle mix screw.(I'm assuming you have access to it... I don't have this carb.)
Increased idle timing also increases the vac level at idle. If you lean mixture and the idle speed increases, adjust it back down with the idle speed screw. Only adjust these things when engine is up to temp.
http://www.superchevy.com/how-to/45638

 

The vacuum advance lines need to be connected for a proper reading, but 14" is way too low unless you have a wild camshaft. A proper tuned stock engine should pull a steady 18-20" at idle at normal operating temp. I've never owned a vehicle that pulled less than 19.5" of vacuum at idle and this includes old stuff back to the 1950's that's worn to hell.

Keep checking, you'll eventually track it down.

 

Unless you are at high altitude ......."Because engine vacuum is based on comparison with atmospheric pressure, it varies with altitude just as atmospheric (barometric) pressure does. The following table shows that as altitude increases, vacuum decreases about 1 inch for every 1000 feet above sea level."

Inches of Altitude Vacuum

Sea level-1000 ft. 18-22

1000-2000 ft. 17-21

2000-3000 ft. 16-20

3000-4000 ft. 15-19

4000-5000 ft. 14-18

5000-6000 ft. 13-17

 

The vac reading is one thing. How the gauge is behaving will tell you more.

https://images.app.goo.gl/1hbSUVXk56uXBQLC9

 

Okay, I finally got my hands on a Tach to set/check engine RPMs. So I'm under the hood getting engine speed set and I go to adjust the air/fuel mixture and the plug is still in place... BUMMER! Any ideas as to the best way to get to the air/fuel needle? I imagine it needs adjustment as the engine has over 220,000 miles on it...

Elevation here is about 2,600 feet so high elevation should not be a problem should it?

Vacuum needle does not move and engine RPMs were about 880...

 

You will need to very carefully drill out the plug to get to the idle mixture screw.

There isn't much room between the plug and the screw head!

 

That's what I was afraid of. I really like Toyotas, but what a dumb set up!
Anyone have an easier way to get to that screw without having to remove the carburetor again? Is it a real cap that can be punched and pulled out with a screw?

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