I am still chasing a problem with my truck idling rough and got thinking about something. When setting the timing on my truck I set it to 0 degrees TDC with the vacuum line plugged. But when I plug the vacuum line back on the distributor my timing does not change unless I rev the engine. It seems to me that when this engine was in the other truck, the timing changed when I hooked the vacuum line back up to the distributor. It also seems to me that I have read that the timing should be set around 10 degrees TDC with the vacuum line attached. Is this right?

Anybody know how much vacuum I am supposed to have at my distributor at idle? Anyone know how I can check to see how much vacuum I should have at different vacuum ports on my engine?

Can anybody help me?

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Buy a mityvac tester.::http://www.ebay.com/itm/Mityvac-MV80...8AAOSwQBFZrXyn

Useful for a myriad of things: test vacuum servos and such, bleed brakes, measure vacuum.

Every toolbox should have one.

 

First I would apply the "vacuum line mouth test" to the vac advance on the distributor to make sure it will hold a vacuum.

 

I have one and yes the distributor vacuum servo holds a vacuum

And yes the vacuum advance does work by mouth and it holds vacuum. I can advance the timing while the engine is running using by putting vacuum on the distributor vacuum line.

But when I hook the vacuum line back on the distributor the timing does not change and it seems to me that it use to. So my question is how much vacuum am I supposed to have at my distributor with engine at idle. I would like to have a basis to know what to look for.

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I can't tell you how many inches of vacuum to expect at each port, but generally if you connect a vac gauge to a smooth idling engine on a DIRECT vac port, you should expect somewhere between 18"-20"hg. If you are connected to a ported vac source, it will be less, possibly 0" until the throttle is opened. Historically, engines from the 60s-70s had their vac advances connected to direct vacuum. Ported vacuum began to be used in the mid-70s as part of the emission control systems.

Perhaps you had it connected to a direct source previously? Is 0 degrees really the timing spec for this engine? Engines run like crap at 0. Typically idle advance is somewhere near 20 degrees. As you advance the timing, vac will read higher also.

Do you have one of those old Chiltons or Haynes manuals with the page showing vacuum gauge behavior for diagnostics? Actually you could just google that up.
If you dont have a vac gauge they are good to have in the tool box.

 

Here is what the Factory manual says:

"Ignition timing: 0 degrees TDC max, (950 RPM) with vacuum advance cut"

I have a factory manual for my truck, both paper and digital. I have always had the vacuum hose to the distributor as shown in my manual.

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If no one knows what the vacuum is supposed to be at the distributor, could a couple of you take the vacuum reading to the distributor vacuum advance on your 22R engine and post it here?
It would be most appreciated,

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Only vacuum gauge I have is the one on my little vacuum pump. I put that on the vacuum line going to the vacuum advance of my distributor and got 12" of vacuum. I can advance the timing on my truck with vacuum, but it will not hold the draw. Is it supposed to hold the draw? If so it appears I have a bad diaphragm. WHY IN THE WORLD ARE THE REPLACEMENTS $150 - $200!?

Trying to find a "good price" on a replacement I have found "New" distributors complete with everything including cap and rotor for $90... I found a re-manufacture Denso for $200. This seems ridicules...

So what do I have to watch should I buy an after market distributor? Why is a new one $87 - $170 and a re-manufacture ones $150 plus?

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LC Engineering sells new ones, thats where I bought mine. Great price too.
http://www.lceperformance.com/Distri...-p/1081123.htm

 

I think I would have liked to have seen this post before I bought a new distributor... I bought one at Merle's Autoparts, a pert of the Parts Plus organization... New unit cost me $150...

 

Okay, I bought a new distributor, a Spectra Premium TY47. It looks like a perfect fit. Went in as I expected, but after installing the distributor with rotor in what appears to be the right position with the engine in the right position and setting the timing, my truck runs flat. At idle it sure runs better then with the vacuum leak with the timing set a 0 degrees BTD.

When I have the timing set 0 degrees BTD with vacuum lines plug, attaching the vacuum lines advance the timing to about 8 degrees BTDC, so it idles very well. But running? It had more power with the vacuum advance not working...

What am I missing here? My gas mileage was at 16.4 MPG before installing the new distributor and with the new one I get 16.7 MPG and the truck is flat! It had more power with the old broken distributor...

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Sounds like the vac advance is not advancing under load but it is working at idle. Its supposed to advance at idle and as rpm's build. Check both sides of the diaphragm are working.

 

How do I check what you are saying?

When I have my timing light on, what should my timing be doing with acceleration? It seems that it drops under a hard acceleration. It increases with a slow acceleration, but stop on it and the timing backs up and then advances as the vacuum increases...


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https://www.yotatech.com/forums/f116...ill-do-108688/

This thread has a lot of good information on how the 22r vac advance works.

 

Okay, yesterday I put vacuum pump to both ports on the vacuum advance on distributor and both advanced the distributor. I looked at my factory service manual and it tells me to set my timing at 12 degrees BTDC with vacuum lines attached. Then it tells me to plug the vacuum lines and my timing should be 0 degrees BTDC*. (see attached pdf of page EC-67) I can't help thinking I have a vacuum leak not allowing enough vacuum to advance the distributor as much as it should be.

If no one knows how much vacuum I should have at the vacuum advance on the distributor, could someone please put a vacuum gauge on these two lines at idle and let me know the vacuum gauge readings? I'd also like to know how much vacuum is required to move the vacuum advance...


* I have never tried setting my timing at 12 degrees BTDC and checking it with vacuum lines plugged because my after market manual tells me to set timing with vacuum lines plugged and no mention of checking it with vacuum attached. I had set my timing this way for years and don't see how anything would have changed so that this method wouldn't work now... I really doubt that setting my timing with vacuum attached and checking timing with vacuum plugged will give me any different readings the I currently have...


I have considered pulling this vacuum mechanism off the new distributor and putting it on my old distributor to see what would happen...

Thoughts? Input?

Thanks,

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