Two vacuum questions

[Mike_Kendall]

Hello, I just finished working on my engine after the equivalent of a grenade went off inside of it. Got it running great now.
I have two questions to ask regarding vacuum.
1) I'm having a high RPM shift problem so connected a vacuum guage to the vacuum generator that is connected to the distributor location of the gas 350. I am getting oscillations at idle between about 6 and 16 pounds of vacuum. When I speed up the engine the oscillatins continue but at a slightly higer value. I disconnected the line from the vacuum and connected the guage as the only item with same value and osciallting vacuum reading. The only line from the vacuum generator is going to a device on the side of my injection pump that can be lossened and adjusted a small amount. I recently replaced the injection pump and don't know what this device is and/or how/if it must be adjusted. What is this device and can it affect the vacuum to the modulator on the tranny?
2) Second question: I connected the vacuum guage to the line going into the modulator on tranny and read zero vacuum at idle. Is this normal and what is the readings supposed to be at idle? Will I need to rev up engine to get a reading?
Advanced thanks to all.

 

[Mike_Kendall]

Another point that I didn't mention. When my engine was out of time and grenaded the cam backed out the freeze plug into the flex plate allowing the freeze plug to take out a few teeth on the flex plate. Is it possible that when the cam backed towards rear of block that it took out the shaft of the vacuum pump? I've seen cracked distributor shafts and have to wonder if the oscillating vacuum is due to a cracked shaft on the vacuum pump? The shaft must be similar to a distributor shaft. When the only line is connected to the pump to the guage and it still osillates from 6-16 at idle I think something is definitely wrong. I read on another post it is supposed to be 20 inches of vacuum.

 

[Blood_of_Tyrants]

I would be looking for a leak in the vacuum system by pulling the line off the vacuum pump and attaching a hand held vacuum pump with a gauge to line. You should have little to no vacuum leak. If you have no leak then it is time to find a new vacuum generator.

 

[Mike_Kendall]

More Troubleshooting results

OK, when I connected the vacuum guage right at the "T" coming off the vacuum pump I had wild fluctuations. When I connected the guage and it's hose to the end of the hose going to the vacuum valve it was a steady 23 inches of vacuum. I think I was too close to the vacuum pump to get a reliable reading. I read after doing a search that I need 20 inches of vacuum so that is not the problem. When I connected to the other side of the vacuum valve I read 3 inches of vacuum. I don't think that is enough. Any thoughts??
Mike

 

[doghead]

Look at the -34 TM for the vacuum valve replacement procedure. They need to be adjusted when they have been replaced.

 

[Warthog]

The vacuum pump drive shaft looks just like a distributor drive shaft. It is driven off of the cam. It may have been damaged when the cam moved. It is easy to remove and check.

The valve on the side of the injector pump regulates the amount of vacuum that is supplied to the modulator on the tranny.

At partial throttle you should have 20" on vaccum from the pump and 8" of vacuum supplied to the tranny.

Here is my writeup of checking and adjusting the valve.

http://www.steelsoldiers.com/cucv/50568-cucv-throttle-vacuum-valve-adjustment.html?highlight=vacuum