I have a noise at idle that sounds kind of like a very fast drumming on a hollow can, it gets very pronounced when first starting and will go away with the slightest increase in rpms. I thought it was the air box vibrating but listening closer it seems like it is coming from the vacuum pump area. Is this a vacuum pump noise and is it normal?
I'll try and record it to be sure, but it might be hard to hear over all the clatter and cackle which is my next issue after doing delivery valve seals and glow plugs. The car sat all summer and the fuel is about 4 months old, plus I have not driven it yet after the delivery valve seals, just ran it a while in the garage, still waiting on the rest of the fuel line shims to arrive. Maybe I still got some air?
The drumming or shuddering noise happens at the same time the idle drops almost like the engine is going to stall but it instantly recovers and the noise stops. So I don't know if it is caused by a drop in RPM or it is causing the drop in RPM. It has been doing this for quite some time, at least a year.
Here is the video. You can hear the "drum roll" or growl just as I bump the accellerator up a bit then again as I let it back down. After careful listening now it sounds like it is coming from the engine internals or from under the valve cover, but it does not get louder with the oil cap removed. This engine has 154K on it.
It's a bit hard to tell on a online video, but I'm gonna guess the noise is coming from the injection pump timer ramp gear.
This gear is driven by the timing chain and the ramp drives the vacuum pump.
The ramp is most likely damaged or has developed spots which will require replacement of the entire gear and the vacuum pump. This can happen when the bearing inside the vacuum pump disintegrates and ball bearing start bouncing around inside the engine, hence my warning about the potential for the engine grenading when this occurs.
Been chasing noises on this engine all afternoon. Found one of the tensioners on the front is clattering pretty bad. As far as the other noise I am still trying to pinpoint it, not sure if it is the vac pump or not but will look at changing it anyway with 155K on her.
Do you remember when the gassers had the A.I.R. systems with the belt driven air pump that would pump fresh air into the exhaust? That is the nearest sound I can compare it to, and it is only occasional, and only at very low idle, like she is getting ready to stall momentarily, shudders, then recovers.
I have everything removed from the front of the engine and next is the vacuum pump. What should I look for when I remove the pump, will any gear damage be obvious? How much more work is involved in changing those gears?
Anything else I should do while the front of the engine is apart? My fan clutch is about 8 years old but only has about 30K on it. Don't know about the water pump. Can the timing chain and guide be changed with the head on? Where do you stop? Spending all this cash on a car with a #14 head is starting to make me nervous!
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