Can't find the "chirp" in my 7.3...

[DrCharles]

There is a moderately loud, metallic high-pitched chirping noise coming from my IDI somewhere. I can hear it best when standing directly in front of the engine, and it's coming from the left (driver's side). The straight-cut gear whine from the IP gear housing is very audible when taking off the oil filler cap, but there is no change to the chirp.

It is slow at idle, about 3/4 to 1 second between chirps. Which points me at a one-cylinder-rate. 600 rpm is 0.1 sec per revolution. So 8 times that is 0.8 sec per chirp which is just about what I count.

It was much more "rattly", faster and even louder after running for a while, before I changed the serpentine tensioner (bearing going bad) & idler pulleys, and just now, the vacuum pump. No change when turning the steering wheel or turning the a/c on and off.

This may be an important clue: it gets louder and suddenly much faster (approximately an every-cylinder rate instead of one cylinder) when I'm driving at about 1500-1700 rpm and abruptly let off the pedal.

Could it be coming from the injection pump, and it changes when dumping fuel back to the return line instead of pressurizing and firing the injectors? But the IP and cam turn at half engine speed (fires each cylinder every other revolution)... I'm going to take a stopwatch and count up 10 or 20 chirps and get a more precise measurement. Maybe it is a cylinder-firing-rate event.

I'm stumped.

 

[Thewespaul]

Is your truck a 93 by chance?

 

[DrCharles]

yes... is there something "special" about that particular year? Other than the changeover from V-belts to serpentine?

 

[hoodshauler]

I would take the belt completely off and run it for a minute or two and see it you hear the chirp. That will eliminate it has anything to do with belt and pulley system!


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[DrCharles]

Good idea, thanks. I will try that soon, now that I have replaced the known rough tensioner bearing and what I thought was the vacuum pump squeaking.

 

[Thewespaul]

That year has an open style tensioner that is just awful. I can almost guaranteed that it’s chirping there. Take a picture of your tensioner, tensioner pulley and idler pulley for me

 

[DrCharles]

That's an interesting idea. I'll see if I can take a pic tomorrow... but how can the tensioner itself be chirping? Both pulleys are brand-new so their bearings are presumably silent. This tensioner has a shock absorber, not sure if it's any good or not.

What is the theory here? On deceleration the belt starts bouncing and making a (failed) tensioner mechanism squeak?

 

[Thewespaul]

The open style tensioner does not apply enough pressure to keep from squeaking and it slips on the tensioner pulley. I have the same truck and same problem but fixed it with an oversized pulley to get more contact area.

 

[DrCharles]

Mine is definitely a closed style. (I think only the closed ones had shock "assist" anyway). From the looks of the bolts/nuts securing the shock's top bracket, I don't think it was original for my '93.

Trying to figure out how to sign up with Flickr so I can put photos here... this board doesn't seem to let you upload pictures directly.

This chirp does not sound like a belt though. Definitely metallic in character. Although I do notice that the belt is running very close to the front edge of the new idler pulley...

 

[Thewespaul]

If you can’t see the spring in the tensioner then it is closed and not stock to your truck, the entire accessory bracket has to be changed for the different style to bolt on

 

[DrCharles]

I found a thread that mentioned that conversion... anyhow I now have the closed one with the shock.

Do you still recommend I replace the tensioner mechanism? Is the shock available separately?
thanks.

 

[Thewespaul]

Check rock auto for that tensioner, the shock piece is a bit rare. Only certain models had it. I think ambulances?

You can identify the location of the squeak by dribbling water on one pulley at a time and seeing which one quits squeaking

 

[DrCharles]

First I'm going to do what hoodshauler suggested and take the belt off completely for a quick test... if the chirp's still there then it's not the tensioner or any accessory pulley

 

[snicklas]

Uploading to the forum is easy....

Click Upload a File..... and you can browse on you phone or computer. I have uploaded from my PC, iPhone and iPad....... I've never used a photo site, all the photos that I have taken and posted, have been direct to the forum

 

[DrCharles]

Aha! that's the secret... I was clicking on the "Image" button in the posting toolbar.

A new and useful data point: I took the belt off and all is quiet! So it's not in the IP or some other "zebra", which is a relief. (Old medical saying: when you hear hoofbeats, think first of horses, not zebras).

I also noticed that the PS pump has about 1/8" of axial endplay (the pulley can be easily moved front and rear). Is this normal when it's not running?

And the alternator bearings are a bit rough (rebuild kit with bearings, slip rings, brushes and regulator on order) but when I pull its pulley forwards and rotate it back and forth, there is a squeak coming from there too.

Notice the far-forward position of the belt on the idler pulley after the engine stopped, too.

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Thoughts?

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