The truck was running great. I shut it off, talked with a friend for a few minutes, and when I started it up again, I heard a slightly loud, consistent knock. I thought I had picked up a stick or something similar.

When I got home (5 minute drive) I opened the hood and looked and listened. It was much louder and more clear with the hood open. It is coming from the front of the engine compartment, seems like just below the ac compressor on the passenger side of the engine. Everything seems tight. and the fan is not hitting anything.

What can I do to begin diagnosing this? Would a pulley do this? This is my main work truck, so I have to get on this problem.

Thank you,
Matthew

Check your vacuum pump and have a look too at your harmonic balancer

my two cents

Thanks for those two tips. I know where the harmonic ballancer is. How do I test it? How also should I check the vac. pump? Will it knock if it is bad?

Thank you.

An easy way of testing the vacuum pump is to take out the serpentine.
Run then your engine for a short time, just enough to see if the knock is still there or not.
While the serpentine is out, take the opportunity to have a closer look to the balancer and see if it is moving. It should not if OK.

How also should I check the vac. pump? Will it knock if it is bad?

Thank you.

Haven't experienced it by myself, but many guys say it produces the same sound as a rod knock when failing.

Hmmmm. I will check that. Thanks. It is a consistent knock. It is hard to miss, and is obviously on that side of the motor and in the front.
Will it hurt to drive it on a bad harm. balancer or bad vac pump?

Bad vac pump, not really, other than losing turbo boost and screwing up EGR on an S engine, possible HVAC issues.

Harmonic Balancer if left alone can cause crank failure.... so that's a must-tend-to item.

Sincerely, I don't know for sure. I believe the balancer, if culprit, will allow you to drive, won't brake tomorrow.
Concerning the vacuum pump, I will be more suspicious. I wonder if it can lock and so ruin your serpentine belt...

See there, the beauty of the forum shows both sides of what can happen...... good show there matuva, hadn't considered that little ditty...

See there, the beauty of the forum shows both sides of what can happen...... good show there matuva, hadn't considered that little ditty...
;) glad to help

Check the rubber on the balancer if you can see it.

Thanks all! What am I looking for with the harmonic balancer? Looseness? ? I almost want to go out there now and try this, but I'm tired and I have class tomorrow.

took the belt off...no knock. So I'll replace the vac. pump. Even with the belt off the h balancer should knock right?
M

could be the crank pulley as well. With the belt off try spinning everything, see if the crank pulley has any wobble in it, or if you can grab it and move the pulley without the motor moving

Ok, looks like it is the vac. pump. I took the old one off, ready to replace it with a new one, only problem is...I cannot figure out the pulley! There are threads inside a stud, but nothing was in there? No threads on the outside of the pump output shaft. Do I need to take this off with a gear puller? If so, how do I remount the pulley to the new shaft? Should I use a bolt?

M

Your old pulley will need to be pressed off & reinstalled on the new vac. pump. Let someone who has the right equipment do it to make sure it is back in the original location. I did mine myself & had a lot of trouble keeping everything together. When i presssed the pulley back on, I pushed the bearings & shaft out the other side & bent up the cap on the back side. It was a pain to get lined back up & I'm still 1/8" or so off alignment with the crank pulley. I tend to like to have everything stock in working order to determine a baseline for changes, But now would probably go with a turbomaster instead of the vac. route. Constant boost pressure, adjustable, etc. etc. I don't believe everything I read, but i believe most everything here is good info. Read alot & then make a decision. Good luck. (Takes a couple of hours to change out vac. pump if you don't mess it up, 4-5 otherwise).

Ok, looks like it is the vac. pump. I took the old one off, ready to replace it with a new one, only problem is...I cannot figure out the pulley! There are threads inside a stud, but nothing was in there? No threads on the outside of the pump output shaft. Do I need to take this off with a gear puller? If so, how do I remount the pulley to the new shaft? Should I use a bolt?

M

As stated above, you need the proper pulley removal and installation tool.

I took mine to a garage and had them swap the pulley.

Also as stated when reinstalling, (before removing the old one, actually) note the position of the pulley in relation to the shaft, it should be flush, and ensure same on the new pump.

Just because the crankshaft pulley didn't make any noise without the belt...don't rule it out as a culprit. It takes about 3 seconds to check it out...without the belt on it, see if the pulley will turn in either direction at all. If it's loose, then it needs to be replaced. If you already have the belt on, you can look at the front of the pulley. You will see that the center of the pulley is solid rubber. It's when this rubber part dryrots and tears apart, that you will have problems with it. Also, you would be able to see where the metal parts of the pulley are hitting the bolts that hold it on, if it's moving.

Thanks all. I took the pump to a shop. They swaped pulleys for me and she's fine. No knocking. The old pump had NO suction.

hmm, I had an 'old pump' with no suction....I swapped her out too.....

Thanks all. I took the pump to a shop. They swaped pulleys for me and she's fine. No knocking. The old pump had NO suction.

Excellent ! :thumb:

By the way, according to your signature, you have a nice and powerful truck.

Congrats!