92 1500 Loud Tapping Noise when accelerating

Jared Stangenberg · September 27, 2015

My truck (92 1500,2wd w/5.7L) has developed a wierd and annoying noise in the last 100 or miles of driving.

It's a loud rattling/tapping that sounds like it is coming from the front driver's side of the truck, it has a very metallic quality to it.

It only happens when the truck is gear and the accelerator is pushed, it seems loudest when the motor is at about 2000-2500 rpm and actually seems to get quieter beyond that point (although the engine may just drown it out at higher rpms).

It only makes the noise when the accelerator is pushed while in motion, if I take my foot off the gas it stops immediately. It doesn't make the noise when rev'd in park or neutral only in drive while in motion. The degree to which the steering wheel is turned or not turned seems to have effect on the presence of the noise.

The truck has 204000 miles on it, I've only been the owner for 4000 of those. The vehicle was previously used as a farm truck and probably saw some semi-abusive use there.

I'd really appreciate any opinions or know how on what's making this noise. I've had wheel bearings go out before on a different vehicle, but this isn't really the same noise or conditions causing the sound. I'm pretty stumped.

LeoS41280 · September 27, 2015

Sounds like a spun rod bearing.

Jared Stangenberg · September 27, 2015

Wouldn't it make the noise at all time if that were the case, not just when in motion?

Jared Stangenberg · September 28, 2015

Symptoms unfortunately got worse today.

I drove to work and back (about 20 mile round trip), the noise continued and I also had noticeable loss of power going up a couple hills.

I managed to shoot a short video on my phone, which was precarious since the truck really has to be in motion to hear the sound. Although I can briefly replicate the noise to some extent in park. I'm leaving the truck in drive-way until this gets sorted out.

LeoS41280 · September 29, 2015

Not the flex plate. I'd bet on a rod bearing. Did the oil pressure change?

Jared Stangenberg · September 29, 2015

Not dramatically, it's read on the gauge between 30 and 45 psi ever since I've had the truck and I haven't noticed any dramatic change.

ifixedit · October 2, 2015

Pull the valve covers and check for a broken or cracked rocker arm, sounds like that's what it is, they can break on a moments notice. If a rod was hammering that hard the engine would have very low oil pressure, would likely be smoking like a steam ship, and probably would have already quit by now, so I doubt it is a rod bearing. The 350 bottom ends are about as bullet proof as they come so it would be very uncommon for anything in the bottom end on these engines to let loose just like that under normal driving on a daily basis, that is unless you had REALLY abused it with some very high and prolonged RPM's over and over which I doubt you've done.

If all the rocker arms are fine, it could also be a collapsed lifter. Get the valve covers off, go over each rocker arm carefully looking for one that's loose. If you find a loose rocker arm that appears to be intact, then you've got a collapsed lifter and possibly a bent or damaged push rod as well as things were likely banging into each other with all the excess clearance. Look the parts over closely for damage before you decide to re-use them. Unfortunately a collapsed lifter that refuses to pump up will require removal of the intake to replace it. An old trick to free up the lifter is to add about a quart or so of kerosene to the oil and let it idle for a few minutes, if that doesn't take care of it the intake is going to have to come off to get at the lifter. If the kerosene trick does work you're going to want to change the oil ASAP.

Edited October 2, 2015 by ifixedit

Jared Stangenberg · October 5, 2015

Thanks, hopefully I'll get to fool with it some in the next fews days. We've just been using my wife's car for everything in the mean time.

We've got our first baby due in less than four weeks, so I've been pretty short on time and money to mess with this recently.

At my wife's request, I did change the spark plugs this morning to see if that made a difference. I hadn't changed them since I got the truck and had no idea how long they had been in (looks like a long long while). the new plugs haven't changed the tapping noise at all, but have brought some power back into the truck.

I know you can supposedly "read" plugs, and I've got the chart to look at for it. I also took pictures of each plug by cylinder to get opinions. Other than they were obviously "vintage", does anything else stand out?

Hopefully I can take the valve covers off later this week and check out the rocker arms.

I also have a question, "What is this and should it be connecting to anything?". It was underneath the air intake pipe/silencer box when I pulled them out.

Edited October 5, 2015 by jstange

00Silverado4x4 · October 5, 2015

How is your oil pressure during the times it "taps". Sounds like it could be a drop off in oil pressure??

Jared Stangenberg · October 5, 2015

How is your oil pressure during the times it "taps". Sounds like it could be a drop off in oil pressure??

The oil pressure never drops during the tapping.

At idle pressure is a little about 30 and when I'm on the gas it goes up to about 45.

Duelin · October 6, 2015

What happens when you power brake it around 2000 to 3000 RPMs? I would try that and have someone listen under the hood. Also check and see if you fan is hitting the shroud.

Jared Stangenberg · October 6, 2015

What happens when you power brake it around 2000 to 3000 RPMs? I would try that and have someone listen under the hood. Also check and see if you fan is hitting the shroud.

By "power braking", do you mean putting it gear and standing on the brakes while revving the engine?

If so I haven't tried it.

Duelin · October 6, 2015

By "power braking", do you mean putting it gear and standing on the brakes while revving the engine?

If so I haven't tried it.

Yes. But when you do this you have to use common sense. Make sure your brakes are good and able to hold at those RPMs and make sure you are no where near something that you could run into in case your brakes let go. And you might have someone standing near the truck so they could hear where the noise is coming from.

1997SierraSLT · October 6, 2015

sounds like a sticking lifter. had it happen at about 120,000 miles on my truck. Ran a cleaner through it purchased at the local auto parts store, changed the oil per instructions, and it solved the problem.