Help narrowing down cause of the tapping noise..

[Fredrickson]

I am apologizing in advance for this being one of those.. "It could be one of any number of things" issues.
I have seen threads on this before, but I would really appreciate some insight from the group to narrow down possibilities.

There is an engine noise (clicking/tapping) that can be heard when the truck is moving.
It's always there when the truck is moving and gets faster with rpms.

The truck idles and revs fine (in PARK).
No noise, no smoke (white or black), and no strange noises at the tail pipe

The tapping starts only when there is load on the engine. (it's a 10k lb 1994 7.3 NA Ambulance)

To my uneducated ear, it sounds like the tap/clack is once per revolution.
So I am thinking it is happening at one cylinder.

Something that probably matters is:
I put in rebuilt injectors, but have not changed the IP or re-timed the engine, yet.

I have read through many threads and watched videos for similar symptoms.
Which left me more confused..than when I started.

So according to the internet
The noise could be:
injector knock, or compression coming back up into the injector, or a leak at the exhaust manifold, or a stuck lifter, or a rod, or the rocker arm or a wrist pin, etc..etc.

I recently drove it a few hundred miles all in one go.
The (idiot) gauges showed good and didn't move once the engine got up to temperature, and there were no smells..or smoke.

HERE IS THE VIDEO LINK
Here is the link in plain format:

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You can hear the noise best in the beginning.. and it disappears when I take my foot off the gas just past 40 MPH

I will be picking up a mechanics stethoscope this week to poke around more.

Thoughts? Things to look for? Things to try?

 

[Nero]

Oh yeah that sounds like fuel knock. Bet it is an injector... I'd get them tested. When I had fuel knock like that it was injector stuck partially open. Could only hear under load, at idle, ran fine.

 

[Jesus Freak]

Oh yeah that sounds like fuel knock. Bet it is an injector... I'd get them tested. When I had fuel knock like that it was injector stuck partially open. Could only hear under load, at idle, ran fine.

....yep.....

 

[Indadesert]

intake valve or injector. If it was an exhaust valve you would hear it in the tail pipe. You really need to have the IP timed. It makes a huge difference.

 

[Jesus Freak]

intake valve or injector. If it was an exhaust valve you would hear it in the tail pipe. You really need to have the IP timed. It makes a huge difference.

Timing a mechanically injected diesel is a myth......it's all baced on emotions!!! Temp, viscosity, altitude, humidity, etc.....his truck/van/ambulance was just fine until an injector stuck......no one needs to drink the "i timed my mechanically injected diesel kool-aid ". I run my truck on stuff i find laying around in the yard, and its a weak kneed piece o junk no matter where you time it!

So here's what the girlies do, they put a turbo on it and an intercooler and a battery under the bed, and then they turn the fuel up, and then they start changing their tail light bulbs because they got E4ODs and they read blah blah blah on the internet. Then they get 35in tires so it'll roll differently or something, then they say their truck goes this fast or this slow and it really doesn't matter......because a prius can pull harder then our boat anchors........so yeah, just buy a different truck, and quit trying to get power out of an idi......

But yeah, timing our trucks IS NOT A SCIENCE, ITS AN EMOTION. If you "feel" you should set it at 7.5* before you eat dinner, then by all means have at it, but if its raining and you check it again.....it'll move.....lol, "feel" away senor......then there's the "dimes width" thing....no one mentions quaters or half dollars......just dimes, idi owners are CHEAP!!! im so cheap I don't even buy diesel.....and i don't use dimes or quaters to "set my timing".......

 

[Jesus Freak]

Whaaaa.....lol

 

[Fredrickson]

Soo.. as a follow up..
Can it be run on the highway for the short term or will I end up burning a hole in a valve or piston top or ..wash the cylinder wall?

or should I dump a bottle of howes/optilube/hot shot/diesel kleen/archoil in the tank at next fill up,
and tap each injector with the handle of a screw driver..
in the hope of popping the pintle loose. (half serious)

 

[IDIBRONCO]

Some fuel treatment might help, but don't be disappointed if it doesn't. I wouldn't wait until the next fill up either unless you're planning on that real soon. My opinion is that the sooner you can figure this out, the less chance you'll have of damaging the engine. The screwdriver tap? I have no idea. I say tap away if you want to. Honestly, I would limit the amount of run time that you give the engine until you can get the problem taken care of. That's assuming that the other tricks don't help.
As for the timing, I doubt that it would help out a fuel knock, but it wouldn't hurt either.

 

[Nero]

If it does not improve I would stop driving it. Fuel knock is unintended fuel detonation and can cause cylinder damage.

 

[Jesus Freak]

If it does not improve I would stop driving it. Fuel knock is unintended fuel detonation and can cause cylinder damage.

Dude, that reads like a "warning label", we're mostly humans here, so liven it up....

 

[Nero]

Like, omg guys, gotta fix the knockey knockey before engine go boom boom like and subscribe if you like my content

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Is that better @Jesus Freak ?

 

[Jesus Freak]

Like, omg guys, gotta fix the knockey knockey before engine go boom boom like and subscribe if you like my content

You must be registered for see images attach

Is that better @Jesus Freak ?

THAT'S THE SPIRIT!!! ill take a YouTube influencer over a warning label any day!

 

[Lumberjackchuck]

Timing might be too advanced, I would check that first. Every time I had fuel knock symptoms they would also happen in park and I could just rev the engine and loosen injectors until it went away.

One time I thought I had a fuel knock and was chasing it forever. It would only happen under load around 1800 rpm. Ended up just being the oil pressure line to my gauge rattling behind the dash

 

[Fredrickson]

Ill check, but with the combination of new injectors with an original IP..
wouldn't it be more likely the injectors are opening late?

 

[Jesus Freak]

Ill check, but with the combination of new injectors with an original IP..
wouldn't it be more likely the injectors are opening late?

Could be, advance it a "dimes width" and see what happens.