HELP---Strange Engine Noise is very puzzling

[raythomas]

I just now found this forum. After browsing around for a while you guys seem very helpful and good at diagnosing weird sounds. I have been dealing with this for the past 2 months. It's got all of us baffled. I'll try to give as much info as possible.

My truck is an 87 Nissan D21 with the Z24i FI engine.

I've had it for 4 years, it was a hand me down from my father-in-law.

I tuned it up, filters, oil, grease, plugs, wires, etc...... And its run great for the past 4 years.

However about 2 months ago it developed a slight clacking sound when under load. I say clacking because its a bit more than a ping, but not quite a knock.

The engine cranks over and starts normal. It idles smooth and when you race up the engine while in neutral it is completely quiet, no noises whatsoever.

Say I'm driving up a small hill or grade is when it started. I could downshift or accelerate more and the noise would go away. I'm old school so I'm thinking it must be pinging, or valve knock coming from some bad gas maybe. I replaced the filter and put octane booster in the tank which according to my math should have been around 101 octane. Thinking this would solve the pinging issues. Well I ran the tank almost dry and it didn't change the sound one bit. A little more time went by and I noticed the sound got more frequent. In fact it does it now going down the road as you increase throttle to accelerate but what baffles me is the sound will go away with application or more throttle. I've removed the valve cover and checked the valve train. All is within spec. Timing chain is tight and cam chain guides are still working properly. I've pulled each plug and inspected inside the cylinders with a camera and all the plugs looked fine and the cylinders were clean with only a little carbon here and there. I loosened the alternator and checked it and the water pump for noise but they are quiet when spun. I pulled the CAT to check for blockage, but it checked fine. Oil level is fine and the truck doesn't use any during changes. Have checked both coils and they are good. I'm at a total loss at this point. Its gotten so bad I'm afraid to drive the truck for fear of damaging something expensive. If it did the noise all the time I'm sure it would be easy to find and fix but it doesn't. It only seems to do it when the truck is in gear and pulling. I'm wondering if it could be clutch or throw out bearings, but they are seem quiet when depressing the clutch pedal and when shifting so I'm not sure at this point. Any tips, advice or suggestions you guys can give me with be greatly appreciated.

Thanks

Ray

[datzenmike]

The throw out bearing will not be in use or spinning when driving but only when using the clutch pedal.

 

It appears to show up while the engine is under load. Which brings several things to mind but the others are too much to dig into right now.

 

You may have a cracked exhaust manifold or bad gasket at the head or the downpipe end. It may be quiet at idle low speeds but what happens is under heavy load more sound escapes. Revving the engine while listening does not show this because there simply is not enough load on it like climbing a hill.

 

What I have done in the past is have someone start the engine cold while you very quickly run your hands over along and behind the equally cold exhaust manifold to locate the puff of air leak. Don't forget the EGR tube that connects to the exhaust manifold and goes around behind the engine to the intake manifold mounter EGR valve. You have probably close to 10 seconds before it becomes too hot. May take several tries.  

[banzai510(hainz)]

if you think pinging then cheak the timing ,

 

[raythomas]

50 minutes ago, banzai510(hainz) said:

if you think pinging then cheak the timing ,

 

 

I haven't thought of exhaust yet. If that was it wouldn't the truck be noticeably louder like all the time if the leak is that close to the head?

Thx

 

I have thought of that actually. Only thing is it cranks and runs so good other than the noise I can't see how it could be timing. Not doubting your idea, just believe unless something is broke inside the DIST I have checked the adjustment bolt and its tight, tight, tight.

Thanks

Ray

[datzenmike]

All exhaust sounds louder under load. Small crack you can't hear till engine is working hard. It's just a guess that can be checked out.

[raythomas]

2 hours ago, datzenmike said:

All exhaust sounds louder under load. Small crack you can't hear till engine is working hard. It's just a guess that can be checked out.

I'll try to check that tomorrow.

Thx

Ray

[620slodat]

Do you have a 2 piece rear drive shaft? One thing I'm wondering about is the center u-joint. Is it loose? I have never dealt with one, and I don[t know what sounds a failing center u-joint makes, but all the people who have say that the sound shows up under load. I do know that a worn regular u-joint can give off a popping sound under load, and the rubber around the center bearing will fail before the bearing does. A quick look/check will tell a lot, and looking won't cost anything (except time).

 

Just a wild thought.

 

Don

Edited December 11, 2022 by 620slodat

[datzenmike]

Only one verified failure of the carrier bearing has ever happened here. The bearing has very little to do actually it only supports a rubber surround that stabilizes the drive shaft and allows it to spin. That rubber support or isolater rots away and the drive shaft will them often flop around under load.

 

 

Ends up looking like this...

 

 

U joints usually squeak when they go dry, wear out to the point that the needle bearings wear out or break, even fall out, and the drive shaft de stabilizes, goes off center and vibrates.

[raythomas]

No sirs

I'm pretty sure its not the driveshaft. I had all that out a few weeks ago when I put in a new rear seal on the 5 speed and changed the trans oil. The center or swing bearing looked fine with all the rubber still intact and no sounds coming from the joints. I greased them all anyway before I put the shaft back in.
The sound actually sounds like its coming from under the hood. Sorta toward the back of the engine close to the firewall up high. That's why I  pulled the valve cover to check in there. It actually sounds like good old fashion valve ping from bad gas, only louder. So i'm still stumped.

Thx

Ray

[raythomas]

Well I checked the exhaust like mentioned above. Turns out that's not it either. No leaks at the manifold by the engine.

If it's anything in the engine, would it not make the noise ALL the time? And the noise speed up or get louder with the application of throttle?

Thx

Ray

[datzenmike]

Did you examine the tube from the exhaust that goes around behind the head to the intake? They do rot out from the corrosive exhaust.

[raythomas]

6 hours ago, datzenmike said:

Did you examine the tube from the exhaust that goes around behind the head to the intake? They do rot out from the corrosive exhaust.

Yes sir I did. It was solid all the way around. No damage. Gaskets were fine between manifold and head as well. No leaks as far as I could tell.

Thx

Ray

[datzenmike]

Just to be clear it's quiet at idle and only makes noise under load when driving?

 

I'm afraid to say this is now moving inside the engine and it might be a rod bearing that is going bad. It fits the description very well. The bearing clearance is excessive. It's still early and you might be able to just replace the bad bearing. I would do all four if doing this at all.

 

Other than the steering cross rod  there is a support brace between the frame rails that supports the torsion rods. The steering cross rod and be dropped by unbolting the idler arm and the frame support just unbolts. You may be able to drop and slide the oil pan out to get access to the rods.  

[Stoffregen Motorsports]

Did you do anything major prior to this noise? Like have the motor out or the trans out or anything like that? Have you checked for broken motor mounts? Loose bolts? Are there coolant or oil leaks up around the top of the block?

 

Under load clacking suggests rod bearing, and the only way to tell is by removing the oil pan and checking for play in the big end of the rod, or better yet, by removing a cap and looking. You can do this in the vehicle, but be careful when removing a cap. I usually hit the rod bolt with the wooden handle of a hammer to loosen the cap. If the bearing looks good, you'll have to be extra sure that everything is clean (no wood chips) before reassembly. Do this at TDC and then 180 degrees out. to check all caps.

 

Rod caps are indexed and machined to each rod, so it is imperative that you get them back on the same rods and in the same direction.

 

Z24 engines have been known to make rocker noises, if one of the rockers or shafts is worn, but this noise should change under load. It may grow louder with RPMs but not necessarily with load.

[datzenmike]

If taking the oil pan off, for all the work, may as well just put new rod bearings in. 

[raythomas]

7 hours ago, datzenmike said:

Just to be clear it's quiet at idle and only makes noise under load when driving?

 

I'm afraid to say this is now moving inside the engine and it might be a rod bearing that is going bad. It fits the description very well. The bearing clearance is excessive. It's still early and you might be able to just replace the bad bearing. I would do all four if doing this at all.

 

Other than the steering cross rod  there is a support brace between the frame rails that supports the torsion rods. The steering cross rod and be dropped by unbolting the idler arm and the frame support just unbolts. You may be able to drop and slide the oil pan out to get access to the rods.  

Yes Sir, quiet when starting, quiet while at idle and still quiet even when revving engine with trans in neutral. Its only under a load, even a slight load. And when the noise starts you can apply more throttle and the noise will stop.

Would bad rod bearings not make a noise all the time? And that noise get louder with application of throttle? Like revving the engine?

 

And No, I haven't had the engine or trans out. I haven't changed a thing. And its been fine up until about 2 months ago. Just started the noise out of the blue. I think I've mentioned before that the noise was only happening when climbing a hill at first, like under a pretty good load. But with time it now even makes the noise while driving down a flat and level road without even climbing a hill. So whatever it is has gotten worse.

 

Thx

Ray

[datzenmike]

Well it''s just a possible cause and runs the entire range from barely noticeable to sledgehammer on metal hard knocking. I'm not there to hear it so.... ? Let's hope not.

 

When the engine is under load it torques over to the right side and will rock back and forth with the throttle. See if the exhaust pipe makes contact with anything. Give it a good hard tug.

 

Apply hand brake or set front bumper against a brick wall. Have someone give it some gas and let the clutch out slowly to load the engine while you have the hood up to listen and try to better locate the sound.

 

[thisismatt]

Try to record the sound?

[datzenmike]

If only under load I assume it's only when driving and thus you are hearing it through the front of the car's firewall and dash?

 

I had a hood do this. It was not supported with rubber and free to shake side to side. Could be the heat shield on the exhaust manifold for the ATC is rusted loose.

[raythomas]

4 hours ago, datzenmike said:

Well it''s just a possible cause and runs the entire range from barely noticeable to sledgehammer on metal hard knocking. I'm not there to hear it so.... ? Let's hope not.

 

When the engine is under load it torques over to the right side and will rock back and forth with the throttle. See if the exhaust pipe makes contact with anything. Give it a good hard tug.

 

Apply hand brake or set front bumper against a brick wall. Have someone give it some gas and let the clutch out slowly to load the engine while you have the hood up to listen and try to better locate the sound.

 

I'll re-check the exhaust. And that's a dang good idea about putting it against something and trying to load the engine with the truck restrained. That just might help me find exactly where it's coming from. And yes, the noise does sound like its coming from the top rear side of the engine compartment which sounds like right behind the dash.

I'll check these things when it finally stops raining here.

Thx

Ray

[datzenmike]

Well this is it... if the sound was at the front of the engine it would get to you, sitting in the driver's seat, right through the firewall and the dash. With sound you can point to a direction that it's coming from but not how far it has traveled.

[raythomas]

8 hours ago, datzenmike said:

Well this is it... if the sound was at the front of the engine it would get to you, sitting in the driver's seat, right through the firewall and the dash. With sound you can point to a direction that it's coming from but not how far it has traveled.

Gotcha ! Can anyone tell me how hard it is to get the fan off the front of the engine?

Thx

Ray

[datzenmike]

It's awkward, but remove the shroud out of the way for room then use a spanner to remove the four 10 mm bolts. Some are two piece with a top and bottom. If one piece perhaps just move it away from the rad towards the engine to get in there to unbolt the fan.

[Stoffregen Motorsports]

Piston wrist pins can also make a knocking noise, but the sounds usually goes away after the engine is up to temp. I say usually.

 

The sound could be coming through the vent in the cowl, making it sound like it's on the upper right side of the engine bay. Isn't that where the cowl vent into the cab is?

[raythomas]

8 hours ago, Stoffregen Motorsports said:

Piston wrist pins can also make a knocking noise, but the sounds usually goes away after the engine is up to temp. I say usually.

 

The sound could be coming through the vent in the cowl, making it sound like it's on the upper right side of the engine bay. Isn't that where the cowl vent into the cab is?

Hope its not  wrist pins. Really hope its nothing inside the engine itself actually. I'll have to look about the vent thing. I'm not sure.

Thx

Ray