Difficulty isolating engine noise

[srtnate]

I have a strange buzzing/honking noise coming from my engine. I've been all over it with a stethoscope trying to track it down, but
the noise is being transmitted throughout the engine. I feel pretty confident that I've eliminated all heat shields, etc that could be
vibrating. I've run the engine (briefly) without belts to eliminate the AC, alternator, water pump.

I'm at the point where I'm about to pull the valve and timing chain covers to see if I'm dealing with any excess slack or chain
slap, or excess valve clearance...but I've wanted to leave the engine in a running (assembled) condition until I've eliminated all
external troubleshooting options.

I've linked a video hoping that someone has encountered this before...


https://www.youtube.com/watch?v=4a4vPH5E8cM

I appreciate any hints!

[DMC-81]

Hi there,

It definitely sounds like two metal parts hitting one another. How about the clearance of your right side coolant pipe next to the coolant expansion tank, or something similar. Based on the "honking" sound it is possibly a hollow part rubbing against something else.

Good luck.

[Bitsyncmaster]

Does it make that noise on a road test? It does sound like a vibrating metal movement.

[Drive Stainless]

There's a bolt in the center of the air meter flap. Check tightness.

[Drive Stainless]

I would also check all heatshields - crossover pipe, muffler, and cat.

[srtnate]

It definitely sounds like two metal parts hitting one another. How about the clearance of your right side coolant pipe next to the coolant expansion tank, or something similar. Based on the "honking" sound it is possibly a hollow part rubbing against something else.



Nope...I've wiggled the cooling pipes around.


I would also check all heatshields - crossover pipe, muffler, and cat.

All checked, crossover shields currently removed.


Does it make that noise on a road test? It does sound like a vibrating metal movement.

I've only had it out on the road once, a few months ago (and that was probably a bit premature), and I don't recall hearing the noise at that point...but it very well could have been present.
It was a "rescue" Delorean that had been long neglected. After my maiden voyage, it was apparent that I needed to do a bit more "dialing in", and in the time since, that is when this noise
had come to my attention. My first thoughts were "heat shield rattling...no big deal!", but it's turned out not to be that simple. However, I do have it up on 4 jack stands right now, so I
could (carefully) put it in gear and see if it occurs. I suspect it won't persist as the RPM's increase though.

[Bitsyncmaster]

I occasionally get a vibration which sounds like the T-panel vibrating on the passenger rear fender at some time during an idle warm up in the garage with the engine covers open. Have not heard it when driving on the road.

[PJ Grady Inc.]

I can't say I've ever heard that exact noise before...how odd. It does not sound internal however so if it were me I'd exhaust all external possibilities first. Hopefully that will save on wasted time. Have you removed or checked the crossover pipe heat shields. They commonly loosen and cause a high pitched rattle at around 2500 rpm when on the road. They don't usually act up when revving unless underway but it's worth a try.
Rob

[srtnate]

I can't say I've ever heard that exact noise before...how odd. It does not sound internal however so if it were me I'd exhaust all external possibilities first. Hopefully that will save on wasted time. Have you removed or checked the crossover pipe heat shields. They commonly loosen and cause a high pitched rattle at around 2500 rpm when on the road. They don't usually act up when revving unless underway but it's worth a try.
Rob

I was strongly suspecting the crossover pipe...it is definitely the most distinct source when using my stethoscope. I removed the heat shields from it last night, but without any improvement. Tonight I decided to remove the whole pipe.

One interesting thing I found, is that it feels as though the pipe ends are VERY close together within the flex coupling. It feels like the pipe was cut, the flex coupling was slid on, but little separation was left between the two ends...I'm wondering
if the two ends could be "clinking" together within the coupling. The connection to the passenger side manifold also seemed like it could have been a little tighter...I don't think it was the source of the noise, but I'm wondering if it was pulled
down tighter, maybe the crossover pipe would splay apart more within the flex coupling. I think that is going to be my next line of experimentation...

This vid shows the max extent of the flex, and how there seems to be very little internal spacing.


https://www.youtube.com/watch?v=r0Apzbgdp88

I really appreciate all the suggestions from everyone!

[FABombjoy]

I too suspect it's the fuel distributor metering plate dragging against the housing. Seems like your car struggles to rev.

On the video it looks like you open the throttles, nothing happens briefly, then "honk honk" and the revs climb. If the plate was stuck it would act like a second throttle that prevents air from entering while simultaneously keeping the fueling constant.

Can you move it freely when the car is off?

For noises like this, if you have some spare vacuum tubing I find it more effective than a stethoscope as it will allow you to directionalize the sounds you're hearing. Just put one end in your ear, plug the other ear, and move the tube around until you find the loudest spot.

[srtnate]

I'm happy to report that I seem to have eliminated "the noise". I removed all my exhaust components, installed new studs and gaskets, and then
reinstalled everything. I can't point to a specific item that solved the problem, but I think it was just the overall re-seating/re-sealing/re-tightening
of the individual exhaust components. (I do suspect that my passenger collector flange was not fully seated, even though it wasn't moving or leaking)

That's a relief...now that I know I don't have a potentially serious issue to deal with, I'll probably have more motivation to move ahead with things! :)

Thank you to everyone that took time to consider my issue!

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