So, I started looking for a new engine for my 3.9 lz9 swapped rx8. I am not finding quite the deals I did even 2 years ago. This got me to thinking that I should probably diagnose what is going on with this engine...
- loud ticking sound that seems to get worse as the car runs longer (over the course of 30 mins or so).
- increases with rpm.
- will do it in neutral
- doesn't make any noise at all on startup when cool for at least a few minutes.
- oil pressure is good.
- engine makes normal power.
Things I have done so far (not much)...
- checked oil. It was a little low so I added some.
- used a screwdriver to listen to various parts of engine. Doesn't sound like 1 valve cover is louder than the other.
- pulled spark plug wires 1 at a time to see if noise goes away... it doesn't.
I'm gonna:
-drain the oil and look for glitter.
- take the accessory belt off and see if the noise goes away.
I can remove the oil filter and cut it apart too.
What else ya got?
Take the accessory belt off and make sure it is the engine. Could be a noise transfer from something belt driven. Next pull the transmission and run again.
Exhaust weld leaking as it warms up?
Dusterbd13-michael said:
Exhaust weld leaking as it warms up?
That is a very interesting thought. Very tough to visually see with the headers buried beside the frame rails. I wonder if I can use a piece of paper or something to see if it "blows" the paper away.
However, I can't hear it on any particular side.
What about from underneath? Have you put it up on stands and climbed underneath it with it running to try to pinpoint where the noise is coming from? With help buried that engine is in the RX8 engine bay I'd have to imagine that the Acoustics are bouncing the noise quite a bit before it hits your ears
Try a piece of 1/4 or 3/8" hose instead of the screwdriver. Stick one end in your ear and point the other end at suspect places.
I'm with Michael. I'll bet you a nickel it's the exhaust manifold... either the gasket or a crack in the manifold.
how long will it hold 7000 rpm?
Dusterbd13-michael said:
Exhaust weld leaking as it warms up?
Wouldn't it be the opposite? As it heats up the metal expands sealing any gap?
wae
PowerDork
12/4/23 11:45 a.m.
wvumtnbkr said:
Dusterbd13-michael said:
Exhaust weld leaking as it warms up?
That is a very interesting thought. Very tough to visually see with the headers buried beside the frame rails. I wonder if I can use a piece of paper or something to see if it "blows" the paper away.
However, I can't hear it on any particular side.
Shove your smoke tester up its tailpipe and see if you get any wisps.
wae said:
wvumtnbkr said:
Dusterbd13-michael said:
Exhaust weld leaking as it warms up?
That is a very interesting thought. Very tough to visually see with the headers buried beside the frame rails. I wonder if I can use a piece of paper or something to see if it "blows" the paper away.
However, I can't hear it on any particular side.
Shove your smoke tester up its tailpipe and see if you get any wisps.
Remind me how to make a smoke tester again? I think you wrote up a procedure and I can't find it at the moment.
wae
PowerDork
12/4/23 1:58 p.m.
In reply to wvumtnbkr :
I stole some instructions from a website somewhere, but I can't find it off the top of my head. Roughly speaking, I took a section of fairly wide PVC pipe that would fit into a floor flange of some sort as a base and then I glued on a coupler with threads so I could screw on a cleanout plug to use as a lid:
I got a set of battery clamps that were pre-attached to some wires and crimped some ring terminals on. The top got two holes drilled into it - one for a hose barb for some clear vinyl tubing that was basically vacuum hose sized and the other for an air connector like this:
Get a couple bolts, washers, and nuts that are a tight fit on the ring terminals for the battery connection. Drill holes about halfway up the side of the PVC body, 180 degrees away from each other. Get some vape wire and a tiki torch wick. Form the wick into a "U" shape such that the ends point down to the bottom of the vessel and wrap the vape wire around the horizontal part. The vape wire get attached to the power by running the bolt through the ring terminal, then through a washer, then through the PVC pipe, then through another washer, then wrap the vape wire around the bolt, then attach the nut. Do that for both sides, of course.
Now you can fill the pot with mineral oil, attach the clamps to a 12V source, plug in about 2-3psi-worth of compressed air, and you'll start getting smoke out the end of the tube almost immediately.
On the exhaust leak thought, also make sure all of the spark plugs are fully installed. I've seen a slightly loose plug produce a noticeable tick.
So here is my plan as of right now:
-Smoke test up the tailpipe to check for exhaust leaks
- check sparkplug for tightness
- take off and cut open oil filter for glitter
If none of this points to any direction, I am gonna take off the valve covers and have a look see.
If that doesn't show anything, I'm dropping the motor. It will give me a chance to redo some stuff anyway.
The smoke tester I linked is the one I bought when I had my BMW. I'm fixing to use it on my subaru. I found that it's easiest to use in a dark garage and then shine a bright flashlight around to spot the smoke. At least for my eyes in my experience.
z31maniac said:
Dusterbd13-michael said:
Exhaust weld leaking as it warms up?
Wouldn't it be the opposite? As it heats up the metal expands sealing any gap?
Not in my experience, but it is probably different depending on the design of the manifold and where the crack is. My 5.4L Mod and my 5.9L Cummins had cracked manifolds and they were both worse when hot.
Compression all good?
Upper end noise or lower end noise?
Does this 3.9L have the cam timing/AFM/DOD thing?
kevinatfms said:
Compression all good?
Upper end noise or lower end noise?
Does this 3.9L have the cam timing/AFM/DOD thing?
It does have cam timing, I don't believe it has dod.
Can't tell where the noise is coming from. It sounds the same everywhere.
Not sure on compression. I have never tested it.
