Bad Engine Noise. Need Urgent Help Diagnosing (Page 1/2)
reinhart JAN 27, 07:21 PM
88 GT (118Kmi auto)

Yesterday when I left to go driving I heard a noise when I first started the car. The noise got progressively worse and is a higher clanging/knocking engine noise. Prior to that the engine was running strong and powerfully. The previous time I had driven it, there was no noise at all when I parked the car.

Tests:
I pulled one plug wire at a time and when I pull the #6 wire, noise mostly disappears. Engine sounds pretty decent.
I changed plug and wire for #6 to eliminate that possiblity and noise is still there with new plug and wire.

Hooked up a compression tester with the rest of the cylinders still hooked up and compression is 135-140psi. I also ran the engine and got a 60 psi for #6 when the engine is running.

I did have a stuck valve lifter a few years back and used some Marvel Mystery Oil which cleared it up. Other than that haven't had any engine problems.

Oil pressure is pretty good (Cold 40 psi idle, 60psi crusing. Warm 25 psi idle and 45 psi crusing) . Not as high as when it as new but not bad IMO.

Oil level is normal and coolant level is normal.

My preliminary research says if the noise goes away after removing the spark to that cylinder then it's a low end (bearing usually) issue. However, the sound sounds more like it's coming from the area between the plenum on top (where a lifter would be) but I couldn't find a location when I was listening with a screwdriver against various places.

What additional tests should I run to narrow this down? I just added some Marvel Oil to

Help please!

[This message has been edited by reinhart (edited 01-27-2022).]

Pyrthian JAN 27, 07:42 PM
one other thing that may make the noise go away when you remove the plug is if the exhaust manifold bolts on that cylinder are loose. but, yeah, usually a rod bearing. check the oil for signs of metal flakes.
reinhart JAN 27, 08:30 PM
Definately not the exhaust. Just replaced the manifolds (broken front) about six months ago so I went over it with a fine toothed comb. Interestingly it was broken in two between the #6 port and #4 port. I wonder if that caused an uneven load on the engine straining that cylinder or throwing off the A/F or something.


Well I was actually going to do the bearings as preventative maintenance, but I guess I'll just pull the oil pan and check the lower end. If it's not the lower end, I might as well do the bearings while I'm in there like I planned to.

If it is bearing spun, to me it's strange how the engine was running perfectly the day before and then when I start it up the next day I start it up and it's got a bearing problem all of a sudden?

[This message has been edited by reinhart (edited 01-27-2022).]

cvxjet JAN 27, 09:28 PM
You can use a piece of heater hose as a stethoscope to try to locate the noise. I haven't any suggestions for what the noise is.
reinhart JAN 28, 03:51 AM
I'm just going to change all the bearings since I was going to do that anyway and I'm leaning heavily toward it being a conrod bearing.

Pyrthian, I stumbled across your engine thread where you changed out just the #2 con rod bearings. I started a new thread inquiting about the bolts.

Did you replace the connecting rod bolts or just reuse the old ones? From what I've read, connecting rod bolts need to be replaced each time.
If you replaced, any info on what bolts you got would be great.
If you reused, did you use the factory torque settings (I believe it's 39 ftlbs but will double check when I get out my manual) or did you have to adjust the torque based on it being a used bolt?
Dennis LaGrua JAN 28, 09:41 AM

quote
Originally posted by cvxjet:

You can use a piece of heater hose as a stethoscope to try to locate the noise. I haven't any suggestions for what the noise is.


Thats' what I do and to further increase the effectiveness I duct tape a funnel on the listening side of the hose.

------------------
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Pyrthian JAN 28, 03:51 PM
I re-used the existing bolts. And, torqued to spec. cannot say if that was right - but I can say it worked out.
Xenoblast JAN 28, 08:00 PM
RIP if its a rod bearing

Oil pressure seems a little low compared to my car, but not rod knock low. I get 75 psi when cold idling, and 35 warm idle.

When should you change your rod bearings btw? I was tempted to check them when I pulled my oil pan but I decided not to mess with it.

Also I wouldnt think rod knock would affect compression? seems strange to me.
reinhart JAN 29, 04:51 AM
On a previous 2.8 I got to about 160 Kmi before it needed lower end work, so I was already thinking about changing the bearings pre-emptively as I was approaching 120Kmi. I would guess anything over 100 Kmi would be a good idea. I'm a little surprised people don't do this as a preventative maintenance item bu never heard about anyone doing this preemptively. You kno like change them every 100 Kmi

Hopefully if it is a rod I caught it early enough that it didn't damage the crank. I literally just drove it at 20 mph for about 2 miles once the sound appeared and then had it running for less than 5 minutes while I was trying to diagnose it.

If I spun a bearing, would the piston be hitting a valve right away or would that take a lot of wear on the connecting rod to get to that point?
Notorio FEB 01, 12:06 AM

quote
Originally posted by reinhart:

If I spun a bearing, would the piston be hitting a valve right away or would that take a lot of wear on the connecting rod to get to that point?



No experience with this but I would think a spun CR bearing would fry a crank journal pretty quickly. Anyway, I vote for dropping the pan and checking #6 CR journal ASAP. I recently did the in-car replacement of all the CR and Main bearings and it was much easier than I feared it would be. The only difficulty is fashioning a little tab that sits in the oiling hole that will gently roll the upper main bearing out the bottom when you rotate the crank by hand. It must not scratch the crank.