Ian01

A week ago my Z31 started making a rattle/tapping (knock?) noise from what I think is the bottom end. Happens intermittently when warm, sometimes disappears completely when at operating temp, but present more often than not. It's not noticeable while driving, except it seems to be down on power by about 10-20 hp. The rattle is most noticeable while at stoplights or next to a wall with the window down, because the sound reflects off of other cars and walls, etc.. A buddy of mine suspects rod knock except when you pull each of the plug wires one at a time, the noise does not change AT ALL. Plus it is not a heavy knock and does not get worse with engine RPMs. I have pulled out my rubber hose and tried to pinpoint the noise...doesn't seem to be coming from timing covers or underneath valve covers, leading me to suspect it's not in the top end. Dont' think it's water pump or AC compressor either. When I get underneath the car with the hose I can somewhat pinpoint it to midway up the block, and more towards the rear of the engine than the front. My question is, could this still be bad hydraulic lifters, or like bad camshaft/bearings or pushrod? Since the rattling/knocking is light not heavy, I am kind of ruling out major things like main bearings, rod bearings for the moment. Also, I did not check compression in the cylinders, but the car was running very very well before this happened and still actually runs pretty well now. I also pulled the spark plugs to find all 6 looking normal, with just slight greyish accumulation. I changed the oil and did not see metal in the oil. One thing I know is screwed up for sure is a broken exhaust manifold stud, passenger side closest to the firewall. My understanding is this would cause a tick, but I believe the rattling I am describing is more of a rapid, light knocking sound and coming from underneath the car. Ideas? BTW, this did happen following a semi-hard run around town.
Thanks in advance!

FreeLanceBum

Try changing your plug wires. This happined on my GF's stratus. Thought the engine was frelled till I investigated a bit. New plugs and wires made it run like new.

Ian01

Actually the cap and rotor just started to go south today, starting to miss alot..you might be on to something there, I'll swap the cap, rotor, and plug wires and see what happens. Thanks!

Ian01

Well the car ran better after the tune, but aggravated the noise...I am pretty sure a bearing or something is going out, just doesn't seem to be any other answer...the noise is constant now too.

FreeLanceBum

Hows the oil level?

Ian01

Yeah the oil level is fine, the car doesn't leak or burn oil much anyway, and I just did a fresh oil change plus used Slick 50 out of desperation, car lasted a few days with intermittent noise, but now it seems constant since changing the cap and rotor fixed the missing problem that was developing. Really sounds like a spun bearing or something. Bunch of clacking when bopping the throttle and at idle too.

jdcollins

welcome to my world

http://www.youtube.com/watch?v=qHtVIyM__5c

johnZboy

With the engine skipping, and, the little metallic pecking sound, I'd have to be looking at something in the valve train. Could be a burnt or warped valve, a seat could have popped out, a rocker or lifter may have failed. When you installed the plugs, did you remove all the debris from the plug wells before you removed the plugs? If not, you may have intaked something that broke the valve as it was passing by. That happens a lot with these engines.

Run a compression check. That will at least tell you in which head the problem is, and, which head is coming off. Actually, if you tear that far into it, both heads should come off for reconditioning.

Better stop driving it. You may damage the block, or, punch a hole in one of the pistons.

The good news is, now you get to freshen up that old vg30....

FreeLanceBum

Holy rod knock BatMan!

z-hag

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