I have a 78’ 280z with a L28ET.

As I’m driving home suddenly a clicking/knocking noise begins that speeds up and slows down with the rpm. I was only a couple blocks from my house so I went all the way home. I popped the hood and it sounds like its coming from of the center cylinder area. If you have any advice I would greatly appreciate it.

Thanks-Lane

if it's a rod knock it's time for a new bottom end, hopefully it's just a colapsed lifter, the hydraulic lifters get stuck and makes a lot of racket and can ever toss a follower, the pedestal "lifters" are easy to replace and can be rebuilt, I recomend keeping your eye open for a spare hydraulic head as it's a lot cheaper than replacing the lifters

I have a 77' 280 as a parts car so I should be able to steal from that. To be honest i don't even know what a lifter is, i checked my repair manual and couldn't find anything about the lifter. Where should I start?

-Lane

the turbo P90a head si the only one tha came with the hydraulic "lifters" they aren't like traditional lifter which is why I also called them "pedestals" when you pull the cam cover you'll see the "followers going under the cam, one end rests on the valve top, the other end rests on the "pedestal lifter" which is hybraulic on the P90A heads and mechanical on all others meaning they are adjustable, check for free play in the "followers" which are the things going under the cam, look at the pedestals and see how many hex serfaces you see, on hydraulic pedestals the only hex at the bade for installing and removla, if you see multiple hex serfaces it's mechanical ans the extra serfaces are for adjusting lash

Consider getting a mechanics stethoscope. $20 for a pro quality one.

With the 'scope you can tell exactly which cylinder, which rod end, even which valve is acting up. A very handy tool everyone should have.

The sound of the knock should give you some clue. A low frequency "thump" at idle that tends to go away with revs would be a rod knock. A higher frequency "rattle" that increases with engine revs is probably a valve train issue.

Did the engine power or performance change? The engine will feel normal with a bottom end problem. A top end problem will tend to limit your valve travel or not open the valve at all and cause a cylinder to loose power.

Which head do you have? If you have a complete turbo engine you have either a P90 or a P90A. The P90 head has a standard valve train with the mechanical valve lash adjusters. The P90A head, the latest turbo head, has hydraulic valve lash adjusters. Most of the aftermarket shop manuals (Chiltons, Haynes) do not address the P90A head. If you hunt, you may get lucky.

Did you ever figured out what was wrong? I have the exact same problem with my 89 300zx. I was just driving home then the knock came. Let me know how you figured it out. Thank you. I got a post up with knocking noise.

Hydraulic lifters are dirty, not worth rebuilding, under $50. for twelve on ebay