Rattling under acceleration

[jmead]

I've got a 70 240z with the stock SUs. A week or two ago I noticed a problem developing. Under hard accelerations there is a rattling sound comming from the engine bay, it is a metalic rattle, almost like the muffled sound of some screws rattling around in a can...almost. It has been getting worse, and is no accompanied by a loss of power. It is much worse in the higher gears, with it almost never happening in 1st, and getting worse into 2nd, 3rd. It seems to be load dependant, only at say 50% throttle or higher, esepically when the revs and low and building.

For some reason I think it is carb related, like something is loose in one of them. I'm really not too famaliar with the internal workings of the SUs, so is there anything that could be causing this? Remember it comes with a loss of power, so it must be something significant.

Thanks for any help/ideas.

[Zedrally]

Under hard acceleration?

Sounds more like pinging?

Check timing or use a higher octane fuel.

[jmead]

Originally posted by Zedrally

Under hard acceleration?

Sounds more like pinging?

Check timing or use a higher octane fuel.

I don't think it is detonation, but then again, I've never really heard the "pinging" before, so this could be it. I'll try a higher octane fuel for the next fillup, but I've already got gas in the tank so it would take me a while to use up all the 87 first

[St.stephen]

is there a heat shield between the carbs and exhaust that perhaps has come loose?

there are several in the 280's which is more my specialty.

[CoastGuardZ]

You're hearing it now buddy!

Logically one would think if anything was loose you'd hear it when ever on bumps or in motion. Sounds like detonation to me. You could try a quality octane booster but I'd fill up with 91 or better when you get a chance. Just don't beat on it untill you get that taken care of.

Nate:cross-eye

[AxtellZ]

check the timing, also- is it valve clatter?

If the valves went way out of adjustment it could lose power and make all kinds of racket under hard acceleration..

Good luck!

[jmead]

my timing was waaaaayyy off. Adjusted it, everything is better now. Still not as much power as before, but I've got some fine tuning to do yet.

I think the engine may be on the way out, there is still some noise under acceleration, but not like what is was.

Oh, and it certainly wasn't a "pinging" like I had thought. I assumed detonation would sound more like a cable snapping, like a "twing, twing", this was more of just a metalic rattle. At least I know what to listen for now

[beandip]

I would still run plus and not reg.

[Gav240z]

what timing did u adjust?

If not electical then mechanical timing if it's feeling really sloppy could it be a timing chain that has streched and slaps around?

The tensioner could have broken?

Sounds like detonation to me have you done as other suggest check valve clearance electrical timing etc??

Maybe it's a broken valve is it just under load what if you rev it at idle sound ok?

You can always check if the engine is on the way out by doing a compression test and checking your oil pressure for a start.

You could have a problem with your distributor are you running a mechanical points type or electronic one?

Pinging is difficult to describe I always say it's a clacking noise sorta like a chain slapping around or when u almost stall a car you hear a similar like noise.

The fact that you mention is higher gears it being more common would mean under higher load and usually means pinging also if your travelling along and your at fairly low revs like 2500rpm - 3000rpm maybe a bit less and you give it wide open throttle do you instantly hear the noise?

If so I'd put my money on an electrical adjustment and definately pinging.

[Ed]

Where are you? Maybe one of us can swing by and take a look.