Rattling noise

[Yahow lam]

Hi,

My stock '87 developed some rattling noise, it seems to be coming from the blow off valve, so I replaced the two gaskets but the noise still exists.

This is what happens, after the car warms up and I drive about 25 miles or so the noise will start when I throttle and continues when I ease off the throttle.Otherwise, it drives fine and the boost is fine.

I need some help to see what else to check to eliminate that noise.

Thanks,

Yahow

[WERK I]

I would go to an auto parts store and buy one of those cheap stethoscopes and try to isolate the sound in that manner. First place I would listen, the valve covers. It could be coming from so many places, hopefully nothing that is a lot of $$$$$$.
Sometimes the fan belts harden in funny ways and you may have a bad belt. Buy belt dressing and spray the belt with the engine running and see if the noise disappears.

[Yahow lam]

Hi Dave,

Thanks for your pointers, I will get it a try.

Yahow

[NathanUK]

Could be one of the idler wheels on the chain tensioners. Use a stethoscope as suggested.
You may have one of the holes partially clogged in one of the cam spray bars. A stretched chain is another possibility. A rocker could be loose.

[Yahow lam]

NathanUK,

I will check them out too.

Thanks, Yahow

[MURF]

Are you sure its not detonation?noise only in boost?

[Yahow lam]

MURF, Thanks for your reply,

The rattling noise only happens when I push the gas pedal @ about 2000rpm or under @ operating temp either when the car is moving or not moving.

Yahow

[MURF]

Tap the cat to see if its partially melted down ..the scavange pump drip shield against the scavange pump line is common rattle

[87 930]

Vacuum leaks sometimes sound like metallic tapping (but not really "rattling") and come and go at different temperatures and rpms. Try to duplicate the conditions where the noise occurs, stick one end of a section of vacuum hose up to your ear and move the other end to where you believe the noise is coming from.

Or, duplicate the noisy condition and use a propane torch hose/wand, deliver a small amount of gas near the noise. If there's a vacuum leak, the engine will suck it up and the idle will change. Be careful! Make sure that you have no sparks or other sources of ignition nearby.

[mark houghton]

Originally Posted by Yahow lam

Hi,

My stock '87 developed some rattling noise, it seems to be coming from the blow off valve, so I replaced the two gaskets but the noise still exists.

Lots of good ideas on where to look so far. I'm intrigued by the location that you seem to hear this from. Do you realize that directly behind and below the boost recirculation valve is the turbo oil scavanging pump, driven off the left side cam? I wonder if something is amiss there. Are you still operating with the emmisions air pump, which drives off a sprocket back there? Just a thought....

[Yahow lam]

Hi Guys, Thanks for all the good ideas to where to check and I will jack the car up to check the underneath as Mark suggested as well.

I will report back to you guys when I find the problem.

Yahow

[Yahow lam]

Hi,

I found the rattle problem by removing the fan belt, discovered a 1"x1" black plastic cap stuck under between the fan pulley and the shroud, I don't know how that thing got in there and what that plastic thing is for, but after I removed it and drove for about 50 miles today no more rattling noise!

Thanks a lot for all you guys help.

Yahow

[WERK I]

Could it be the black plastic nut cover that goes over the pulley/alternator shaft nut? It just slips over the nut for ornamentation.

[Yahow lam]

Hi Dave,

You are right on, after I read your reply I went to try slip that black plastic cap on to the pulley nut and it fits perfecfly, I am not going to put it back on and it is going to the trash can.

Thanks, Yahow

[WERK I]

I suspect someone left the cap laying around the engine somewhere during maintenance and forgot to put it back on. The turbulence and vibration dropped it in there.
I've had mine on my engine for over 20K miles and it never came close to coming off.

[A930Rocket]

You would be amazed at what gets sucked in the fan as well. I've seen shop racgs and paper towels get sucked in before you could move.