roncee

Hi guys, I have been a longtime lurker and now signed up due to needing some expert help.

I have an 02 Boxster S 86k on the clock, has had routine maintainence including oil and filter 3 months ago (Shell Helix 5w-40)
Has not had the IMS changed.

Anyway 1 week ago I heard a loud banging noise on startup, I immediately thought it was the IMS and turned the engine off. I gave it 2 mins and restarted and the banging had gone. Engine was silky smooth and went 20 miles home.

No problems for about 1 week and similar situation occured. Went 2 miles, parked up and when I got back into the car and started loud banging sounds almost rotary in nature. Sounds to be coming from under the boot (trunk).

Took some video,


Then restarted the car - noise gone and engine silky smooth and drove home no problems.

Any ideas anyone? Sounds terrible when it occurs (as you can hear) but I don't think catastrophic as the car drives perfect when you restart the engine.

Could it be a stuck lifter? Why would this noise be intermittentCould anyone advise please?

Many Thanks

Ron

Macster

Loud banging noise is right.

It is not clear to me -- due to the noise -- but is the engine actually running when you hear this noise?

If so then does the noise increase or decrease with engine RPM increases/decreases?

If so my advice is to flat bed the car to a qualified shop for a pro's diagnosis.

If the noise is present with the engine not running -- but the key on -- it could come from something in the A/C cabin fan. Something like a piece of insulation or perhaps a piece of hardware or even a leaf or twig. You can use the dash control to turn the fan speed off.

If the noise is coming from the engine area and doesn't follow engine RPMs the noise could be coming from the air injection pump.

You would have to expose the engine then reproduce the noise and check the pump for any indication it was the source of the noise.

I'm trying to think of what else it could be. I wonder if a bad relay could cause that clacking noise? If the noise is present with just the key on or the key on and engine running but the noise doesn't change with engine RPMs I like a noisy relay for this but that doesn't mean that is what it is. That the noise is not present upon a restart does point to something electrical.

You would have to expose the relay panels and with the noise present feel the relays to figure out which relay is making the noise.

JayG

You might want to let you kid out of the trunk... Just sayin......

BTW, you may want to check out 986forum.com
Lots more Boxster people there than here

roncee

Thanks Macster, very helpful.

Yes it was with the engine running. I dont think the rpm made much difference to the loud banging although I must confess i didnt dare give it too much throttle whilst making that noise.

Ive driven it all day today and no banging.

Air injection pump - sounds interesting

Macster

Well, it makes a difference if the banging varies slower faster with slower or faster engine speed.

The air injection pump runs at cold start. It has a vane compressor of sorts. While it could account for the noise I can't imagine an intermittent failure mode that would account for that noise yet not render the pump/motor non-operational in a short time.

With that level of noise and with the noise present I think if you *carefully* touch the injection pump -- you can even just touch with a long screwdriver -- I think you'd know the pump is the source of the noise.

If the noise is dependent upon engine speed another place to consider is the accessory drive. The noise your car generaates doesn't quite sound like the noise I recall hearing when someone posted an audio clip but there have been a couple (well, at least one) report of someone finding a loose bolt caught in the crankshaft pulley in its rear facing recess. The noise was not that loud as I recall and even though the engine speed was steady was not that regular.

But it worth a check I think but with the engine off of course and the key out of the ignition.

navair

Exhaust leak? Header-engine, or secondary cat gasket?

roncee

Thanks for the replies, I haven't had a chance to fully inspect yet but can report its happened a few times again. Same story of the loud rhytmic banging. It doesnt seem to respond or change according to rpm. Switching off thr engine and restarting cures the problem (for now). I cant identify any clear pattern why it occurs e.g cold start or warm start etc.
Hopefully i will get a chance to have a better look and or get into a mechanic to look at it

roncee

ok so just a quick update, I haven't had time to fully inspect the noise but got a half diagnosis. It has always been dark when it has occured and usually 5 seconds after a start.
It corresponds with me putting the dipped beam headlights on. Not always but happened consistently the other day - it was wet.
I have done a xenon retrofit with the ballasts hiding behind the main headlights in the cavity. Maybe a short in ballast when wet - although they should be weather sealed.
Secondly it is not clear why it causes a banging noise - sound like coming from the alternator.
Anyways I will get round to checking the ballast or changing to one of the led h7 bulbs.

Anker

Its most probably a bad serpentine belt. When you turn the lights on the alternator gets harder to turn and the belts starts slipping.