Strange Sound on Start-Up

Over the past several weeks, on starting up my MY98 (77K) I periodically get a quick "howl" (that seems the best way to describe it) as the engine turns over which lasts for less than a second. After that, all seems normal and the engine idles and accellerates properly. It doesn't seem to happen all the time, but enough to make me concerned. Any thoughts as to what this might be or what it might be forewarning? I'd appreciate whatever input the board can offer. Thanks in advance.

injection pump is switched on and valves opened/closed to inject air into the exhaust system ahead of the converters to warm them up quicker.

The howl can be the signs of a secondary air injection pump going out.

The air injection pump is not switched on when the engine is warm or hot.

If you are confident you can reproduce the symptom on demand then remove the serpentine belt -- note its routing and direction of rotation -- and start the engine. You can let the engine idle a moment or two (or longer) but since the howl is quick you shouldn't have to run the engine very long at all.

If the noise present and since you have the engine access panel removed and ideally you should have the engine compartment cover removed too you might be able to note if the noise is coming from the secondary air injection pump. If you want, if you're sure of yourself, locate this pump and carefully get an ear close to it, even put your hand on it and then have someone else start the engine. If the pump is making the noise you'll know it. Of course, be prepared to if the noise is not coming from the pump to try to identify the source of the noise. Is it from the starter perhaps?

If the noise present and you're sure the pump is not making the noise then check the oil filler tube cap is secure, not leaking, but suspicion has to switch to the AOS.

If the noise is not present then the howl's source might be a bad roller or tensioner roller bearing or even one of the accessory drives. Check then all for any play, looseness. You'll have a lot of good tight ones and possibly one not so tight so you'll have to check them several times to locate the one that wiggles. The movement can be ever so slight but you should be able to detect if, it it is present.

Sincerely,

MarcW.

Mark, thanks for the analysis. No, it doesn't seem to happen when the engine is hot. Unfortunately, I'm not sure I'm confident enough in my diagnostic abilities to go through the process you described. I can change oil, brake pads, rotors, etc. but determining relative belt tensions may be beyond me.

Jong...thanks. That actually sounds like something I can do! I'll give it a try and report back!

Quote
JTK San Diego
Jong...thanks. That actually sounds like something I can do! I'll give it a try and report back!

In fact, I inspected all the pulleys and belt before disassembling the starter, but no luck. So, before bring my car to the shop, I decided to give it a try, because it's less than one hour job without special tools (oh, you will need long extension for your socket. I used 2x 12" long extension set from inside car to one of the stater bolts). When I disassembled it, I cleaned and lubed the gears only, and put it back. But, there was still noise. So, I disassembled it one more time (less than 15 min for the 2nd try. :-)), cleaned and lubed most of the parts (light green plastics, small gears, outside gear and everything except coils). Until I felt those gears and spring inside very smooth and much less resistance. Then, it worked like a charm without any noise.
BTW, if you could, don't forget to clean throttle body and MAF sensor checking/cleaning, because you will have to disconnect the rubber hoses and TB anyway to get access to the starter. All the instructions are in Pedro's dyi section. Good luck, and I hope you could solve it. I know it's little bit annoying whenever you start the car, and it's fairly common issue in old(?) boxsters. That's what I have read about it in 986forum.

What you have is possibly one 'bad' one (say the water pump -- in the case of my Boxster) and all the rest are good.

I was able to with a high degree of confidence diagnose the water pump cause when I wiggled its pulley -- up and down and in and out -- there was a bit of play. Not much. But the other accessory drive pulley/shafts didn't have any play.

Also, if the serpentine belt has a sharp edge this is because a pulley drive has play and belt tension pulls the pulley out of position some that the belt's edge (innter edge in the case of my car) to rub against a pulley's side and the sharp edge is the result. Unlikely that both of the belt's edges will rub so you should find a dull/blunt edge and a sharp edge. The difference between the two is nearly night and day.

The belt idler roller bearings are tested and eliminated in a similar fashion. Chances are good there's just one bad one and the rest are ok. Thus you can wiggle/shake and spin each one and the one that feels different is *probably* the bad one.

Sincerely,

MarcW.

Now I see...sorry for the misunderstanding! I will dig in and begin to evaluate the pulleys and see what I can find.

Thanks!!!!!

and some patience you should be able to identify if the noise is coming from the secondary air injection pump, the starter, or some other location.

I hate to see someone pull out a starter to clean and grease it unless it is clear that is where the noise is coming from but I do not know how much work this entails. If you feel the amount of work is tolerable then you might do the starter R&R with a clean/greasing as covered by Jong.

While I'm not in favor of throwing parts at a symptom (noise in this case) or even expensive shop labor your labor is very much less expensive. Or to put it another way, if you do the labor you essentially save yourself $150/hour (or whatever the going shop rate is where you take your car).

Sincerely,

MarcW.

I'm sorry to hear your problem. In my opinion, It seems to be a starter noise. I used to have the same noise or elephant trumpet sound for about 2-3 second whenever I started my car in cold weather. I removed the starter, disassembled, cleaned and lubricated it, and since then I've not had any noise. It's easy process and worth to try. I found no grease in mine. :-)) I will post some links for the job if you want to try. There's step by step instruction on the pelicanparts tech article.

[www.pelicanparts.com]

Once you take the starter out, remove two long bolts off of it, and disassemble the gears. Clean them with some brake parts cleaner or our best friend WD40. I was not sure wd40 was ok for the job, but it was the only thing I had, so I used it and cleaned any residue of it. Then I put some CV joint grease (few bucks from autoparts store) among gears. That's it. Put it back to the car, and try if it works. Maybe, I was lucky. Good luck!

Jong in Orlando