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Help needed for engine noise identification - Maserati Quattroporte III

Discussion in 'Maserati' started by jamespeter26, Oct 22, 2019.

  1. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
    6
    Rome, Italy
    Full Name:
    Peter
    Dear all,

    This is my first post in this forum so I'd like to take this opportunity to first express my gratitude for this community to exist and exchange in such a constructive and friendly mindset! I really like it!

    I recently acquired a Maserati Quattroporte III in very good overall condition and I've driven it without any issue over about 1,500 kilometers since then. To say the least, it drives beautifully and I haven't had any problem. The car has no significant flaw or mechanical issue, a few things here and there which I'm addressing gradually. This is the automatic, 4.9-liter version and this one is from 1982.

    The vendor sold it to me with 11.4 liters of new engine oil - they used 10W40 but both my Maserati specialised garage and I agree that 10W60 would be more appropriate given the age and mileage (100,000 km approximately) so that's what I will use the next time I'll replace the oil.

    However, there is one thing that I want to investigate. Ever since I bought the car, the engine makes a small, repeated noise under specific circumstances.

    The noise is somewhat similar to popcorn hitting the pot lid, or the noise that a metallic resistance makes when heating up or cooling down (the users of a sauna will know what I'm talking about).

    Regarding the “specific circumstances” under which I hear the noise:
    - when the car is NOT moving (transmission on N position), no noise at all unless I push the engine above 2000 rpm, from which point the noise starts with a relatively slow frequency (once every 1.5 second or less) and the frequency then increases with rpm - in other terms, the noise only appears when I DO push the pedal
    - when the car IS moving (transmission on D, typically at highway speed), there is no noise as long as I keep pushing the pedal, but as soon as I take my foot off, the same noise starts popping as the car decelerates, and then eventually stops once the car gets below a certain speed – in other terms, the noise only appears when I do NOT push the pedal

    The garage initially thought this could be related to ignition sparks and cables. We replaced them, which was needed anyways, because the tips of the sparks were quite black, but it didn't resolve the problem. He now thinks the noise could be related to the carburettors, which might benefit from cleaning and rebuild, but nothing urgent according to him. He doesn't think I should worry about it, and told me I just need to drive the car a lot. According to him the noise could even fade away after a few thousand kilometers.

    I'd like to add that I haven't noticed any performance issue, and all indicators are OK (oil temp, water temp, oil pressure). I exclusively use unleaded, 100 RON gasoline with no additive.

    Any ideas? Does that ring a bell to fellow owners of the same engine (Maserati V8 which also equipped the Kyalami and a few other cars)? Could this be linked to the exhaust system? Valve clearances? I'm not (yet) very conversant in car mechanics but willing to learn and I understand that two major maintenances I will have to undertake at some point with this car are rebuilding the carburettors and adjusting valve clearances, so this noise may very possibly be related to either of them.

    I will try to record it when I have a moment but would welcome any thoughts.

    Sincerely,

    Peter
     
  2. Froggie

    Froggie Karting

    Sep 27, 2017
    153
    Belgium
    I am wondering from your description if that could not be due to dilatation/contraction of metallic components, in particular exhaust or nearby.
    I am not a mechanic though...
     
  3. EastMemphis

    EastMemphis Karting
    Silver Subscribed Owner

    May 25, 2019
    243
    Memphis, TN
    Full Name:
    John
    >> Does that ring a bell

    While I am not familiar with your model of car, I am familiar with this type of noise. Typically, it's from something loose. It's a metal on metal sound, right? I'm guessing you have a bracket, fastener or some other gizzmo rattling around and it just happens to hit something under the situations you describe. When you have a chance, just go around your car and start wiggling things. Lock down anything loose. It might not be in the engine compartment. It could be a brake line or an exhaust bracket. It could be something under the dash. Sounds can be extremely deceiving. This is going to be a tricky thing to track down since it only happens when you're moving. Since you mentioned it doesn't happen when you're pressing the pedal, it could be in the throttle linkage or one of the linkages in the carbs.

    The frequency of your rattle pretty much eliminates any rotating components. Once every 15 seconds nails it to a loose item, at least that's my opinion.

    I've had this type of annoying problem in several of my cars and each time it turned out to be something easy to rectify, once identified, by locking it down.
     
  4. DWR46

    DWR46 Formula 3
    Honorary

    Jun 19, 2012
    1,174
    Check the cam chain tension on both chains. This can be done without removing the cam covers. The Owners and Shop Manuals show how to do this.
     
  5. thecarnut

    thecarnut Formula 3
    Rossa Subscribed

    Apr 22, 2006
    2,299
    Atlanta
    Full Name:
    The Car Nut
    +1 That is also my guess .... the chain rattling against the head. Rather common.

    Ivan
     
  6. staatsof

    staatsof Six Time F1 World Champ
    Silver Subscribed

    Mar 13, 2005
    63,984
    Fuggetaboutitland
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    Bob
    Here's another possible cause

    that's a lot simpler to fix.

    These cars have a very specific design of v belt that's known to produce a snapping sound if the belts are old or the pulleys are out of alignment. The belt crawls up the side of the pulley and SNAPS back in place. Most often when cold. You can try some belt lubrication spray on it when the noise happens and seen if it disappears.
     
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  7. staatsof

    staatsof Six Time F1 World Champ
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    Mar 13, 2005
    63,984
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    Bob
    Yes it can but you DAMN well better be sure that no cam lobe has it's tip like a knife edge pushing the bucket fully down and ready to snap either direction.
    Otherwise you can have it snap and throw a wave in the chain causing it to jump the timing teeth and end up with much bigger job. It's happen to a couple people including me.
     
  8. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
    6
    Rome, Italy
    Full Name:
    Peter
    Guys this is incredibly helpful, thank you so much! I will test these hypotheses as soon as I have a moment with the car.

    For the moment, I managed to record the noise - both when revving up and down (I thought the latter was happening only when actually driving the car but it seems that it's not the case): https://drive.google.com/file/d/16EoCVkaZiEJ2IMPSWM09dgMCgdJ-_uQf/view?usp=drivesdk

    The noise I'm referring to is distinctly audible at the following moments:
    - from 00:14 to 00:20
    - from 00:27 to 00:29
    - from 00:44 to 00:50
    - from 00:57 to 00:59
    - from 01:12 to 01:17

    As you can hear, the noise appears only when I'm in the region of 2000 rpm, but is absent when revving at 3000 rpm or idling. It always appears around 2000 rpm, regardless of whether I just fired up the car (as in this recording, which immediately follows a cold start) or after driving 600 km almost non-stop (as I did a month ago). Always the same noise, same frequency, same pattern. This morning was a cold start and the car hasn't had enough time to warm up.

    You may notice there is another noise, which appears when idling at 800-1000 rpm. That one is only here after a cold start and quickly fades away as soon as I start driving. Doesn't appear upon warm start. My garage thinks it's a belt which needs to stretch a little bit, once again nothing to worry about according to him. Let me know if you think otherwise and/or if you want more recordings of that noise (I already have a few).
     
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  9. italiancars

    italiancars Formula 3

    Apr 18, 2004
    2,420
    Hershey, PA
    Bob is correct on this, the misaligned pulleys cause the belts to produce a very frightening metallic sound.
     
  10. thecarnut

    thecarnut Formula 3
    Rossa Subscribed

    Apr 22, 2006
    2,299
    Atlanta
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    The Car Nut
    To me it sounds like a carburetor popping. Is the air filter off where you can see the tops of the carbs?

    Ivan
     
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  11. staatsof

    staatsof Six Time F1 World Champ
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    Mar 13, 2005
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    Bob
    #11 staatsof, Oct 23, 2019
    Last edited: Oct 23, 2019
    I think you've got belt snap. Try some of this while it's happening.
    Those belts are quite stiff and if they're new your garage could be spot on. If they're old then maybe a new set. When the pulleys are really badly out of alignment it's much worse and also a lot of work to fix. So try the spray for a while if it has no effect look much deeper. I too seemed to hear a carb pop in there at higher rpms but that doesn't explain the quite sharp noise at idle.

    Oh and BTW ... chasing odd noises on old Maseratis is the the surest quick trip yo the loony bin! :p

    Image Unavailable, Please Login

     
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  12. boralogist

    boralogist Formula Junior

    Jun 21, 2005
    418
    AGREED!
     
  13. JulianMerak

    JulianMerak Formula 3

    I had lots of popping on my Merak until I replaced the main needle valves on the carbs [ fuel wasn't cutting off when there was no throttle so it would pop and fart like crazy as the fuel burnt off ] and it ran much better afterwards but lost a lot of theatrical noise!!
     
  14. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
    6
    Rome, Italy
    Full Name:
    Peter
    Gentlemen, thank you all so much for stepping in and helping me with this case. Your support is very much appreciated!

    This is a nice looking machine which does have a few issues, and it's likely that more than one of your suggestions may prove true. After listening to a few more carburettor popping videos, I must say the similarity with my noise is striking. I am taking the car to a carburettor specialist this afternoon for diagnosis.

    The misaligned pulleys is also something I will investigate, perhaps causing the sharp noise at idle noticed by Bob. I'll try the spray and will ask my garage to give it a closer look.

    Regarding timing chains, I don't know what to think. On the one hand, I've asked my garage specifically about them, and he responded that they don't make any abnormal noise. On the other hand, the car is nearing 100,000 kilometers so checking the chain stretchers wouldn't be a luxury and I definitely don't want one of these to fail me on the road. I guess I'll have to insist the next time I'll see him.

    In any case I will keep you posted. Thanks again to all!
     

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