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Thread: LS1 Chev noise cold

  1. #1
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    LS1 Chev noise cold

    I have a curious noise in the LS1 too; sounds like pinking [knocking tinking] but goes away after engine is warm... and if it is belt or tensioner why only under acceleration?, if it is pre-igntion or exhaust why does it disappear after about 5kms of driving?
    A good one for the late Joe Woods' "Clank Factor" pages in trade magazines of the 90s. It's got me stumped.
    I'm suspecting the belt tensioner but only under acceleration?
    The alternator is working after a cold start... nope it's only under acceleration, even very light acceleation
    by the time I get to a mechanic the damn thing is silent again.
    The 'tinking' noise is quite loud. ... throttle dependent, but isn't quite like pre-ignition, more like under any acceleration cold there is a kid hitting a tin drum, serioisly audible to anybody on the street. And at Dave's V8-building workshop they went right over the serpentine belts found no obvious faults.
    I don't know if the ECU could be getting a bad signal cold but if it was maybe it should show 'check engine' ... and this is after the new exhaust system and probable issues with the double-skin manifold-pipe flange [a exhaust rattle on start up in the same general area as the tink tink noise]
    I could always solve it by selling the SOB. I'd say it was that exhaust thing but it is seriously loud... and why does it entirely go away warm?

  2. #2
    DonTom
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    Re: LS1 Chev noise cold

    "I have a curious noise in the LS1 too; sounds like pinking [knocking tinking] but goes away after engine is warm."

    An OBD2 system? It might really be pinging. If you think it's pinging, it could be. You think that's not logical because it goes away when engine is warm? NOPE, not at all.

    When your engine is cold, you're in "open loop". This means your main O2 sensor is doing nothing at all and it's getting all the required information form all the other sensors. Let's say you have a MAP sensor or other sensor problem (or a bad hose) making the engine extra lean. Lean can cause pinging. But when engine warms up, it ignores the bad sensor and starts to use the main O2 sensor only (closed loop) to give you the perfect 14.7 to one mixture and no more pinging. Now you are back to a normal running engine until it gets cold again.

    However, there are other times you can be in open loop, even with a warm engine, such as when accelerating up a hill or at idle. But with a bad sensor, it can still be worse when cold, depending on what's wrong.

    So your first step is to somehow determine if it's really a ping or not.

    You may not get a check engine light if the condition goes away by the time it's in closed loop.

    -Don-





  3. #3
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    Re: LS1 Chev noise cold

    Quote Originally Posted by DonTom
    "I have a curious noise in the LS1 too; sounds like pinking [knocking tinking] but goes away after engine is warm."

    An OBD2 system? It might really be pinging. If you think it's pinging, it could be. You think that's not logical because it goes away when engine is warm? NOPE, not at all.

    When your engine is cold, you're in "open loop". This means your main O2 sensor is doing nothing at all and it's getting all the required information form all the other sensors. Let's say you have a MAP sensor or other sensor problem (or a bad hose) making the engine extra lean. Lean can cause pinging. But when engine warms up, it ignores the bad sensor and starts to use the main O2 sensor only (closed loop) to give you the perfect 14.7 to one mixture and no more pinging. Now you are back to a normal running engine until it gets cold again.

    However, there are other times you can be in open loop, even with a warm engine, such as when accelerating up a hill or at idle. But with a bad sensor, it can still be worse when cold, depending on what's wrong.

    So your first step is to somehow determine if it's really a ping or not.

    You may not get a check engine light if the condition goes away by the time it's in closed loop.

    -Don-
    That is quite alarmingly possible. It is OBD2.
    I guess I'll have to do serious visual checks for hoses etc and maybe put the car in the shop .

    It SOUNDS like serious pinging when cold. I would have thought open loop would give satisfactory settings cold but there might be a faulty sensor. It runs cleanly and has good power hot or cold.

    Thanks for the opinion.

    Rob

  4. #4
    DonTom
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    Re: LS1 Chev noise cold

    "It SOUNDS like serious pinging when cold."

    When the engine is still cold, can you go downhill somewhere and check for the ping?

    And some other time with the engine cold again, go uphill and see if there's a noticeable change at the same RPM's.

    If it sounds the same both times with a cold engine, it's most likely NOT a ping.

    Open loop will normally run you a bit rich. But if there's something wrong, it can easily change to extra lean. But too lean usually will not work well with a cold engine and I would think you would also notice a difference in performance.

    But IAC, check the simple stuff (hoses, etc.) first.

    -Don-

  5. #5
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    Re: LS1 Chev noise cold

    Quote Originally Posted by robmcg
    I don't know if the ECU could be getting a bad signal cold but if it was maybe it should show 'check engine' ...
    Depends on the fault. I had a faulty coolant temp sensor which was causing the engine to run rich, as it was reading lower than the actual temperature, but as it was giving a reading within acceptable values the ECU didn't see a fault. It did, however, show up on a diagnostic check - maybe that's your best bet?

  6. #6
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    Re: LS1 Chev noise cold

    Quote Originally Posted by Dave Brand
    Quote Originally Posted by robmcg
    I don't know if the ECU could be getting a bad signal cold but if it was maybe it should show 'check engine' ...
    Depends on the fault. I had a faulty coolant temp sensor which was causing the engine to run rich, as it was reading lower than the actual temperature, but as it was giving a reading within acceptable values the ECU didn't see a fault. It did, however, show up on a diagnostic check - maybe that's your best bet?
    I have to say this drove me mad, and now seems logical, I'm almost reluctant to say but a loud tinging pinging noise cold acceleration only is in fact the roller-bearing inside the tensioner pulley; which thankfully made the noise so well cold strart this morning [after a nice chat with Sue my neighbour... she uses a push mower and we discussed hops] that it was clearly\\


    11 11 1918 60 seconds silence please
    that we were able to go about things and the noise is what I judge to be a failing belt tensioner which with the extra load and revs with cold acceleration

    makes severe clicking and ticking, with cold rubber and it goes away warm because the tensioner/belt both warm less load and probably one roller inside is breaking up like a German warship scuttled at Scapa Flow, you don't know how fast it will go down.

  7. #7
    MikeHalloran
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    Re: LS1 Chev noise cold

    Or it could be running lean open loop because it has no cats.

    But you should check the tensioner, too.


  8. #8
    DonTom
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    Re: LS1 Chev noise cold

    "Depends on the fault."

    Yep. They do a lot in OBD2 to prevent a false check engine light. For an example, when I had a problem with my "no secondary air injection" (translates to having a bad electric air pump for the smog) in my 1999 Mustang (3.8L), it had to see no air for two consecutive start ups and a total of so many seconds before the check engine light would come on. Then it's latched on and won't go out even if the problem is cleared. I never would have known this if I did not have the factory shop manual. But I read many of the other codes and saw very similar stuff with many of the codes. Simply having the problem for a few seconds (or sometimes minutes) might get ignored by the system for several reasons, depending on the code.

    And then when the problem is cleared, the code and check engine light may still be on. Some codes require a reset and some do not. Some will clear after a number of start ups if there's no more problem. Not all the codes work the same way (not even in the same vehicle), making it almost a necessity to have the factory manuals.

    -Don-

  9. #9
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    Re: LS1 Chev noise cold

    thanks

    I'll do the tensioner by replacement.
    The sound is definetely from there. After neighbours and kids all friendly I am the middle of a new pic. All well.

    OBD2 can handle slightly less exhaust backflow surely? Ran OK max 195kW It's inaudible at 30mph cruise

    My theory is that the tensioner is failing and has a bad bearing . Car has open-loop acceleration over 2/3rs throttle OK., BUT it's still a mystery.

    FWIW I just start and warm it up with suburan driving .. it's 60K miles and 6 years... it spends most of it's life on cruise at 1,700rpm.

  10. #10
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    Re: LS1 Chev noise cold

    Two tensioners on the LS1 replaced, still like a bag of nails cold, noise disappears on overrun, VERY metallic 'tinging' engine-rev-dependent. Doesn't sound like pre-ignition... one ping per engine rev.

    normal hot running, quiet has good power and is smooth...

    valve-lifter? sticking valve?


    a COMPLETE POS can't diguise and sell because I am too honest.

    If a GM apologist walked in I could kill him with my bare hands

  11. #11
    MikeHalloran
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    Re: LS1 Chev noise cold

    Shots in the dark:

    I've heard noises like that from loose water pump pulley bolts.

    I'd also check the flex plate to flywheel bolts.

    What rotating bolts have been loosened in the last year or so?




  12. #12
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    Re: LS1 Chev noise cold

    Quote Originally Posted by MikeHalloran
    Shots in the dark:

    I've heard noises like that from loose water pump pulley bolts.

    I'd also check the flex plate to flywheel bolts.

    What rotating bolts have been loosened in the last year or so?
    Thanks Mike.
    Yes, I would have suspected something loose like that [why only cold then for 2-3 miles?]

    Nothong has been touched in the last 7 months that I know of except a diff seal a year ago and the two belt tensioners yesterday.

    I spent few minutes engine on-off looking for things just now and it now sounds like generalized light pinging. Engine covers are non-factory they aren't making noise. At steady revs it pings for a minute or so from cold then slowly gets quieter unti after several minutes you think it was perfect. Has good knock sensors I presume these work from cold?

    Otherwise as you say mechanical checks.. then OBD2 ?

  13. #13
    MikeHalloran
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    Re: LS1 Chev noise cold

    Mine makes extra mechanical noise when the oil level is way low. I should not have discovered that...

    I don't think the ECU pays any attention to the knock sensors when it's in open loop/cold.
    Try partially occluding the tailpipes next, I guess.



  14. #14
    DonTom
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    Re: LS1 Chev noise cold

    "I don't think the ECU pays any attention to the knock sensors when it's in open loop/cold. "

    I would assume it still does as there's no reason to ignore any sensor, other than the main O2 sensor, while in open loop. In fact, when you accelerate up a hill (even with a totally warmed up engine) you're in open loop and that's when you're going to need the knock sensor the most.

    -Don-

  15. #15
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    Re: LS1 Chev noise cold

    Quote Originally Posted by MikeHalloran
    Mine makes extra mechanical noise when the oil level is way low. I should not have discovered that...

    I don't think the ECU pays any attention to the knock sensors when it's in open loop/cold.
    Try partially occluding the tailpipes next, I guess.
    The noise I'm getting seems to me to be in the body of the engine ... I'll check the oil [was changed a couple of weeks ago by a generally good mechanic]] but really is more like pinging and tinking.

    I'm thinking maybe air leak between throttle body and inlet, but there's no visible deformation looseness or anything and I thought running lean when cold would have meant rough running. It might need OBD for this. The car has never been 'messed' by poor mechanical work in my ownership and before that it was factory GM with full paperwork which looks genuine.

    There is no sign of abuse on any bolt nuts harnesses etc.

    I'll try giving back-pressure and see if that has an effect, but I only get two-three minutes cold so I might tape a cloth over the single large taipipe or something. Woman's stocking?


  16. #16
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    Re: LS1 Chev noise cold

    Quote Originally Posted by DonTom
    "I don't think the ECU pays any attention to the knock sensors when it's in open loop/cold. "

    I would assume it still does as there's no reason to ignore any sensor, other than the main O2 sensor, while in open loop. In fact, when you accelerate up a hill (even with a totally warmed up engine) you're in open loop and that's when you're going to need the knock sensor the most.

    -Don-
    Thanks Don,

    That's interesting; the knock sensor might [or might not] be read as part of basic inputs including temp. If it requires temp the knock sensors would still work in open loop warm/hot,

    FWIW The O2 sensors [2 on this version Aust ] were removed properly and didn't need force and were stored carefully and replaced carefully when the exhaust was replaced... but I don't see them being involved in cold startup , to the contrary, they may be involved in the noise reducing warm.
    There is a momentary startup rattle from the exhaust [hot or cold] which has always been in the car in my ownership, ... presumable in some double skin section around the factory manifolf-pipe flange.

    Thanks for your replies. This car will be running less back pressure than most, with factory 4-1 manifolds -> 2 free flow boxes - > 1 large free flow resonator.

    Today I felt thoroughly disempowered. By a GM car! If it turns out to be low oil I will kill the mechanic, but I *think* I checked when I got home and it was right on max.
    Something is causing bad settings cold, if it ain't mechanical/oil.. The OBD codes ought to show lean or something cold but it's obvious things first. I can't get at the OBD port myself, I ain't as flexible and dextrous as when I was younger, I haven't got a scan tool and I'm unclear as to whether they are worth whatever they cost. The local dealer here would charge me a lot of money just to plug in their tools ... I need a mobile mechanic with a tool to get the cold start, otherwise I would have to do several car transfers and remove the hand controls... a complete pain and leave the car with them overnight at least..

    I'm a bit unclear as to read trouble codes... cannot start the engine with the port earthed as required in Haynes, yet half the codes are about 'lean running' etc. Which is ambiguous stuff...

    Maybe I hould disconnect the battery for 10 minutes and pray?

  17. #17
    MikeHalloran
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    Re: LS1 Chev noise cold

    See the fat rubber elbow between the MAF sensor and the throttle body? Try to pull it off the throttle body. Try to pull the MAF sensor out of it. Use a mirror to inspect all the way around both ends.

    On at least some units, it's pretty easy to get the hose doubled up under the clamp in such a way that it leaks a little air. It doesn't leak enough to cause hard starting until it's about to fall off. And it doesn't set a code, but the engine does run lean and ping until it goes closed loop.

    Don't overtighten the clamp. Just make sure the rubber is trapped under it like it's supposed to be, all the locating fins protrude through the slots in the band, and make the clamp snug.


  18. #18
    DonTom
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    Re: LS1 Chev noise cold

    "There is a momentary startup rattle from the exhaust [hot or cold]"

    That sounds like a bad catalytic converter to me.

    A scan tool to check smog codes can be as cheap as $25.00 (and that includes shipping) on E-Bay.

    But if you don't have or recently had a "check engine" light, it won't do you any good.

    You can try disconnecting the battery, and it is possible, in some cars to make a noticeable difference. Some cars "learn" the way you drive for the fist 50 miles or so and change some programming based on that.

    I had a 1988 Biretta (OBD1) that did that, and it would die at every stop for the first ten miles and be perfect after that until the battery is replaced again.

    BTW, disconnecting the battery on a OBD2 system resets the codes to a "not set" condition. After so many miles and restarts (depending on the code) they will set and show any possible problems by it lighting up the "check engine" lamp. You will flunk a smog test if you change the battery just before such a test as the codes will show as "not set" because there has not been enough miles to show such a problem. IOW, the OBD2 system does NOT allow any type of "cheating".

    -Don-


  19. #19
    mrblanche
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    Re: LS1 Chev noise cold

    I would be reluctant to generally condemn GM...not that they don't deserve it, but I'm not sure it accomplishes anything.

    I would check on what has changed in the last little while; the odds are good that that is where the problem lies.

    Or I could introduce you to a friend with a Jag V12 that would like to take it out and use it as a boat anchor, just to help you keep your perspective.

  20. #20
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    Re: LS1 Chev noise cold

    Quote Originally Posted by DonTom
    "There is a momentary startup rattle from the exhaust [hot or cold]"

    That sounds like a bad catalytic converter to me.

    A scan tool to check smog codes can be as cheap as $25.00 (and that includes shipping) on E-Bay.

    But if you don't have or recently had a "check engine" light, it won't do you any good.

    You can try disconnecting the battery, and it is possible, in some cars to make a noticeable difference. Some cars "learn" the way you drive for the fist 50 miles or so and change some programming based on that.

    I had a 1988 Biretta (OBD1) that did that, and it would die at every stop for the first ten miles and be perfect after that until the battery is replaced again.

    BTW, disconnecting the battery on a OBD2 system resets the codes to a "not set" condition. After so many miles and restarts (depending on the code) they will set and show any possible problems by it lighting up the "check engine" lamp. You will flunk a smog test if you change the battery just before such a test as the codes will show as "not set" because there has not been enough miles to show such a problem. IOW, the OBD2 system does NOT allow any type of "cheating".

    -Don-

    Thanks Don,

    The car doesn't have catalytic converters. NZ doesn't require them. It was two O2 sensors with all the usual Australian spec sensors.

    Still sound like a bag of ball bearings being rattled in a can when cold, rev-depenent . Oil looks good. All lights out. No visible sign of damage to any phusical part with stripping and replacing everything.
    NOISE goes away entirely when warm.

    Strong hot open loop full throttle no funny noises ... this cold noise is LOUD and embrassing

    I'm gonna disconnect the battery again, this time 16 hours. And I have filled with 98 octane [RON you guys call it 93] replacing a remaining bit of 95RON

    Apart from that, until something breaks completely, I'm beaten. I suspect something mechanical Apart from belt change/two tensions there hasn't been work or messing with the engine apart from filers oil etc. I doubt running the highest octane available here at the pump will make any difference. I disconnecting the battery for 16 hours because these cars remember *some* things for eight hours according to the owners manual.

    HOW CAN IT RUN SO WELL WARM AND YET HAVE SUCH OBSCENE NOISE COLD AND NOT SHOW ANYTHING OBVIOUS ??????

    Water pump needs to build pressure?. Damned if I know. And it will cost $200 to get a diagnosis which may be a black hole into which I can pour money... and I cannot sell the damn thing because nobody would buy a car with death-sounds in the cold engine.


    Mike's friend's V12 Jag would be a doddle to fix...





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