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  • Slight rattle under boost.

    Main Q: Detonation or Bearings going out?

    Information:

    89 NA engine
    converted w/ 84 turbo/injectors
    stock boost
    ~150k miles
    Castrol GTX 20w50
    84T oil pump, not rebuilt, but cleaned etc etc.
    Semi-rebuild heads about 7k miles ago, new lifters & 84T cam installed.
    93 octane.

    It runs excellent under normal driving conditions. However, sometimes under boost / hard acceleration i can hear a small "rattle" from the engine bay.

    I don't really think it's detonation. Running stock boost and 93 octane should keep that to a minimum. However i've never truly heard an engine detonate, so i could be mistaken in this.

    Which of the bearings are most likely go to bad? I'm guessing the rods. Reading other threads, someone stated that rod bearings rarely go bad...so i don't really know.

    Also, what would be the most obvious cause of this? Reading through random other threads someone suggested lack of oil circulation.

    I have an aftermarket oil pressure gauge:

    Starting up i have 60-80 psi for about 1-2 minutes.
    After it's warmed up i have 20-30psi idle, and 50-60 psi driving

    Basically, what's Z31P's opinion of the source, and cause of my rattle. I'm not looking for an indepth answer...im just curious, more or less.

  • #2
    Re: Slight "rattle" under boost.

    JustinCase wrote: Main Q: Detonation or Bearings going out?

    Information:

    89 NA engine
    converted w/ 84 turbo/injectors
    stock boost
    ~150k miles
    Castrol GTX 20w50
    84T oil pump, not rebuilt, but cleaned etc etc.
    Semi-rebuild heads about 7k miles ago, new lifters & 84T cam installed.
    93 octane.

    It runs excellent under normal driving conditions. However, sometimes under boost / hard acceleration i can hear a small "rattle" from the engine bay.

    I don't really think it's detonation. Running stock boost and 93 octane should keep that to a minimum. However i've never truly heard an engine detonate, so i could be mistaken in this.

    Which of the bearings are most likely go to bad? I'm guessing the rods. Reading other threads, someone stated that rod bearings rarely go bad...so i don't really know.

    Also, what would be the most obvious cause of this? Reading through random other threads someone suggested lack of oil circulation.

    I have an aftermarket oil pressure gauge:

    Starting up i have 60-80 psi for about 1-2 minutes.
    After it's warmed up i have 20-30psi idle, and 50-60 psi driving

    Basically, what's Z31P's opinion of the source, and cause of my rattle. I'm not looking for an indepth answer...im just curious, more or less.
    UH thats PLENTY of oil pressure.

    If it was detonating it would stay there until you got off the throttle most likley. the bearings are hard to hear after about 3500rpm detonation is not.
    85 Z31 6.0 LSX turbo 766whp/792wtq
    04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

    Comment


    • #3
      Yeah i guessed my oil pressure was ok, i just wanted to provide enough information so someone could accurately help me.

      Honestly, what does detonation sound most like?

      The best way i can describe the sound is like a pair of old pliers, where the screw holding each side in the center is loose, then wiggling one of the handles, if that makes any sense.

      If i remember correctly (i don't go into boost often), it typically "rattles" when i'm under a load & boosting around or above 4 psi.

      Performance is odd, in boost. Sometimes it pulls very hard, sometimes it doesn't really pull at all (i beleve the sound is more prevalent at this point, if i remember correctly)

      Now that i think about it, i checked my plugs a while back and they had a very slight whitish ash to them, this means i'm running lean correct?
      After seeing this, i ran the ECU to find out that it was running a good a/f ratio (the green light test)

      Comment


      • #4
        JustinCase wrote: Honestly, what does detonation sound most like?
        An aluminium can slowly crushing.
        imagination is a virtue

        Comment


        • #5
          JustinCase wrote:
          Now that i think about it, i checked my plugs a while back and they had a very slight whitish ash to them, this means i'm running lean correct?
          After seeing this, i ran the ECU to find out that it was running a good a/f ratio (the green light test)
          tsk, tsk. stop hitting thoes high RPM until you tune for it. White ashing is relevent to high speed glazing. shouldnt be an issue with running lean, as the ECU perimeters limit dwell cycle to run close to stoicometric levels in closed loop for optimal efficency (below WOT) as most stock PROMs are set for, assuming your O2 sensor, and CHTS is in working order. (which control the ECU to enter closed loop cycle)

          you could always switch to a colder plug (though also affecting engine performace without the right tune)

          Could be a variety of other engine issues that wouldnt set a code off. keep matinence, or get into recalibrating for these changes in engine VE.

          As to the varying performace, sounds like a Vac issue to me.

          Comment


          • #6
            I rarely go into the higher rpm's.

            I don't know what there is to tune for, everything is stock.

            There are no engine codes being thrown. The CHTS and o2 sensor are new.

            All Vac lines have been replaced. The EGR is plugged. I don't think it's a vac issue.

            Also, my turbo is brand new. Only has about 7,500 miles on it.

            I'm thinking about replacing the head gaskets for an excuse to take a look at the pistons, and clean the heads & add my 3 angle'd valves.

            Comment


            • #7
              I took my car to the lake today and put my little camera in the engine bay. There's a lot of distortion from windage and other loud noises but you can still hear the rattle.

              So yeah, pretty sure it's detonation.

              http://palmettofx.com/hosted/Engine.mov

              2mb

              Comment


              • #8
                Where is the base timing set?
                imagination is a virtue

                Comment


                • #9
                  20 last time i checked.

                  Comment


                  • #10
                    Sounds like detonation.Make sure your boost gauge is working and lower the timing a bit and see if the noise continues.
                    Has it been happenning for awhile or just with this tank of gas? Maybe bad gas.
                    Shiro #443

                    Comment


                    • #11
                      Check fuel pressure; injectors might need to be cleaned.
                      Chuck Stong
                      300+ Parts and Performance owner
                      http://www.300-plus.com
                      2002 ZCOT president and always active member

                      Comment


                      • #12
                        It's pretty much been happening for a while. I rarely go into boost so it's not an everyday occurance.

                        The injectors are out of my parts 84AE, it had ~144k miles on it, but when i got it, it had been sitting for about 6 years. Funny thing was it cranked up on the first try - all it needed was a battery.

                        I just bought some Mercedes 450SEL injectors off ebay that look to be in shitty shape, but they were inexpensive. I want to get those cleaned/flow tested by Jason. I don't have the money to get my current injectors cleaned & tested. What's a good solution for this? I've run injector cleaner through my gas before but it didn't really do anything for my problem.

                        Other than having them serviced by someone else, how could i clean them?

                        Comment


                        • #13
                          Back your timing out a few degree's, and or double check to make sure your timing is 100% correct.

                          I had that sound rarely @ full boost after about 5 seconds in 5th gear. Which I beleive was mild detonation. It should not be doing it though on stock boost, if you have the car tuned correctly.

                          If you can back the timing out a few degrees to at least test. If it gets rid of it great. You will lose a bit for HP from the timing loss.

                          Hmm did I mention play with the timing?
                          84' 300ZX Turbo / '86 300ZX NA to Turbo (Retired)

                          Comment


                          • #14
                            I don't have a timing light. When i did the turbo install, me and a neighbor did it. His dad bought us a timing light and we had it set. Since then we're no longer on talking terms becuase he's a complete ass. So, i no longer have access to his tools.

                            Stupid question:

                            Clockwise, or CClockwise retards the timing?

                            I plan on getting a light soon, however i don't like the sound of paying 30-40$ for one. There really isn't much to the basic ones.

                            I need a lot of things at the moment.

                            compression tester
                            fuel pressure tester
                            timing light
                            money

                            If anyone wants to donate any of these 4 items, i'd appreciate it :lol:

                            Comment


                            • #15
                              Haha,

                              Yah money is critical. Well two options. If you have any pawn shops nearby?.. I got my timing light for $10.00. I also got my compression tester for $12.95.

                              Dont quote me on this but turn your dist clockwise to retard the timing a bit. Seriously its so important to having timing on though. Really try out the second hand store, or go and buy these parts. Use them gently, then return it and say you didnt need it afterall.

                              The second is morally wrong, but financially right.. haha. After I had mild detonation, I just backed off a few degree's, and it went away.
                              84' 300ZX Turbo / '86 300ZX NA to Turbo (Retired)

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