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Engine tapping noise only when accelerating

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here Engine tapping noise only when accelerating

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  • #883816
    Michael KerichMichael Kerich
    Participant

      My car makes a tapping noise only while driving it. I tried to record the noise when driving, but the noise wasn’t audible in the video. I tried running it in idle for a while and pushing on the gas pedal hard, but no matter what I do, if the car is in park or neutral I can’t get it to make the noise. When she is in neutral she roars like a lion, but when I am driving I hear tap tap tap tap. When not pressing on the gas pedal, but moving I don’t hear it. This doesn’t sound like a noise I should be driving around with. Anyone have any idea what might be causing this noise? Or tips on finding out what is making the noise? If you need me to provide any other information I would be happy to do so. My car is listed right below this post (1999 suburban).

    Viewing 15 replies - 1 through 15 (of 22 total)
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    • #883819
      MikeMike
      Participant

        I’m guessing this is your 1999 Chevy K2500 Suburban with the 7.4….

        There are many things it could be and yes, you’re right, it should be fixed without delay.

        Is it running well otherwise?
        It can be something as simple as gas that’s too low octane.
        Going up one or more octane grades would remedy this.

        Is the check engine light on?
        Did you check for any set or pending codes?
        Rattling noise on acceleration can be a sticking EGR valve.
        Also, on some engines the EGR passages also get clogged.
        Not sure if yours is one of them.

        First and foremost, make sure the car has the right amount of oil and , if your car has a gauge, see if the oil pressure is OK.
        Check the vacuum hoses and make sure none are cracked or broken.

        After this , check all the basics.
        An engine that needs a “tune up” can poorly burn the fuel, causing some awful noises as a result -and yes, it can do engine damage .
        Check spark plugs for wear and proper gap.
        If the fuel filter hasn’t been replaced in the last 15K miles or you can’t remember when it was changed, change it.
        Air filter should be clean.
        PCV, which should be an ACDelco one, should be recent.
        If the spark plug wires are old, this would be a good time to put a fresh set of ACDelco OE wires on.
        The cap and rotor should also be replaced if they show signs of wear–pitting on the rotor tip , corrosion of the internal contacts , a worn center carbon contact.
        Make sure there isn’t much play in the distributor shaft.
        Unfortunately, you can’t set the ignition timing yourself, unless you have a GM Tech 2 scan tool or better.
        Rattling noise on acceleration can be a sticking EGR valve.
        Also, on some engines the EGR passages get clogged. Not sure if yours is one of them.

        #883825
        Michael KerichMichael Kerich
        Participant

          I freaking typed up a whole long message to reply to you and when I clicked submit it said I needed to log in again and my whole message was lost. So, here I go again. Thank you for your response. Yes, I am referring to my Suburban. It seems to be running well otherwise. I don’t really notice any performance issues. I am currently running 87 octane. I can try running a higher octane next time, but that might not be a while since I don’t feel comfortable driving it with the noise and it has an almost full 44 gallon tank. Engine check light is not on. I attempted to check for codes but I don’t understand how to work my scan tool. It is a OBDLink LX bluetooth scan tool. As far as I can tell I wasted $50. It definitely isn’t a rattling noise, rattling makes me think of a vibration, this is a tapping. Oil level is fine, I just changed it and it wasn’t low before then. Oil pressure has never been too high. What vacuum hoses are you talking about? I just changed the spark plugs and checked the gap before installing them. According to some service records on the car that I got through carfax the last time the fuel filter was replaced was back in 9/06/2007 when the truck had 105,000 miles on it. Now it has 189,000 miles on it and it is 10/1/2017. Air filter is pretty clean. Not really sure where my PCVs are or how old they are. I can try to check em out. I just put in some new American-made Taylor spark plug wires in it. I haven’t checked the distributor cap or rotor since they are in kind of a hard to get to spot behind my engine.

          #883838
          MikeMike
          Participant

            I hate when that happens.
            What I do is copy the entire message, so I can just paste it if I get logged out between starting to type and finishing.

            Did the noise start within a few days after you filled the tank?
            If so, I’d suspect the gas.

            Modern gas may be relatively clean but 84K is too long to go between fuel filter changes.
            GM recommends changing it every 30K miles.
            The cap and rotor may be worn out by this time, too. They don’t last forever.

            As far as which vacuum hose. I’d check all of them.
            Usually there’s an underhood sticker with a diagram of vacuum hoses and PCV locations.

            This guy has a video on installing the OBDLink LX

            These are the user manuals to tell you how to link the phone and dongle
            http://www.obdlink.com/setup-category/lxbt/

            At least you will know if any codes are pending (or set) and can see if anything is amiss with sensors timing, etc.

            #883844
            Michael KerichMichael Kerich
            Participant

              No, the noise has been happening for a long time. It isn’t a new noise.

              #883846
              MikeMike
              Participant

                Then the recent gas is off the hook.

                As far as inconveniently placed parts, like the dist. cap, that increases the chances that it has never been changed.

                Let us know how things turn out.

                #883847
                Michael KerichMichael Kerich
                Participant

                  I appreciate you taking the time to look up a video on my scan tool, but I have already looked, there isn’t any videos out there that go into detail how to use the app. I got far enough to pairing the scan tool with my phone and getting the app to recognize the scan tool. I saw it said OK no codes, but pretty much everything else in the scan tool I am clueless on. I will start looking into the things we talked about tomorrow. I don’t think this is going to be a problem that is going to be solved anytime soon. I have been fairly busy lately. I will definitely keep you updated. You gave me quite a few things to look into.

                  #883848
                  Michael KerichMichael Kerich
                  Participant

                    Side question: while my main topic question is on hold, my fuel lines are a little rusty. A mechanic suggested I replace them. Do they really need to be replaced? They don’t really look that bad to me. I can take pictures of them if you need to see them. I found a picture of some fuel lines that look pretty similar to mine on the internet and attached it (but I think mine look a little bit better).

                    #883851
                    MikeMike
                    Participant

                      They’re probably ok for a while but it’s impossible to say with any certainty.
                      The line might be fine in most places but behind a clamp or somewhere less visible, they could be on the verge of bursting.

                      #883854
                      MikeMike
                      Participant

                        I should add that the video I linked is only partly about installing the OBDLink.
                        Much of it shows the guy actually using the included app.

                        #883875
                        Michael KerichMichael Kerich
                        Participant

                          Yes I watched the whole thing.

                          #884927
                          Michael KerichMichael Kerich
                          Participant

                            I think I checked all the vacuum hoses and I believe they are all in good condition. I replaced the fuel filter, distributor cap, and distributor rotor since we last communicated. So, things I have left to try checking on your to-do list is…
                            1) Check the Egr valves and passages
                            2) Check the PCV
                            3) Check the ignition timing
                            4) Double check for codes
                            5) Double check for bad vacuum hoses

                            The issue is still present as of writing this post. Nothing has changed. I plan to try to do some of the things on the to-do list this weekend. The noise is only present when driving. I wish it made the noise while I was in neutral or park, then I could poke my long prybar in places to try to locate the source of the sound. It just sounds like it is coming from the engine, but I can’t tell anything more specific from inside the car.

                            #884976
                            MikeMike
                            Participant

                              I looked up your EGR valve and it’s fully electronically controlled.
                              It should set a low flow code if the passages get blocked or it sticks closed due to deposits/wear .

                              The pcv valve is plugged into the driver’s side valve cover/rocker arm cover.
                              Use an ACDelco pcv to avoid issues.
                              The timing cannot be changed in the old way with a timing light.
                              You may have to rely on a shop, as not all scanners can read the necessary data.
                              You’re actually adjusting cam retard offset and it must be done at 1000 rpm
                              Details here on the proper procedure and on the software needed (under comments)

                              Other things to try include decarbonizing the engine

                              #884984
                              Michael KerichMichael Kerich
                              Participant

                                I just ordered two PCV valves. They were only $9 (including shipping) so I was like might as well just replace them. I am cleaning out my EGR passages and checking my EGR valve after dinner tonight.

                                #885008
                                Michael KerichMichael Kerich
                                Participant

                                  Is this an accurate way to check the EGR valve?

                                  #885021
                                  Michael KerichMichael Kerich
                                  Participant

                                    I tried to clean out my egr passages with a nylon fiber spout brush, but some of the needles started to fall off so I stopped. I wish they made them with metal bristles. The passages didn’t looked clogged at the egr valve. When I try to run my suburban with the egr off the intake manifold, but still connected to the wire it runs for about 10 seconds and then conks out. In that 10 seconds or so the pintle doesn’t move. I am thinking maybe this video isn’t correct. Maybe the pintle only moves when the egr valve is bolted to the intake manifold? Idk. If it is suppose to move when the egr valve isn’t bolted to the intake manifold then I guess it isn’t necessarily the egr valve being the problem, it could the wiring or the PCM. Could someone with a good running GM vehicle try this test and see how their vehicle performs?

                                  Viewing 15 replies - 1 through 15 (of 22 total)
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