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  • OT- Car engine question

    94 Jeep with a 4.0L High Output engine.

    When it first starts up, there is knocking in the front. It knocks faster with higher revs.

    It goes away when then the engine is warmed up. About 100 degrees on my thermostat.

    Any clue as to how big a problem I have?

  • #2
    I think you might get some good guesses. I would take it to a shop.

    Pinning down engine noises is best done live and in person.
    Gene

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    • #3
      Originally posted by cuemaker
      94 Jeep with a 4.0L High Output engine.

      When it first starts up, there is knocking in the front. It knocks faster with higher revs.

      It goes away when then the engine is warmed up. About 100 degrees on my thermostat.

      Any clue as to how big a problem I have?
      You don't have your radio turned up loud enough...

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      • #4
        Originally posted by Wayne02
        You don't have your radio turned up loud enough...

        LOL, I am working on that one!!! So far I only have 1 speaker working. Cant get any reception. I am going to have to take the dash off I bet.

        Comment


        • #5
          I bought a brand new 93 Grand Cherokee with the 4.0. After about six months, the engine sounded like a diesel. I took it to the dealer on four occasions and they did nothing. The valves clattered and pistons skirts slapped the walls until it warmed up.

          Also during this time, I was stranded in Jackson, TN once and at Salt Fork State Park in Ohio with a boat. Both times, the coil went belly up. Driving home from work one day, I took the usual exit off I77. When I touched the brake, the Jeep nearly went flying off into the ditch. I was able to limp it to dealer and found out a bolt broke in the front end. About three months after all this, I got recall notices for the coil and front end.

          That was about a month before I got rid of it and never looked back. Needless to say, I don't have anything good to say about Chrysler products. The noise you hear when it's cold is probably piston skirt slap and is considered normal for that engine. Take it to a dealer and they'll want to replace the pistons--About a $3000 job. When you get it back, the pistons will slap when cold but it won't be quite as loud.

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          • #6
            'Long as we are guessing.....

            It must be something that is moving, and probably something that reciprocates..... i.e. associated with crankshaft, rods, pistons, cam, or valve train.

            Sure, could be piston slap. That's pretty usual and even some new vehicles do it (that kinda sucks).

            Could be a lube issue, if the oil pump isn't getting oil to all the right places fast enough, or not until the engine warms up for some reason. Big ends, piston pin, etc.

            Could be lifters, if it happens to have hydraulic ones, although there might be other things happen (or not happen) too.

            Could be something glued with old oil goo until it warms up.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              "Could be lifters, if it happens to have hydraulic ones, although there might be other things happen (or not happen) too."


              I agree, it may be lifters.
              "The men the American people admire most extravagantly are the greatest liars; the men they detest most violently are those who try to tell them the truth." H. L. Mencken

              "All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."

              "When fear rules, reason and logic are ruled out."

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              • #8
                What weight oil are you running and what is the typical ambient temp you drive in?

                Comment


                • #9
                  Just Everybody Elses Parts

                  Might it be something like a fan clutch or smog pump going south?The quiting after warmup makes me think something other than engine knocks,unless it is really gooed up.
                  I just need one more tool,just one!

                  Comment


                  • #10
                    Simple test. If you shut it off for half an hour and then start does it make the noise? If not then it's probably the lifters. The oil drains out of them over night but not is a short time.
                    Free software for calculating bolt circles and similar: Click Here

                    Comment


                    • #11
                      never looked back

                      My dad is/was a big dodge fan.
                      In 1982 the local dodge dealer took in a Datson/nissan pick up on a trade.
                      Dad bought it,mostly as a joke.
                      The joke was on him.
                      It ran great.It started every morning regards of how much ice and snow there was.
                      Long story short, he has never driver anything but Japanese Trucks since.
                      e
                      ps my 91' tercel still gets 45+ mpg and runs great!
                      please visit my webpage:
                      http://motorworks88.webs.com/

                      Comment


                      • #12
                        I think Evan has it right. Lifters (hydraulic) probably bleeding down overnight?
                        "The men the American people admire most extravagantly are the greatest liars; the men they detest most violently are those who try to tell them the truth." H. L. Mencken

                        "All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."

                        "When fear rules, reason and logic are ruled out."

                        Comment


                        • #13
                          mystery noise

                          yes its something that rotates,i think i would disconnect all the belts. which would confirm or rule out, the alternator,smog pump,power steering pump,air commpresser! if its something inside the motor, warm it up and trade in before it gets worse! good luck.
                          rick

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                          • #14
                            I parked the car at 10 am after driving it 23 minutes

                            Started it again at 4:10 pm, no knocking sound.

                            Temp this morning was in the high 40's, maybe low 50's? I dont know

                            Comment


                            • #15
                              I'll go with lifters as well. Check your oil level, if it's low you'll almost always get lifter noise. One good way to isolate the problem is to time the sound say for 10-30 seconds. If it's a piston or rod it will happen once every revolution on an unloaded engine, if it's in the valve trail it will happen once every two revolutions since the cam rotates at half crank speed. Barring an mechanics stethoscope I've been known to use a broom handle lightly against my ear and touch the engine in various places with the other end, the problem lies wherever the sound is loudest 99% of the time. Forged pistons always slap a bit on startup but it goes away quickly as the heat of combustion expands the pistons. Hypereutechic (sp?) or cast aluminum expand less and therefore have less cold clearance, the slap isn't audible to most unless they pistons are badly worn.

                              Next oil change warm the vehicle fully then pour in about a quart of kerosene into the oil and let it idle in park (DO NOT REV OR LOAD THE ENGINE DURING THIS TIME) after about 10-15 minutes remove the drain plug and replace the filter, let the oil drain completely, I like to let it drip for an hour or so. Then replace with a quality oil of the proper grade and viscosity for the climate per your owners manual. A couple of oil changes with kerosene will flush a lot of gunk out of your engine and often free a sticking lifter. For high mileage or heavily used engines I always run one viscosity range higher than originally recommended conditional upon allowing the engine to idle for at least 2 minutes before driving. On my 911 with it's 13 quart oil system I run 20W50 due to aggressive driving and always I let the oil temp reach 100F minimum before driving and then drive it lightly until it's reached full operating temp. Once at full temp the engine prefers to be revved and I never let it lug down below 3500 rpm which I don't recommend for anything less than a high performance engine.

                              Some might question the kero trick but I bought a beat Toyota 4x4 with the nearly indestructable 22R engine in it with an honest 380,000 miles on the title and odometer, I sold it 90,000 miles and 30 oil changes later with no problems other than routine maintenance and the typical Toyota frame cancer (I think the was more added sheet metal than original frame!) it didn't smoke or leak and more or less than the day I bought it. I also ran a 2.3L 4cyl Capri from 95,000 to 180,000 the same way and it was still running great when I sold it. 2.3L Fords and they're "horseshoe" valve cover gasket are notorious oil leakers and I could always tell the engine was a quart low when I heard the lifter knock at startup. That car was hilarious, the only part of the car with zero rust was the middle half of the under carriage as it always had a fresh coating of oil!
                              Last edited by rsr911; 09-29-2006, 12:55 AM.

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