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Doug, ASE Master Technician
Category: Chevy
Satisfied Customers: 440
Experience:  ASE Master Tech. 32 years experice
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1997 chevy: I have a loud ignition knock on take..warmed..cap..rotor

Customer Question

have a 1997 chevy c3500 with a 350 5.7l engine. I have a loud ignition knock on take off after truck is warmed up. Cant remeber if it was doing it before I changed the plugs or not but I have changed them along with the wires, cap and rotor button. Cannot figure it out. Could it be a bad plug? Could it be a knock sensor? There is no trouble light. Any suggestions?
Submitted: 6 years ago.
Category: Chevy
Expert:  John replied 6 years ago.

Hello & Welcome to JA,


This problem can be a faulty EGR valve,EGR valve inoperativer,or intake stopped up to keep EGR froM operating properly. A scan tool can be used to open & close the EGR to see if it is operating properly.




Exhaust Gas Recirculation Valve Replacement (5.0L, 5.7L)

Important: Do not try to disassemble the linear EGR valve. Service only as a complete assembly.

Object Number: 22072  Size: SH

Important: Carefully note the position of the exhaust gas recirculation (EGR) valve before removal. Do not rotate the EGR valve 180 degrees.

    Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

    For Vehicles equipped with OnStar® (UE1) with Back Up Battery:



    The Back Up Battery is a redundant power supply to allow limited OnStar® functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar®module). Do not disconnect the main vehicle battery or remove the OnStar® fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar® module in any way while the ignition is On or with RAP activated may cause activation of the OnStar® Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.



  1. Disconnect the negative battery cable.
    Object Number: 281993  Size: SH

  2. Remove the EGR valve harness connector.

    Notice: The Linear EGR valve is an electrical component. DO NOT soak in any liquid cleaner or solvent because damage may result.

  3. Remove the EGR valve to flange attaching bolts.
    Object Number: 22078  Size: SH

  4. Remove the linear EGR valve.
  5. Remove the flange gasket.
  6. Clean the linear EGR valve gasket surface.

    Object Number: 22078  Size: SH

  1. Install the new flange gasket
  2. Install the linear EGR valve.
    Object Number: 22075  Size: SH

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  3. Install the valve to flange bolts.


    1. Tighten the bolts the first time to 10 N·m (89 lb in) each.
    2. Tighten the bolts a final time to 25 N·m (18 lb ft) each.

    Object Number: 281993  Size: SH

  4. Install the EGR valve harness connector.
  5. Connect the negative battery cable.
Customer: replied 6 years ago.

Just to clarify. First thing in the morning when the truck is cold, it will not make the noise. Only when I get down the road about 3 or 4 miles it will start. It only does it on the first initial load like taking off from a stop light or something like that. The truck never runs rough or anything, it just sounds like there is a leak in a plug wire. I makes a real loud ticking noise only when taking off and stops when you get going. I am pretty familliar with how everything works, I have built several of these engines but this one is really cutting my butt!!


I am not saying it is not the EGR valve but I just wanted to make sure you were clear on what it was doing. In my experience with EGR valves, the engine will usually run rough but mine is not. Is your answer still the same?? P.S. Will a bad plug cause this? Could I have gotten a bad plug when I bought them? They were autolites by the way.

Expert:  John replied 6 years ago.
Ok, if you are hearing the arcing of spark (which makes a ticking sound ,not an ignition clatter) your problem is most likely a faulty connection or faulty ignition part.
Customer: replied 6 years ago.
Relist: Answer was something that I already know and have already checked. .
Answer was something that I already know and have already checked.
Expert:  John replied 6 years ago.
LOL... I hope you have a good evening. I will opt out so another expert can help you.
Expert:  Doug replied 6 years ago.
Thank you for choosing,I look forward to helping you,Doug Castillo. Are you hearing detonation [engine ping ] , Can you get it to do it every time under heavy acceleration, Doug