• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

thumping sound coming from air intake

At low speed it might sound funny. I thought mine had more resistance to "cam over" the hard spot. Not excess but it took a little effort. You look like it didn't take much.

Did you test it with a vacuum gage? It should pull 20 or 26 in"Hg iirc at the pump itself and hold steady. The vacuum solenoid will vary vacuum to the turbo actuator from 10? to 15? in" Hg depending on fuel rate and rpm. IIRC it drops near 1900 rpm and light fuel rate. Then will recover if you give it more fuel or return to idle.
 
Ive had my MBN cat single turbo for 17yrs. Had this issue more than once with the thumping at the air cleaner assembly. Its actually very simple to diagnose. Use a stethoscope you can get at Harbor Freight fairly cheap. Listen to each exhaust port at the manifold. Listen for the thumping and align it with the culprit cylinder. Its either a bad injector or a bad intake rocker on that cylinder. Over the years Ive had to replace an injector on one cylinder and an intake rocker on another. When inspecting the intake rocker, check the button. The button is held on by an oring and pivots on a stud that wears out giving the intake a huge amount of valve lash which allows you to hear the thumping. If your out on the highway and need to get home, just take the valve lash out of the culprit rocker and it should smooth out but vibrate slightly. it will run and should get you home. Over time, the injectors can mess up too. The oring on the lower side of the injector hardens from the heat and breaks apart allowing more fuel into the cylinder than usual. Check your return check valve on the secondary filter housing for small pieces of oring..
 
You must log in or register to reply here.
Back
Top