wierd thump,thump,thump at idle....

[tobaccogrower]

04. 5 600

every once in a while, when i come to a stop after driving(like at a stop light) there is a wierd thud noise and vibration. it happens about 2 seconds apart and 4 or 5 times. i may feel it once a week. it definatly is spirratic. i can feel it more then i can hear it. i cant pinpoint where it's coming from though. any ideas? thanks... james

 

[rbattelle]

Maybe something binding up in the 4wd system? Just a guess...

 

[tobaccogrower]

the truck does it in 2 wheel drive. it almost feels like it's in the motor.

 

[rbattelle]

But remember that the entire front drivetrain is always rotating.

 

[R.M.THOMPSON]

Possibly an injector , although if it was consistant on every firing or misfiring as it were , one should feel and hear a pulse about every 700rpm / 2 = 350 injection events per minute or 5. 8 per sec. and finally . 97 times per sec. per cyl. My understanding is that if all other cylinders are consistant(even) that the odd event will stand out to the extent of the exhaust note becoming pronounced enough to increase the effect(audible) and further mask the remaining cylinders normalcy. Hope this helps with the fault tracing. Last point,,, A infrared thermometer may help if this becomes consistant ,but pay little mind to the actual temperature and most to the differance from the other cylinders. Don't tell a service writer that temp is a form of diagnosing either ! It starts all kinds of disclaiming behaviors to manifest themselves... ... ...

 

[Timinator]

What about fuel sloshing in the tank?

 

[rbattelle]

What about fuel sloshing in the tank?

Usually the simplest answer is correct.