New and unpleasant sound from my 170

[claptonfan]

The 170 in my car developed a strange sound tonight. I was driving alot more than is normal due to some peculiar circumstances, and as I was nearing home my car began to make a loud, almost "farty" tapping sound. It only makes the sound when i press the accelerator, and only while its in gear (C4). There doesn't seem to be any loss of power, and I don't smell anything out of the ordinary either. Any ideas on what might be causing this would be greatly appreciated. Thanks.

 

[Jamie Miles]

Sounds like an exaust leak to me, but it's hard to say without actually hearing it.

 

[claptonfan]

That was my first thought, but I've had problems with exhaust leaks before and it wasn't restricted to those conditions and it doesn't really sound the same. I'll check once its light out, though.

 

[rickwrench]

I had an econoline FC truck that had a sticky lifter that was not bleeding off and not closing the exhaust valve. "Farty" describes the sound it made well. Kind of like- "ffart-ffart-ffart-ffart-ffart". I backed off the lash and then it clattered like hell until it pumped full, I drove it that way for two years and then sold it (I was poor then, and, ever worked on an econoline's engine?).
Pull the valve cover off, if it's not an exhaust leak, and check the springs and see if any of the pushrods are binding. It could be a clogged up lifter floating the exhaust valve off it's seat.
Rick(wrench)