KBar

I noticed 2 days ago on the highway when i let off the throttle the motor makes a engine breaking noise( just like a semi engine brake) but it only does it on the highway. I'm baffled I don't even know what would cause this. Any ideas on where to start. Just did a tune up today, still makes engine brake sound

Kiroshu

Exhaust leaks...?

KBar

no exhaust leak.
I've tried to make it happen in the driveway at open throttle than let go of throttle, but nothing nor does it do it driving around town

RylerTust

Do you get a sort or shuffle feeling when it does it? Like its going in and out of engine brake? Is it actually as loud as a semi trucks jake brake? Mine did it at certain RPM's when my tps was bad. Try checking that, if its in spec, try the whole circuit from the computer to the plug, or even just unplug your tps and drive down the highway and see if it fixes it. If you have a carburetor, you may have a vacuum leak, or your dashpot could be out of adjustment not allowing the throttle to fully close allowing the engine to properly lean out when you let off the throttle. Dashpot is for efi and carburetor engines on these trucks. Sorry for the log response, but you didn't specify if you have a carb or efi engine.

RSR

Sounds like dashpot failure: http://personal.utulsa.edu/~nathan-b...93throttle.pdf

KBar

its not as loud as a jake brake but it does the same thing a semi will do when you turn the engine brake. I have efi I'll try unhooking my tps