Quote:
Originally Posted by tinkerr
Diesel motors don't provide alot of back pressure for engine braking.
|
Granted, but they do have some. On a stick shifter, if you downshift you'll notice some engine braking. On a 4R100 automagic with a properly functioning coast brake and a locked torque converter, you have some. But if you touch the brakes that unlocks the torque converter and then you're almost free-wheeling.
Quote:
|
Can't speak to the whys, somebody smarter than me will have to chime in.
|
I've never won any smart contests, but I've read why.
Most gas engines have a throttle, and the throttle plate acts as an exhaust brake when you let off the go pedal. But diesels don't have a throttle plate, so if you want similar engine braking you have to add a butterfly in the exhaust system in place of a throttle plate. The 7.3L PSD already has a small butterfly in the exhaust system called the exhaust back pressure valve (EBPV) that the cheap exhaust brakes use as their butterfly. If you keep the RPM up over about 2,000, keep the torque converter locked, and have a good tranny with a properly functioning coast clutch then you can have a decent exhaust brake for comin' down the mountain by simply closing the EBPV.
The EBPV is part of the cold ambient package (CAP), designed into our engines only to provide faster warm-up of a cold engine. International and Ford never intended us to use the EBPV as an exhaust brake, but it's a simple electronic wiring project to get'er done.
One caveat: Our PSDs have hydraulic valve lifters, and Ford says an exhaust brake can damage the engine. So back when our engines were under warranty, Ford would void the engine warranty on any PSD that had an exhaust brake. However, for the last 10 years and hundreds of manhours spent reading TheDieselStop forums, I have not heard of even one case of an exhaust brake damaging a PSD.
