460 with engine brakes
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460 with engine brakes
I have a 1993 f250 with a 460 and 5 speed manual. I purchased it about a year ago and have noticed that any time I am off the gas and the RPMs get to 2500 it feels like there is an increase in compression like the engine brakes on my rigs. As soon as I get below 2500 I can feel and hear the change in the engine compression. It holds back a 28' trisport trailer quite well on a 8% grade in 2nd gear, about 30 mph, if I lightly put my foot on the clutch I can make it kick on and off.
Is there a computer chip that has been installed or is this normal on the 460? This is the first big block I have owned.
Is there a computer chip that has been installed or is this normal on the 460? This is the first big block I have owned.
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From: Rhode Island
That's what you get when you have 7.5 liters of displacement at a high speed trying to suck against a closed throttle plate with no fuel being injected. These engine's computers are programed with Deceleration Fuel Shut Off. If the throttle is at 0%, and the engine RPM is above a certain point long enough, the computer will completely turn the injectors off.
The factory DFSO timeout is pretty long and you usually never reach it with an automatic. As you've found out though, using the engine to hold the truck back on a big hill with a manual long enough will trigger it.
The injectors will turn back on once the revs drop below 1400 RPM, the the throttle increases above 0%, if the transmission is put into neutral, or if the clutch is pushed in.
The factory DFSO timeout is pretty long and you usually never reach it with an automatic. As you've found out though, using the engine to hold the truck back on a big hill with a manual long enough will trigger it.
The injectors will turn back on once the revs drop below 1400 RPM, the the throttle increases above 0%, if the transmission is put into neutral, or if the clutch is pushed in.
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I didn't know these trucks had DFSO. In my Focus (5 speed manual), I can feel it easily, and it only takes a few seconds to kick in. Any idea what the time-out for DFSO to cut in is on the 460? Any idea on what the minimum RPM for operation is?
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From: Rhode Island
As far as I know every EEC-IV vehicle has it programed, even the automatics.
The minimum RPM is usually around 1400-1600 RPM, and I believe the delay is about 3-4 seconds. Possibly longer. There might also be a minimum speed, but I don't quite remember from when I was tuning my buddy's truck.
Oddly enough, Ford implemented it to prevent popping out the exhaust during long engine braking runs, not to save fuel.
The minimum RPM is usually around 1400-1600 RPM, and I believe the delay is about 3-4 seconds. Possibly longer. There might also be a minimum speed, but I don't quite remember from when I was tuning my buddy's truck.
Oddly enough, Ford implemented it to prevent popping out the exhaust during long engine braking runs, not to save fuel.
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1400-1600 is too high to be useful for fuel economy reasons (at least in the automatic). My Focus's DFSO re-enables fuel around 1100-1200 RPM which is easy to utilize as fuel economy boost instead of braking.
Has anybody with programming capabilities on the ECU ever tried tuning the DFSO for fuel economy purposes?
Has anybody with programming capabilities on the ECU ever tried tuning the DFSO for fuel economy purposes?
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From: Rhode Island
We did in my buddy's 460 E4OD. Delay is less than 1 second, and it will stay engaged down to around 1000 RPM if I remember correctly. We did it mainly because he's got a straight pipe with no muffler or cat, and the after-firing out the exhaust while slowing down was insane.
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Lead Driver
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From: Rhode Island
It's pretty much locked up all the time. It really doesn't save any fuel. It only turns the injectors off when coasting, and when the injectors are still on with 0% throttle they're injecting hardly any fuel anyways.
I believe vehicles with DFSO designed in mind for fuel economy gains only see about 0.5-1% savings in fuel - and that's on a vehicle that already gets far better fuel economy.
I believe vehicles with DFSO designed in mind for fuel economy gains only see about 0.5-1% savings in fuel - and that's on a vehicle that already gets far better fuel economy.
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