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Old 08-14-2009, 04:42 AM   #61
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You 1993 Buick may not do DFCO (Deceleration Fuel Cut Off) well, or at all. If it doesn't, then engine braking costs you fuel. With those short descents, if your brakes are good you might want to use them instead.

An alternative would be a manual fuel injector cutoff switch. It's been discussed a few times and it should be easy to implement. You just install a switch that interrupts the fuel injectors' common wire. If your car has TBI then it wouldn't even matter if you find the injector's positive or negative wire.

Can anyone comment on the idea's feasability? Would it be necessary to worry about the spark plugs continuing to fire without fuel or anything like that?
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Old 08-14-2009, 08:37 AM   #62
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Depends if the motor has a tendency to puddle fuel or not in the intakes, or if it has a large amount of blowby and oil burning... either of those will mean it will possibly lean detonate if you cut fuel.


edit: in the case of high oil consumption, it could possibly lean detonate on compression.... if you've got a car that doesn't cut immediately when you turn the key off, then suspect it won't like it... even just a few fires like pup-pup-poom.
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Old 08-14-2009, 05:06 PM   #63
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The first vehicle I tried engine braking with was a Forward Control Land Rover on a very long down grade, maybe thirty minutes driving, down to the bridge on the Blue Nile. Simply shut off the ignition and the electric fuel pump stopped, so I wasn't pumping raw fuel into the cylinders. I've done this with a few other vehicles too, with similar results.
On the theory that a wide open throttle let in more air to be compressed, I held the pedal on the floor. Also, foot off the throttle. There was a difference in the sound.

Engine braking a gas engine is a bit like masturbating; you feel good but havn't really accomplished anything.

Diesels with an engine brake have a device that blocks the exhaust pipe. That is where the compression comes from that slows you down.
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Old 08-14-2009, 10:05 PM   #64
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Quote:
Originally Posted by RoadWarrior View Post
Depends if the motor has a tendency to puddle fuel or not in the intakes, or if it has a large amount of blowby and oil burning... either of those will mean it will possibly lean detonate if you cut fuel.


edit: in the case of high oil consumption, it could possibly lean detonate on compression.... if you've got a car that doesn't cut immediately when you turn the key off, then suspect it won't like it... even just a few fires like pup-pup-poom.
The car doesn't burn any oil at all. It only has 116,000 miles on it.

No clue about DFCO, but I know when I coast down a hill in gear, I keep a relatively constant speed until I get past 35mph?... then it starts going down the hill as if I'm in neutral and I start gaining speed, and you can hear/feel the shift (if you listen for it).

...as for braking the entire way down the hill... I dunno. I've needed a brake job every single year due to these hills. The excess heat warps my rotors. Last summer I spent the extra $$ for vented and slotted rotors, and haven't had any issues since, and still have a lot of my brake pads left. ....these are hills, where to get up them in the winter, you have to get as much momentum as possible at the bottom, then essentially floor the car... speedometer usually says 70mph, where you're only moving about 15mph. If you start to lose momentum, you're done for and have to dangerously back down the hill (well, not back down, but slide down). Of course, this is without traction control. With traction control, it's near impossible to get up the hills (sounds odd, but 'tis true). That's why I store the car for the winter and drive my 4x4 gas-hog Explorer (10mpg city, 16 hwy - something's wrong with it)
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