[nj1266]

Originally Posted by RobertSmalls

I disagree.

Shutting off the engine isn't dangerous if done correctly. If you wait until the engine is hot, and use a fuel cut switch, there's very little risk of damage to the engine or other components. The loss of power brakes is very predictable, and if you don't press and release the brakes much, you retain assist. As for power steering, well, you don't need that anyway, but some cars have electric power steering or even manual steering.

There are so many things that can go wrong when you shut off the engine. Among them:

1. Your steering can lock if you inadvertantely turn the key all the way back to the complete off position. That is damned danegerous if you ask me. The last thing that I want is for my steering wheel to go into the lock position while gliding down from 65-70 mph. It just scares the hell out of me. Sorry, I will take the trade-off of less fuel economy for safety.

2. The brakes lose assist and ABS. You might get away with it while gliding, but what if you need to stop in an emergency while gliding. It can happen if you are a dedicted hypermiler. You have no idea what circumstances can come up when driving. Pretty dammned dangerous if you ask me.

3. There is a lot of wear and tear on your starter, battery, solenoids, etc...Is the wear and tear on these components worth the slight extra mpg that you are going to get? You will pay for the extra mpg, by replacing these components earlier than you would have with my pulse and glide method.

The technique you describe is "pulse-and-DFCO", which underperforms pulse-and-glide. Spinning the engine during DFCO takes energy, and you slow down much faster than you would in neutral. Because P&G allows much longer glides, it's more practical so you can use it more often, and your car uses less energy per mile for more mpg.

I think you can have three versions of pulse and glide:

1. Pulse and glide while shutting off the engine. This gets you the most fuel saving, but it is dangerous and it puts huge wear and tear on your starter/solenoid components. You pay for the fuel savings, by changing parts earleir than you would.

2. Pulse and glide in neutral. That gets you fuel savings, but keeps the AFR at stoich while in gliding. So your still wasting fuel. It also puts more stress on the shifting linkage, clutch, tranny. They are not going to fail, but there performance gets degraded over time.

3. Pulse and DFCO, as you put it. This shuts down your injectors and makes the AFR 20.xx:1 which is leaner than stoich and should get you better gas mileage than method 2. The car does slow down faster than method 2, but you have less wear and tear on the tranny, linkage and clutch. So from the cost prespective, it method 2 and 3 might end up the same.

IMO, method three is the safest, does not put as much strain on the starter/solenoid, tranny, clutch, shift linkeage as the other two methods and that saves money as well. It might not get you the best gas mileage, but it has its advantages over the other two.

BTW, your AFR should approach infinity, as you've got clean atmospheric air being pumped through the engine, and almost no combustion products mixed with it.

The gauge is limited to 20.xx. I know it is infinity.