6SPM: Engine braking stops at low RPM, stall prevention?

I've been doing this experiment in my GT and I'm curious if anyone knows the explanation for what's happening:
- turn on your air/fuel ratio gauge
- maintain speed in 3rd gear around 3,500 RPM
- take foot off the accelerator pedal and let the engine brake
- air/fuel ratio maxes out because no fuel being consumed (ecowarrior mode on)
- as the revs drop to around 1500 RPM:
- the air/fuel ratio goes back to normal
- car feels like it is now coasting and no longer braking

My previous 2 cars had manual transmissions and were both happy to engine brake to the point of stalling the engine. Is the mustang electronically applying the throttle to avoid stalling the engine?

This is a bit weird to get used to, especially when I am planning to come to a stop at a red light and predicting that I only need, say, 3 more car lengths before clutching in and using the brake pedal - but suddenly the car starts coasting and I have to clutch in and brake early.

Pretty common. Even on auto, it would do that to allow normal coasting.
Engine braking on big engines are much higher than small engine so it would feel too much if not compensated.
If you are slowing down for a red light, I would just pop in neutral.

jasonstang said:

Engine braking on big engines are much higher than small engine so it would feel too much if not compensated.
If you are slowing down for a red light, I would just pop in neutral.

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Oh good point - my old cars were 4 cylinders. This is my first V8. I used to like to wait till just before stalling before putting it in neutral - maybe that was just a bad habit that the mustang is forcing me to give up Although my old clutch and engine had 145,000 km (90,000 miles) without any problems.

jank said:

Oh good point - my old cars were 4 cylinders. This is my first V8. I used to like to wait till just before stalling before putting it in neutral - maybe that was just a bad habit that the mustang is forcing me to give up Although my old clutch and engine had 145,000 km (90,000 miles) without any problems.

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Shifting it in neutral almost have no wear on the clutch. Actually the only time you wear clutch is start moving in 1st gear. Once you are moving changing gear won't wear clutch.

Try S and paddle shift it down to 2nd. D and S unmolested might stay 3rd until something like 1 mph on coast down. This is so driving in slow bumper to bumper traffic can be done in 3rd which works great frankly.

sigintel said:

Try S and paddle shift it down to 2nd. D and S unmolested might stay 3rd until something like 1 mph on coast down. This is so driving in slow bumper to bumper traffic can be done in 3rd which works great frankly.

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(He's got a clutch in his car . . . and no gears called S or D)


jank - what you're feeling sounds like the fuel cut on decel (mpg improver of small value) ending, where your older fours simply decelerated on closed throttle with some fueling. When all 5 liters and 8 cylinders kick back on, they'll provide quite a bit more forward thrust than the fours did.


Norm

I am a Auto Tech and I can tell you what is happening.When you let off the gas when the engine is warm,the fuel injectors turn off for better mileage and to give the cat a rest.when the engine slows to 1200-1300 rpms the injectors turn back on so the engine doesn't stall.All newer cars do this but you can feel it better with a manual transmission.

888mustang said:

I am a Auto Tech and I can tell you what is happening.When you let off the gas when the engine is warm,the fuel injectors turn off for better mileage and to give the cat a rest.when the engine slows to 1200-1300 rpms the injectors turn back on so the engine doesn't stall.All newer cars do this but you can feel it better with a manual transmission.

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Thanks Bill. It's satisfying to know what my car is doing for me and it's better than shuddering and stalling. It's good to know things are still improving for the ICE.