i.e a temperature sensitive thermocouple with a specific switching temperature. In this case 32 Deg C. rather than one that variably reduces the enrichment as the engine warms up much of which happens in the ECU itself dependent on signals fed by such thermocouple & other sources. A matter of semantics.

Thermocouples come in all shapes, sizes & functions. The list is a mile long. They are extremely accurate.

The ECU in the modern car takes many inputs from a variety of sources including the transmission. e.g. total fuel cut off at zero throttle input from the pedal hall sensors with fly by wire throttles. (which is most of them today). If you run down a hill with zero throttle input gas is cut off entirely. I could write an entire white paper on the subject.

 

That's one thing that I could not understand about EFI, I very often take my foot of the accelerator pedal and the engine still keeps running at idle, or so it appears.
So I put the clutch in, and indeed it is at idle _ maybe it's different for a standard ?
So how does the engine still stay running with zero throttle and the input of fuel is cut off entirely when the clutch is in ?
It's my 99 Mazda B3000 truck.

 

It depends on the vehicle & what mode it's in. But they will always return to idle at minimum. A Merc, as an example, will shut off gas completely while the vehicle is moving/coasting downhill but when it detects speed drop below 5Km/h it will bring in the idle circuit & activate the Park Distance Control if you have it activated in the convenience menu. The minute you touch the throttle it takes over of course.

No engine will be allowed to stall. But they will do everything to save gas. Merc & BMW have had it for well over 20 years.

I'm of course talking Automatics. Manuals will return to idle should you de-clutch. Should you not de-clutch they will cut off gas completely until low speed is detected where they will bring in the idle circuit.

Sorry I did not explain adequately and I'm talking relatively modern vehicles.

We are now ignoring the latest vehicles where the engine stops running & restarts the minute you accelerate. Heavy duty starter motors required. You can imagine the number of stops and starts crawling in traffic. Stop start cars are not for me. It's amazingly seamless but the number of restarts would drive me mad. Fortunately manufacturers like Toyota allow you to defeat it.

I'm not a candidate for stop/start cars.

 

The fuel is cut when your are coasting with the throttle closed and there is the vehicles momentum carrying it forward. I'm not sure if it's cut entirely to zero, or just reduced substantially. I expect it's very dynamic depending on the exact circumstances that instant - speed, load, AC demand etc.

I have done EFI on my S Type and I have not cut fuel off under coast. It basically goes to minimum idle fuel.

 

Mercedes & BMW go to zero. And many other vehicles. Vehicles that use CAN networks etc. with multiway comms like Merc even cut alternator & A/C as appropriate dependent on demand.

At WOT they also cut the Alternator & A/C compressor etc. A Mercs A/C remains cold for a hell of a long time with the Swash Plate compressor not running. This maximises performance. No draw/load when not needed. Sniffer fan in the overhead console reads the interior temperature of the car in various directions.

If transmission becomes too hot they change down automatically to increase pump revs & increase fluid flow through the cooler. The joys of modern technology ~ and seamless. With 7, 8, & 9 speed transmissions you are not even aware of it. Not even audibly.

Having the Alternator, as an example, talking to the ECU & vice versa is great.

Having multiway comms cuts down on wiring hugely. e.g. Having the network feed the front or rear SAM (signal acquisition module) tell the rear or front lighting what to do is magic ~ flash L or R, brake, reverse, parking, headlight, heated headlight washer, Xenon or LED dip, heated mirrors, heated seats etc. etc. No more point to point wiring.

My car even reads the position of the sun & blows colder on that side of the car.

The modern Automobile has come a very long way. All this saves fuel & reduces emissions.


Sun Sensor Dome

 

Over run fuel cut off goes back at least to Bosch D-Jetronic in the 1960s. It often didn't work as nicely as it might as it was a simple on-off at somewhere between one and two thousand rev/min. In a car without any sort of fluid coupling in the drive, there could be quite severe severe transmission shunt. Of course those systems were fairly primitive. The ECUs were basically a box of analogue devices that conspired to produce approximately correct characteristics. In many ways, they weren't as good as a carburettor. And it would probably be possible to arrange as good an overrun cut off by mechanical means on a carb.

 

Yup ~ correct. The D-Jetronic was a crude device. Things have improved a long way since then with seamless operation. For well over 20 or 30 years or longer now it's been absolutely perfect & seamless.

 

Logically it can't be cut to zero, if it was, the engine would stall and there would be no power brakes, I agree that the system would have to be dynamic, but a zero fuel situation can't happen if the given vehicle doesn't have the auto start feature.
Even then it makes no sense, suppose a driver is coasting down a long mountain road, eg the Coquihalla here in B.C, one would soon run out of vacuum from the tank.

Maybe in a standard one is expected to leave it in gear (over-drive) and that keeps the engine turning over, but then you would coasting down hill against the compression of the engine.
With the clutch in, it returns to idle, there is no zero fuel mode, at least on my truck.

 

Jeff: Your truck has a Ford EEC V ECU and with some digging I came across this:

EEC-V turns the fuel injectors OFF any time the following conditions are all met:

ECT shows temp. over 140 degrees F..
TPS shows closed throttle.
VSS shows vehicle is moving.
RPM is over 1500.

For a manual I'm assuming that the clutch wold have to be engaged, and not coasting in neutral. Although once the revs fall below 1500 the fuel would come back on.

 

Jeff ~ Wrong. It can and is cut completely. The engine does not cease to rotate. It rotates with zero fuel input. Hence you have brakes etc. I know the Mercedes systems like the back of my hand. I am the reason that MBWorld is permitted to use the WIS & EPC unedited. No Glyn Ruck. No access to the Mercedes Star computer and all it's data. Mercedes is more than satisfied that I will never corrupt their data in any fashion and present as they do & in full. That is the relationship I have with them.

The fuel is cut completely ~ don't argue ~ learn. Yes you are coasting against the compression of your engine.

All manufacturers operate at different parameters ~ Yes.

BTW TPS = Throttle Position Sensor.

See JB's example for one of your vehicles above.

JB you are correct the clutch would have to be engaged as I explained many posts back. If you disengage the clutch & coast the engine will return to idle & use fuel.

 

I'm pretty sure that almost every car built in the last 30 years with a torque converter and any sort of electronic fuel injection will have over run fuel cut off. Some manual cars won't have it because of drive line shunt in less sophisticated engine management systems. It's so easy to arrange and saves fuel.

 

Yes ~ Datsun's GO & the like from India lack the sophistication to have a proper system.