How To maintain brakes while engine off coasting

[Piwoslaw]

Originally Posted by ecomodded

Piwoslaw i am going to look for the crankshaft position sensor. What does the motor think happened when the switch is opened ? it sounds unconventional but effective. I like it.

Here is the long answer.

The short answer is that a diesel will run as long as you supply fuel, no spark plug is needed, so in order to stop it you have to cut the fuel. You could just kill the injectors, but the newer TDs might now like that, so the ECU has its own stopping procedure. There are a few ways to invoke this safe procedure, for example when the ignition key is turned to OFF, the engine starts to stall, etc. If you cut the signal from the camshaft or crankshaft sensor, then the ECU might(*) not know the engine speed, so it'll go into shutdown mode.

*) Some ECUs calibrate the two sensors at startup, so if one is lost during operation the engine can still turn. In my case unplugging the camshaft position sensor wouldn't allow the engine to start, but wouldn't stop it once it got turning. The crankshaft sensor, on the other hand, is needed both for starting and operation.

[bobo333]

Sounds like a good idea, and should be great in your Beetle.

But just a warning to other who might be keen to try this out, if your car isnt EFI then this is a very bad idea, keying off will cut the ignition but leaving it in gear the engine will still suck in fuel from a carby (or mechanical injectors?) so when you turn the ignition back on you have a lot of unburnt fuel through the car and get get a large explosion, this can destroy intakes or mufflers and makes a frighteningly loud bang.

[ecomodded]

I read your linked thread Piwoslaw.
I take it the check engine light turned off after you switched the crank sensor back on ?

First plan is to pull the crankshaft sensor wire with the car running to see if it will shut down.
If that works then a switch will be wired / placed so a unplanned deactivation will not be likely and it is still easy to reach.
My car is small, everything is in reach so placement should not be much of a challenge..

bobo i think this mod is a must if, like you say ,your car is fuel injected, scary scenario you described, that would certainly wake a person up in the morning!
But kidding aside i think this mod is going to catapult my mpg to new heights.

[Piwoslaw]

I take it you know that a turbo'ed car shouldn't be EOC'ed too often?

Originally Posted by ecomodded

I take it the check engine light turned off after you switched the crank sensor back on ?

Everything goes back to normal, only the ScanGauge sees a P0335 code, which I clear every now and then.

Originally Posted by ecomodded

If that works then a switch will be wired / placed so a unplanned deactivation will not be likely and it is still easy to reach.

A few members have their kill switch on the gear shift knob.
You can also wire a second switch in series, only this one hidden, to use as anti-theft protection.

We're drifting off topic...

[ecomodded]

Glad to hear about the code, its nice to retain the use of the check engine light.
The switch is a important part of engine off coasting, having the car there to coast with is important to.

I will now be looking for a spot that is somewhat hidden yet easy to reach and difficult to switch by accident..

The plot thickens:

As the oil heats and thins.

I did not think about my turbo's lubrication, but i better.
Often if not always i have to climb a hill to coast a hill, heating the oil/motor and spinning the turbo at near max boost in the process , making cooling a very real concern.
I think if i cycle it in and out of gear i can still coast and cool the turbo as well as provide vacuum for braking.
The complexity is growing.

I found my crankshaft speed sensor, after lunch i will disconnect it and double check the engine shuts down, then buy some shrink tube and get started.

[ecomodded]

After inspecting and thinking.. I deduced i am going to cut into the crank speed sensor at the diesel ECM as the wires already run that far so i'll cut and splice in that location,off to the side and away from the engine. I was hesitant to splice into the thin wires running from the crank sensor as the area is very exposed.
I needed to use my car yesterday and again today, so the switch will not be put in until tomorrow, too bad as i will be doing alot of engine On coasting on the 150 mile drive today.

[ecomodded]

The EOC (engine off coasting) begins.

The kill switch is in, it was a piece of cake once i took the plunge and cut the first 2 wires leading to the ECU, from the G28 engine speed sensor.
The G28 is the RPM sensor / engine speed sensor, not the vehicle speed sensor.
If the G28 sensor fails the ecu shuts down the motor. If i flip the switch the ecu see's this as a failure and kills the engine.
I would say this method is the absolutely best way to install a kill switch in a VW tdi that i could have hoped for. A BIG thanks to Piwoslaw for discovering this method and telling me about it !

1st- Mount the switch where you can reach it conveniently.
2nd- Near the ECU cut the tape and unravel about 6 inches.
Give the wires some space to ease the reattachment by exposing 5 inches of wires then cutting in the middle to share the length evenly, as instructed below.

Cut into black wire sheath that contains a yellow wire, white wire and black wire. There is two black sheaths the one with a blue wire inside is the wrong sheath.
Once you found the right black wire sheath to cut, cut it along the top to expose the wires inside, cut the black wire , cut the white wire.

3rd- Wirer from the cut to the switch then the switch to the cut in the wire harness.

Strip the wires a 1/2 inch or so and wire together then apply some solder paste to the wire and solder it fairly quickly so you do not melt the wire sheath.
I clean up the solder paste remnants with alcohol and a rag to insure a clean surface for the tape.

4th
Once all 4 wires (2 out 2 in) are soldered & cleaned you can tape the exposed wires, then tape it all to the wiring loom and finally re-wrap the loom with the original tape you cut to gain access and secure it with fresh tape.

[ksa8907]

Originally Posted by Piwoslaw

Here is the long answer.

The short answer is that a diesel will run as long as you supply fuel, no spark plug is needed, so in order to stop it you have to cut the fuel. You could just kill the injectors, but the newer TDs might now like that, so the ECU has its own stopping procedure. There are a few ways to invoke this safe procedure, for example when the ignition key is turned to OFF, the engine starts to stall, etc. If you cut the signal from the camshaft or crankshaft sensor, then the ECU might(*) not know the engine speed, so it'll go into shutdown mode.

*) Some ECUs calibrate the two sensors at startup, so if one is lost during operation the engine can still turn. In my case unplugging the camshaft position sensor wouldn't allow the engine to start, but wouldn't stop it once it got turning. The crankshaft sensor, on the other hand, is needed both for starting and operation.

what he said, and to elaborate, engine controllers will read the crank sensor for timing up to around 2500rpm then switch to the cam sensor above that, because it runs at half the engine speed.

[UFO]

Once the engine is killed, how do you restart?

And how is your steering? My Beetle's steering gets extremely heavy with the engine off, that's why I will not do EOC, but I am curious.

[ecomodded]

UFO, Once the engine is killed i have to cycle the key then i can switch the switch back to the on position and bump start it, or use the key, i bump it.
The beauty of the rocker type kill switch( on or off) is that you can coast in gear with the engine off with full brakes and power steering.
In neutral I will only have the break reserve vacuum and no power steering, if i need brakes or desire some power steering I put it in gear.
The car does coast surprisingly well in 5th gear, engine off with power steering & brakes.
On the steeper hills i will be in gear engine off maintaining my brakes and steering.
I myself find the powerless power steering manageable but it is indeed heavy, i look at as exercise..