Bump start

HOOPER65 · Nov 17, 2017

AndyBees said:
As previously stated, unplugging the CTS results in the ECU having a reading that defaults to minus 40c. The use of Vag Com Diagnostic System (VCDS) verifies this ....... thus no Theory. This will cause the GPs to glow as well as an increase fueling.

Bump/roll/kick starting is just a means to rotate the engine fast enough (at least at the rate of 250 RPMs) to create compression sufficient enough to ignite the fuel upon injection. Obviously, the ignition needs to be in the ON position for at least three reasons 1). so you can guide the vehicle, 2). so the fuel shut-off/on solenoid is ON. and, 3). so the GPs will glow if necessary (with the CTS unplugged, they will glow).

Thanks - a useful & educational conversation.
Under different circumstances in a less congested parking lot
or with a hill available, I'm sure the car would have stared.
Where I was stuck, I think flashing the plugs
would have helped obtain combustion.
All good info should I run into this again, or can assist others.

KLXD · Nov 17, 2017

I wonder if the 250 RPM threshold applies since it isn't in "start mode".

The way I do it, lifting the clutch and immediately depressing it, I doubt the engine turns more than one revolution.

AndyBees · Nov 18, 2017

KLXD, I use to be skeptical of the 250 RPM thingy, because in my mind I tried to visualize the engine literally spinning 250 times in a minute. I too have had the ALH engine in my Van to start when I thought the battery given up the ghost.

I believe we have to think of it in terms of "at the rate of" 250 RPMs. Thus, if the Plate on the crankshaft with the "notches" goes past the Engine Speed Sensor (ESS) at that rate, the ECU gets the info. I think there are 4 notches, thus, if just two or three of those notches spin past the ESS at the rate of 250 RPMs, the ECU will recognize and send the signal for the IP to inject fuel...

The above is total speculation .....

The ignition "start mode" is unique with all cars. The X circuits are cut-out via a Relay when the ignition is in the start mode position. The X circuits involve things like, head lights, heater fan, AC system, dome lights, radio, etc. The ECU has no clue, other than that the 109 Relay has activated all the electrical systems necessary to start the engine ......... then the starter does it's thingy!

HOOPER65 · Nov 18, 2017

AndyBees said:
As JDSwan87 stated, the Sensor is the Coolant Temperature Sensor (CTS) in the coolant flange on the end of the head. It is a two in one.. Gauge and ECU. If you disconnect the sensor plug, the ECU defaults to -40c. I suspect that will cause the ECU to trip the GPs as well as increase fueling. VCDS will show Engine Temp at -40c with the CTS unplugged.

As the OP, my first VW Diesel was a new 1980 Rabbit with the 1.5 engine. The OE GP Relay was notorious to give up the ghost. So, I installed a Push Button switch below the dash (very heavy duty) to provide direct current to the GPs without the use of a Relay.

When bump starting, the higher gear usage provides better leverage in the opposite direction (wheels>axles>diff>gear>engine) to rotate the engine. At a very slow roll (especially on flat ground), 1st or 2nd gear tend to just stop the car, while 3rd or 4th gear will more likely turn the engine over............ < that's the difference (yeah, and don't forget to turn-on the ignition).

My drive-way at the main highway is down hill. When I stop to check snail mail box (in my ALH Vanagon), I usually cut the engine off. When I get back in the Van, I just bump start it down the drive-way in 2nd gear, never fails and is always smooth.

------------------------------

Just a simple question - actually 2 of them :

And maybe this is a stupid question ... but hey, why not ask anyway!

Assuming one did this :

- ( unplug the CTS ( Coolant Temperature Sensor )
to fool a warm engine into flashing the plugs ) -

Is there any danger of damaging expensive plugs
in so far as also disconnecting any timer that may be associated with
turning the plugs off after a certain amount of time ?

Also:
Would this action of unplugging the CTS
be fine to leave it unplugged after the engine is running,
or would it be advisable to -
( while the engine is now running,
assuming the bump start was successful
and we're NOT going to turn the engine off now
until we drive to where a new starter
is going to be put in .... or a nice hill to park on ) -
.... would it be advisable to reach in while the engine is running
and plug the CTS back in ? - or can you just drive about with the
CTS unplugged ?

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KLXD · Nov 18, 2017

I don't think the timer is disabled so the plugs will be shut off. I don't think there'd be any harm in leaving it disconnected nor do I think there'd be any harm done in connecting it while running. My 2 cents.

Andy, I get that the ECU doesn't need a full rev to compute the RPM but I assumed there was an input to the ECU so it recognized the start mode. Must be since the ECU cuts off fuel if the starter isn't engaged after some interval if the key is turned to run but not start. But if after that one does turn it to start it fires up.

On the other hand it could be the speed sensor output that reenables fueling.

AndyBees · Nov 18, 2017

KLXD, yeah, I forgot about the IP shut-off/on solenoid. However, I also believe, as you stated, the ESS must activate the ECU when the engine spins from a kick-start, thus, turning the valve back on.

As for leaving the coolant temp sensor unplugged, keep in mind, the ECU has defaulted to an assumption that the ambient temp is minus 40. So, it will be over fueling rather heavily. I experienced this with my cousin's 99 NB. When installed a new CTS, VCDS showed the real temp and the engine quit belching black smoke. He had been driving that way for several weeks... complained about fuel economy and his back bumper was smoked black.

Something I just thought of...

Interestingly, as you may know, I installed the OE Jetta Ignition Assembly in the dash of my Vanagon. I leave the key in that ignition and in the ON position. That system is "juiced-up" when I turn the OE Vanagon ignition ON. The Vanagon ignition is used to "spin" (start) the ALH engine. So, that would be very similar to bump/kick starting. Think about it.....

KLXD · Nov 18, 2017

Sounds like it would be.

I think I'm going to take the car out and do some experimenting on a hill.

I didn't mean to leave it disconnected alla time. Just till one gets home after getting the car started.

Bump start

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