Mk 3.5 mk4 Golf no crank, G28 sensor fault code, stall when cold

Thank in advance
Car : mk3.5 vw golf cabriolet, 2000/w, 80,000m
No issues apart from every few months it might start then die instantly (fine once cranked started a second or 2 later.
2 weeks ago for MOT I replaced the clockring (this having been diagnosed by local auto electrician) then auto electricain cleared latched on airbag fault light for me. so all good.

1 week/approx 50miles later on 3 consequtive days:
start from cold, drive for approx 1 mile engine just dies (like dead electrics)
1st 2 days cranks and fires back up within a min or 2 then fine afterwards.
3rd day, start from cold, dies, cranks but dont fire up again. typically this is when I'm in the fast lane on a dual carriageway.

AA called, upon arrival my battery now a bit flat from attempts to crank- towed to safe location.
AA guy sticks jump pack on battery, cranking but not firing.
plugs in diagnostic, and starts fishing around in fuseboard area using multimeter & cable links(fuse inline).

Initially I believe he was getting connection via ODB port, but he later exclaimed he couldn't.
Also now the engine would not crank, key switch gave no sign off life crankwise. (starter is good(I proved this/linked live to it).
Eventually had to be towed home and dropped there.

Fuel pump relay is closing/pump priming (i can hear this), proving ignition switch.
Not getting any crossover in continuity when flexing cables to crank sensor
Using a neighbours cheap fault reader it shows G028 Engine Speed Sensor.
Ecu pins look clean n shiny.
All fuses good.

Questions:

1. Has AA bloke added to faults (induced not cranking?) maybe by linking something/wiping ECU? (apologies in advance to recovery men out there- not wishing to apportion blame just trying to get it fixed)- I've msgd him politely asking what he was doing (i assumed fuel pump/control relay proving) but no response.
2. does the G028 code result from lack of signalliing from ECU or a real fault of engine speed sensor?

3. initial fault would this be caused by engine speed sensor/ auto electrician(sorry autoelectricians ! )/ cable/sensor age?
4. how do i fix myself (cheaply) ?
5. relay positions/numbers -photo of fuseboard anyone? (the haynes for this model is crap/brief, and no RJ FAQ for mk3.5 fuseboard )

BTW- I've cocked the odd thing up myself in the past so understand mistakes do happen and am fairly chilled about this, so not trying to point fingers/ slander good tradesmen.
Any help appreciated.

 

Thanks Rubjonny.
I will take this info and work through some of your suggestions in the next few days (reporting back on here for future reference).

Airbag Clockring/clock spring is a doughnut slip ring that sits under the steering wheel/over the steering column providing electrical contact via the brass ring (for horn?) and a lead that plugs into the airbag ignitor in the steering wheel airbag/other end plugs into connector plug near indicator stork.
https://www.ebay.co.uk/itm/123487630732?fits=Model:Golf|Plat_Gen:MK+III&hash=item1cc06fb58c:g:d8MAAOSw3BJb6wmT

Q. When the engine cuts at speed do the clocks go dead and come back on briefly (coolant warning light flash up for example)
A. didnt notice clocks, it seems like its been switched off/on - Oil and Battery lights lit.

Also if you source a new ignition switch
I've got a 90 spec mk2 golf steering column/ignition switch in shed - would that be usable ?

AA bloke has gotten back to me and suggested checking fuseboard/internal power rails as he was getting intermittant supply/continuity when he was testing it/ dead battery wouldn't do this ?
I've got a spare CE2 FB in shed I can swap if reqd.
I will check FB feeds.

Luckily after a quick once over the Caddy glided through its MOT, having been parked 2 years, so she's my wheels while the ragtop is sick.

 

Some slight progress.
noticed a individual fuseholder floating about (possibly alarm/immobiliser?) with a blown 5A fuse. replaced it.
Cranked, fired, started. engine ran for a couple of minutes (just long enough to 3 poinnt turn so drivers door is now kerbside) then cut out.
back to original fault -cranking but not firing.
looks like AA might have shorted/blown the fuse.
I've swapped a couple of fuel pump and ECU relays in -not noticed owt.
Now with fault reader (IGN on) I can't obtain earlier G28 engine speed sensor, now getting immobiliser fault- not convinced.
Rain tomorrow but will see if initial fault is replicated (starts then cuts out within 2-3mins )/ what fault codes if any.

 

So 0513 (G028) -Engine speed sensor fault code update.
RossTech site suggests this can be several things
http://wiki.ross-tech.com/wiki/index.php/16705/P0321/000801
'When an engine will not start due to mechanical (spark/fuel/compression/timing) related issues it is not uncommon to set a false G28 fault codes due to extended cranking with a no-start condition.'

Having previously been able to crank, spark, start and run for a couple of minutes before cutting out, having let with battery disconnected for 2 weeks when i try to start it would crank but not start.
Removed sensor (held in by m5 allen bolt) by removing front engine mount, wiggled free without much bother.

For a mk3.5 cabby 2.0 2000 this was the part (the internal part being approx 25mm long)
https://www.heritagepartscentre.com/uk/037906433a-crankshaft-sensor.html

Fitted and car started straight away, sounded like it was learning to idle for a few moments (?) then ok.

So it was
1.an intermittant fault with the sensor manifesting as cutting out after a couple o minutes from cold start/ then restarting fine after cranking for a few seconds.
2.blown fuse on immobilser caused by linking out contacts in fuseboard trying to fault find.
3. issue 1 progressing to car not even firing.

Resolution = new crankshaft sensor.

Thanks again RJ

 

update,
2 crank sensors & 1500miles in last 12 months.
Fault (cranking but not starting) reappeared in Jan 22. I installed another crank sensor to no avail.
Gave up and drove the pick up for a couple of months.
managed to get the mk3.5 started a couple of months ago (god knows how/thought it was wiggling the key a bit)
this last fortnight driving the mk3.5 I have had 3 or 4 temporary failure to start/ eventually started episodes.
2 days ago -cranking but failing to start.
fuel is getting through, dizzy pins scored so new one replaced.
Spark is getting down every HT lead to plugs, -

1. would this happen if crank sensor broke ?
2. does cranking and spark rule out ignition switch ?
I'll check the plug gaps next.

getting fed up having had 2 months parked then 2 months of resuming confidence in it.
immobiliser reader spool, ignition barrel , ECU relay.-

3. any other thoughts what could give intermittant progressing to permanent crank/no fire issue ?

 

Thanks RJ, only have access at moment to a cheap reader of a neighbour that doesn't provide much -will have to ask him.
medium term whats the cheapest route to Vagcom that can be used on several vehicles ?

I'm not 100% the key wiggle was the issue- it's not resolving it now.
battery in key fob also replaced.
Coolant sensor ordered £5.
looking back over this thread i saw ignition switch- so today i'll dig the spare out of the shed for a try like you mentioned earlier.
my helper is a fluke and insulation tape for crank readings .

 

Hello, Ambrose,


1. would this happen if crank sensor broke ?

That's the symptom I've seen with the 'AGG' engine. Beginning with an occasional falter, even at motorway speeds, and progressing to a non-start. Unless it's left for a while, when it deigns to run for a while, until the engine begins to warm up. Enough to turn the car around, as in your case. Mine was the crank sensor, as a code (which I'm sorry I don't recall) finally admitted, after I'd changed the sensor.

If you haven't seen my contribution re. the crank sensor, I believe it produces the Rpm displayed as the 'digital tachometer' (even at cranking speed) in a special mode programmed into the instrument cluster. It certainly remained at 0 when I tried it in the non-start situation.

If you like to try this, here it is again;

1. Switch On and wait for any service indicator to finish
2. Make sure that Total Mileage is displayed
3. Press and Hold Down the trip mileage reset button, while you turn the ignition Off and back On
4. Upon releasing the trip reset, the mileage display changes to show a '1', then some figures, which depend on the cluster, and depends in turn on the engine and transmission
5. There are eight separate functions in this mode, scrolled through by pressing trip reset. Most are fixed (as far as I can tell) but after No.5, the display test, No.6 is a distance counter advanced by the speedometer sender, and No.7 is an Rpm indication
6. Exit simply by switching Off

 

I cant find any ignition phillips screw that a bendy screwdriver would be used on, as advised on this thread
https://clubgti.com/forums/index.php?threads/changing-ignition-switch-mk2.240811/#post-2117572

Slightly ot, how'd u get the ignition barrel off mk2 90 spec steering column-with key in, tapped it a bit with hammer having removed m8 bolt. It just moves 10-15mm up n down the outer steering column.
Have just been sat in mk3. 5 with the 2nd steering trying to Plumb it in but the car ignition loom won't stretch far enough.
I'm scared the lump hammer will result in column ball bearings n copper race being spat out. See images.

 

Thanks Dougie,
I asked because I had an issue with a blown fuse in tandem with crank sensor issue 1 a year ago, resulting in it not cranking or firing.
a 2nd sensor resulted in it working for a few months, then in Jan this year the issue arose again. so only about a thousand odd miles later.
a 3rd sensor was put it about march this year. and issue has returned after a couple of months without issue.
surely crank sensors dont go this often ?

anyway what really caught my eye in your response was "rpm displayed even at cranking RPM"- I've just tried this on 7 (RPM) value stays at zero while cranking.

 

Thanks again RJ sorry for the silly questions.
1. Ok so the spline adapter is removed using a puller ?
Quality parts? - the link i posted above (topran sensor from heritage £20) cant recall if this was the first 1 I bought May 21.
I think the last 1 Mar this year was off ebay.
I dont think there was much difference in price (maybe heritage was a couple of quid dearer with postage)
I've just another crank ordered from Heritage.
And I'll give the linking ignition loom a try.

 

Thanks again RJ sorry for the silly questions.
1. Ok so the spline adapter is removed using a puller ?
Quality parts? - the link i posted above (topran sensor from heritage £20) cant recall if this was the first 1 I bought May 21.
I think the last 1 Mar this year was off ebay.
I dont think there was much difference in price (maybe heritage was a couple of quid dearer with postage)
I've just another crank ordered from Heritage.
And I'll give the linking ignition loom a try.