Disco 2 (Solved) Crank sensor problems

Hey, so one of the work trucks was getting hard to start etc. Traced it down to crank sensor. Wiring was butchered and had been soldered with no insulation around it. Fixed all the wiring up, put the sensor back in and now have 0rpm with the odd jump to 30. Continuety between the plug and the ECU is fine. Sensor ohms were acceptable. (I've tried 2 sensor's) sensor is giving out AC voltage when cranking, although the lowest meter goes is 200 so it's showing 0.03. Have it hooked on jump leads so 13+v when cranking.
It's an auto and as far as I know didn't have any spacers on it, unless it fell and I didn't see.. any ideas? Tia

Bump.. I tried putting a temporary washer under the securing bolt that was around 0.5-1mm.. but still roughly the same, maybe once in 30 secs it showed about 200rpm.. really giving up now, was meant to have it back to work tomorrow. The sensor that was on the truck may well be dead, but the spare I took off my manual should be alright, she started "ok". But same results. If I bought a new sensor would it come with shims? If that's what it needs..?

I believe manual has shims and auto does not.
Plenty on here about starter motor interfering with crank signal. Have a search.

Lazydave said:

I believe manual has shims and auto does not.
Plenty on here about starter motor interfering with crank signal. Have a search.

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Cant say I saw a shim on my manual when I removed the sensor.. but either way this ones an auto so guess it doesn't need it.
Is there actually any way to tell if its the starter on an auto, since with the manual you can just bump start it? In all fairness the starter cranks pretty fast etc.. Could I snip the wires before they go into the ECU and try running new wires from the sensor direct to the ECU? assuming that a bad starter interferes with the wiring and the not the cps itself.

Jamiegreen said:

Could I snip the wires before they go into the ECU and try running new wires from the sensor direct to the ECU?

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Yes you could and better do it just use proper wiring otherwise you work in vain, this is what you need https://www.efi-parts.co.uk/index.php?productID=324 and connect the shield to a "solid" ground

sierrafery said:

Yes you could and better do it just use proper wiring otherwise you work in vain, this is what you need https://www.efi-parts.co.uk/index.php?productID=324 and connect the shield to a "solid" ground

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Ok thanks, just for testing purposes can I just use regular wire and keep it as far away from the engine components etc as possible?

I'd not consider it a relevant test... the sensor's circuit must have a certain impedance to work well which might not be OK with unproper wiring

I'll get the proper wiring then. Would you be able to just show me which way round the wires go, as it's different colour wires down on the sensor plug to the ecu and I haven't got electrical digram handy. Thanks

Unless somebody messed with the wiring the sensor should be hardwired to the ECU red plug with same colour wires, pink/black pin 1 sensor to pin 13 ECU, white/blue pin 2 sensor to pin 36 ECU and shield pin 16 ECU... download a RAVE if you want to work with wirings

Would this stuff be any use? It's the only kind of shielded stuff I've got. If I earthed the metal shield and just left the other cores in there would that be alright?
Cheers

As i said it's about the impedance of the cable ... are the wires twisted inside the shield? and what gauge are they? ... you can try with that and the shield to earth but as long as we dont know if it's the right impedance the test might not be relevant unless the engine will start with it then you know it's a wiring issue, btw, the ECU needs at least 250 rpm input as the engine to start otherwise it will just crank in vain

sierrafery said:

As i said it's about the impedance of the cable ... are the wires twisted inside the shield? and what gauge are they? ... you can try with that and the shield to earth but as long as we dont know if it's the right impedance the test might not be relevant unless the engine will start with it then you know it's a wiring issue, btw, the ECU needs at least 250 rpm input as the engine to start otherwise it will just crank in vain

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I understand, it's just this is a work truck and I'm trying my best to get it back on the road even before the proper cable arrives from online.
The cable is maybe a touch thinner bit not by a lot, should I use one core each or double up and use 2 cores each? It looks untwisted. And just leave the other cores and not ground them too?

Use only two wires and only the shield to earth

Ok done all that, now she cranks and now she jumps between 0rpm and 230 rpm quite quickly. Sometimes holding at 230 for couple seconds. Have had to put it on jumper leads from my engine.. still no start.. guess I need that extra 20rpm reading. So I'm guessing the cable just isn't good enough or could it be something with the starter? But on jump cables it doesn't go below 11.2 when cranking..

If the voltage drops with jump cables too below 12V the starter is very suspect

sierrafery said:

If the voltage drops with jump cables too below 12V the starter is very suspect

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Can get it just down under 11v after about 4 secs cranking with my cables.. although they aren't the best, and without cables I can get it to jump between 9 and 10v pretty easy

The voltage should not drop more than 1V with a good starter... You should rule it out if you have a spare

sierrafery said:

The voltage should not drop more than 1V with a good starter... You should rule it out if you have a spare

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Was just checking my good disco with Hawkeye and the injector harness unplugged. She doesn't seem to drop below 11.5 when cranking and shows 270rpm ish.
So it's really worth changing the starter..? I've got a spare, it cranks fairly quick and whatnot.. but guess the high current draw could mess with the CPS signal..? Maybe that makes sense for it to drop and rise so rapidly as the engine becomes easier and harder to turn.. or maybe I'm just making stuff up now haha
Will get my spare off and try it..

All finished, good and and not so good news. Crank sensor now reading 300-350 on cranking. Last garage monkeys didn't put the top bolt in starter, and only hand tightened the other two, but overtightened the main feed and snapped part of the solenoid. Now no codes thrown. Bad news is, she is spluttering trying to start but just won't fire..

run a 5 pedal purge on it then try again