intermittent starting

ashleywood.ash · Oct 20, 2021

hi guys. Still having intermittent starting issues with 98 300tdi manual with dds immobiliser.

yesterday it started fine 5 out of 6 times. I was on a hill when it didn't start so bump started fine.

today it started 5 out of 6 times. it was on flat so had to bridge the starter to start.

so guessing this is not the immobiliser as that would stop fuel and therefore wouldn't bump or bridge start if it was messing up.

is it likely to be an ignition fault given its temperamental.

only thing I can see is I know exactly when its going to do it as you turn the ignition and the glow plug light flashes on and then off again in about half a second. when its going to start fine the glow plug light stays on the usual amount of time depending on engine temp.

its been fine for last few weeks. wonder if it doesn't like rain

discool · Oct 20, 2021

ashleywood.ash said:
hi guys. Still having intermittent starting issues with 98 300tdi manual with dds immobiliser.

yesterday it started fine 5 out of 6 times. I was on a hill when it didn't start so bump started fine.

today it started 5 out of 6 times. it was on flat so had to bridge the starter to start.

so guessing this is not the immobiliser as that would stop fuel and therefore wouldn't bump or bridge start if it was messing up.

is it likely to be an ignition fault given its temperamental.

only thing I can see is I know exactly when its going to do it as you turn the ignition and the glow plug light flashes on and then off again in about half a second. when its going to start fine the glow plug light stays on the usual amount of time depending on engine temp.

its been fine for last few weeks. wonder if it doesn't like rain

Ok an immobiliser has two independent circuits, one will inhibit the starter cranking the other fuelling.
So question, what’s intermittent the cranking or the engine always turns over but wont fire. ?
If you can bump start and the engine fires and runs then the immobiliser fuelling circuit hasn’t been inhibited.

ashleywood.ash · Oct 20, 2021

yeah, always bumps, when doesn't start it doesn't crank. lights on dash, just the blink of glow plug light and nothing

discool · Oct 21, 2021

ashleywood.ash said:
yeah, always bumps, when doesn't start it doesn't crank. lights on dash, just the blink of glow plug light and nothing

Then it could be an iffy immobiliser but also the ignition switch, starter relay, starter solenoid or the wiring in between.

ashleywood.ash · Oct 21, 2021

thanks. I'll work my way through

discool · Oct 21, 2021

ashleywood.ash said:
thanks. I'll work my way through

Thats all u can do, a Haynes manual shows the complete starting circuit on one page which is handy, It’s unfortunate that your fault finding will only get a result if carried out while the engine refuses to crank.

But first, in readiness locate the starter relay, and the coil terminal that receives the 12v when cranking is normal, with the cranking issue the 12v will be missing then its either a faulty ignition switch or immobiliser issue.
Also check the solenoid/ starter motor connections plus of course all the earthing connections u can find.

A single piece of wire installed can bypass the faulty immobiliser circuit. I’ve been there but with the fuel side of the immobiliser, intermittent starting for a year than complete failure. So just installed a permanent wire as a overlay to the immobiliser circuit that gave me the issue.

ashleywood.ash · Oct 21, 2021

thats all really helpful thanks.
it is the gift that keeps on giving. again 6 starts, 5 of them fine 1 non start, an as if to mock me I think it was the fuel one this time as fired, instantly cut out and then was cranking but wouldn't fire
left it for 20 mins and went in my van, came back and then started fine.

KiwiTDI · Oct 25, 2021

My 96 auto sometimes doesn’t crank (so start), rarely, lights on dash dim but no starter motor turning, I have never been able to get it to do it when I have diagnostic stuff available like a volt meter. After the issue occurs It usually cranks if I put it in and out of gear a few times, and if that doesn’t work, rock it in gear.
I read somewhere it could be a faulty sensor in the box that ensures it is not started in gear.
Does a manual have a sensor as well?

discool · Oct 25, 2021

KiwiTDI said:
My 96 auto sometimes doesn’t crank (so start), rarely, lights on dash dim but no starter motor turning, I have never been able to get it to do it when I have diagnostic stuff available like a volt meter. After the issue occurs It usually cranks if I put it in and out of gear a few times, and if that doesn’t work, rock it in gear.
I read somewhere it could be a faulty sensor in the box that ensures it is not started in gear.
Does a manual have a sensor as well?

No. Only autos have a starter inhibit unless the selector is in position D or N.

intermittent starting

ashleywood.ash

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discool

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ashleywood.ash

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discool

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ashleywood.ash

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discool

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ashleywood.ash

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KiwiTDI

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discool

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