Intermittent hot start problem.

In the summer I had an issue where the car wouldn't start when it was hot. It was diagnosed as a faulty immobiliser and the usual spider fix was done and things were fine until just recently. However three times recently when the car was warm both from an engine and a cabin perspective it refused to restart. Would not even crank over, just dash lights and nothing else. Left it for 10 mins and she fired up just fine. Any ideas? Someone has suggested that it might be the auto-box neutral/park switch which I assume is somewhere in the centre console which was very warm from the heater.

Tks in advance.

When it happens you need to be ready with some diagnostic plans, intermittent issues are the worst. Maybe practice hot wiring the starter motor so when it happens you see if its the starter motor circuit?

Then if it turns over ut wont start you can suspect the immobilisor items, and maybe hot wiremthe fuel cut off solenoid to get it going.

Check your battery connections and earth before doing anyting I guess, as well.

when it happens there are a couple of things you can try before you break out your voltage meter or power probe. First off try moving the gear shift back and fourth a few times rapidly and then try cranking it over again. If that doesn't work, try wiggling the fly lead (small spade connector on the starter motor) and then try cranking again.

If that still doesn't work you will need to check to see if you have a live feed at the starter fly lead when the ignition is turned to the crank position.

KiwiTDI said:

When it happens you need to be ready with some diagnostic plans, intermittent issues are the worst. Maybe practice hot wiring the starter motor so when it happens you see if its the starter motor circuit?

Then if it turns over ut wont start you can suspect the immobilisor items, and maybe hot wiremthe fuel cut off solenoid to get it going.

Check your battery connections and earth before doing anyting I guess, as well.

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Fuel cut off solenoid? Not on a V8

Does it refuse to start point blank i.e. turn the key and nothing at all, not even the starter relay clicking?
Have you cleaned the earth behind the coil?

It won't crank at all. not even a solenoid click. turn key and all you get is the noise of the cabin fan turning on. I can't tell whether having the immobiliser bypassed (done at a LR main dealer) would remove it from the list of suspects. My immediate thoughts were that it was a faulty neutral/park/reverse switch on the autobox, as I understand that this would isolate the starter when engaged. I wiggled the gearshifter like mad with no effect. (in fact I think the interlock is bust as it is possible to shift the selector into any gear while the engine is off without the need to press the brakes). I will look at the coil earth but that should not in itself prevent the starter motor engaging, should it?

On my 1996...

Open bonnet and on RHS, behind the headlight there'll be the coil and or an earth, unbolt this [ 10 or 12mm bolts x2, use a rat**** spanner/extension bar/uj] unbolt the lot, wire wool and wd40 the mounting and all the gubbins associated with it, put it back together and try to start it.

Sometimes shorting the starter motor will kick the starter motor clear but I'd clean your earth first.

Ok will give it a go cheers

bushwwacker said:

On my 1996...

..........but I'd clean your earth first.

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Thanks for the advice. Did what you suggested and when I went to check the engine end of the earth strap it was very loose. So brightened it all with wire wool and retightened it. Hopefully this should sort it all out.

I'm suffering similar symptoms on my '96 300tdi automatic.
However, I understand that as it's an auto they don't suffer spider issues as they don't have one?

Is this not the case? In my scenario I feel I've eliminated the switch on the box as the shifter has not been moved between failed starting attempts and successful ones. Clearly something is getting hot and deciding it doesn't want to play ball.

I wonder if in both cases it's a faulty starter solenoid causing the issue?

MGBGTV8 said:

I'm suffering similar symptoms on my '96 300tdi automatic.
However, I understand that as it's an auto they don't suffer spider issues as they don't have one?

Is this not the case? In my scenario I feel I've eliminated the switch on the box as the shifter has not been moved between failed starting attempts and successful ones. Clearly something is getting hot and deciding it doesn't want to play ball.

I wonder if in both cases it's a faulty starter solenoid causing the issue?

Click to expand...

My V8 seemed to suffer from the spider issue. The main dealer bypassed it with the requisite LR part. It is possible of course that the spider was not the cause of the problem rather it was what ever is the cause of the current issue. Shortly after the dealer did the bypass, I took the car to Cornwall over the Autumn and it got plenty warm but did not fail to start at all. I have a strong suspicion that the loose earth strap might be the cause but I'm monitoring things. If the problem recurs then I'll look to the solenoid.

couchiedemon said:

Thanks for the advice. Did what you suggested and when I went to check the engine end of the earth strap it was very loose. So brightened it all with wire wool and retightened it. Hopefully this should sort it all out.

Click to expand...

Problem has recurred. After a 15 mile gentle run it refused to start again (i'd just started it twice in quick succession but no dice a third time). Since the last Post I've replaced the battery with a good quality new one so it definitely ain't that. Left it 15 mins while I called the AA but then it started and got me home.

Beginning to suspect the starter motor, solenoid, the AT interlock, the starter relay or possibly the coolant sensor.Will replace the relay and coolant sensor as they are both cheap moving on to the starter if that fails to address the problem. Any other inspiration gratefully received..........

I think I have this cracked. It suddenly dawned on me that the starter motor heat shield was missing. This coupled with the fact that this only fails to start when its really hot suggests that excessive heat compromises the solenoidc which when slightly coolerkicks in again. Off to the shops for some heat sheilding. Sad thing is, that I had a large dealership -H*rwoods- look at it twice. They were convinced it was the immobiliser and so bypassed the spider. Shame they did not notice the missing heat shield....