Cutting Out... 96 3.9V8

[V8 Disco]

Hm. Looks like I am back to the start of my intermittent cutting out problem with the Disco. Having originally thought that the new ignition leads had done the trick, my cutting out problems returned, albeit very occasionally. However after a particularly bad bout of the hiccups, A mate and I spent Tuesday evening pulling the dash out to replace the immobiliser spider, a well-known trouble spot for intermittent problems. However...

Last night she's back to her old ways suddenly the engine revs drop and just as suddenly they come back up. It's as if the ignition was cut for a mo (hence the items so far changed). One interesting thing is that the engine has never stopped completely. Now IIRC, it's not possible to bump start an automatic, so I reckon that it can't be stalling completely.

Looking in the dark at the ignition leads, I can see a ring of light around the neck of the coil, particularly at higher revs. I realise this is wrong, anyone have any suggestions as to ignition coil failure modes? Time/heat related?

I will fit a new coil next week anyway, as they are relatively cheap. I also have a new distributor cap and rotor arm to fit tomorrow.

If anyone has any suggestions as to what to check/change if that doesn't work, I'd be glad to hear!

[talkwrench]

It is perfectly conceivable that the coil is at fault. The Corona discharge that you are seeing would indicate that the insulation is breaking down at the top of the coil.
Coils fail over time and a common symptom is that the coil weakens itermittantly when it gets hot. It is caused by the internal insulation breaking down and the coil effectively shorting out its own high tension secondary winding, resulting in little or no spark.
The distributor cap and rotor arm are unlikely to give such a dramatic intermittant problem but, given the condition of the rest of your ignition system, they will certainly benefit from being replaced!

[V8 Disco]

Update: I changed the coil last night for a new one - drove beautifully last night, Mrs V8 used it today and it's kangarooing all the time. (aaaagh!)

I need some alternative ideas - has anyone here experienced problems with fuel pump and/or it's assosciated relay?

Also, can anyone suggest any other components that might cause a sudden and intermittent cut in power? One significant point is that this has never caused a full stall.. the engine never actually stops.

Hope someone can help.. getting low on ideas now.

[P100]

HI, I would try changing the dissy cap and rotor arm as these are always a problem when the car gets older. What leads have you fitted?? I have had loads of problems with rubbish cheap leads. I now only use Magnecore leads as they have not failed me yet.
What year is your discovery?? Is it carb or efi??
Cheers Roy

[V8 Disco]

Hi Roy - it's a 1996 with Efi.. The leads look OK quality, but I have heard good things about Magnecor. The weird thing is the intermittent nature of the fault - can go days without seeing it and then it goes several times in a day...

I'll do the cap and rotor at the weekend, maybe I'll be lucky! Might also change the coil - dizzy lead again - just to be sure!

Cheers

[P100]

Hi, if its an EFi I would suggest you check the contacts on the temp sensor fitted to the right of the top hose on the inlet manifold. The sensor is not expensive but does give faults similar to yours.Also check the contacts in the wiring plug, over time they become loose due to heat and give intermittant faults.
Magnecores are well worth the extra money. if you need some drop me a mail to [e-mail]
Good Luck

Roy

[Liszt]

Is this on LPG or petrol. LPG is verg fussy about good ignition. Petrol will hide a multitude of sins. In the short term leads don't have to be great. I use a set of original Lucas leads and they work fine on my LPG. Original Lucas dizzy cap and rotor arm are essential. Pattern parts tend to be crap. Is this just at idle? If it is I would bet that it is a spark problem. I had a similar situation which was due to the coil having slipped and arcing against a brake pipe.

If you are on petrol, I'd guess it could be a fuelling problem. When was fuel filter last changed? Has timing bee checked? Injectors cleaned etc?

[V8 Disco]

Hi there - it's on petrol and occurs while driving - not at idle. Engine seems to drop to idle during the 'blip' and then once it has passed, behaves normally in every respect (till the next time!)

Fuel has been suggested on another forum - maybe I'll change pump and filter..

Thanks for your suggestions - greatly appreciated!

[steve_d]

Similar symtoms on my RR classic were fixed with a replacement ignition amplifier module on the side of the dizzy. Don't know if the disco has the same.
Also this module is prone to failing if it has not been installed with thermal transfer grease behind it. Without transfering its heat to the dizzy body it cooks and burns out.

Steve

[Denis O]

Amplifier is on the dizzy on early models and tucked up near the radiator on later models. I agree this could be the problem.

[V8 Disco]

Hi - thanks for the suggestions - I found the ignition amp when I changed the coil, it's the later location on an ally plate by the rad. I will change it and report back!! - for good measure I have bought a new fuel pump relay today - useful spare as it's the same at the main Efi relay - so will change that asap too. Genuine Lucas Dist Cap and rotor going on at the weekend.

Cheers again... much appreciated!