Failing ignition amp / coil symptoms please!

[CaptiV8ed]

Well, after chasing my arse for the last few days, I'm wondering if my hot weather related misfire / stutter could be down to one of these.

Could anyone who has had a definate failure of either their coil or ignition amp describe the way the car behaved before diagnosis. I'm gonna have a go at a few tests listed in the bible ands then I fear it will be off to a dealers.

For the record, I've changed the ECU temp sensor, plugs, cap, rotor arm and leads all to no avail. It seems to be aggravated by heat and will occur at all throttle openings and revs. Too top it off, it's intermittent too. Any RV8 experts opinions welcomed!

Nick

[BIG DUNC]

I have had 2 ignition amps fail ( different cars, but both TVR ). In both cases, the car was VERY difficult to start, but when it did start it ran fine until it was turned off. However, I have heard of them giving the symptons you have.
I have never had a coil fail, but did change one once as I had the symptons that you have, and more than one expert said "its the coil" ( actualy turned out to be the air flow meter, but by then I had allready changed all the things you have ).

If I were you, I would change the ignition amp and the coil. They are not that expencive, and once they are new, you should have piece of mind that you will not need to change them again in the future. Besides, the rest of the ignition system is now new, so it makes sense to do the last couple of bits.

[CaptiV8ed]

Thanks Dunc. The whole scenario is a b4stard because it only seems to do it when the weather is very hot. I drove it late the other night and it was (almost) fine. Hot day again yesterday, it was awful! I shall see if I can test the amp and coil once they get up to temp. I'm sure there's something in the bible about it.

Many thanks,

Nick

[That Daddy]

Remember if you change the ign module to put the heat transfer paste on the back(many dont)it needs to pass the heat thru the piece of ali its bolted to,i use computer cpu heat sink paste(better quality)this may be your problem they can be affected with heat and lets face it they see more of that than was intended,good luck.

Edited by That Daddy on Thursday 7th June 08:29

[Torquemada]

Very similar symptoms a few years back - misfiring and cutting out when hot. A new ignition amp cured the problem (thanks to Dave Batty).

[jonnyb]

To be honest, if its related to outside air temps then its most likely to be the AFM or the coolant temp sender. My monies on the AFM.

[Dinnov]

I had exactly the same symptoms on my Griff 500 a couple of summers ago. On a hot day the engine would run for up to an hour, then misfire and die. Leave the bonnet open for 15 minutes and it would run again! I changed numerous bits to no avail. It turned out to be the ignition coil. Over the years, some of the oil had seeped out allowing the coil to breakdown internally when hot. My advice is to fit a TVR spec replacement coil. Apparently the Lucas item (as per Range Rover) cant take the heat under a TVR bonnet.

[CaptiV8ed]

Here's the latest. I've done some diags this afternoon. Air flow meter voltage ever so slightly high at idle, but right higher up the range. Throttle pot voltage ok (both readings taken from back of ecu).

Can't test the ignition amp except for 12v with ignition on. The engine does run, so this must be there. ( I know that this could be failing though)

HOWEVER! The coil secondary resistance according to the bible should be 7500 ohms to 9500 ohms. Mine is 5800 ohms. The primary is ok at 1.2 ohms. Could this be my problem? There are no signs of leaking oil from the coil, but my god, the car hates heat at the moment. Right from fire up, it's pants.

As always, any help greatly appreciated!

Nick

Edited by CaptiV8ed on Thursday 7th June 19:04

[GreenV8S]

I've had to use the 'wrong' coil to get home, the engine ran but definitely didn't feel right. If the resistance isn't to spec then I'd suspect you have the wrong coil. Does it have any branding / part numbers?

[CaptiV8ed]

Can't see any. My point really is if it was originally 7500 ohms +, is the fact that it is now 5800 a sign of it breaking down?

[Zumbruk]

FWIW, I had a poorly V8 Range Rover which died completely when hot and sprang back to life when it cooled down, which turned out to be the pickup inside the distributor which sensed the rotating "starfish" wheel which the ignition uses to know when to trigger (it's called a "reluctor", BTW). Replaced that and it was fine.

[GreenV8S]

Zumbruk said:

it's called a "reluctor", BTW

Also known as a Magnetic Variable Reluctance (MVR) sensor.

[That Daddy]

GreenV8S said:

Zumbruk said:

it's called a "reluctor", BTW

Also known as a Magnetic Variable Reluctance (MVR) sensor.

Or Limb/ Magnetic coil/constant energy

[CaptiV8ed]

I have now tried a new coil and ignition amp - and the verdict is!! - just the bloody same

Thankfully, the kindly supplier took them back. With the exception of this MVR thingy, I have tried an entire new ignition system. Could I have been barking up the wrong tree and it's actually a fuelling issue??????