The V8 Owners Forum -

Hi all

I've had a couple of "fail to starts" recently when the car has been sitting for 10 minutes or so after a long run, lift the bonnet and molest various wires and fuel pipes, nothing obvious, car then starts immediately. Ignition amp is about 3 years and 15k miles old, it wasn't expensive when I bought it.

Any suggestions please for a replacement, prices seem to range from GBP10.87 upwards, part numbers are DAB118 and STC1184.

Lots of reports elsewhere about these new 'Lucas' amps causing problems.
I'd be inclined to get one from Rimmer - at least they should honour any warranty.

I've had several of these fail on my SD1 over the years including genuine ones. Later Range Rovers moved them to a cooler place.

Fed_up_Stag-owner wrote:Hi all

I've had a couple of "fail to starts" recently when the car has been sitting for 10 minutes or so after a long run,

Are you just presuming that the ignition amplifier is faulty or have you proved it by observing nil sparks at the king lead immediately upon opening the bonnet?

What if it it not the ignition system but latent heat that is affecting the fuel delivery system.

Known as "Hot Start Problem caused by Fuel Vaporization" latent heat can prevent the engine from starting whilst very hot after a long run and a short stop.

By raising the bonnet and fiddling, thinking and complaining about ignition amplifiers, all of a sudden ten minutes later when the super-heating of the plenum area has had time to dissipate, the system goes back to normal, the fuel in the fuel rail condenses back to a liquid once again and 'orf we jolly well go'!

You can read all about this known phenomenon from here:

http://www.vintagemodelairplane.com/pag ... art01.html

As you will read, Rover did come up with a technical 'fix', but the definitive solution is to open the bonnet immediately you stop to allow the heat dissipation to begin straight-away.

My SD1 used to suffer badly from vapour lock - but even if left to cool down wouldn't start as normal. It would still require lots of churning before firing, and have a poor idle for a few seconds.

If you have a dwell meter setting on your DVM - or have one lying around - that will show if the amp is faulty when hot.

Thanks for the quick replies. I've not had a chance to check for sparks yet, the fault clears too quickly. I must admit that I discounted fuel vapourisation on the basis that it was fuel injected! Thought that was a carb problem only.

I have a couple of in-line spark testers I can leave installed on a couple of the HT leads for a quick check.

The last time it happened (at the weekend) was after 2 hours out and about, finishing with 10 miles or so at "making good progress" on an empty dual carriageway, 1/2 mile of 30mph to parking spot, 10 minute or so switched off, so it's a possibility it's an under bonnet temperature issue. But this could also affect a weak ignition amp.

No - the injection SD1s suffer from it too. Maybe worse than the carb ones.

A trick to check if it is that is to arrange a switch to run the fuel pump for some time (20 secs or so) before attempting a start. This cools down the fuel and lines.

I'd be surprised if the ignition amp exhibited these symptoms for long without failing completely, though. I don't think it's clever enough to have a thermal shutdown circuit.

Thanks Dave
Fault has got worse (which should make it easier to find!), definitely an intermittent spark from the HT king lead, used another HT lead as the king lead, still intermittent spark. LT wiring looks OK. Limped back to the lock-up, so will probably replace the ignition amp, perhaps with one of the remotely mounted versions. HT leads are of unknown age (at least 6 years old), so I'll probably change those as well, although doubtful if causing this fault.

Hi, I also have a stag which was fitted with flapper injection ECU & had exactly the same problems. I spent months trying to track down the problem, remote mounted the trigger amp, changed coils etc only to find it was fuel vaporization caused by the earlier very small diameter fuel rail used on the earlier injection. The Stag engine bay is small and gets very hot!
If you had to machine down the Plenum/ Trumpet base for under bonnet clearance it makes things worse too. I changed the rail to the later 3.9 which is a neater solution anyway and used appropriate low impedance injectors.

Hope that helps,

Dorian

Thanks Dorian, do you have a any photos of your Stag with the flapper RV8? It's a project I've been considering. My Stag has been resting for a few years now with blown head gasket and corroded heads

This fault was resolved with a new ignition amp and a new coil. Tried to make a remotely fitted ignition amp, but it didn't work, possible earthing issue, amp fitted in the traditional place (with heat paste!).

Car now running well.