Just bought an Excel - and it's broken down already!

[rbgos]

Hi all - I just bought myself an Excel (1990 SE, in Midnight Blue), but an Elise-owning friend promised me you'd still be friendly

I bought it in Suffolk at the weekend, and had a glorious trip north, until I finally hit Aberdeen traffic and it conked out 10 miles from home. Engine seemed very weak, particularly at low revs (i.e. pulling away from traffic lights) for a couple of minutes, then the engine just died, wouldn't re-start, not a hint of it firing.

Back home on the back of a trailer, and into the diagnosis. Looks like an ignition fault - no response from my timing light on any of the HT leads (including coil-to-distributor). Ignition is electronic, of sorts - there's a coil and a distributor, and a black box with "Lucas" (Prince of Darkness) on it, attached to the wing in the middle of the photo below. The other photo is the dizzy, although you can hardly see it hidden under the carbs there. My experience so far is Spitfire and MGB, so I could diagnose an old points ignition system (probably), but am at a bit of a loss with electronic systems.

Any pointers or suggestions would be most welcome...

Cheers,

Richard

[mac]

If your not getting a pulse on the king lead lead (coil to dizzy) then it's either not getting the signal to trigger or it is and the field in the coil is too weak.

Check your earths and the LT wires going to the coil. If it's not a hugely expensive item try changing out the coil, if that doesn't work or is too expensive then we'll need to find out if the electronic ignition module is working.

Can you take some photos of the coil & the Lucas box please?



Mac

Ps welcome!

[neilj37]

Welcome Richard, it was me that pointed him to this site so play nice with him lads and losses

[rbgos]

The coil and Lucas box are in the top photo. The coil looks like a very standard off-the-shelf item, no specification or item number visible (at least without taking it off). Tempted just to replace it, easy and cheap-ish check. Service notes state that it should be a "32 C5" (whatever that means).

The Lucas box is the black box attached to the wing. Not much to it really, just a couple of leads to the coil, another two to the dizzy. It's an AB14, which is what it says it should be in the service notes. There's a smaller black box on the side which is apparently a rev limiter; it was suggested I try unplugging this to see if it makes any difference, but it didn't.

Done some basic voltage checks as suggested in the service notes, which have confirmed good voltage at the coil, and that the Lucas box is earthed.

Service notes also suggest checking the resistance between the two LT wires going into the distributor. Should apparently be 2-5kOhms; I get 1.5kOhms, so just below the correct range. The advice (having made the previous checks) is to replace the distributor pick-up if the resistance is wrong, otherwise replace the Lucas amplifier box. Previous owner states he already replaced the pick-up once due to starting problems, didn't mention how long ago that was.

I might have reached the point where I've run out of home diagnosis tools and just have to start replacing bits until it works again

Richard

[ABZ-Elise]

Give these guys a call http://www.lotusbits.com used them before for parts for my dads Excel. They should be able to let you know whats wrong with it and supply the parts, new or second hand.

Kev.

[Rich H]

Hello!

Fellow 910 engine owner here! but I have no dizzy or carbs and it's in an Esprit!

Best bet would probably pop over to thelotusforums.com and ask there
It's the old Excel owners club forum, plus it's the Old Esprit owners forum too.

[robin]

If you work out which wire is the low tension earth from the box-o-magic to the coil, remove it at the coil end.

Now put the rest of the HT system back together, or put a spark plug on the block somewhere and connect it to the king lead (it would be better to assemble it all properly, assuming the engine can be rotated to a position where the distributor rotor arm routes the king lead to one of the plug leads).

Attach your timing strobe light thingmy to the king lead.

Using a length of wire (something with good insulation - e.g. a length of mains flex), earth one end and then strike the other end across the -ve LT terminal on the coil. You should see your strobe light trigger. Essentially you've become the points ... If the strobe light triggers you know the HT side is all working and the problem is either the box or the sensor.

I'm pretty sure that the distributor will contain a hall effect sensor. If you get a multimeter set to 20v DC scale across the pair of wires coming from the sensor (i.e. multimeter connected to the sensor in the distributor whilst the box-o-magic is disconnected) then you need a glamorous assistant to turn on the ignition and crank the engine (please make sure no leads or body parts are dangling in the path of moving parts!). You should see a voltage appear on the two wires; it might be a more-or-less constant voltage, or it might be a pulsing voltage (it depends how fast it cranks and how slow your meter is). The key thing is that is should change when the engine is cranking.

If the output is 0v all the time, then it's fair to say the sensor is gubbed I think. If you see a nice healthy voltage (no idea how much - suspect it will produce ~5V when pulsing, which will be once or twice per engine revolution) then the chances are it's the box-o-magic.

Cheers,
Robin

[rbgos]

Thanks Robin, I'll check that out.

I'll need to check to make sure, but I think that the only wires going to the distributor (other than HT) are the two connecting to the Lucas amplifier. If I've disconnected them from the amplifier so I can measure voltage across them, where is the distributor getting that voltage from? Does the Hall Effect sensor generate voltage? Or is there another supply to the dizzy I haven't spotted yet?

Cheers,

Richard

[robin]

That does depend on the type of sensor; if you get no voltage on cranking open circuit, try looking at the voltage with cables routed normally, ignition on, no cranking. At this point you should measure the voltage on both wires relative to ground. Then do the same whilst cranking.

Given there are two wires the choices are between a variable reluctance sensor (this will generate a voltage all by itself) and a variable impedance hall sensor (this will change its resistance according to the magnetic field).

The VR sensor produces 0V most of the time, then a pulse that has a negative going leading edge, a sharp transition through 0 into positive at the middle and then a return to 0 at the end (or the inverse - depends which way you look at the wires ).

The variable impedance hall sensor will draw current from the black box down one wire and return it on the other wire (which is possibly grounded). Assuming the black box supplies the current to the sensor through a resistor, then as the sensor uses more/less current, the voltage drop across that feed resistor will change and so if the black box monitors the voltage on that pin it can "see" the changes in magnetic field at the other end.

Cheers,
Robin

[steviej]

Small point and not wishing to state the obvious but check that the distributor is actually turning when cranking the engine incase the drive is broken

[mac]

Dizzy spinning or not you should still see a life in the king lead?

Mac

[steviej]

wont get an HT spark from king lead without the dist turning

[mac]

Is the pulse generator attached to the distributor shaft on Lucas style electronic ignition? I've no experience with that particular box of tricks and assumed that it picked up the timing from a different source.

[robin]

Good point, should check the dizzy is turning! Whether or not you would get a spark if the dizzy wasn't turning is debatable, but the engine won't work if it isn't, will it

[rbgos]

Tried Robin's suggestion about jumping the -ve terminal of the coil direct to earth, bypassing the "electronic points". Didn't cause any reaction from my timing light - although an enthusiastic spark from the earthing wire when I made the connection to earth! Guess that means the coil is the first culprit to try replacing.

Update when I've done that...

Richard