Help! GT40 Starting Problem......

marcoos_1 · Post by **marcoos_1** » Mon Oct 26, 2009 2:08 pm

Hi,

I have an SD1 engine in my car (GT40 Replica). I thought I was close to getting the thing on the road, but I seem to have taken a step beck. Hopefully some of you guys can give some advice....I will try to keep this short and factual.......

OK, firstly the set-up. I have a Holley 390CFM carb and Offenhauser on the engine. It was new about 10yrs ago (i.e. it has never yet been on the road!). I seem to have some kind of electronic ignition module - it's a lucas unit which looks quite dated and is basically a flat alluminium housing with two bolt holes in it. I have an aftermarket electronic ignition coil.

Now the problem. The car fired up (running a bit rough) and drove onto my four poster ramp to get some more work done. For some reason the right hand bank (2,4,6,8) were always cold and not firing. Taking the plugs out and cleaning them did the trick for a few minutes, but then it would go back to the same (with lots of black runny crap coming out of the cross-over exhaust which I assume is just unburnt fuel). I thought too much fuel. I bought a couple of books on the Holley, went out to do the initial set-up,.......checked my fuel pressures (now correct), did my float heights (now correct), did the idle mixture screws (now correct), Still running really rough at this point, but ticking over. I then went to check the ignition timing with a light. The light wouldn't flash. I tried it on another car - timing light works great! Back on my car - nothing. By this time the car will not run at all. I messed around with the distributor - it won't start. The spark looks kind of weak, so I changed the coil - no change. I measured the voltage feeding the +ve side of the coil and it is only 4.5V, but goes up to 8-9v on cranking (I can't tell you what it runs at because it now won't start). I have checked the plug leads and the firing order is correct. I then got TDC on the flywheel, checked no1 piston was at the top with a screwdriver through the plug hole, then set my distributor so that no1 lead was aligned with the rotor arm, thinking that if I did this, then the timing can't be too far out. It still doesn't run. I spent the whole day on it yesterday and all I seemed to do was go backwards! I would have thought that with the carb roughly set-up and the timing close then I would at least get it to fire.

Questions.

1) could my ignition moudule have just gone? If so - does anyone have one!

2) is it right that I only get 4.5v at the coil with the ignition on?

3) why won't my timing light work on my car. Is it anything to do with a weak spark?

4) which pugs should I have in there?

5) is there anyone that lives near Glasgow/Ayrshire that can help me???

Any suggestions very welcome. Apologies, but that was about as short as I could make it!

bones · Post by **bones** » Mon Oct 26, 2009 2:26 pm

Hi ,ive had alook at my sd1 book and the coil should be within 1v of the battery power which should be no lower than 11.7v with ignition on, if its not check the wiring to the + side of coil all the way back to ignition switch and check battery earthing, hope this helps abit,

rich

gelmonkey · Post by **gelmonkey** » Mon Oct 26, 2009 2:46 pm

Hi
Have you checked that the dizzy cap is clean,not cracked between poles,
the leads are in good condition and not furred up/corroded.
Have you changed the rotor arm/cleaned it up?
Is the battery fully charged?
Will the motor turn over now?
What fuel pump are you using and is it running properly?
Have you got a really good earth from the motor to the chassis?
Lots of questions back but the more info available will mean that the more the guys on here will be able to hopefully help you.
cheers
Paul

ChrisJC · Post by **ChrisJC** » Mon Oct 26, 2009 5:36 pm

Have you got a picture of the ignition setup so we can be 100% sure about it?

Chris.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Oct 26, 2009 6:30 pm

From the variation of voltage when cranking it would appear you have a ballast resistor in the wiring.

Your ignition system coil and distributor need to matched to each other and the voltage supply.

You mention new coil which one did you buy as it's not just the voltage but the resistance thats also important.

Which Lucas distributor do you have, it should have a number starting with 35D.

Is the amp seperate from the distributor or attached?

Kevin.

marcoos_1 · Post by **marcoos_1** » Mon Oct 26, 2009 11:00 pm

OK,

Thanks for all the questions:

1) the coil I have is a Power Train Electronic Ignition Coil - the car has run with this unit before, but I did swap it incase there is a problem.

2) The battery is brand new and seems to have plenty of power (its continually been cranking the car trying to get it going!)

3) Not too sure which distributor I have - its really close to the bulkhead now as I have had to move the engine forward quite a bit. I have taken some pics of this and my ignition module - hopefully they will be attached to this post.

I tried my timing light again tonight - nothing on the GT, but working great on another running car. I took a positive feed straight from the battery and put it to the +ve side of the coild and cranked it. It tried to fire - and the light started working???

Couldn't upload pics - how do I do this?

marcoos_1 · Post by **marcoos_1** » Mon Oct 26, 2009 11:12 pm

OK - hopefully this will work. This should be a pic of the distributor internals and the module I have.

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marcoos_1 · Post by **marcoos_1** » Mon Oct 26, 2009 11:18 pm

OK,

to answer some of the toher questions I missed.........

Have you checked that the dizzy cap is clean,not cracked between poles, yes - it's new and hardly used.the leads are in good condition and not furred up/corroded - pretty new also and no sign of corrosion
Have you changed the rotor arm/cleaned it up? cleaned it up - seems OK.
Is the battery fully charged? yeah - brand new and fully charged
Will the motor turn over now? no sign of starting...the very occasional fire
What fuel pump are you using and is it running properly? twin fuel pumps matched for Holley carb....checked the fuel pressure from each and both spot on at 4psi. renewed fuel lines and new low pressure filters on each also.
Have you got a really good earth from the motor to the chassis? just re-did all this tonight and no improvement.

marcoos_1 · Post by **marcoos_1** » Mon Oct 26, 2009 11:25 pm

one other question.....

you will see on the pic above of the ignition module that there are two connectors on the left hand side. The top one is in the right place and seems to be the wire that is giving out 4.5v

the bottom connector is the 12v feed in (I have checked and I am getting 12v at this wire) and it can be on one of two spades coming out of the unit. One is marked SW+, the one below at the bottom (the one which has the connector on it in the pic) has no label on the housing. If I use the bottom one I get no power to the coil (then the car will definately not start), but if I put the feed on the SW+ connector then I get the 4.5V. I'm assuming the SW+ is the correct one to use, but should there be something on the bottom one at all?

So many questions.......thanks guys for your help so far.

bones · Post by **bones** » Tue Oct 27, 2009 12:56 pm

the silver plate is a ballast resister, the coil should show nomore than 1v less with ignition on, than the battery voltage. The dizzy looks like a Lucas 35DM8. the book i use is a old rover sd1 workshop manual one , and it doesnt mention the ballast as a fault. On the wiring diagrams its got,WHITE/BROWN from the dizzy to the coil, from the coil it should have 2 WHITE/YELLOW wires 1 going to the starter and 1 going to the ballast resistor, from the otherside of the resistor going to the ignition switch, Or thats what the diagram shows anyway. thats alot of looking up for me, i better go and have a nap

rich

marcoos_1 · Post by **marcoos_1** » Tue Oct 27, 2009 1:29 pm

When I turn the ignition on, I only have 4.5v at the positive side of the coil (with the connector in the SW+ terminal).

Do you mean the unit in the picture is a ballast resistor - I thought it was some kind of electronic ignition module!

ChrisJC · Post by **ChrisJC** » Tue Oct 27, 2009 1:33 pm

The silver thing is indeed a Ballast resistor. The ignition amplifier is the circuitry inside the distributor.

I think it's Lucas 'Opus'. Hopefully somebody can confirm that.

I think most people ditch it and fit something from a later V8 with a constant energy ignition amplifier.

The ballast resistor should be bypassed whilst cranking, i.e. the coil +ve should be directly connected to the battery +ve (via the ignition key). When she runs, coil +ve is fed from batt +ve via the ballast resistor to drop a few volts. That way the voltage on coil +ve is pretty constant (at least, it compensated for lower battery voltage when starting).
That means that the coil MUST be one designed for a ballasted ignition circuit, which means it should be less than 12V rated.

Chris.

marcoos_1 · Post by **marcoos_1** » Tue Oct 27, 2009 2:10 pm

Chris,

I'm confused.........should I be buying a new coil or ballast resistor then, or do I change the whole lot for something more modern like you said (if so - do I need to change distributors etc?).

Do you think the fact that I'm only getting 4.5v at the coil +ve side means the resistor is knackered then? Might the coil be OK? The only thing I know is that the coil was bought for a car with electronic ignition.......not sure if it was specificed for a ballast system.

sh*t.....i really don't understand electrics.........

Ian Anderson · Post by **Ian Anderson** » Tue Oct 27, 2009 2:14 pm

Hell I wish you well as another GT40 guy

But I cannot help as to me it's electrickery

Ian

ChrisJC · Post by **ChrisJC** » Tue Oct 27, 2009 2:33 pm

Hmm, tricky!

If the coil was specced for electronic igntion, I suspect it's the wrong one. Constant Energy ignition has quite different coil requirements.

I'm also a bit nervous about the 4.5V when you're not cranking, but I've never actually played with a ballasted system myself.

If it were me, there are two options:
1. Get a known coil and ballast resistor from somewhere reputable like Rimmer Bros. It won't necessarily be cheap, but at least it will be the right one:
http://www.rimmerbros.co.uk/Item--i-DRC1638
Can't see the coil for sure, but maybe ring them and say you want the one for the 35DE8 OPUS type distributor.

2. Get a distributor from a later engine. Then you can do away with the ballast resistor. The issue is that there are two types of body with the vac advance in a different place:

And I'm not sure about compatibility with oil pump drive.
And you'd still need a matching coil (although the one you have may be OK)

I think I would power the ignition circuit independently from a different 12V battery and see if the engine started then. I'd ignore the ballast resistor and just hook the battery straight onto coil +ve and chassis earth.

Chris.