Starting Problems

[Stagless Steve]

For a couple of years now my engine will only fire up when I release the ignition key. From experience with previous cars I have always associated this with a weak spark, hence the engine won't fire up until the starter motor load is removed from the battery. Since this problem started I have replaced the battery, spark plugs, HT leads, coil, Powerspark electronic ignition module and have had the distributor rebuilt by Distributor Doctor. I also have a relay in the starter motor circuit which I fitted when I replaced the solenoid, but I did that well before this problem started.
Can anyone think of anything that may be causing this?
TIA
Steve

[Lester]

The Stag has a 6V coil fed via a ballast resistor for normal running.
To aid starting a feed (white yellow wire from memory) directly from the starter to the coil becomes active when turning over the engine.
If this wire is disconnected at either end or damaged it could cause your issue. It is a particularly vulnerable spade connector where connected to the Starter motor solenoid below the car.

[NeilR]

As it doesn't want to run when cranking, it's more than likely the feed from starter motor to coil is open cct (missing).

[Stagless Steve]

The Stag has a 6V coil fed via a ballast resistor for normal running.
To aid starting a feed (white yellow wire from memory) directly from the starter to the coil becomes active when turning over the engine.
If this wire is disconnected at either end or damaged it could cause your issue. It is a particularly vulnerable spade connector where connected to the Starter motor solenoid below the car.

Thanks Lester. My Stag was modified by the previous owner. The ballast resistor has been bypassed and it uses a 12v coil. Does that make any difference?
Also, my coil only has one wire attached to the +ve terminal. Your post suggests there should be two. Is that correct?

[Stagless Steve]

As it doesn't want to run when cranking, it's more than likely the feed from starter motor to coil is open cct (missing).

Thanks NeilR. Is there a way I can check for that? Do you think the relay I installed in the starter motor circuit might be the culprit? Also, as I mentioned to Lester, my coil only has one wire attached to the +ve terminal.

[NeilR]

As you have a 12v coil & no ballast resistor, I would have thought unlikely your start relay has any impact on that.
can you put a voltmeter between chassis & positive side of coil & see what happens to the voltage.

I did not have a ballasted system for 15 years & had no starting issues with a 12v coil.
But I run wasted spark now with effectively 4 coils, so not applicable anymore anyway.

[Stagless Steve]

As you have a 12v coil & no ballast resistor, I would have thought unlikely your start relay has any impact on that.
can you put a voltmeter between chassis & positive side of coil & see what happens to the voltage.

I did not have a ballasted system for 15 years & had no starting issues with a 12v coil.
But I run wasted spark now with effectively 4 coils, so not applicable anymore anyway.

The voltage between the coil +ve and the engine block is 12.5 before cranking and 10.6 during cranking.

[DZP]

Hi Steve,
The Stags 6v ballasted coil system was designed to improve starting from cold, but in normal conditions e.g. not freezing cold, then it should not be that much of an issue using a12v unballasted system.
I was going to suggest you check the battery with a discharge test, but as you have already replaced this, then it is obviously not the battery.
The only thing I can suggest is to check the ignition switch.
Maybe the ignition circuit is being disconnected during cranking position. If you have the problem when the engine is hot, as well as cold, then it is looking like a voltage disconnect somewhere.
Prior to having a starter relay fitted (as you have done) the Ignition switch does have quite a hard time handling the starter current for the solenoid.
You could try disconnecting the +ve coil terminal and connecting this to a bulb or meter, so that you can see if voltage is still present whilst cranking.
If this gives cause for concern, then connect 12v directly to the coil prior to cranking.
I would take a fused fly lead form the battery, but if using the normally unfused ignition circuit then take care.
Regards,
Den

[Tdafforn]

I had a similar issue with my stag at the end of the rbrr. Seemed to be one of 2 things. Either the battery was getting to the end of its life. I replaced it and it helped somewhat. Or the chassis earth was not making good contact. I found it loose with paint under the contact so cleaned it up and tightened it up. I cannot say which solved the problem as I did both and then tested and all ran fine.
tim

[NeilR]

10.6v during cranking should be sufficient for it to start, maybe worth looking at the rest of the ignition system - plugs, plug leads cap rotor arm etc.
It would seem to be you are not getting much of a spark during cranking.

Just a thought :- is the earth lead from the plate to casing inside the dizzy intact & in good condition ?, might be worth checking that.

[Stagless Steve]

10.6v during cranking should be sufficient for it to start, maybe worth looking at the rest of the ignition system - plugs, plug leads cap rotor arm etc.
It would seem to be you are not getting much of a spark during cranking.

Just a thought :- is the earth lead from the plate to casing inside the dizzy intact & in good condition ?, might be worth checking that.

Thanks NeilR. I replaced everything recently, and the distributor has been refurbished by Distributor Doctor. The earth lead was new and looked in good condition.

[NeilR]

Ok, so how about pulling a plug lead off & connecting it to a spare spark plug & held against the block somewhere where it can be easily seen,
then see if it sparks during cranking.

[Tdafforn]

10.6v during cranking should be sufficient for it to start, maybe worth looking at the rest of the ignition system - plugs, plug leads cap rotor arm etc.
It would seem to be you are not getting much of a spark during cranking.

Just a thought :- is the earth lead from the plate to casing inside the dizzy intact & in good condition ?, might be worth checking that.

Are we sure that 10.6v is enough for your powerspark ignition system to fire? I seem to recollect that if you drop below a set value you get nothing. Unlike points which will still work.
Tim

[NeilR]

That is a valid point.

But I'm sure there are other cars using those that don't have that issue.

[Stagless Steve]

Thanks guys. Plenty of good suggestions which I shall try. If I do run a lead from the battery to the coil +ve (temporarily to see if the engine fires up normally) can anyone suggest what amp fuse I should put in the line?