Starting Ignition Problem

[rob_mitch 0 1 Cars]

Hi,

 

Recently purchased a 1.9 Tarmac Rally car to use for Trackdays and Sprints.  It is fitted with twin Webers.

 

Had it out for first time 2 weeks ago and the battery started to fail, needed jumpstarted in morning when cold and push-started after lunch halt.

 

I have replaced the battery with a new "Duracell" one.

 

Engine now turns over well on starter but will not fire up any more.

 

Checked for spark by removing one plug.  Most of the time there is no spark when starter is turning except just one spark when starter motor is released.

 

Voltage +ve  feed to coil shows 13 V until starter turned on when it drops close to zero.  When starter is released, 13V returns to coil feed, coinciding with single spark from plug.

 

Only change (that I know of) is the battery.

 

I have tried swapping over the ignition module but no change.

 

I have started looking at the wiring and it is looking a bit scary.  Whoever built the car appears to have had only red wire.

 

Before I start pulling the wiring apart, I wondered if anyone has had a similar problem or could advise where to start.

 

Thanks,

 

Rob

 

[PhilNW 44]

Is it on standard ignition? 

[Thijs_Rallye 87 4 Cars]

What do you mean with a duracell one? Are both grounds connected properly? (one to gearbox and the one to the inner wing)

 

 

[rob_mitch 0 1 Cars]

Yes still running standard ignition system. Got hold of a new ignition module but problem still there.

 

Battery has been moved to boot in battery box.  Earth connection here appears good.  I haven't checked gearbox earth but will do.

 

However when I had bad earth on my autotest Mini a while ago  the starter would only turn over slowly. Starter is now turning engine over very well with new battery.

 

 

[Tom Fenton 1,542]

All the cranking information comes from the pick up inside the distributor. I would start there and check the connections. I've once had a pin push back into the plug.

[rob_mitch 0 1 Cars]

Hi, thanks for your replies, it looks like it could be some sort of earth problem due to the "rally-wiring" conversion.

 

I replaced the fuse for the air-horn relay on the dashboard and it now fires up immediately.  During auto solo event 2 weeks ago I had to borrow the fuse from the horn relay as the fuse for the Saxo power-steering motor had failed.  It didn't cause problem at the time as  the engine was left running all afternoon due to the failing battery.

 

There is also this relay cable-tied to the ignition module plate.  The switch input for the really comes from a wire spliced into the starter-solenoid wire so only switches when starter turning. The output feed from the power side of the relay is spliced into the wiring connected to the horn switch.

 

Looks like a winter project sorting  out this winding.

 

 

[rob_mitch 0 1 Cars]

Hi,

 

I have traced through the wiring on this relay circuit attached by cable-ties to the ignition module plate and now understand what has happened.

 

• The relay on this circuit is switched by the supply to the starter solenoid.
   
• The power-side of the relay supplies 12v to the +ve terminal of the coil (when the starter is turning).
   
• The main power supply for this relay was taken from the "rally-prep" air-horn circuit.
   
• So when I borrowed the fuse from the air-horn circuit to power the electric hydraulic pump for the steering, I stopped this backup power supply to the coil when starter is active, hence no spark.
   

However it is still not clear why this add-on to the +ve supply to the coil is required and why power is lost from the normal supply to the coil when the starter is active.  

 

Is this somehow linked to the tachymetric relay circuit which presumably is not required as the car has been converted to Webers.  

 

As this carb conversion appears quite popular I wondered if anyone had come across any similar problems.

 

Thanks.

[Ozymandis 97]

Many cars once had a similar idea,  the run posistion feed was through a ballast resistor, whereas the start posistion was fed full battery voltage for a bigger spark on cranking. The coils were not 12v.

Could it be something of that ilk maybe?

In fact my kit car has exactly that arrangement, now i think about it.