P5b starting problems

[dirkco]

Hello all,

Well I took my P5B coupe on its first long drive to a car show
(Won club choice award) had a great time and the car ran flawlessly. I drove her home or near home and stopped at a bookstore. When I came out the car seemed to start right up BUT only when the starter motor is engaged. As soon as I release the key from the starter position I appear to loose spark and she dies immediately. I can even rev the engine while trying to start her.

I have a Crane electronic ignition XR 700 system and cannot find any mention of this type of problem on the net.

I have checked all fuses and changed the ignition control 4TR unit.

I have tried another coil.

I could change the crane system but it is allot of work if it is not the problem.

Could this be a ignition switch failure?
Or a wiring problem?
Has anyone heard of this as a problem?

Any help would be appreciated

Thanks
Dirk in the States

[harvey]

Sounds like you're losing the ignition feed to the coil once you release the ignition switch back from the "Start" position, which is when you no longer get the feed from the starter motor.
Try running a temporary live from a 12v supply to the switch side of the coil and see if this cures the problem. If so you need to find the point at which you're losing the ignition supply, which could be as you say, the ignition switch, a fuse, or the ballast resistor.

[dirkco]

Update,

Changed the ignition switch same problem.

Thanks Harvey, good advice I will run a 12volt line to the coil and try that.

Thanks
Dirk

[Phil Nottingham]

Is the ignition switch connected up properly? You are also aware that some early P5B's have ballast shunt wiring which only supplies 12v when starter motor engages?

[dirkco]

Hi Guys,

It's too bad I don't have my manual handy I lent it out.

The car is 1970 P5b coupe so I would assume it is a later model.

I brought 12volts to the coil and sure enough she ran after I let the key release from starting. So is there a fuse that would be for this this if it is not in the fuse box? Where would the ballast resistor be and what does it look like? I am familiar with how they look in a 3 litre but there is nothing like this in the 3.5 litre. Perhaps it was removed when the electronic ignition was installed I did not install this. Given that power to the coil goes through the Crane unit then perhaps the problem is there?

Your thoughts?

Thanks Guys!
Dirk

[harvey]

Check out how your electronic ignition system is wired up, and then trace back from the coil along the lead that should be your power supply until you get to a point where the supply is there and there's your break in the circuit.
IIRC there is an ignition control fuse which should be the one where the supply originates.

[dirkco]

Update,

After Harvey suggested I run power to the coil and it ran I started to look for a fuse or a wire break. None found. I removed the underside of the front parcel tray and looked at the wires coming in from the firewall and everything looked fine. I removed power to the coil and then tried starting again just for kicks and it started now it seems fine. Perhaps it is a broken wire I disturbed.

I was wrong before the power to the coil it comes from the original harness and then goes to the Crane unit. So I think this means that the problem is before the Crane unit if it runs when power is brought to it.

So it all still a mystery
Can anyone tell me what the ballast resistor looks like? Is the ignition fuse the one in the fuse box labeled Ignition? or is a there a mystery fuse behind the dash somewhere?

Thanks again
Dirk

[Phil Nottingham]

One your model the resister is a temp coefficient wire (pink) built into the wiring loom (previously it was on the inner wing just under the coil and required the shunt).

All you need to do is to take a feed from the unfused ignition sode of the fuse box and dispense with the existing coil supply. There are no fuses.

Ballast resisters were not fitted to 3 Litres either as standard.

You really need to find a wiring diagram for the electronic system - the Rover P5B ignition is most basic standard really