Ignition circuit

[Sandgrounder]

I know there are wiring diagrams in the Steve Heath book, but I find them somewhat confusing.

Does anyone know whether the ignition circuit has a fuse or relay?

I am trying to trace an intermittent fault with the starter motor.

Thanks

[GreenV8S]

It's powered from the ignition switch, usually via an alarm/immobilser.

Have you checked the dreaded yellow connector?

[Sandgrounder]

no alarm on mine. Removed that when I did the dash refurb years ago. Also, no yellow connector, a previous owner must have got rid of that potential issue also.
So no fuse or relay to check then.

I am thinking it is the battery as it is at least 8 years old, but when I took it to Halfords for a check, they told me it was ok.
Just don't want to buy another to find it has same problem.

[Sandgrounder]

I should add that I can rule out the Starter motor, as I have already fitted a replacement!

[magpies]

so that basically leaves the ignition switch and the wiring, both of which are 30 years old.

It is not unknown for a break in the wiring loom - happened to mine (lost an ign live while on outside lane on motorway)

Relatively easy to run a new (temporary) cable and s if tat curs the issue.

[phillpot]

Blown fuses don't usually give intermittent faults?
Brand new starter motors can fail?
When it doesn't start what do you do to get it started? Unless you charge up the battery it shouldn't be the battery?
Breaks in cables can happen but not common, more likely a loose/poor connection somewhere?

[v8s4me]

Sandgrounder said:

...I am trying to trace an intermittent fault with the starter motor.....

What exactly is the intermittent fault? Starter not turning? Starter clicking? Nothing at all? Hot or cold?

Have you checked the earth from the starter to the chassis?
Dodgy connection on the relay?

Phillpot - can't you find anything better to on holiday? Is your hotel locked down? Do you want me to send you some face masks?

[TVR-Stu]

Have a close look at the connections on the starters solenoid. I had an intermittent fault with my starting and that was the problem.

I'm not sure if the original terminals on the solenoid where designed for a nut to secure the cable and I think it's very easy to over tighten it which causes the threaded post to rotate within the solenoid body and give a dodgy connection. Might have just been like this on mine of course.

[mentall]

I had that one too.

Tried to rectify it three times (starter in and out each time); finished up with a remanufactured starter motor.

[GreenV8S]

Sandgrounder said:

I should add that I can rule out the Starter motor, as I have already fitted a replacement!

Intermittent starter problems are quite common on these cars. I suggest to start with you monitor the voltage across the starter motor solenoid when the problem happens so that you can tell whether you have a problem with the electrical supply, or a problem within the starter assembly.

[Penelope Stopit]

Difficult to find if not happening often

The problem is that it takes 3 volt meters or high wattage test lamps temporarily wired into the circuit until the fault shows

Other than the above

As mentioned in above post by GreenV8S, wire in a voltmeter

Voltmeter test 1, connect to starter body and main battery positive at starter solenoid

If the above is checking ok when fault appears

Voltmeter test 2, connect to starter body and ignition crank wire at solenoid

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Have you checked interior loom to engine loom plug?

[Sandgrounder]

Thanks for the responses. The fault is starter clicking, with no spin. Did it about 5 times this morning before firing into life on 6th attempt.

Ran the engine for 30 mins while I sorted my bonnet hinges. Stopped for lunch, then went back to car, and it started first time.

When the weather warms up a bit, I'll put it on ramps, so I can get to the starter, and do some voltage testing.

[GreenV8S]

Sandgrounder said:

Thanks for the responses. The fault is starter clicking, with no spin. Did it about 5 times this morning before firing into life on 6th attempt.

That is the symptom of a sticking starter solenoid. It can be caused by an insufficient voltage, or a starter assembly that needs maintenance, or both. The volt meter results will tell you which. It's often caused by a combination of factors and can be fixed by addressing any of them, but ideally you'd fix all the contributing factors while you're at it.

If you end up taking the starter off, it's worth adding a heat shield to protect it from the exhaust heat. This is very easy to do with a piece of aluminium backed fibreglass cloth secured with lock wire while you have the starter off.

[phillpot]

Penelope Stopit said:

---

Have you checked interior loom to engine loom plug?

Where will he find that?

[Penelope Stopit]

Sandgrounder said:

Thanks for the responses. The fault is starter clicking, with no spin. Did it about 5 times this morning before firing into life on 6th attempt.

Ran the engine for 30 mins while I sorted my bonnet hinges. Stopped for lunch, then went back to car, and it started first time.

When the weather warms up a bit, I'll put it on ramps, so I can get to the starter, and do some voltage testing.

Ah, if this is the case........

Solenoid clicking in ok and motor not turning is often caused by bad commutation, faulty armature or burnt solenoid contacts

The thing is........

Solenoid needs starter body earth to click in, even though the solenoid clicks in it doesn't prove that the starter earth isn't breaking down when voltage is applied to the motor through the solenoid contacts

Yes, voltage testing will help much

[v8s4me]

Start with the simplest thing.
Attach one end of a jump lead to the earth terminal on the starter and the other end to the negative on the battery. Turn the key; if the problem goes away it's a typical TVR dodgy earth problem.

If that fails; leave the jump lead earth on, make sure the ignition is off. Take a live direct from the battery and briefly touch the smaller +ve terminal on the starter. If the starter engages and starts to turn then you know you need to trace the wiring back via the relay to the ignition switch.

You've said the starter is a new unit so my money would be on the dodgy earth (or faulty connection on the starter) because that's the most common cause of the problem you describe.

GreenV8S said:

....If you end up taking the starter off, it's worth adding a heat shield to protect it from the exhaust heat. This is very easy to do with a piece of aluminium backed fibreglass cloth secured with lock wire while you have the starter off...

Definitely

[Sandgrounder]

So there is a relay?
Anyone got a photo where. I looked at steve heath book but couldnt see anything to suggest there was one.

Thanks for the guidance on using thd jump leads. I’ll give that a go when car is on ramps.

[v8s4me]

Sandgrounder said:

....So there is a relay?....

Usually. Follow the thinner +ve wire back up from the starter motor. That should lead (pun pun ) you to the relay.

[Penelope Stopit]

Sandgrounder said:

So there is a relay?
Anyone got a photo where. I looked at steve heath book but couldnt see anything to suggest there was one.

Thanks for the guidance on using thd jump leads. I’ll give that a go when car is on ramps.

Don't know why you mention there is a relay

There will be a relay if someone has fitted one as a modification

Here's a circuit that may be of interest should you wish to fit and wire a relay

Taken from Starter Interlock Relay, Kill 3 birds With 1 Stone

[Sandgrounder]

With reference the solenoid heat protection, what would be the symptoms?

The only issue I have had (prior to this intermittent cranking problem!) is after trying to start after a long run, the starter spins very fast without engine firing. Usually pressing accelerator to the floor sorts that??