Slow Cranking and smoking terminations!

[ALAN COCHRANE]

Hi Everyone

For some time now I've been having issues with the high torque starter slow cranking when the car has been laid up for an extended period. I've cleaned up or replaced all the earth connections but this hasn't solved the problem. At all other times the car starts on the button.
More worryingly is the smoking termination on the brown wire at fuse 3! This only happens during the slow cranking and appears to indicate that it's carrying excessive current most likely to the stater motor-a parallel circuit in other words. I've attached a copy of the car's wiring diagram with the offending termination circled. The wiring has been modified over the years with the addition of a 4.2 front wiring harness and additional relays.
I've poured over it in detail but for the life of me can't see any parallel path. Fuse 3 has never blown and none of the other connected wires are affected.



I've ordered a new starter switch from SNGB because the insulation on the brown cables marshalled on it showed signs of heat degradation. I've re-terminated all the affected spade connectors but know this will not have solved the problem.
I'm also going to invest in a CT clamp attachment for my multimeter. This will allow me to monitor the current flow in the brown wire during start up.
I suspect it happens every time the car is started but normally the cranking period is so short that the brown cable can cope with the short burst of high current.
Frankly I'm stumped so any suggestions will be gratefully received.

Cheers

[flatfloor 3.8]

Hi, my brother had a similar issue on his car with slow cranking with an "Edge" high torque starter. After checking all the terminals etc we removed the starter and had it tested and stripped and it was shot, so had to buy a new one as spares to rebuild were not available.New starter fitted and all now OK. The starter was about 20 years old.

[lowact]

Yes almost certainly the starter motor itself. Bearing shot/seized or melted resin gluing the rotor, so the motor pulls huge current trying to overcome this. That it is worse after the car has been laid up is consistent with this, before high current has heated enough to loosen things.

[MarekH]

There isn't enough resolution to make out what your modifications around the ignition components are, but I would swap out the three fuses next to your written "hot" annotation with 2amp fuses and see which one blows. Most of those circuits have nothing to do with starting and can be disconnected for diagnostic purposes. I can see no good reason to be using a high current anywhere during starting other than for the starter motor itself.

kind regards
Marek

[christopher storey]

I am with those who say that this is either a starter motor fault , or a fault in the wiring to the starter motor . The slow cranking in itself points to insufficient motor power causing an excessive current draw which the circuit is having trouble meeting

However, perhaps before writing the motor off, it is worth cleaning ALL the connections between battery, ammeter , and fuses, to make sure that it is not a high resistance connection resulting in very high current draw when cranking. Also measuring the resistance of each lead in case it is concealed broken strands causing high resistance

[caveman]

I had a similar issue some years back but with my standard starter, I doubled up on the gearbox (to body) earth-strap, placing one on each side and haven’t looked back since.

[caveman]

I see you had similar issue in 2020;

viewtopic.php?p=136919#p136919

[MarekH]

The starter motor wants to pull a HUGE current when it runs. If dirty connections and/or some malfunctionng item/connection/wiring on the fuse3 path is drawing sufficient current to almost melt wiring, then that is current which isn't available to the starter motor, hence that would case slow cranking and eventually heat on the starter motor circuit aswell.

kind regards
Marek

[caveman]

Casing point, a friend of mine purchased one of the first electronic dash versions of the Astra GTE, (going back to 90’s), when it’s engine earth failed at a petrol station, on subsequent start up smoke billowed from behind the dash and after pushing the car clear of the pumps and disconnecting battery, we found the starter had used the next best earth, in this case the clutch cable now well and truly cooked! The least path of resistance as they say!

[ALAN COCHRANE]

Thanks for all the replies.
Just to clarify a few points:-
All earth connection from the battery to the bodywork etc have all previously been checked, cleaned or replaced.
The starter cranks normally at all times except after a long lay up.
The brown cable loops from fuse 3 to the ammeter and then on to the starter switch. All other connections on this cable run are unaffected by the slow cranking.
It also loops to fuses 4&6. The three fuses control the horn, dipped beam and main beam respectively.
Even if the brown cable between fuse 3 and the ammeter has a high resistance why would this be visible only when the engine is cranking? Surely it would become evident when the lights were on.
I’m beginning to think that the starter motor is the most likely culprit for the slow cranking which in turn is highlighting a second problem, the overheating cable.
Further investigation will hopefully reveal all.

[abowie]

Correct me if I'm wrong but the starter motor draws current directly from the battery via a really thick cable.

The starter solenoid is triggered by the starter switch, but it too should be getting its power directly from the battery via a skip from that cable.

So neither should be affecting your brown wire as they aren't pulling current from it.

That brown wire does connect to the starter switch in the engine bay; maybe your problem lies there?

[lowact]

Alan yr wiring diag is labelled S1.5 however it is wrong imo, power supply should be directly from the battery to the starter. It is only the power to the solenoid that is via the switch/relay. Here is the correct S1.5 arrangement:


When cranking, what is voltage drop across the solenoid switch/relay? Should be negligible.

To check the starter, completely disconnect the starter (incl solenoid), completely disconnect the battery, connect the starter motor directly to the battery, then jump the solenoid from the battery. If performance is not improved, the issue is the starter (or your engine).

Aftermarket starter installation generally includes procedure to check/adjust/align the pinion with the flywheel ring gear. This may be as simple as running the starter for a bit before tightening the mounting bolts. If not aligned there may be binding/side-load between the pinion and ring-gear, forcing the starter to draw a lot more current to overcome this unnecessary additional load. Ultimately damaging the starter bearings resulting in even more current.

[lowact]

Do it like this?
Note this also resolves the issue of duplicate wiring routes from the terminal to the solenoid switch/relay, one via the ammeter. no wonder yr wires were smoking. Starting current can be in excess of 200 A, no brown wire is large enough for this.


The WR wire from the push button to the solenoid switch/relay; better if it was WY. This energizes the coil to close the switch that connects from brown to the WR supply to the solenoid.

[MarekH]

Have you wired up your ignition relay correctly?
If, during your meanderings, you have accidentally swapped c1 and w2, or have used a 3pole relay here, or jumpered c1 to w2, then there is a second (indirect) path for starter motor current to flow. I'd go via the brown wire where you marked smoke escaping at fuse3.

EDIT:- I would measure the contacts of that relay with a meter to see whether there is any cross connection possible. Other than purple accessories, there is no obvious source of making smoke at fuse3, especially during cranking.

kind regards
Marek

[lowact]

Is there any possibility that the smoke observed near fuse 3 did not originate at fuse 3? Could it have leaked along inside the insulation?

[mgcjag]

Hi Alan.....looking at your diagram and your comments you say that input to fuse 3,4,6 are are all looped by the incommong brown thats smoking...although on the diagram the input to fuse 4 isnt shown...however fuse 4 goes to your fuel pump.....it look to me from the diagram that the pump would run continuously as its not controled via the ignition switch.....something not right here.....Steve

[ALAN COCHRANE]

A lot to think about here.

Steve-yes there's a mistake concerning the fuel pump wiring-it definitely doesn't run 24/7!

All-I've taken your suggestions onboard and will report back.

This diagram is a work in progress. I've been trying to fathom out exactly what the PO had done with the addition of the 4.2 front loom. When it comes to the electrics my car has a confusing mix of 3.8 and 4.2 features. I've added to this with additional relays, hazard flasher wiring and a headlight warning buzzer to name but a few.
I added the eight way connector(top left in diagram) to properly marshal all the wires that were previously stuffed behind the voltage regulator and twisted together!

I now just need to get some more garage time allocated. I need to speak to the boss about that.

Thanks

[MarekH]

Connectors get hot when they are poorly connecting and carrying high currents. The reported brown wire connector smoldering looks to be a separate issue only consistent with the ignition relay shorting out and/or a loose connector at fuse3. I'd check c2 to w2 connectivity as this is only reported as a problem during cranking.

If the ignition relay isn't properly connecting when asked to, then your starter push isn't making the starter switch connect the starter motor up. I would clean all of the contacts on that path, especially in the starter switch, as high current poor connectivity leads to arcing. Any duff corroded connections on that path mean the starter motor only partially runs. It might also explain why you have a problem only after a long lay-up. (1)

As a separate point, if fuse3 blows, then you won't be able to start the car. A more logical (unfused) way to connect the ignition switch bypass relay is to have w1(w2) as a switched brown wire and earth w2(w1). That gives the most protection from relay malfunction. It means the relay winding isn't live 24 hours a day.

As pictured, your ammeter is not showing any of the purple wire current draw.

It's important not to bother cranking until the float bowls are full. Most starting problems are fuel problems. See (1) earlier.

kind regards
Marek

[ALAN COCHRANE]

Marek

Thanks for your comments.

I always let the fuel pump run for a good 30 seconds before starting after a long layup. Even with very slow cranking it usually fires up.
I have to hold my hand up installing the ignition relay after having the car conk out due to burnt contacts in the dashboard switch. I see your point about fuse 3 blowing and I'll rewire the relay to avoid this potential problem.
I need to bell the wiring connected to the ammeter and see exactly what is connected where. There are two brown wires at the starter switch but only one shown on the diagram so again I need to see where they both go.
Finally I'll replace the starter switch and see where I need to go from there.

Cheers

[MarekH]

There are two brown wires at the starter switch but only one shown on the diagram so again I need to see where they both go.
Finally I'll replace the starter switch and see where I need to go from there.

See the s1 wiring diagram for the two brown wires. On the s1, one goes to the ammeter and the other to fuse3. The starter switch (or starter relay as it later becomes known) also acts as a brown wire distribution point on a s1.

I'm more worried about your ignition switch relay and its wiring, as the melting connector at fuse3 needs explaining. I don't see how that is on the starter motor path from your diagram and I don't see a high current usage path for it at cranking.

kind regards
Marek