Slow Cranking and smoking terminations!

[ALAN COCHRANE]

Yes I've been checking the S1 diagram and see the routing of the two brown cables.
I'm also convinced that the burning termination is a separate issue which is only highlighted during slow cranking but probably present all the time but at a less spectacular level.

[lowact]

Alan, your diagram shows a “starter switch” that switches all power to the starter motor, i.e.


This arrangement, whereby the only power supply to the starter motor is via this switch, imo would be so dangerous that i feel sort of obligated to comment/persist, despite the time/effort to do so and despite increasing revelations that your diagram is not an accurate reflection of your car’s wiring. Is the actual wiring the same as the above detail or not? If it’s not the same that’s great, don’t read further.

If it is the same it is 99% of your problems, the solution is to rewire to as shown in post #13. Note that the diag. in post #13 is a mark-up of your diagram incorporating significant corrections.

The function of the "starter-switch" is changed. Note it is only called a “starter switch” on your diagram. In all other illustrations of circuits that have such device it is called a starter-solenoid relay.
Your aftermarket starter motor has a “starter motor solenoid” that switches the power to the motor; it is why there can (should) be an uninterrupted and heavy cable directly connecting the starter motor to the battery terminal post, being the isolated and only conductor designed for and subjected to the very high starting currents. For this there needs to be a switched supply to the starter motor solenoid (a switch for the switch).

On your diagram there is no switched supply to the starter motor solenoid; the WR “solenoid operating wire” at the starter motor is permanently connected to the power supply that it is meant to be switching; (why, is the starter motor faulty?). Therefore your diagram has an additional switch (the infamous “starter-switch”) to perform the starter motor solenoid’s starting-current switching function. No way would it be rated for this duty.

In the post #13 marked-up diagram the design function of the starter motor solenoid is reinstated, therefore there is no alternative device required for switching the starting current. Instead the “starter-switch” is used to operate starter motor solenoid according to the start requirement. Note however that such use of a starter switch/solenoid relay is not essential. Instead it could be removed and the WR wire from the start push-button joined directly to the WR “solenoid operating wire” at the starter motor, same as all S1’s and how yours would have been originally. The only benefit of keeping the “starter switch/solenoid relay is that current needing to be passed through the push-button is much reduced.

Clear as mud?
Cheers.

[ALAN COCHRANE]

Colin

Thanks for your expansive post.
The starter switch is fully rated for the starter motor. I’ve already stated my car is a confusing mix of 3.8 & 4.2. The starter switch was originally the remote starter solenoid for the dynamo. Simply put it’s a giant relay.
I’ve been doing further head scratching and think the burning terminal may be due to a high resistance short at the fuse holder. This then becomes a dead short when there’s 160A flowing during cranking.
At least this theory includes all the facts.
Frustratingly I can’t put any of this to the test until the middle of next week because I’m currently away on a short family break.

[MarekH]

On your diagram there is no switched supply to the starter motor solenoid; the WR “solenoid operating wire” at the starter motor is permanently connected to the power supply that it is meant to be switching; (why, is the starter motor faulty?). Therefore your diagram has an additional switch (the infamous “starter-switch”) to perform the starter motor solenoid’s starting-current switching function. No way would it be rated for this duty.

As pictured, the bendix and the actual starter both drop out as soon as you take your finger off of the starter push because that controls the white/red reaching the starter switch.

The starter switch via starter push method is straight from the s1 wiring diagram, so the starter switch probably is rated for that duty. Just think of it as an off-site bendix.

You are right to point out that the starter switch is totally superfluous - you can connect up the white/red to the gear reduction directly and also bypass the big cable as per your post#13 and that is a better implementation. There is no point in doubling up whatsoever.

None of this explains the smoke at fuse3 on prolonged cranking. I think there is a loose connection at fuse3 and/or high current usage downstream from there. Take your pick from the wiring, the connectors, faulty or incorrectly wired ignition relay, fuel pump (yes I know we've been told that's wrong....), cigar lighter, map, interior or door light circuits, headlight flasher, hazard can and light relays or horn relay.) EDIT:- I see Alan has finally got to looking at the fuse3 issue.

kind regards
Marek

[MarekH]

I'll caveat what I said earlier - if the starter push can handle the bendix current, then the starter switch is superfluous. If the starter push is a flimsy low current item, then I'd go with the post #13 version. Either way, there is still no reason for the big current to go through starter switch.

kind regards
Marek

[ALAN COCHRANE]

Well I managed to spend the whole of yesterday afternoon in the garage
I decided the first thing to do was "bell" all the wiring in and around the starter switch. It yielded some interesting results and here's how the wiring currently is:-



As you can see there are at least two alternative loops along the run of the main battery lead. This was probably done when the PO converted the car to negative earth, at the same time installing an 11AC alternator and high torque starter but confusingly leaving the remote starter switch/solenoid in situ.
I think the front wiring loom was replaced with that from a series 2 because of the inclusion of the alternator relay.

I also checked for any shorts to the bodywork around the fuse holders but there were none. I now strongly suspect that there's a high resistance within the primary cranking circuit and as a result these loops are providing an alternative route for the starting current.

I will now remove these loops and tidy up the over complicated wiring. I've also bought a new starter switch so will replace this as well. Ultimately I will remove this and rewire the starter motor solenoid to suit.

The fuel pump supply is looped from fuse 6 which is ignition controlled.

Cheers

[phoenix]

I would have thought a bad earth connection .

[Tommd]

Many have posted some good thoughts that are well worth investigating. I will add two possibly far fetched thoughts.
1. You say it cranks slow after it is laid up for a while. What is the chance of a weak battery?
2. What type of fuel pump do you have? If it is a motor driven pump, I wonder if the fuse 3 heat could be caused by the weak battery supplying low voltage to the fuel pump motor, causing high current draw?

You do seem to say all is well when the unit is used regularly.
Tom
Edit, I am sorry on the fuel pump, I thought it was wired through fuse 3, but I guess not. Did you determine where it is wired?

[ALAN COCHRANE]

Well I've managed to cure the problem but not quite sure how. There was no smoking gun or should I say terminal but I suspect that the most likely problem was a loose battery terminal on the starter switch.
I swapped the switch and rejigged the wiring so that the secondary loops have been removed.
The engine now cranks at "full speed" even after a two week lay up.
I'm considering wiring out the starter switch but must admit it's handy being able to crank the engine while your head's stuck under the bonnet.
Thanks for all your suggestions.

[ALAN COCHRANE]

I thought I'd give an update on my slow cranking odyssey.
The new remote starter switch lasted all of three weeks and then failed! SNGB to their credit replaced it without a quibble.
In the interim we had a car show scheduled for the following weekend. As a quick fix I re-installed the original starter switch which got us safely there and back only to conk out in the driveway
In the meantime the replacement had arrived, so I fitted it just to get the car in the garage.
By now I'd lost all faith in the remote starter set-up and decided that a direct feed to the starter motor was required.
I spent yesterday morning fitting the new battery lead and extending the ignition wire. Result-the engine cranks even faster from cold than it's ever done
This makes me think that there was a resistance across the closed terminals of all three remote switches-even when they were working. This may also help to explain the smoking terminations on the parallel secondary wiring.
It always puzzled me how the Triumph cranked much faster than the E-Type with the same high torque starter. This may have been the main reason.
Anyway I'm now very happy with the end result.

[MarekH]

By now I'd lost all faith in the remote starter set-up and decided that a direct feed to the starter motor was required.

This makes me think that there was a resistance across the closed terminals of all three remote switches-even when they were working.

Yes, that's completely logical.
I'm glad you adopted Colin's suggestions.

kind regards
Marek

[phoenix]

I would think bad earth. It will find an earth such as speedo cable throttle linkage etc.

[Bill Michigan]

A big “thank you” to all who contributed to this 2022 thread. Referencing it was a huge help to me recently as I tried to troubleshoot my 1963 3.8’s extremely sluggish starter motor, which could barely turn over the engine, even with the spark plugs removed.

Troubleshooting was frustrating. Aside from the apparently low torque, the only other anomaly seemed to be low voltage at the starter motor; it was around 4 or 5 volts when cranking and apparently should have been between 10 and 12.

Based on comments in this thread, I tried just about everything to solve the problem, such as running a jumper cable from the positive (earth) terminal to the bell housing to negate problems due to a poor ground, as well as several other suggestions posted in this thread.

The battery was fully charged, but just to make sure it was good I took it to the battery experts to be sure it could provide 500+ CCA, and they said it was fine. Then I pulled the starter motor (that was fun) and took it to the starter motor rebuilders, and they said it was fine.

So, I decided to change my approach, and instead of starting with the complete system and working back, I simplified everything and started with only 4 elements:
1. Starter motor (re-installed)
2. Battery
3. Custom-made 6’ Negative cable (with battery clamp on one end and proper hole-in-tab connector for starter motor on the other)
4. Single jumper cable with heavy duty clamps (one end clamped to bell housing near starter motor and the other end to be clamped to positive terminal on battery).

In other words,
1. No old cables
2. No battery or chassis ground straps
3. No ignition switch, no starter button
4. No solenoids or relays
5. No intermediate connections
6. No taps of wires connected to other devices
7. No fuses

When I completed my 4-piece ensemble and connected the positive earth jumper cable clamp to the battery, it was…magic! Even with the spark plugs re-installed, the engine spun like a jet turbine. It has never turned over like that in the 6 years I’ve owned it. I swear—I could drive 2 or 3 miles on the starter motor alone, and still get a speeding ticket.

I believe the reason the troubleshooting was ineffective was that there were TWO problems, so bypassing each of them one at a time didn’t have much impact. First, the positive earth connection had consisted of bolting the endpiece through two painted panels…the paint had not been scraped to bare metal to allow good grounding. Second, the negative connector (original equipment replacement part) from the battery terminal to the solenoid/relay was defective—likely a weak connection at one end or the other, or broken strands of wires internally. (The troubleshooting problem was also complicated by the fact that poor connections still showed “zero ohms” on a meter, but couldn’t handle the high current.)

Thanks again.

Bill