Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) High mileage cars

Never underestimate the importance of earth points. When I was struggling with the GDI immobiliser, the first advice was to redo the earths. When I had my recent bad running, first advice was check the earths. They were good. No resistance. Then when the dealer approached the factory, it was, resite the earth adjacent to the servo onto the chassis. It made no difference but this regular advice tells you a lot. On my GDI, that earth adjacent to the servo was a large circular eyelet on a smaller bolt, trapped between two penny washers. Not the best fix. Now it's way more professional with two separate earths onto the chassis inside the engine bay. So whatever you suffer from, whatever Morgan, check the earths.

It does seem that modern digital systems are likely to spit out alarm as a battery ages, thus perhaps the simplest check it to have the battery load checked, as that may require a lot less effort than getting in amongst things... Digital systems can be very dependant on voltage and more so if your Morgan is not in regular use, as in such situations a battery seem likely to have a shorter life span that one`s daily transport. I suspect any garage will have load testing kit that only takes a few minutes to disconnect the battery and test it.... Perhaps best if you have the battery fully charged first, perhaps after a long run , with a hour or two`s rest before the test is applied...?[/quote

Interesting what you say about battery life. I was just thinking how well the original AGM 105ah battery is doing on my 2018 60k mile BMW 740LD. At 8 years old it is finally starting to show some signs of failing only holding 12.2v, and I am about to change it before it strands me. I've also just given my daughter what was my wifes 2018 40k mile Subaru XV also on its original 8 year old battery - and still going strong!

Seems the above post appears to be somewhat jumbled up, given the first line is from Robbie`s post and the second paragraph outside the quote enclosure is my response to Robbie....creating confused dot com... (-:

Just to add that the sudden death of my four year old AGM battery fitted to my 2012 non Morgan was perhaps due to the minimal use of the car over those four years, circa 6 k miles I think. Whereas the same spec original battery had lasted 9 years, having covered circa 40k miles over that time, but was obviously coming to the end of it`s useful life at the time..I may just go back to replacing my batteries every three years or so in the hope of avoiding breakdown so related, given the risk of all the inconvenience involved as the result of battery failure ...

I thought I might tag this posting from DevaMog member on their forum....Worth checking the battery leads.

Mon 07:23
Msg from Tony Gibson Devamog
160826

If you have a CX model, check the tightness of your battery leads under the rubber covers.
We refuelled at petrol station 3 miles from home. Car lumpy , tried to turn over then all electrics went off. Called a friend out to jump it. Car didn’t register the new charge. The dash clock stopped at 4.10. Even that should run on fine current. So, call the RAC. Sunday in August with petrol station not happy with me blocking the forecourt. 😀🥸. Friend took Jo to our home. I waited ………. RAC diagnosed an extremely slightly loose battery lead to battery connection which couldn’t supply sufficient current to the starter resulting in the 300 amp main fuse blowing!!!! He tested the battery which was spot on. He has a 150 amp fuss on his car which he fitted and the car fired up immediately. I’ll fit a new 300smp tomorrow. Take 2 minutes to check yours!!!! No one got hurt. Otherwise a top day out .

Mike Wright
We had that, I replaced the starter motor.

John, I am somewhat confused re your post above.... I must admit that I am in no way up to date on vehicle electric systems though have heard of more modern vehicles having items described as pyro "fuses" which are of high enough amperage to carry the current of everything in the electrical system including the starter motor... I think the idea is that in a crash the "fuse" disconnects the battery from the rest of the electrical system reducing the risk of fire....? I have no idea whether the idea of high current "fuses" have become part of the of construction and use regs..?

In my limited electrical experience I have not come across a fuse that blew as the result of a loose battery connection, a loose connection usually creates the generation of heat under load causing signs or the aroma of burning, thus unlikely to "blow"the element within a fuse...? However using nothing more than perhaps flawed logic, I am guessing a pyro fuse may have a third low current input connection from an ECU which effectively acts like a relay control in that a small switched current can control a much higher current switching device, and in the case of a pyro fuse, instead of switching the device on, it switches the high current off as a one time operation...?

If my logic might be in any way reasonably accurate, then I do wonder if the loose battery connection, caused random fault codes to e generated and in this case provided a spurious output to that which may have been a pyro fuse...?

I really look forward to be proven to have been entirely incorrect..

I agree with Luddite: if the battery cannot supply enough current to start the car due to a loose connection, i don't understand how it could supply in excess of 300 amps to blow a fuse. Nevertheless, I also agree that a loose battery connection is something to avoid!

To pull 300 amps when starting an engine it must be the live connection to the starter motor , it is direct ( always live) the solenoid makes the circuit, from my experience starting cold was fine it was hot starting that was getting difficult, I did not blow a fuse but would have if I kept trying to turn the engine, BMW have had a recall notice on the B58 engine to replace the starter motor with this very problem and advised to park outside as it could result in a fire.

I went off to the interweb in the hope of finding some info on pyro fuse functionality and found this one which is rated for EV usage, in terms of it`s higher current capacity circa 2k amps as opposed to the 300 amps suggested as fitted to the Morgan in question... The pyro element of the name seems likely related to the explosive charge.

Now whether the fuse fitted to the Morgan in question was a pyro fuse or not, I have no idea, though it would be interesting to find out if it was, and where it might be located for those owners of similarly equipped Morgans... If the 300 amp fuse is other than of the pyro variety, I am left to wonder quite how it might have blown and quite how a loose battery terminal could cause it so to do...?

Hopefully the link to the very short vid below may help provide a degree of understanding as to the mechanical operation of the "fuse"


https://www.youtube.com/shorts/vkGsjETxisE?feature=share

AI explaination


A pyro 300 fuse (pyrotechnic safety fuse) is fitted on modern CX-generation Morgan Plus Four models.
Its Core Purpose

The pyro fuse serves as a critical emergency safety disconnect designed to minimize fire risks during a severe accident. It works through an integration with the car's crash-sensing systems:

Instant Power Cut:

Upon a collision severe enough to deploy the airbags, the Engine Control Unit (ECU) instantly sends an electrical signal to the fuse

.Explosive Disconnect:

The fuse contains a tiny, controlled pyrotechnic (explosive) charge. When triggered, it physically blows apart the main heavy-duty circuit connection inside the car within milliseconds.Isolates

Major Electrical Lines:

It completely cuts the primary electrical power flowing from the battery to high-draw systems like the starter motor and alternator.

Fire and Restart Prevention:

By instantly cutting the power, it eliminates the risk of short-circuits sparking near ruptured fuel lines and prevents the vehicle from being restarted after a crash.Important

Ownership NotesNon-Resettable:

Because it uses a physical explosive charge, once a pyro fuse is deployed, it is completely destroyed and must be replaced entirely to restore electrical power to the vehicle.

No Crank Condition:

If a CX Plus Four has been involved in an impact and has completely dead electronics or refuses to crank despite a healthy battery, a blown pyro fuse is usually the culprit.

BMW Architecture Integration:

Because the modern CX-platform Morgans rely heavily on BMW electronic architecture and powertrains, they utilize these modern, BMW-standard safety components rather than the traditional, simple glass or blade fuses found in older classic Morgans.

The pyro fuse on a Morgan CX Plus Four will fail or trigger for two reasons: it was intentionally fired by the car's safety computer, or it suffered a physical or electrical hardware failure.

Here is the exhaustive breakdown of exactly why this happens.

1. Intentional Safety Triggers (The System Worked)

In these cases, the car's computer actively tells the fuse to blow

.A Severe Accident:

This is the primary design reason. If the car undergoes a severe impact, the airbag control module instantly fires the fuse to isolate the battery.

Minor Jolts or Curb Strikes:

The crash sensors cannot always tell the difference between a fender-bender and a harsh mechanical shock. Hitting a massive pothole, striking a high curb hard, or a severe underside jolt can accidentally satisfy the sensor's threshold, triggering the fuse without deploying the airbags

.Electrical Short Circuits:

If a major power cable (like the main line feeding the starter) chaffes against the aluminum chassis and causes a massive, dangerous current spike, the electrical system may force a shutdown.

2. Hardware and Environmental Failures

Because the fuse is an electrical component, it can stop working or trip accidentally due to age, wear, or installation issues.

Loose Chassis Earth (Ground) Connections:

Morgan CX models are known to occasionally suffer from loose earth leads where the battery connects to the alloy chassis panels. Bad grounding causes massive voltage fluctuations that can confuse the system or cause localized heat.

Moisture and Corrosion:

The lightweight Morgan chassis exposes various components to the elements more than a standard enclosed steel sedan. Moisture seeping into the battery junction area can corrode the delicate signal pins that connect the fuse to the computer, causing a false trip or a broken internal connection

.Manufacturing Defects:

The physical explosive charge or the internal metal bridge can simply fail internally over time due to heat cycling and vibration, leading to an open circuit with zero external trigger.

Battery Replacement Spikes:

If a battery is changed incorrectly, or if the car is jump-started with backwards polarity, the sudden electrical surge can accidentally pop the trigger mechanism.

How to Check ItIf you suspect the fuse has deployed or failed, look for these three signs:

The "Loose Cable" Test:

On these BMW-style safety terminals, the thick power cable will often feel physically loose or detached from its plastic housing after firing because the internal piston pushed it out.

Perfect Dash, No Crank:

Often, the smaller wire powering the dashboard remains live, but the heavy wire to the starter is dead. Your screens might light up, but turning the key results in absolute silence.

Diagnostic Codes:

Plugging a scanner into the OBD port will usually reveal a fault code explicitly stating "Battery Safety Terminal - Resistance Too High" or "Open Circuit."If you need to fix a dead car,


I know understand a little more as to the pyro fuse function and likely reasons for a trigger.,even a jolt to the car could cause it to trigger, let alone a loose battery cable electrical spike..........or an earthing issue.

Had any luck with the ABS issue resolution and if so what was the cause?