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Old 13-09-2024, 15:15   #16
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Re: Engine Spontaneously Starting

The saga continues without a solution yet. The electrician ive now got has found some dodgy work done by a previous so called electrician including that the isolation switches dont totally isolate the system and he seem to have put a switch on the negative cable somewhere which apparently could be the problem. I dont understand this bit so im going back for more explanation. The thing that puzzles me is why it is acting up now. I got rid of the dodgy electrician a couple of years ago and this self starting is a new phenomenon. It’s also puzzling that when it self starts it stops when the engine starts running. It doesnt continue to drive the starter motor (fortunately!). Anyway I’ll keep updating this thread till it’s solved.
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Old 13-09-2024, 15:24   #17
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Re: Engine Spontaneously Starting

ghosts in the machine?
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Old 13-09-2024, 15:24   #18
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Re: Engine Spontaneously Starting

If you open the switch on the negative cable, it SHOULD keep the engine from starting.

In any case, if the starter is energized by the normal methods, it is stopped by taking your finger off a button or letting go of a key. It is truly amazing that whatever circuit is energizing the starter also de-energizes it when the engine starts.
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Old 13-09-2024, 16:05   #19
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Re: Engine Spontaneously Starting

Hi micwhite, chilly morning today .

Regarding your engine starting, obviously the issue is an intermittent electrical problem i.e. the hardest problem to solve. While I have a couple ideas, first let me ask -

1. are you using the Volvo supplied engine panel or a custom instrument panel?
2. What is the switching / charging arrangement between the start and house batteries?
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Old 13-09-2024, 16:14   #20
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Re: Engine Spontaneously Starting

Assuming you have separate starter and house batteries, there will be some sort of device splitting the charging current from the alternator to to each battery bank. This can be a mechanical switch, a splitter diode or a voltage-controlled relay. That gadget keeps the two batteries separate, stopping one from discharging the other, but allows them to be connected together to be charged from one alternator. If it fails, it can mean that the house and starter batteries are effectively coupled together all the time, not just when the engine is running, and the battery isolation switch is effectively bypassed. I would look very carefully at any voltage-controlled relay and its associated wiring. I had one once—never again.
My own preference is to have two completely separate circuits—the factory-fitted alternator charging only the starter battery, and a second alternator charging only the house batteries.
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Old 13-09-2024, 16:22   #21
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Re: Engine Spontaneously Starting

Your wiring harness has dodgy connections.
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Old 13-09-2024, 19:33   #22
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Re: Engine Spontaneously Starting

I feel for you... We had the same issue , engine starting by itself, or refusing ro start when needed...
The cause : MDI (electric black box attached on the exhaust manifold).

Do a google search on the Volvo MDI

... I don't want to relive that nightmare.
Volvo tried to fix unsuccessfully their MDI I believe 7 times in the last 8 years.

We ended up getting rid of that MDI and wired new analog gauges. Old fashion way.

Done ✅
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Old 14-09-2024, 04:35   #23
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Re: Engine Spontaneously Starting

Hi guys,

Thanks for the thoughts and some excellent ideas. Firstly just a couple of answers -

I am using the Volvo supplied engine panel and have replaced the ignition switch with a Volvo part not an aftermarket one.

Mike Burch and wotname seem to be heading in the same direction with the possibility of a problem with the switching/charging arrangement between the start and the house batteries. That's looking like a possibility to me. I do have separate engine start batteries and house batteries and there is a splitter diode that keeps the two battery banks separate. Mike could be right, that is perhaps this splitting arrangement has failed and if that means the house and starter batteries are effectively coupled together all the time it could be that the engine is starting on the house batteries rather than on the engine batteries.

And thanks yobird for the heads up about the MDI. I'll bring this to the electrician's attention and see if it gives him any clues.

And for those who think I've got ghosts, you're probably right. The rest of it seems to defy logic so I guess ghosts it is!

Cheers and thanks for your help

Michael
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Old 14-09-2024, 05:24   #24
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Re: Engine Spontaneously Starting

Quote:
Originally Posted by micwhite View Post
Hi guys,
Thanks for the thoughts and some excellent ideas...


... And for those who think I've got ghosts, you're probably right. The rest of it seems to defy logic so I guess ghosts it is!
Cheers and thanks for your help
Michael
Years ago, when helping a Haitian boat, with another electrical problem, I was informed that the boat had a “ghost”.
The engine would occasionally start, unexpectedly, on it’s own.
It turned out be a metal coffee can, floating in the very wet bilge, that would sometimes short the starter motor terminals.
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Old 14-09-2024, 06:55   #25
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Re: Engine Spontaneously Starting

I suggest there are two problems (at least).

1. There is an issue with the isolation and combining of the start and house batteries which allowed power to be available for the engine start circuit. This will be a hard fault i.e. not intermittent. However this issue will not be responsible for the actual phantom starts.

2. An intermittent problem in the engine instrument panel or more likely, the MDI (if fitted). This will be intermittently activating the start circuit. Most likely corrosion (or burnt sections) on a PCB within the instrument panel and/or MDI or perhaps water ingress.

If a close inspection of the insides of the instrument panel or MDI does not show up any obvious faults, you may have to bit the bullet and just replace them anyway - but you will need deep pockets.

Regardless, #1 needs to be fixed ASAP so you can be certain the engine can not be activated when the start battery is isolated.
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