can anyone help with a engine fuse problem?

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can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 3:10 pm

So as many of you know I'm pretty handy at looking after an 8 however my downfall has to be electronics and it seems my first ever problem with my 8 is just that. The 15amp engine fuse in the engine bay fuse box is blowing constantly :evil:
Does anyone have an idea what this actually is connected to, I have done some research and done some work. I know it's not the coils and leads as I have tried a tester set. It's not the starter motor as I have changed that too as I had a spare.
So what actually happens is
1. I replace the fuse
2. Most of the time the fuse will go as soon as I turn the ignition fully on, sometimes it'll wait till I try turning it over before it blows, today it started for about 3 seconds before blowing but it always blows.
3. Once it blows the immobiliser light flashes quickly and the passenger airbag light comes on and stays on (traction light etc is on due to taking the battery off)
I did try looking at a wiring diagram but it might as well have been in Klingon as it wasn't like the diagrams I'm used to #-o
So any help would be great as the weather isn't playing ball either [-X
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Re: can anyone help with a engine fuse problem?

Post by Harrizone » Sat Jan 13, 2018 4:30 pm

If I remember correctly (maybe not at my age though #-o ) but 'casey' had a similar issue when main lead for the coil kit that he had fitted fouled somewhere against a pulley, or the engine block and where it had worn through the lead it led to something similar to this. Have tried looking for his thread with the exact details and cannot find it. Have you fitted a 585 coil kit at some stage :?: .
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 4:51 pm

Aye I have read about this happening with the converter harness however I swapped out the coils for original ones (only to test) and it made no difference :( The harness did actually have a wire through so I replaced the harness too and removed the engine hook so it won't happen again however this hasn't actually solved the problem :( cheers anyways :thumleft:
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Re: can anyone help with a engine fuse problem?

Post by Conan » Sat Jan 13, 2018 4:56 pm

Does the engine still run with the fuse blown or start with it blown ?
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Re: can anyone help with a engine fuse problem?

Post by Harrizone » Sat Jan 13, 2018 5:00 pm

Believe Clive also had issue with this, but cannot remember for the life of me how it was resolved, and come to think of it may have had something to do with all the mods he has made, again cannot remember the precise details. Maybe worth dropping him a PM, or giving him a call, failing that Aston, or casey, may remember what his issue was.
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Re: can anyone help with a engine fuse problem?

Post by HwAoRrDk » Sat Jan 13, 2018 5:04 pm

The 15A ENGINE fuse supplies ignition-switched power to the following (although for the latter three it should be noted that it's not the main power feed):

- PCM
- Immobiliser
- Air bag system
- DSC
- ABS
- Electric power steering

Makes sense that the fuse only blows when you turn the ignition, as the power feed that goes through the ENGINE fuse is switched on by the IGNITION relay in the fuse box. Also, because that circuit is the sole power feed to the airbag system and the immobiliser, the warning lights for those are probably a symptom of the instrument cluster losing communication with them.

The obvious answer is that you have a short to ground somewhere. It may be that a wire has come loose, worn through and is rubbing on part of the chassis or the engine. I'd start by going to the units mentioned above (well, the ones in the engine bay that is) and following the wiring coming from them and looking for damage.

You might want to see if you can get yourself one of those circuit-breaker resettable fuses, because otherwise it could be a pain going through many fuses when troubleshooting. :)
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 5:05 pm

Pete the engine has only run once for seconds and once the fuse has blown the car won't turn over or run.

harrizone when I have looked online many people point to the harness adapter just a shame this didn't work for me :(
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Re: can anyone help with a engine fuse problem?

Post by PeteH » Sat Jan 13, 2018 5:13 pm

Presumably if the PCM is deprived of power then that would stop it turning over.

If you take the fuse out maybe you will be able to measure a short to ground from the fuse terminal? You could possibly then trace the short through the modules mentioned previously.
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 5:16 pm

Sooo as I said electronics aren't my strong point sorry pete how would I actually go about doing what you have suggested ;) cheers
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Re: can anyone help with a engine fuse problem?

Post by arginite » Sat Jan 13, 2018 5:25 pm

A multi meter would be the tool you need.
If the above modules have separated fuses you could try removing them and replacing one by one until you blow the engine fuse again. Then last replaced fuse is the system that has the issue.

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Re: can anyone help with a engine fuse problem?

Post by bigpete » Sat Jan 13, 2018 5:29 pm

Check the rear o2 sensor wires as I e seen these damaged and will keep blowing that fuse. Just unplug it from the car and try it
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Re: can anyone help with a engine fuse problem?

Post by Conan » Sat Jan 13, 2018 5:32 pm

That’s the way to do it at first.
Nice and simple and could point to the fault :thumleft:
BigPete also has a point: Just the other day some ran over a curb and scrapped the o2 sensor which shorted a fuse to the fuel pump.
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Re: can anyone help with a engine fuse problem?

Post by PeteH » Sat Jan 13, 2018 5:32 pm

They are not mine either!

I'd have thought that there must be continuity between the "downstream" terminal of the fuse (not the battery side), and ground. That just means there must be very low resistance between the terminal and the body shell / negative battery terminal. So stick a volt meter across those two places, set to measure resistance (or to beep if it sees continuity). I don't know how low the resistance would need to be to indicate continuity, but a bit of maths suggests anything less than one ohm is probably going to blow the fuse.

If you find low resistance you can then work further and further "down stream" until you see high resistance. Doing that should allow you to isolate where the low resistance occurs. That's your short.

But some electrical bloke should probably comment, because I hate electrics..... :lol:
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 5:43 pm

bigpete wrote:
Sat Jan 13, 2018 5:29 pm
Check the rear o2 sensor wires as I e seen these damaged and will keep blowing that fuse. Just unplug it from the car and try it
cheers but I don't have a second O2 sensor in with the de-cat :thumleft:
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Re: can anyone help with a engine fuse problem?

Post by warpc0il » Sat Jan 13, 2018 5:47 pm

Your biggest problem is that the fuse doesn't blow immediately, every time, so you have some intermittent variable.

One thing that's always a variable is how you sit in the drivers seat, so it could be something to do with the airbag system that runs under the seat.

Otherwise you're looking at a frayed wire that's just touching or not touching something it shouldn't, or a component with an internal short.

Where is the second O2 sensor wire fixed?
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Re: can anyone help with a engine fuse problem?

Post by HwAoRrDk » Sat Jan 13, 2018 5:54 pm

arginite wrote:
Sat Jan 13, 2018 5:25 pm
If the above modules have separated fuses you could try removing them and replacing one by one until you blow the engine fuse again. Then last replaced fuse is the system that has the issue.
Could be worth a try. The EPS, ABS and DSC all have separate main fuses. Although, the EPS fuse is by the battery, not in the fuse box.
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 5:55 pm

warpc0il wrote:
Sat Jan 13, 2018 5:47 pm
Your biggest problem is that the fuse doesn't blow immediately, every time, so you have some intermittent variable.

One thing that's always a variable is how you sit in the drivers seat, so it could be something to do with the airbag system that runs under the seat.

Otherwise you're looking at a frayed wire that's just touching or not touching something it shouldn't, or a component with an internal short.

Where is the second O2 sensor wire fixed?
I'll check this as soon as I can as I actually lent over from the passenger seat when it started for a few seconds today. The O2 sensor is removed from the plug under the car. 90% of the time it seems to blow as soon as I turn the key to turn it over.
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can anyone help with a engine fuse problem?

Post by Big Bob » Sat Jan 13, 2018 6:05 pm

Replace the fuse with a 12v bulb. If there is a short, the bulb will light up.
Start disconnecting all the lightly things that may be short. When you disconnect the problem the bulb will go out.
Hope this helps


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Re: can anyone help with a engine fuse problem?

Post by warpc0il » Sat Jan 13, 2018 6:30 pm

That method is good for most circuits but I'd be a bit wary doing it on a circuit that includes the PCM, as it doesn't like being supplied with low voltage i.e. 12V less the drop through the bulb.
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 6:34 pm

I'll look at the airbag wires under the seat and try the removing other fuse method asap any other suggestions or ideas are very welcome including ways to test thanks
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Re: can anyone help with a engine fuse problem?

Post by bigpete » Sat Jan 13, 2018 6:37 pm

What other mods have you done that would be to do with wiring?
Have you got an obd plugged in? If so remove it
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Re: can anyone help with a engine fuse problem?

Post by SeeJay » Sat Jan 13, 2018 6:47 pm

If there's a possibility that something under the seat is moving and causing the fuse to blow,then simply start the car without being sat in it..if it contnues to run,then drop in the seat and if it blows you've isolated the problem area..

It probably won't be that simple a fix but good luck! :thumleft:
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Re: can anyone help with a engine fuse problem?

Post by minisaki » Sat Jan 13, 2018 7:04 pm

Cheers I have already took the obd out. I have tried starting while not on the seat I'm just hoping it's as easy to find as a wire under the seat. I have already took the cigarette lighter fuse out as I have a tablet install but not much else that I have done but this didn't work.
I have one of them wire tracing things that's ment to beep if there's a bad wire, it was going off a bit around the tablet but stopped once the fuse was removed this however made no difference to my problem I think it was going off due to charging. the wire trace doesn't go off anywhere else :(
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Re: can anyone help with a engine fuse problem?

Post by dac69er » Sat Jan 13, 2018 10:11 pm

Going from the list above and the issues I have read regarding water effecting the power steering via the connectors, I would start there myself.

Failing that, unplugging everything not immediately required to start the car off that list and giving that a try.

They are he easiest methods of electrics aren’t your strong point. Simple process of elimination.

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Re: can anyone help with a engine fuse problem?

Post by 13Black » Sun Jan 14, 2018 12:35 am

Maybe an odd suggestion for additional diagnosis, and I have no idea if it will work for sure...

But perhaps try disconnecting the ESS connector on the front cover.

Try and crank the engine over now, if it cranks and cranks (it of course won't ever start like this), then because it (probably) shouldn't be providing any power to the coils, this might point to a problem with the coil wires sommmmewhere.

There are numerous reasons why this could be a pointless test, but if it makes a difference then it could narrow it down, somehow, maybe, perhaps, in some way. Or might not.

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