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Main Fuse Problem?

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Main Fuse Problem?

Postby leebee » Wed Feb 15, 2012 11:40 am

We are having a problem with 300amp main fuse link keeps blowing. Suspected battery problem at first so changed one of the two batteries - replaced the blown main fuse at same time. Van ok for 24hours then main fuse blew again. Suspected starter motor fault so renewed the starter - replaced second main fuse at this time. Drove van 5 miles - stopped for fuel, then tried to start it after 10 minutes - main fuse blown again. Can't afford to keep changing this fuse and no more available locally - Has anybody had similar problem and located a short circuit which could be common on these vehicles. 2006 LWB High top new shape transit. Any help appreciated?
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Re: Main Fuse Problem?

Postby leebee » Thu Feb 16, 2012 9:41 pm

Still struggling to locate this fault 2006 new shape transit. Anybody had a problem with main fuse keep blowing? Is there anywhere I can download a wiring diagram for this vehicle please? Thanks again.
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Re: Main Fuse Problem?

Postby KH_Towbars » Thu Feb 16, 2012 9:48 pm

is the battery secured firmly & does it blow when you do something like start the van :?:
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Re: Main Fuse Problem?

Postby leebee » Thu Feb 16, 2012 11:14 pm

KH_Towbars wrote:is the battery secured firmly & does it blow when you do something like start the van :?:

Yes both batteries secure. Van will start several times in situ after changing fuse, but when driving on road appeared to lose power, then pick up again. After stopping van would not start and fuse had blown again - which is the reason I thought it was a short circuit whilst on the move - but where? Initial thought was starter motor which I renewed first time fuse blew, but fault is still there after replacing both fuse and starter..
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Re: Main Fuse Problem?

Postby KH_Towbars » Thu Feb 16, 2012 11:52 pm

Gotta be a dead short to blow a 300amp fuse so, somethings happening whilst driving. there is a big live from batt to starter which you have replaced :?: , alternator & fuse box. 1 of these wires must be going to earth at some point whilst driving to blow the main fuse
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Re: Main Fuse Problem?

Postby KH_Towbars » Thu Feb 16, 2012 11:55 pm

when driving on the road & you lose power that will be the fuse blowing then, the smart charge system picks it up & compensates for the difference :?
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Re: Main Fuse Problem?

Postby leebee » Fri Feb 17, 2012 12:47 am

KH_Towbars wrote:when driving on the road & you lose power that will be the fuse blowing then, the smart charge system picks it up & compensates for the difference :?


That makes sense to me. I will check wiring as best as I can.

I was just hoping somebody could point me in the right direction as to where the short may be (if there was a common place that a main cable wears through). Its just a little awkward crawling underneath with no ramps - what is visible under bonnet looks ok. Thanks again
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Re: Main Fuse Problem?

Postby KH_Towbars » Fri Feb 17, 2012 12:54 am

leebee wrote:
KH_Towbars wrote:when driving on the road & you lose power that will be the fuse blowing then, the smart charge system picks it up & compensates for the difference :?


That makes sense to me. I will check wiring as best as I can.

I was just hoping somebody could point me in the right direction as to where the short may be (if there was a common place that a main cable wears through). Its just a little awkward crawling underneath with no ramps - what is visible under bonnet looks ok. Thanks again
it's early days, I was just going through the obvious, someone will no doubt reply to this who had the same problem or knows more than i do :oops:
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Re: Main Fuse Problem?

Postby leebee » Fri May 11, 2012 9:07 am

Update. After replacing 4 main fuses, we removed all wiring harnesses, changed alternator and starter motor - no short circuit found. Couldn't keep changing main fuse so soldered up the last one. It held for three weeks but then the starter motor failed.

On inspection the brush wires in starter had overheated and burn't out so they were replaced. The starter brushes were replaced but the brush wires were found burn't out again after one day's use.

A second set of brushes were renewed and a separate feed with push button switch was attached to the solenoid to rule out any problems with ignition switch and wiring. The engine turned over normally on the switch - we tested it on short bursts about ten times - absolutely fine, and the engine /pulleys etc did not seem tight in any way. We then started the engine and ran it for twenty minutes. After turning off the starter brushes had burn't out again.

In short, I believe because we soldered the main fuse, it is not working as it should and burning the brush wires out as the next weakest point. We cannot find an electrical short circuit so I can only assume the starter is running in mesh with the engine, as the fault only occurs after the engine has run for a while. There is no sign of filings or debris on the starter pinion each time it has been removed and the fly wheel looks ok. I don't want to put a solid flywheel, new clutch, starter and new main fuse on as I am not confident that this is the problem.

Any ideas appreciated?
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Re: Main Fuse Problem?

Postby KH_Towbars » Fri May 11, 2012 11:02 pm

leebee wrote:Update. After replacing 4 main fuses, we removed all wiring harnesses, changed alternator and starter motor - no short circuit found. Couldn't keep changing main fuse so soldered up the last one. It held for three weeks but then the starter motor failed.

On inspection the brush wires in starter had overheated and burn't out so they were replaced. The starter brushes were replaced but the brush wires were found burn't out again after one day's use.

A second set of brushes were renewed and a separate feed with push button switch was attached to the solenoid to rule out any problems with ignition switch and wiring. The engine turned over normally on the switch - we tested it on short bursts about ten times - absolutely fine, and the engine /pulleys etc did not seem tight in any way. We then started the engine and ran it for twenty minutes. After turning off the starter brushes had burn't out again.

In short, I believe because we soldered the main fuse, it is not working as it should and burning the brush wires out as the next weakest point. We cannot find an electrical short circuit so I can only assume the starter is running in mesh with the engine, as the fault only occurs after the engine has run for a while. There is no sign of filings or debris on the starter pinion each time it has been removed and the fly wheel looks ok. I don't want to put a solid flywheel, new clutch, starter and new main fuse on as I am not confident that this is the problem.

Any ideas appreciated?


so could be starter selenoid stuck in start position ??
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Re: Main Fuse Problem?

Postby ake » Sat May 12, 2012 11:11 am

Have you completely removed and checked the battery cables, from battery to starter , and from battery to engine bay fuse box:?:
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Re: Main Fuse Problem?

Postby leebee » Sat May 19, 2012 8:18 pm

ake wrote:Have you completely removed and checked the battery cables, from battery to starter , and from battery to engine bay fuse box:?:

Not yet. The main battery cable runs from under driver's seat to engine bay fuse box, then from engine bay fuse box to starter. I am going to try and fit a new starter cable from battery direct to starter , the solenoid is already wired direct via a push switch ..... this way the starter will be totally isolated from all other wiring. If the starter burns out after this then surely it can only be running in mesh with the engine (though I thought it would smash the pinion and armature if this was the case).
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Re: Main Fuse Problem/Starter Motor problem

Postby leebee » Sun May 20, 2012 9:31 am

I tried bridging out main fuse as I exhausted every avenue to locate the short circuit after replacing 4 main fuses. The starter lasted about three weeks after bridging the fuse out. The brush wires on two brushes had burnt through completely.

I isolated the starter by fitting a new live feed to solenoid via a push switch direct from the battery. I did not exchange the existing main starter cable which runs from the batter to the engine bay fuse box, and then from the engine bay to the starter. We burn't out two sets of brushes since then.

However, it was noted that the new push switch would turn the engine over well in short bursts with the ignition off - ie the starter seemed to work ok. The problem arises after the engine has been running and you come to start it again - the brushes are burn't out.

I have taken the belts off all pulleys in case one was seized therefore making the engine tight ..... all ok. I can only think it can be running in mesh with the engine, or a clutch / flywheel problem, but there is no evidence of filings on the starter and I thought if in mesh it would show damage to starter pinion or armature ....... I can only hope there is an intermittent short circuit on main starter lead, or I will need a job lot of starter brushes and main fuses.

Any advice/ideas appreciated?
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Re: Main Fuse Problem?

Postby APH » Sun May 20, 2012 7:53 pm

Hmm....reading this with interest :shock: Where was the starter purchased from? as if not a genuine ford one then that would definately be a problem. However, you say that you have wired the starter main feed straight from battery, as well as the solenoid feed. correct? If so, start the van then Disconnect the main cable from the battery to the starter at the battery end, and connect a multimeter set to 20 volts dc to this lead and earth. Insulate the lead so it can't touch any bodywork. Provided you can drive the van without staling it, you should see NO voltage on the starter cable, If however, as you suspect the starter is not fully disengaging you will see a voltage as it will work as a generator :wink:

If you get nothing, then I would suspect an internal short within the starter causing it to draw current continuously, could even be carbon from brushes "bridging" the main switch (inside the solenoid).

Hope that makes sense,
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Re: Main Fuse Problem?

Postby leebee » Sun May 20, 2012 11:16 pm

APH wrote:Hmm....reading this with interest :shock: Where was the starter purchased from? as if not a genuine ford one then that would definately be a problem. However, you say that you have wired the starter main feed straight from battery, as well as the solenoid feed. correct? If so, start the van then Disconnect the main cable from the battery to the starter at the battery end, and connect a multimeter set to 20 volts dc to this lead and earth. Insulate the lead so it can't touch any bodywork. Provided you can drive the van without staling it, you should see NO voltage on the starter cable, If however, as you suspect the starter is not fully disengaging you will see a voltage as it will work as a generator :wink:

If you get nothing, then I would suspect an internal short within the starter causing it to draw current continuously, could even be carbon from brushes "bridging" the main switch (inside the solenoid).

Hope that makes sense,
Andy :D

Thanks - yes it makes sense. The original starter motor was given to a local reconditioning firm. I fitted a replacement off the shelf only for us to find the brushes burn't out in exactly the same place on both starters. (ie, the brush wires acted as a fuse in the absence of a main fuse) A second starter was fitted with exactly the same result even after wiring the solenoid direct from battery via a push button switch. The original starter motor has now been reconditioned and ready to fit back on the vehicle - problem is I am scared of fitting it as I know we have not found the fault yet.

I can follow your idea and disconnect the starter cable at the main engine bay fuse box and check for current between the starter wire and earth quite easily whilst it is running - as you say this will prove whether or not it is running with the engine and acting like a generator.

Thanks - I will keep you posted
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