Engine management fuse blowing

[nigelrtaylor]

Checking the bike ready for a ride out, turned ignition on and nothing other than rear light and front position light. The 15A engine management fuse had blown. Replaced the fuse and all appeared well until I pressed the starter and the engine cranked for a second or so and fuse blew. Replaced again and same thing. Engine cranked then fuse blew. Any ideas anyone?

[Coconut]

Hi,

I've had a look at the Circuit Diagram in the Service Manual :

Fuse No.2. ( 15A ) of the rear fuse box provides power
via a Brown wire with Pink tracer to Pin 3 of the Engine Management Relay.

The Engine Management Relay is on the Left side of the Trophy as shown below.

Hopefully, your fault is due to this Relay being faulty.

To Test it, unplug it from it's position, and switch the Ignition ON.
Don't try to start the engine !
If the Fuse blows this will indicate a short circuit to Ground
on the Brown / Pink wire from the fuse to the Relay Base.

If the Fuse did NOT blow in the above test, then the Relay itself may be faulty.

Relay No.4 is the Headlight Relay, so try unplugging that and putting it
into the Engine Management Relay Position.

Switch the Ignition ON, then start the engine ( The Headlamp won't work  ! ).

If the Fuse doesn't blow, this indicates the Relay is faulty - get a new one  ( Part : T2506040) !

If the Fuse still blows, switch off the Ignition and put the Headlight Relay back in it's "proper" place.

The other wires from the Engine Management Relay are :

Pin 1 - ( Yellow with Slate Grey Tracer ) +12V from ECU  Pin B31 
Pin 2 - ( Black ) Ground
Pin 4 - ( Also Brown and Pink ) 12V supply to various sensors - see below.

In operation, when the Ignition is switched ON the ECU provides +12V to Pin 1 of the Relay,
energising it and closing the contacts between Pin 3 ( +12V from Fusebox ) and Pin 4.

Pin 4 provides +12V to the following :

• Pin 1 of the Cooling Fan Relay
• Purge Valve
• Oxygen Sensor
• Windscreen Motor
• Injectors
• Secondary Air Injection Solenoid
• Coil 1
• Coil 2
• Coil 3

Any of the above could be the cause of the Fuse blowing.

Probably the easiest to check is to pull the Cooling Fan ( Relay No.3 - See below image ),
and start the engine.  If the engine runs without the Fuse blowing
then suspect the Cooling Fan Relay to be faulty.
( Note that on the World of Triumph Parts list, it shows all 4 relays as being the same ! ).

Hope some of this helps you to identify what's wrong !

Cheers 

[nigelrtaylor]

Coconut, you are a hero. Thank you for the research.  I've run out of 15A fuses just now so will try your suggested diagnostics on Monday when I have a stock of fuses. I'm comfortable with vehicle electrics so happy to try the various swapping of relays. Thanks for the wiring diagram.

I do hope it's a faulty relay as a replacement Ecu sounds expensive.

[Coconut]

No problem - I've Edited my previous post to add a few items
to the list of components that are supplied by the Relay.

Attached below is the specific Wiring Diagram for the Engine Management Circuit only.

Cheers 

[Coconut]

I've been giving this some ( more ) thought,
and would recommend after changing the Fuse again,
BEFORE starting the engine, to just switch the Ignition to ON,
and then check to see if any Diagnostic Trouble Codes ( DTC's ) have been stored.

It's easy to do this and have any DTC's displayed on the Instrument Panel.

See this Topic : Servicing Data, Reference Info. & DTC ( Fault ) Codes at Reply #8,
where you will also find ( if you are Logged in to the Forum )
a downloadable Word Document that lists all of the DTC codes,
and gives an explanation of what they mean, and other information.

If it turns out that the Relays are all good, and it's one of the components that the Relay feeds
that has the fault, then a DTC code may be stored, which will hopefully point to the culprit ! 

Let us know how you get on 

Cheers 

[nigelrtaylor]

Coconut, I did check the DTC yesterday and it said P0000

[nigelrtaylor]

The mystery deepens.
Replaced the fuse without swapping any relays, ignition on, everything OK for 5-10 seconds then fuse blows.
Removed EMS relay, new fuse, ignition on and fuse doesn't blow.
Used headlamp relay for EMS relay, new fuse, ignition on, fuse is ok but engine wouldn't start.
Put all relays back in original position, new fuse, ignition on, and engine starts?

I suspect I have a wiring fault and disturbing the relays has temporarily fixed it.

I'll disassemble things to have a better look at the wiring to see if there is any chaffing.

[Coconut]

The more I think about this, the more I am convinced it is a fault with the Relay.

I can't comment on why the engine wouldn't start without the Headlamp Relay connected,
but would suspect that is "normal".

The fact that swapping the EMS Relay allowed the Ignition to be switched ON
without blowing the Fuse, would tend to indicate the original Relay was faulty.

With that Relay in the Headlamp position, the engine starts and all appears well,
without the Headlamp circuit Fuse blowing, and swapping the Relays over
is the only thing that has changed.

I agree that there could be a wiring fault at the Relay bases ( or elsewhere ) but this is less likely.

It is strange however, that with the "Suspect" Relay in the Headlamp Position,
the Headlamp Circuit fuse doesn't blow, but that circuit has a 20A Fuse
compared to the 15A Fuse of the Engine Management circuit, which might explain why !

For the sake of around £10 I wouldn't risk leaving the "Suspect" Relay in the Headlamp position,
and would buy a new one, fit it, and see how it goes 

Cheers