Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

[PeterM]

Fuel pump and ignition circuit blowing fuse.

Hi, can any one help with ideas on common causes for this problen.
My cabrio has developed an intermittent fault causing the fuse to blow on the ignition and fuel pump combined circuit. V inconvenient as it happened on the pass of glencoe road in pouring rain resulting in the car needing recovery to a garage in Fort William. The fault resolved itself after 4 blown fuses and the cause was not found by the local garage. All of the other car systems worked normally.
It happened again 200 miles later on the Isle of bute and resolved after another 6 blown fuses during fault finding. The Island's mechanic again could not find the fault and it finally resolved again long enough for us to drive onto the ferry back to the mainland and load the marlin onto a recovery truck to take us home to leeds. A bit of a saga!

The cabrio has mechanicals from a 1993 ford sierra 2.0 DOHC EFI including the fuel pump and ecu.
The wiring loom is from Premier wiring systems. There is no fuel pump cut off or relay.
there is no damage to the loom on the visible parts and no evidence of burnt wires.

Current thoughts are;
1) Is there an intermittent fault in the fuel pump causing the short. Next time it happens I will see if the fuse still blows with the pump disconnected
2) Is there a fault in the ignition circuit, if so where and how do I isolate it to test it. The PWS loom instructions do not help for this.

Does anyone have other Ideas, similar experiences or knowledge about the commenest causes of this problem?

Here is hoping
Best wishes to all
Peter

[lizbillings]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Was it raining when it blew on the Isle of Bute or dry?

[PeterM]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

raining both times.

[copperleaves11]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Damp near the fuel pump relay?

[greyV8pete]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Anything else on the same fuse? Wipers, screenwash pump etc? Did you switch something else on when the pump stopped, or did it just stop working?I would disconnect each component supplied by that fuse, at the component itself, then switch on and wiggle all wiring. Then reconnect each component in turn and wiggle the wiring each time, in case something live is touching the chassis. Is the fuse the correct rating? Is it the correct type? If supplying a motor I would expect to see a slow blow type fuse. Have you recently fitted or serviced anything else electrical recently? Even new parts can be faulty! Peter.

[dogoncrazy]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Did you notice if the pump was warm/hot to touch?

[PeterM]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Thanks for your replies.
I have not found a fuel relay yet but assume there must be one as the original sierra wiring diagram shows one between the ecu and the pump and it seems unlikely that the ecu will put out enough current to work the pump. I will keep looking.

re; other items on the same circuit. the fuse still blew after I had disconnected all connections to the steering column switches ie. lights, indicators, horn, wipers, screen washer.

re was the pump hot. it is an in tank pump so you can not touch it. Happily there was no smell of boiling fuel!

re did it happen when I switched something else on or off? No I was not switching any other control.

re fuse. normal 15 amp fuse which had worked without problems for 10 years and 30000 miles

thanks for yor thoughts.
looking forwards to hearing any other Ideas which members have
Peter

[jon_cox]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Hi Peter
All cars fitted with an electronic fuel pump, in theory, should also have an inertia cut off switch in the case of an accident. It basically has a ball bearing in it that moves under heavy deceleration due to an impact, that cuts off electrical power to the pump. A safety feature in case the fuel line is compromised so you don't pump gallons of fuel all over the place creating a significant fire hazard.
I do not know where it is positioned in the Cabrio (or if there is one at all ) but this could be the cause of the problem if it has corroded connectors.
It should look like this:

FORD-GALAXY-1998-FUEL-CUT-OFF-SWITCH-F2AB-9341-AA.jpg

[dogoncrazy]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Apologies, I missed the fact that you stated pump was from the donor Sierra.

[greyV8pete]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Jon_cox’s comment above reminds me that my son had the same problem with his classic Range Rover and the cut out switch on those was a known cause of the random cutting out problem on those vehicles. As I have the L/R Disco V8 engine in my Hunter I have the same switch which looks like the photo below. On my Hunter it is mounted in the engine compartment on the nearside bulkhead and next to the 100A fusible link. The round end is mounted facing upwards. It has a flexible rubber cover which you press in to reset it. Peter.
E217A361-AAE4-444C-A010-1A749CA5ACBB.jpeg

[chris_cussen]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Cut out switch is a very good idea. I got mine from Car Builder solutions.
However it is most unlikely to be causing the fuse to blow.
Unfortuantely I would hazard a guess that either the fuel pump has a fault or you have a chaffed wire that is causing an intermittant short.

[philmcgrath]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

I have the same switch on my Cabrio which has Ford DOHC engine but mine is mounted in the boot.

[Ye Ol Ripper]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Hi Peter
Some of the early Ford fuel pumps were prone to failing which is from the same era of the Sierra Pump.

The main cause was people driving continually low on fuel and particularly this problem worsened on a hot day.
The fuel pump relies on the fuel itself for lubrication & cooling.

If your stuck in a traffic jam , you will often hear the fuel pumps of other cars buzzing away because of this phenomenon.

I would recommend removing the pump from the tank and checking that the mesh filter isn't clogged and before doing that you could also measure the current draw of that pump whilst its still fitted in the tank.

When was the fuel filter last changed?

My line of thought is if that's partially blocked that could be putting a strain on the pump.

If your engine has the DIS ignition system with a crank sensor , then also check the crank sensor wiring.

All Fords had a fuel pump relay and I would expect it to be present , have you looked for the relay up behind the dash, perhaps the contacts where it plugs in have been arcing causing the fuse to blow?

If you need a new pump the cheapest place for a replacement will be to call Terry at Glenco, as he is the wholesaler supplying everybody else.
https://www.glencoeltd.co.uk/

[dogoncrazy]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Hi Peter
I've been trawling the archives on this and came up with the following. Look under 'fuel pump relay' posted 29/07 /2014 , some interesting stuff there by PhilCoyle regarding activation of the relay . There is also a post by myself on a not dissimilar problem I had with my BMW powered Cabrio.

[PeterM]

Re: Fuel pump and ignition circuit fuse blowing on mu Cabrio. Help!

Thanks everyone for your info and advice.
I will have a lot to do chasing down your suggestions.
I get the feeling that progressive replacement of parts on the pump/ignition circuit will be the way foreward as it is an intermittent fault, so when it disappears it might not be because of my action!
I will start with replacing relays (cheap) and fuel pump (common things are common and it is now getting old, 28 yrs and 60k miles)
I will let you know how it goes
Best wishes
Peter