Ford Focus MK II blowing IGN 10A fuse under bonnet.

[TonyRPH]

My O/H's Focus has had a persistent misfire for a few weeks now.

It went into my local indy who said that the spark plug holes were full of water and he dried them out (but plugs apparently badly rusted).

Anyway, we go it back and it was quite a bit better, but then I got into a week or so later and it started but then immediately died, and wouldn't start again.

Suspecting the coil pack (and going by the fault codes) I ordered a replacement coil pack, fitted it but it still wouldn't start, and this is when I found the blown fuse.

So before I get it recovered to my local auto electrician, I thought I'd look for ideas as to what could be wrong here first.

It's a 1.4 MK II - coil pack has been replaced with a Bosch unit.

I can't see anything else wrong, so are there any common faults?

TIA.

Fault codes (but under pending fault codes?) - Android Torque(lite)

[Scrump]

Water in the spark plug holes again?
Were the (rusty) spark plugs replaced?

[TonyRPH]

No, it won't even start now, and just blows the 10A fuse that feeds the ignition module (I presume as it's marked IGN)

[GreenV8S]

Identify which side of the fuse holder is the +12V supply side and which side is connected to the ignition system. That is easy to do using a volt meter.

With the fuse out, measure the resistance between the output terminal, and ground. It should be more than 1 Ohm. If it's less, disconnect stuff on the ignition circuit until you find the cause. Injectors and coils would be the first thing to try.

[TonyRPH]

Following on from a disastrous visit from a so called "Auto Electrician"....

Said chap replaced the 10A fuse with a 20A fuse !!!

Reckoned that the fuel pump wasn't working (it is).

Then attempted to get the car running - held it (with it misfiring badly) at around 6k RPM on a cold engine...

And then the inevitable smoke......

And one destroyed coil pack.

So I sent him packing as quickly as I could (after paying £40 for the privilege)

This morning I performed a set of diagnostics of my own.

When measuring the 3 pin connector to the coil pack, I see the following: (all measurements referenced to vehicle ground)

Pin 1: 247 ohms
Pin 2: 740 ohms
Pin 3: open circuit (I think this should be ground?)

With ignition on:

Pin 1: 0V (I guess this is the trigger connection)
Pin 2: 12V
Pin 3: 0V (I have a hunch this should be ground?)

The old coil is practically short circuit across all terminals - and I'm guessing the new one was already destroyed by the time my friendly auto electrician got his hands on it.

So - should that pin 3 be connected to ground?

For your amusement, here is the failed coil pack after allowing 20A through it.

[GreenV8S]

That looks like a four cylinder wasted spark coil pack, with the two low tension coils sharing a common terminal.

I expect you'll find that the common terminal receives a 12V ignition switched supply; the other two are grounded by the ECU to energise the two coils.

If the coil is faulty it will need to be replaced. Fitting a 20A fuse was extraordinarily reckless, so you'll have to hope that the coil wiring and driver circuit haven't been damaged.

[TonyRPH]

Given that: when measuring the 3 pin connector* to the coil pack, I see the following: (all measurements referenced to vehicle ground)

Pin 1: 247 ohms
Pin 2: 740 ohms
Pin 3: open circuit

If pin 3 is open circuit, that then suggests that the driver has indeed been damaged (or was already previously non functional).

It's worth noting that after fitting the new coil, the 10A fuse blew immediately - right after the ignition was switched on.

So simply applying 12V to the new coil caused something to fail (possibly the new coil, I'll never know) but perhaps the driver had already failed due to the plug cavities filling up with water. The "auto electrician" obviously exacerbated the situation with his 20A fuse trick.

My guess is the car was only firing on 2 cylinders and would explain why one half of the feed measures open circuit, as that I guess supplies 2 cylinders?

EDIT: * This refers to the 3 pin connector from the harness *to* the coil pack - not the coil pack itself.

Edited by TonyRPH on Wednesday 22 May 16:08

[Penelope Stopit]

I haven't been visiting here much lately hence my late reply

As mentioned above, the unit is 2 coils in one package

2 of the 3 terminals connect to the ECU, the 3rd terminal that's common to one end of each coil is supplied by the ignition switch and this supply seems to be fused




Keeping things simple for now, the coil had water in it and caused rough running, water was dried out and the rough running wasn't as bad, later engine won't start and fuse is found blown, fuse blows with new coil

The problem could be as simple as an incorrect new coil

or

There could be a short to earth (Ground) on one of the coil to ECU cables and this short is overheating and burning the coil out and blowing the fuse.....The thing is it would take longer than a quick on/off action of the ignition switch to burn a coil out if one of the ECU cables was shorting to ground

Good luck in finding it

[TonyRPH]

Penelope Stopit said:

Helpful stuff.

Thanks, I have now concluded that the PCM module is dead (or partly dead) - the replacement coil part numbers matched, as did the size etc.

I suspect what happened was that the water caused a misfire, and even though the spark plug 'chambers' were then dried out, the misfire improved but was still there.

The next attempt at starting the car seemingly destroyed the coil pack (which caused the 10A fuse to blow) and at this point also damaged the PCM module.

When I fitted the new coil pack, the fuse blew as soon as I turned the key (without even cranking).

We have decided to scrap the car, as we only bought it 8 months ago, but it has cost us nearly £600 in repairs since then.

I've also discovered (via Google) that this is a very common fault and there was actually a factory recall to modify the washer jets with a non return valve, to prevent water dripping on to the cam cover. This recall was never carried out to our car.

It's a 13 year old Focus 1.4 "Studio" which is probably worth 'buttons' anyway.

So it's going to scrap, complete with nearly new front tyres and (expensive!!!) front suspension arms...

[Novexx]

TonyRPH said:

I've also discovered (via Google) that this is a very common fault and there was actually a factory recall to modify the washer jets with a non return valve, to prevent water dripping on to the cam cover.

It's a total ball sack of design oversight & has the potential for pretty disastrous consequence;

4.5 Y/O Focus, outwith any warranty arrives with an occasional misfire, open the bonnet & from the rust stains running from the cam cover it's pretty obvious that there has been a water issue for some time - said area is full to the brim!

Leads duff with corrosion, 2 plugs that simply will not come out of their inserts & the other 2 inserts loose. Head that much of a mess it ended coming off for inspection / correction. Expensive already.

Corrected head refitted, job nutted down, car started & "BOOM", plastic inlet manifold blown to bits, turns out that there are a small number of engines with incorrectly manufactured timing gear (can't remember the specifics)..... Inlet manifold on 6 week backorder... Huge cost, long wait, very embarrasing, customer distraught & all for a 50p NRV.

Faulty seal between the washer jet & bonnet can also cause the same issue & if memory serves correctly it's the same engine that suffers from core plug failure in exactly the same area.