S5 Vert - Fuses a pop-pop-popping!

dezzah · May 10, 2011, 01:44:27 PM

Hi wondering if anyone can help...

I taxed and MOTed my UK cab at the weekend (hasn\'t been driven since October) and I\'ve just taken it out for the first journey since the MOT. However after about 5 miles (on a dual carriageway) the engine just cut out.

I managed to get it up to a roundabout and off the road (phew). Turns out the 10A fuse marked \'METER\' had blown.
Now the only electrical thing I\'d done was just swapped the head unit out (from an old Kenwood to a newer one). Could that be related?

I replaced the fuse and off I went only for it to blow again a mile or so on.

I was out of 10A\'s but stuck a 15A in and pulled the head unit out (just in case!) Got home and loaded up on 10 amp fuses then attempted my journey again.

Yep a couple of miles out it cuts again only this time its the 15A ENGINE fuse.
And this time it takes an indicator bulb with it (also the brake pedal seemed to push down a lot further than before). So I replace the 15A and decide enough is enough and head home.

Sooo... I\'m guessing theres an electrical problem somewhere! :yes

Any tips on where to start?

Prof · May 10, 2011, 07:09:58 PM

Does it happen when you go into 5th Gear by any chance ?

m1tch · May 10, 2011, 07:10:52 PM

Its would be SO ironic if that was what is happening lol

dezzah · May 10, 2011, 07:35:17 PM

Urm... I would have been in 5th when they blew, but not as soon as I changed (it\'s a manual btw!) Sounds like there\'s a story here

Prof · May 10, 2011, 08:03:53 PM

Mitch had this issue - turned out to be some sort of short in the gearbox, when 5th gear is selected, there is a switch that connects +ve (via fuse) to a pin on the ECU. The same switch module also houses the reverse switch, which connects ground to the reversing lights circuit. What seemed to be happening on Mitch\'s switch was that when 5th is selected, the fuse would pop within a few seconds - sometimes a bit longer.

It may be worth investing in some of those fuses with led\'s in, pop one in the circuit and then select 5th - see if it blows - when it does the led will light.

A few folk over on the rx7club forum have had the same issue.

m1tch · May 10, 2011, 08:17:18 PM

Just unplug the 2 connectors on the back of the box

I wonder why they go funny in the same way?

dezzah · May 11, 2011, 06:01:34 PM

Yep thats definitely the problem, just ran it up and down my street and once I got into 5th the 15A fuse popped again!

Weird! So by disconnecting the connectors do I lose the reverse light?

Cheers for your help on this fella\'s - I can\'t imagine how long it would have taken me to work it out otherwise

m1tch · May 11, 2011, 10:07:51 PM

Yeah you do lose the reverse light, but its not part of the MOT, the actual sensor is screw in, so should be simple to replace, the other one is for emissions which sorts stuff out when you are cruising in 5th

Prof · May 11, 2011, 10:45:51 PM

You might get away with just unplugging the 5th gear pair of wires. On a UK car, these are Black and Black with Blue stripe. One of these should read ground (Black Wire), the other may have a couple of volts on it, as it\'s an input to the ECU.

On Mitch\'s Car, the reverse switch actually doesn\'t work, but it is shorting out to the 5th gear switch.

The 5th gear switch controls operation of one of the emissions solenoids, not much else, so you shouldn\'t suffer any loss of performance with it disconnected.

dezzah · May 12, 2011, 12:16:23 PM

Cheers for your help guys, I\'ve diconnected the black and black/blue cables and so far been into fifth 3-4 times without the fuse blowing (admittedly not for very long yet but it blew very quickly yesterday when I tested).

These are the connectors I disconnected.

Left two still connected a red and a black with yellow stripe... Also my reverse light still works... :Thumbs-up

Prof · May 12, 2011, 01:04:20 PM

Makes you wonder how common this failure is - Your\'s and Mitch\'s cars are the only ones I know of that have had the issue in the UK, and maybe 10 or so in the US, judging by the threads over on the rx7club.com.

I don\'t know if the gearbox switch is an item that can be serviced, be difficult as it\'s in an environmentally unfriendly place where it is so probably sealed.

At least you won\'t be spending all your pocket money on fuses now

dezzah · May 13, 2011, 01:12:21 PM

Harrumph, the 10A fuse has blown again (after about 5 miles in fifth this time). Just had to drive 20 miles in 4th! Guess I\'ll try disconnecting the two remaining wires too then...

Prof · May 13, 2011, 03:19:23 PM

Strange - unless the reverse switch is shorting to the grounded body of the switch, and you are just catching it when engaging 5th gear.

If it stops blowing fuses when all 4 connectors are off - it\'s definitely the switch that\'s up the swanny

dezzah · May 13, 2011, 07:34:54 PM

Well I\'ve disconnected all 4 now so just gotta test it!

Do you not reckon that switch on the side of the gearbox is replaceable then?

Although it does crunch the gears when going down from 3rd to 4th which isn\'t too good either!

Prof · May 13, 2011, 07:39:02 PM

Quote from: dezzah;762367Well I\'ve disconnected all 4 now so just gotta test it!

Do you not reckon that switch on the side of the gearbox is replaceable then?

Although it does crunch the gears when going down from 3rd to 4th which isn\'t too good either!

I think it is replaceable - probably not repairable. The switch just screws in, but I bet it ain\'t cheap for a new one from Mazda.