does any one know if kits are still avaliable or would I have to improvise and make my own.
Cheers Ash

There was one in parts for sale a few months back, might be worth a post in wanted section.

For the effort involved I'd just make one. A relay, a fuse, some crimps, and some lengths of wire.

Although why anyone would bother is beyond me.

If you're experiencing a voltage drop why not just piggyback the existing cables with new, thicker ones?

Ignoring the question as to whether the mod is *necessary* - piggybacking the existing cables would require four separate lengths (or perhaps five) to cope with the relays, fuses, switches, and connectors in line.

Running a fat wire to the relay, making sure you have a good local earth, and using the existing cables to drive the relay will ensure you have the highest voltage at the pump.

However - you *must* fuse the new wire where you connect it to the 12v close to the battery.

I have been advised to have this mod performed before I go for the Livemap. I have looked for the guides on the How to section and cannot seem to find any. I preusme it is a live feed from the battery to the pump with a larger wire with less ohms.

Cheers for the knowledge Barnacle. So I'm looking at buying a length of 18amp wire going from the Battery to the relay and having an inline fuse?
Ash

Guides are here:

http://homepage.ntlworld.com/sinister/coupe/PDF/Rewiring%20the%20fuel%20pump%201.pdf

http://homepage.ntlworld.com/sinister/coupe/PDF/Rewiring%20the%20fuel%20pump%202.pdf

Thank you very much. This will help the top end fueling when I get the live map.

Not aimed at you barnacle. But it does seem to be a theme around here. In this instance I fail to see how adding another layer of switching to the circuit can be a good thing?

As I originally discovered this need back in my hay day when I was running around in the Brick (turbo'd tipo), I had a A/F gauge wired into my narrowband sensor. I could see under load, that the fuelling was going from green, into amber and into red the higher the RPM. I stuck a voltmeter on the fuel pump wiring and got someone to watch it whilst driving about, under load the voltage would drop to 9v, which would mean a drop in fuel flow, and I'm sure I don't need to explain to you why that is bad

I think you've missed my point. I don't argue the point about voltage drop. Fully happy with that.

It's the way it's fixed I take issue with.

What you highlighted was a deficiency in your wiring; most likely caused by age. Now piling a relay and more wiring on top of that is a tad gash.

I'd argue that the correct way to fix the issue is to sort the existing wiring.

The argument is that the original wiring is a little thin (= higher resistance) for the current required to maintain the pump at full chat - leading to voltage drop across the wire itself and therefore a lower voltage at the pump.

Using the existing wiring to drive the relay means the voltage drop is immaterial - the relay is a fairly high impedance device and very little current (in auto electric terms) is flowing. It also means that the existing safety devices, in particular the inertia switch, still act on the supply to the pump, though indirectly.

A nice fat wire direct from the 60A fuse (I'd suggest 30A rated, and fused at 15A or 20A - the fuse is to prevent the wire heating and potentially causing a fire if a short to ground occurs, and the pump won't pull any more than that) to the relay, from the relay to the pump, and from the pump to ground will provide a low-resistance path with a proportionally lower voltage drop.

It is possible there is a deficiency in the original wiring - as I pointed out earlier, there is one relay, one inertia switch, one (or two) cable link(s), and I think a fuse link in the path. Any of those could have corrosion on the contacts and should be resolved lest they lead to further problems. But the original observed problem is that the cable appears to be underspecced.

Looks like I did miss the point, apologies.

As Neil as high lighted above, to replace the wiring would be quite a hard job due to what is involved and where the wires run off to. The existing wiring just for the fuel pump alone, is a power wire from somewhere behind the dashboard, down the length of the car into the pump. The earth for the pump then runs back the length of the car into the dashboard.

No apologies needed. I didn't't want this to come across confrontational, and I sincerely hope that I haven't.

In my experience it's the positive wire from the pump to the relay that takes the beating and fails. What I'm suggesting is that this wire only would need a piggyback to restore the voltage drop.

Adding a relay on top to cover a deficiency prolongs the failure at best.

I think where I disagree is the wire being under specified. I find it unlikely any cars would have made it 15 years plus.

I believe what's being observed is failure.

Just been doing some research and the same method is done on the mish 3000's as well. Same technique and everything.

It's relatively common for high current wiring like this to age and go high resistance and then fail to meet the original power requirements.

Same thing happened to the starter motor wiring from the ignition in my mate's 1989 BMW 635 CSI, around 3-4 years ago (so at about 20 years old). The starter would fail to turn over... direct feed from battery via a relay, switched by the original wiring and all was well.

i suggest to use OFC wires

Hi, Szkom. It's a theme because it works! Dsocovered many, many times over - including myself! It's not needed for completely stock cars but when you start modifying, the stock wiring quickly proves inadequate. The stock wiring is thin and the route to and from the pump is long, which means the voltage at the pump is less than 12V. Taking a direct feed from the battery, through more manly wire, and a short ground to the chassis means there is next to no voltage drop. Not to mention that the voltage at the battery will typically be higher when running - typically 13.5V (as opposed to the -presumably- regulated 12V of the stock wiring). That translates to a surprisingly significant increase in fuel flow from the pump.

Using the original wiring to power a relay is just an easy way to switch the direct feed power.

Well your assumptions are wrong.
Its not an age problem, this problem occured looong ago when our Coupe's were still only a few year's old. The wires are too thin - period.
(Not for a std Coupe obviously, Fiat did their research, but for our tuned ones)

My degree in car electrics tells me wire's do not age. They are simple stuff, copper w plastic surround. The only aging possible is through heavy corroding, and I do not think you'll find it in your pump wires, other than easily spotted earth points etc. The plastic surround can harden a little but that does'nt change the resistance.

Back on topic, Would 2mm2, 17.5amp be adequate for the wire trailing back to the pump?

Depends, what's the continuous current draw of your pump?

Assuming 10 amps you want about 12mm^2 to give you approx a 0.2 volt drop for a cable running front to rear.

Kj16v, I'd agree it's a simple way to restore voltage drop. I just don't see why a standard fuel pump shouldn't work correctly on healthy wiring.

Per, not sure how you rule out an age problem without using NEW cars as a test platform? But you do acknowledge that a standard pump with standard wiring is adequate, unless damaged?

I think I'll disagree that wire doesn't age with use. Putting a current through it creates heat. Cycle it enough times you alter the properties of the material; as demonstrated by GrahamL's post.

I'm happy to accept that drawing more current than the original specification will need a work around of some sort.

A thought: assume that the standard wiring on a standard engine gives and always has given a smallish voltage drop.

On the standard engine, the pump is capable of delivering sufficient fuel at this reduced voltage - and some small amount extra to maintain fuel pressure in the header bar.

One might postulate that the fuel need of a tuned engine - potentially twice as much - might not be met by the standard pump (particularly with any voltage drop in the system) and that an uprated pump is required to feed it. But a more powerful pump can be expected to require more current than the standard, exacerbating the voltage drop issue...

While I am not one for modifications, I would offer the following:

- a standard engine with wiring in good condition and a standard pump should be fine (but the only way to tell are with a fuel pressure meter and a voltmeter at the pump, at full load)
- a tuned engine requires at a minimum a standard pump with good volts at the pump, which *may* require a wiring mod
- a highly tuned engine will require an uprated pump to avoid fuel starvation and that will almost certainly require the wiring mod
- if the wiring mod is required, you will need cable of at least 30A capacity, or even thicker per Szkom's calculation. 17.5A is not significantly thicker than the original equipment.

are you sure? try the same size new and 15 years aged and see if the ohm is the same
OFC wires is the answer

it all comes down to one thing ,

standard coupe = standard wiring

modified coupe = modified wiring and uprated fuel pump

simples

Barnacle I think you've demonstrated my point. If a standard pump can't pump to it's design capacity through a lack of volts owing to a drop across the wiring, the wiring is defective. I firmly believe the mod as described here to be inappropriate for this scenario.

The cable I outlined to feed the pump is a hefty lump, but still shows a loss.

I wonder how many cars are running around with a wiring mod that's barely better than the standard?

Spot on.

A 300bhp coupe might be fine on the stock wiring, or it might not....makes sense to have the wiring mod done, otherwise you'll need a second live map session to get the most out of it.

The guide suggests I use a 2mm cable rated for 17.5 amp. KJ is mapping my car to stage one.
If I was going to do this mod, if its right or wrong. Would I need 2mm cable or 12mm cable that szkom suggests.
Advice from people have had this mod done on there cars would be helpful.

Easy; by knowledge of electrics in general, it's not rocket science. Yes, both me and many others have done the wire-mod.

I did it even with my std turbo + Novitec-chip, and there was a clear raise in boost afterwards. (meaning there was slightly too little before = hot/pinking)