Help please!!

[Quantum Steve]

Hi guys, looking for some help from the collective genius on the forum here....
Noble been up on stands since Christmas, floors off, inner panels out, painted, chassis and suspension painted, new rubbers fitted, new hoses, Protechs (thanks Tux!), wheels refurbished, new tyres, new battery when the floor was out, all back together but won't start....

Ignition on, push button on alarm fob, relay clicks then clicks again about 3 seconds later, no fuel pump noise though, starter turns but as no fuel wont start.
Taking the cables off the fuel pump and powering from a battery the pump runs fine and the car will start and run.

The car has had the fuel pump mod, there is a direct 20A fused supply from the battery to a relay in the engine bay passenger side powering the fuel pump. I checked the in line fuse, the holder was brown but the fuse looked OK but as the cable was just hanging on to the holder by one or two wires I thought this was the problem, stripped out this part of the loom and made a new section with a new fuse holder. No difference.

I'm stuck. If I hear the relay click on and off I guess the ECU is telling the pump to prime and then cut off so probably not ECU? If the fob button makes the relay click and the car will start with the pump powered I guess not alarm related?

It's cold standing in the garage trying to think what this might be.... Any help much appreciated.

[Zoobeef]

Guessing your new relay is activated by the old relay on the bulk head? Is that being activated by the ecu? Is power getting from there to the new relay to acivate that?
It does just sound like powers no getting to the pump.

[StreetDragster]

So if i understand correctly, you have the fuel pump wiring mod. The mod relay clicking suggesting the trigger is working, but the pump isn't powering up.

So either its the high power feed to the relay, the relay itself, the wire to the pump, or the earth from the pump,

I'd start by checking the earth on the pump with a multimeter, if ok, then trigger the alarm and see if 12v is being supplied to the pump.

If no 12v at the pump check the terminals to the relay for power, and from the relay to the pump for continuitity, and all that ok finally replace the relay.

Matt

Edited by StreetDragster on Tuesday 3rd March 21:55

[Quantum Steve]

Hi Zoo, to be honest I'm not sure - ran out of energy and warmth, the new relay is 4 pin, it's receiving power direct from the battery not sure where the output signal goes to or how the signal from the original bulkhead relay is used, is this a common mod? I'm guessing it's for an uprated fuel pump. Does seem like power not getting to the pump just not sure where to start tracing....

[Quantum Steve]

Hi Matt, cheers, that's a perfect answer, I'll go see what voltage I have where.

[StreetDragster]

Although from the reply above it seems there is two relays in the triggering circuit for the pump. So make sure the relay mod relay is getting power from the other (standard) relay first.

Thanks

Matt

[Quantum Steve]

Thanks Matt. I'm only guessing the original relay is still in circuit, I'm assuming what I have is the fuel pump mod, do you know how this normally wired in? I have three pairs bound together by the new relay, a pair direct from the battery (+ and -), a pair feeding the pump and a pair that disappear down past the pump and out behind the fuel tank somewhere. Does this sound normal?

[Tuscanny]

Have you checked the bank of 4 fuses above the ecu I had this problem mo and one of mines had came out.You probably have checked this.

[Quantum Steve]

Thanks, yes, checked those as well, all fine. I'm a bit clearer after a good sleep, I'll get a replacement relay today to rule that out and set to with a meter to see what power is getting to where. Frustrating though, got a day at Castle Combe on Sunday and had hoped to get it all together and over there to set up the new Protechs and give it a shake down. I didn't want to get all the front and rear floors back on until I had a chance to run it up and make sure there are no leaks or issues.

[TuxMan]

You could also put a 12volt feed onto the pump just to make sure it's ok and not buggered !!

[Quantum Steve]

Cheers Tux, tried that early on, pump works fine and the car starts easily. It just doesn't get power.

[AMG Merc]

Maplin sell a very useful car relay tester and under £20 AFAIR. Might be a fast and easy way to rule out any relay issue.

[Quantum Steve]

Thanks, just checked, on offer at £9.99 - just ordered one click and collect....

[andygtt]

The ecu provides a negative feed to switch on the original relay rather than a positive, as other have said if your hearing the relay switch then it seems the ecu is fine (I had one fail and not send a signal to prime to the pump).

I guess its either the relays or the wiring from the relays.

[Quantum Steve]

Thanks Andy, I'm hoping it's as simple as a relay. Just so I am clear does the ECU send a signal to an original (bulkhead mounted?) relay which fires up the original (lightweight) pump power supply and it's that power supply that switches the fuel pump mod relay to provide the power to the upgraded pump? Or is the ECU sending it's signal direct to the fuel pump mod relay? It's weird, I did 5500 miles in it last year, caned round all sorts of airfields and circuits, the only time it's had a problem was when it was not used for a couple of weeks and both times it was the pump not priming, both those times the 20A in line fuel pump fuse was melted.

[StreetDragster]

Sounds like there is a wire chafing somewhere between the relay and pump to me

[andygtt]

Quantum Steve said:

Just so I am clear does the ECU send a signal to an original (bulkhead mounted?) relay which fires up the original (lightweight) pump power supply and it's that power supply that switches the fuel pump mod relay to provide the power to the upgraded pump?

This is correct on mine which is the normal method for the pump wiring upgrade.

I had my 20Amp fuse go once and upgraded to a 25Amp... the 044 can draw up to 15Amps (if thats what you have fitted) which is quite a bit more than the stock pump so I felt the stronger fuse was wise if not technically needed.
Never had one blow since.

In truth the wiring generally coming from my loom into the engine bay was a right dogs dinner and was clearly like that from new. I tidied it up a lot when I removed the tub last winter and completely resolved the slight battery drain that had crept in over the years.

[Quantum Steve]

That really is helpful. The pump mod was on it when I bought it and you are right - the original wiring looks pants. I had been working on the supply wiring to the mod relay and from there to the pump, however the relay I can hear is possibly the original one and perhaps I should be looking at the wiring from the original relay to the mod relay if that triggers it, it's that wiring that looks tatty. A 25A fuse sounds sensible too, lets see if I can get it to run at all first.....

[Quantum Steve]

Guys, as always thanks for the help on here, much appreciated, it makes a difference to be able to go through a problem and get so much useful advice. Took all the rear turbo hoses out, got the meter on the wiring from the standard relay feeding the original pump, no voltage for the 3 seconds after the alarm is off, pulled all the old wiring out, it was in a pickle, ran in a new set of temporary wires to trigger the relay, pump buzzed and it started and ran beautifully. A proper ballache to get to, I guess having all the floor, side panels and engine covers off for the winter sort out made access easier. I think she was just sad not being used for a while. Thanks again.....

[Zoobeef]

Happy days.