Arrgh. S2 cut out now wont start

[nick9one1]

Having a new problem with my S2.

Just left work to grab lunch and it has cut out 500 meters down the road. It was running absolutely fine, then all of a sudden stopped and doesnt want to restart.

First instict is DME relay, I popped the bonnet, removed it, gave it a few taps and put it back in. Tried to restart and no joy.

I'm back at the office now (towed).

Anything I can try while I'm here?

I cant tell if the fuel pup is running, should I be able to hear it?
Was thinking of hard wiring the dme relay with a few scaps of wire.

other ideas??.. reference sensor (only one on the S2?), AFM?

Thanks!

 

[alwigley]

Are we talking instant cut-out, or stumbling to a stop ?

What you described sounds like a fault with the electrics, possibly even just a duff connection somewhere. When you try and restart, are you getting fuel smell from the exhaust, and does she even attempt to start, or just turn over with nothing happening at all ?

Hard wiring DME relay will rule that side out (makes fuel pump permanantly live, so you should then hear it whirring).

Best of luck !

 

[nick9one1]

Instant cut out!

I've managed to get it working temporarily
And you were on the right tracks...

Turns out fuse 34 was blown (fuel pump).. replaced it with another 15 amp and it blew again, so tried a 20 and seems ok.
Going to get it home and investigate further!

 

[nick9one1]

A bit more googling revels a faulty O2 sensor can cause the fuel pump to draw more current than it should?! Although cant see why. Going to try unplugging it later tonight and see if it still blows a 15amp fuse.

 

[repsol]

just a note mate its 15 amp for a reason bigger fuse will melt something if its a short somewhere

 

[sulzeruk]

Check for chafed wires underneath where the loom comes out under the body. The wires have a habit of danign down near the driveshaft if not stashed out of the way in their little plug! Could also be your fuel pump has seized so disconnect the plug and see if it is down to earth. The pump may be fine when cold but shorting or going O/C when hot. Rare but not unheard of.
Alasdair

 

[alwigley]

Hope you got home OK.....

+1 on the fuse comments - suspect Alasdair's on the right track, but have no idea about the O2 sensor (don't have one on mine !). I know the sensors can hugely affect what the DME does, but not sure how it could raise the current to the fuel pump which I would have thought should be static, not fluctuating....... barks944 may have a better idea because of his recent dme exploits (we have some clever chaps on this forum) !

 

[nick9one1]

Thanks for the replies and yep made it home without it blowing again thankfully!

Got the multimeter hooked up and was reading 0.5? Not too familiar with ohms, but guessing thats 5 amps? 0.5amps seems a bit low considering it was blowing a 15?

 

[Mike_Pollock]

Not exactly[8|]

Its showing a 0.5 ohm resistance, very low I would guess, but I'm not too sure, for the fuel pump motor, which is why it is drawing too much current and blowing the fuse.

If its 0.0 ohm - its a dead short, so I'd be looking where Alistair mentioned.

 

[nick9one1]

ok, that's confused me even more!

I thought there were 4 main settings on a multimeter.. AC, DC, Resistance (ohms), and Amps.
In the picture I have the fuse pulled out and the two probes in either of the fuse terminals. Multimeter is set to 'A' which I presumed was amps? When I pulled one of the probes out the car died, proving it was connected in circuit.

I haven't actually looked for the fuel pump yet... guessing is round the back, somewhere near the fuel tank?

I may just buy a new pump anyway. If this is the right one they're cheap as chips!

new fuel pump - eBay

 

[VanhireBoys]

Hi Nick - My advice is to disconnect the pump 2 wires underneath and go to start - If the fuse blows then disconnect the O2 sensor (male/female plug at the top back of the engine) - If it blows again its the loom as the lads said ! Simples !

 

[nick9one1]

Thanks for the replies.

Tried to make it to the petrol station today (2 miles) and the fuse was constantly blowing after 2 seconds of running.

I've followed your advice with my investigations today..
Wires for the pump looked fine - nicely ziptied.
disconnected pump and tried to start... doesn't blow 15A (although normally its only after the car starts that the fuse blows, maybe 2-3 seconds).

Connected pump directly to battery with some test leads and it runs fine, so took some more current readings.

What's strange is they all look fine. fuel pump is drawing less than 5Amps and the lambda sensor is drawing just over 1 Amp (they both go through fuse 34).

so I guess the fault must shorted/chafed wires be between the fuse box and the pump?

 

[david924s]

Sorry to be pedantic but you cant measure current in parallel as you describe both probes in either side of the fuse will measure voltage OK and resistance with no power on the system but to measure current you would need to put the probes in series with the circuit.

 

[nick9one1]

sorry my mistake, when I said I had the probes in 'circuit' I meant I had connected the probes in series, not parallel.

I removed the fuse all together and put one probe in each of the terminals that the fuse normally goes into. so all the current is flowing through the multimeter. When the cars running if I remove either of the probes the car cuts out as the pump is no longer powered.

 

[nick9one1]

All connected back together and running fine for the time being. I would have liked to actually solved the problem rather than it just going away! grrr.

I suppose it could have been corrosion on the round plug near the fuel pump?

 

[VanhireBoys]

ORIGINAL: sulzeruk

Check for chafed wires underneath where the loom comes out under the body. The wires have a habit of danign down near the driveshaft if not stashed out of the way in their little plug! Could also be your fuel pump has seized so disconnect the plug and see if it is down to earth. The pump may be fine when cold but shorting or going O/C when hot. Rare but not unheard of.
Alasdair

Good that the car is running
Bad you havent found the problem

Did you check Alasdairs suggestion of where the loom actually goes through the body to make sure it isnt bare ? With a bit of pulling and movement the problem could clear but is just waiting to bite again !

 

[nick9one1]

Yes I did and the wires looked fine, it was all ziptied in place so no room for it to rub through.

A few days on I still havent blown any fuses, although I seem to have experienced another strange problem..

When hot starting the car will run for 5-10 seconds and die, very similar to what it was doing before althoguh lasting a bit longer. Then after starting again it runs fine. Its done this twice now.
Like I said not blowing any fuses, and the DME relay looks new (all clean and shiney inside). I would guess its been replaced in the last 1-2 years.

 

[peanut]

I'd check the fuel pump earthing point on the rear valance behind the carpet. (big brown wires) there could be a corroded earth causing high resistance.

You shouldn't hear the pump when you first switch the ignition on. The pump will only run momentarily for about half a second if that. Just enough to pressurize the fuel injection system for starting.

When the engine cranks the ECU sees the voltage from the crank speed sensor and provided the engine cranks at 200rpm plus ,earths the DME relay terminal 85b which in turn supplies a continuous 12v+ from terminal 87b on the DME relay to the fuel pump via fuse 34

 

[nick9one1]

Thanks for the tip on the fuel pump wires - I will definitely check. Although as Im only seeing 5amps drawn from the pump now its probably unlikely its got a bad earth.

I'm still 50/50 on if it was caused by fuel pump or O2. When I managed to get it working I had unplugged both of them. Prehaps I should have taken a more logical approach.

It's been running fine for the last 6 days, a bit frustrating really.. as I've no real idea what caused it!

 

[peanut]

ORIGINAL: nick9one1

as Im only seeing 5amps drawn from the pump now its probably unlikely its got a bad earth.

Thats precisely why you could have a low current flow !

A poor earth connection will give a high resistance and cause a low current flow .

I guess you didn't do O level Physics lol[]

The 12v+ supply to your fuel pump comes from fuse 34 its a single wire to the pump and the pump is then constantly earthed at the MP1 earth point near the number plate light behind the carpet