Only 4V at the fuel pump?

[Guest]

My 1.6 electronic ignition K-Series cranks but won't start.

 

Initially the car was completely dead, but fiddling around with the kill switch at least got the ignition on. Now the starter motor will crank away, but just get an occasional cough for its efforts. The car does not have an immobiliser and short circuiting the inertia switch changes nothing.

 

Next suspect: fuel pump. My cheapo voltmeter shows just 4V at the internal fuel pump's terminals - which drops to 3V when the starter motor cranks. These voltages are the same when taken from the wires leading to the pump and the pump itself is disconnected.

 

That doesn't seem right. Where do these two suspects come from? Some sort of relay? Any and all advice gratefully received as always!

 

[revilla]

What voltage does your multimeter read across the battery? What voltages does it read when connected between each of the fuel pump wires in turn and a good clean earth point on the chassis?

[Guest]

Hi Revilla,

12.4V in the battery.

4V live to earth.

100mV or so earth to earth.

 

[Jonathan Kay]

What's the voltage at the battery while cranking?

 

When was it last running happily, and have you done anything to it?

 

I'd run a good lead from the battery to the fuel pump, check you're getting 12V and then try and start.

 

Some people recommend squirting Easy Start into the air intake and seeing if it will start. But you already know there's a problem with the fuel pump.

 

Jonathan

 

PS: Morning, Andrew :-)

 

 

[revilla]

Morning 5719,

 

So the fault is primarily on the supply side. It is however odd that you are getting a large voltage drop even with the the pump disconnected - sounds like there might be a short somewhere.

 

The supply for the fuel pump is ultimately switched by a relay in the Multi Function Relay Unit (MFRU) which sits on top of the ECU. This is wired into the engine loom rather than the main body loom, so the wiring takes a slightly convoluted route:

 

- MFRU Output Plug (the larger of the two)

- Engine Loom to Body Loom Connector (Pin 9) (large grey plug and socket cable tied to the chassis rail at the front of the engine bay, right hand side)

- Fuse 13 (on the fuse box, passenger footwell)

- Inertial Cutoff Switch

- Fuel Pump

 

It's easy to see which wire it is at each point as it is consistently Yellow/Green all the way through. If you measure the voltage at each of these points to a good ground, you should find at what point it drops from about 12V to about 4V. If you find it is still only 4V out of the MFRU, check the voltage on the large brown wires into the MFRU output plug as these are the feeds into the relays from the battery. Given the problems that people have with the starter relay inside the MFRU, and given that all four relays inside the MFRU are basically the same, it could well be oxidised contacts in the fuel pump relay inside the MFRU. For the engine loom plug, the fuse and the inertia cutoff switch, measure the voltage on both sides of the component to see if the voltage drop is within the part.

 

Let us know what you find!

 

PS: Morning Jonathan :-)

[Guest]

Saturday jobs decided.

 

Thank you both!

 

[Guest]

Report time:

 

I was able to swap in a new (well, different) MFRU - no change.

Also connected the battery to a fancy charger - 12.4V but only 10% "good" whatever that means.

 

So trickle charged the thing over night and got the magic number up to 90% "good". But not good enough to start the engine it seems. So started to follow the green and yellow brick road from the MFRU.

 

When cranking:

8V at departure from both MFRUs.

7V at Engine Loom to Body Loom Connector.

5V at Inertia Switch.

 

Then cheap voltmeter went on strike, or possibly topped itself, and I ran out of time.

 

Last thing I did was get my kids (good hearing) to open the fuel filler and listen down the pipe when:

1. Switching on ignition

2. Turning over starter motor

 

No noise. Perhaps it is the fuel pump after all? Next chance I have, will run Johnathan's good wire direct to the pump.

 

Answers to Johnathan's questions - ran faultlessly in February, but was left out in rain for much of March without a cover over the bonnet louvres. Probably not such a great idea.

[revilla]

The progressive reduction in voltage all long the chain would be odd. It would suggest that either:

 

1) You have lots of points of resistance along the wire (UNLIKELY) OR

2) Your cheap voltmeter, that kicked the bucket shortly thereafter, was already on its way out!

 

I would suggest that number (2) is the more likely. If I were you I would replace the voltmeter battery (or the voltmeter with one you can trust) and see if it makes any more sense.

[elie boone]

I think you need to see 9.5V minimum to switch on the ECU, did you tried jump leads ? or another good battery ? You should hear the fuel pump prime if you switch the power on, if in doubt undo the fuel line so that you know there is no fuel pressure before you switch on the power so that the fuel pump will prime.

You could always use contact spray on the connectors from the ECU & MFRU but in theory the connectors are sealed when pushed fully home.

[richy]

Run a flying lead cable direct from the battery +ve to the fuel pump fuse socket (with fuse removed). This should start the fuel pump so you can check it runs.

(This worked on my Sigma. Assume it would on a K-series?)

Richy