EU2 K Series fuel pump cutting out

[susser]

1996 K Series 1600 EU2 fuel pump loses power and cuts out at seemingly random times.

Traced the fault (?) back to the trigger wire from ECU to FP relay in the MFRU. In the case of this EU2, it's the Black/ Purple (“BP”) that feeds into the MFRU Input plug on pin 3. (It goes to earth to energise the Fuel Pump "FP" relay.)

Probing this wire shows the following characteristics:

Ign on; BP goes to 2.4V, FP runs for a second or two as normal, BP goes to 12V

Starter initiated; BP goes to 2.4V engine starts and runs.

Engine running; BP at 2.4V (occasionally going to 13.4V very briefly.)

Engine warm; BP flicking between 2.4V and 0.7V

BP goes to 13.4V, engine falters and gradually dies. Tachometer follows RPM.

Starter initiated; BP sits at 12V

Ign cycled off-on, starter initiated; Engine starts and runs.

With my limited ideas about how the thing works:

It seems that the ECU itself is intending the engine to keep running but shuts down the fuel pump: it's supplying sparks, the CPS is being read and the ECU is driving the tachometer. (AS far as the ECU is concerned: things that shut the Fuel Pump down are, Lack of rotation of the crankshaft (crash detectected ?), Immobiliser armed, anything else?

[apjenkins]

Hi Susser.

What about dodgy fuel pump relay contacts not taking BP to ground properly when the contacts heat up a little and producing an open circuit. Open up the MFRU and check the contacts or replace with a known working EU2 MFRU  (you probably know the EU3 MFRU looks the same but is different and won't work)

@ndrew

[SM25T]

Or bypass the little relay in the MFRU and fit a 12V relay externally. Just cut the wires 8n and out of MFRU to connect to new relay.

[susser]

Thanks for your input Andrew.

I think that the BP is taking the coil to ground, thus completing the coil circuit. So, if the BP goes to 12V, it's possibly the ECU open circuiting the BP to shut the Fuel Pump down?

I'll open up the MFRU and put a Volt meter across the contacts to test your theory all the same.

[susser]

Thanks SM25T.

I've been thinking along those lines as a get out. In the meantime, I've ordered one of those "Add a circuit" things to enable me to feed into the fuse that feeds the pump in case the thing strands me.

The thing that bothers me most is: why is the ECU trying to stop the fuel pump?

If I fit an external relay and use the BP trigger wire to allow the ECU to run the Fuel Pump as intended (ie prime 2 sec on ignition energised) (and the ECU is intending to shut down the Fuel Pump) then I'll be no better off. (If the MFRU is not the faulty component)

I'll stop before I get confused

 

[CharlesElliott]

Immobiliser issue? The immobiliser disables the fuel pump.

[Jonathan Kay]

It goes to earth to energise the Fuel Pump "FP" relay.

What does that mean, please?

Are those voltage readings of 2.4V measured from the ECU with the wire connected to the relay or disconnected?

Jonathan

[susser]

Hi Charles.

I had wondered about the immobiliser: it flashes and clicks etc as normal. When the Fuel Pump switches off, the red led doesn't come on, as it would if I tried to start the engine with the Immobiliser armed. That's why I wasn't thinking that the Immobiliser is the problem. HOWEVER. The car's been standing for yonks with a flat battery or no battery at all and I had to press the disarm 5 times before the immobiliser would respond. Maybe it's a bit unhappy?

Hi there Jonathan.

I understand it is the "Trigger" wire. It sits "downstream" of the relay coil and the ECU earths it to complete the circuit and allow the coil to energise. The reading of 2.4V is obtained by probing the wire that comes out of the MFRU and goes to the ECU, I imagine that it's at that voltage as a result of the resistance and current flow in the circuit as it makes it's way to earth. The wire goes to 13.4V at the time the Fuel Pump fuse goes from 13 or so Volts to zero and the engine starts to falter.

(All the plugs are in.)

All clear I hope

Paul.

[Jonathan Kay]

Thanks, Paul.

Jonathan

[Ian Mackenzie]

Thought I'd chip in....

As others have mentioned.

The ECU will switch to earth to run the fuel pump, ie ground the fuel pump relay coil. This will then power up the fuel pump supplying +12V via the relay.

The 2 second fuel pump run before starting is the ECU pressurizing the fuel rail (It may also provide a priming pulse, but I cant remember) and is normal.

I'd start with the basics and check all +12V supplies and earths to the ECU / MFRU as a bad connection may be causing these symptoms.

 

Cheers

Ian 

[susser]

I've fitted a bypass switch that feeds 12V into the Fuel Pump fuse, so I don't get stranded.

Checking the earths around the place, it seems that there is about 0.04V between the ECU casing and the battery when the engine's running. I assume that is normal. I guess the next step could be wiring a Voltmeter to the ECU casing and see if the earth fails and the casing goes to 12V (assuming that the ECU casing shares the ECU board earth.) Based on the assumption (yet again!!) that the ECU fails to earth the Fuel Pump signal (BG) wire and precipitates FP shutdown.

I've taken the car out today, for the first time for a long time. The fuel pump cut out 4 times within a few minutes under road conditions. That suggests a loose connection somewhere I suggest, but I don't want to start pulling the ECU apart.

Can't just screw in another ECU from the scrappy can I ?

 

[susser]

OK another info injection.

Checked the earths (I could find) around the place, all clean and secure.

MFRU dismantled. The PCB track from pin 3 to the Fuel Pump relay has some corrosion. Resistance checked at 2.8Ω (this could be intermittently going high). Wire soldered in to bypass this section.

Subsequently went for a drive and cut out after 3 miles. This time recycling the ignition a number of times failed to power the FP. Got home on the ECU bypass switch.

The Black/ Purple (Fuel Pump signal) wire was at 12+V indicating that the ECU did not want to run the pump.

Installed a wire to take the place of the ECU switching: a lead to earth the BP (terminal 3 of the MFRU Input plug). This pulls 140mA. The Fuel pump pulls 4.3A.

Again, this supports the theory that the ECU is shutting the fuel pump down by making the relay earth path go open circuit.

OK I can override the ECU and take control of the Fuel Pump, feeding into the fuse directly or grounding the signal wire from the MFRU,  but what else could I do?

Replacing the ECU would involve a new/ reprogrammed Immobiliser. Not only that, it's has the Supersport upgrade; higher RPM limit and shift light, so a set off fleabay won't support my supersport head/ cams.

 

 

[Jonathan Kay]

Thanks for the update.

Can't get the Photobucket link to work !

What's the URL... I think that we can now get most commercially served images to display inline.

Jonathan

[susser]

I've err mailed you Jonathan.

Brain fade and general ineptitude on my part !

[Jonathan Kay]

I can now see the image at the very top of post #13.

The one after:

I think it's significant that this whole problem started after I'd taken the inlet manifold off to facilitate flushing out the cooling system. !!

shows a duff link in Blatchat but leads to the same image in PhotoBucket... should there be two different images?

Jonathan

PS: No email or Private Message received.

[susser]

No, that's the right image, just in the wrong place. I might mess with it in a bit,,,,,,,,,,,,,,,,,,,,Sorted. Thanks Jonathan.

 

[susser]

Bit of an update on this "Mystery": I have Angus and Tessa to thank for their "My Caterham" series and the Red Herring Alert, appearing in Technical/ Engine 2-Electrical.

My problem was almost certainly the same as Angus describes his. The ECU was, I believe, shutting down the Fuel Pump as it was getting a confusing or intermittent signal from the CPS. If the problem still existed, I suppose I could check it by displaying the CPS signal on an oscilloscope, but as it seems to have cleared up by just rearranging the harness, I'll leave it alone.

I think it's significant that this whole problem started after I'd taken the inlet manifold off to facilitate flushing out the cooling system. !!

http://i4.photobucket.com/albums/y127/susser/Cars/Caterham/DSCF9244.jpg

 

One of my red herrings was a dodgy section of track within the MFRU !

Couldn't get the Photobucket link to work--brain fade. Sorted no.

DOH ! Should have left the original  comment in place.

 

Thank You Angus and Tessa for this insight into my problem and Thank You L7C for just "being there".