Hi All,

I hope someone can help me with this issue. Had a search on this and the Alfa forums but found nothing.
Had a breakdown in my JTDm 120 Multipla some months ago, the car stopped and just wouldn't start again. Changed the crank and cam sensors but nothing.
I towed it to try and start and an error of no high pressure came up so I assumed it was the HP pump.
Winter kicked in so I just got a spare car to tide me over. Have since taken off the HP pump and it seems fine, so I looked further.
To cut a long story short, the low pressure diesel lift pump from the tank only starts for a second and then turns off. It can still provide over 2.5 bar of pressure in that time but doesn't continue to pump. So maybe it was a diesel starvation issue after all.

Anyway, anyone know why the pump might want to stop pumping? It literally is for a half a second, so won't fill the diesel filter never mind bring fuel to the HP pump.

Thanks.

S/H ones can be had on ebay for around £20-25, delivered. Might it be worth buying one of those, just to see if it is the pump that's at fault?

Is the power to the pump permanently there when you have the ignition on? I'd check that first. Unless of course, it is interlocked and if you don't get pressure it turns off the pump. Seems unlikely though. Check the power with and without the pump, in case it's the pump causing power loss (if the power is lost of course).

widemouthfrog said:

S/H ones can be had on ebay for around £20-25, delivered. Might it be worth buying one of those, just to see if it is the pump that's at fault?

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I don't think the pump itself is at fault, I think it is the control of the pump. Is there a pressure control for the pump? Maybe it is pumping to too high a pressure, I measured at least 2.5 Bar (36psi), it could be higher as the gauge max-ed out. Is there a fail safe that shuts down the pump if the pressure goes too high?

Crickleymal said:

Is the power to the pump permanently there when you have the ignition on? I'd check that first. Unless of course, it is interlocked and if you don't get pressure it turns off the pump. Seems unlikely though. Check the power with and without the pump, in case it's the pump causing power loss (if the power is lost of course).

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Power to the pump is as normal and I'd expect it to run for the standard 20-30 seconds if there wasn't an issue. My thoughts is that the power is being shut off very quickly by something or other - over pressure switch maybe? If such a thing exists on the lift pump circuit. I have some info on the '00 Marea JTD so I'll see if there is something in this.

DiamondDave said:

I don't think the pump itself is at fault, I think it is the control of the pump. Is there a pressure control for the pump? Maybe it is pumping to too high a pressure, I measured at least 2.5 Bar (36psi), it could be higher as the gauge max-ed out. Is there a fail safe that shuts down the pump if the pressure goes too high?

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Hi,
The pump is controlled by the engine ECU via a relay. There is also an inertia (crash) switch in the ground circuit. As it runs briefly it is probably a sensor or sensor circuit fault. Do you have Multiecuscan? This will allow you to read fault codes, check sensor readings, see if thr ECU has commanded the pump on (or off) and manually turn the pump on.

Robert G8RPI.

I was thinking about this and figured that if the ECU is controlling the relay to the pump then maybe the ECU sees something amiss and decides to turn off the pump.
I had the HP pump removed from the car, so I fitted it temporarily and plugged in the pressure control valve at the end; tested it again and off the pump went for a full 5 seconds pumping diesel.
I disconnected the injectors as well, just to see, but this didn't stop the pump working.
So, it looks like my original problem isn't fuel delivery to the HP pump. That would just be too handy, wouldn't it!

DiamondDave said:

I was thinking about this and figured that if the ECU is controlling the relay to the pump then maybe the ECU sees something amiss and decides to turn off the pump.
I had the HP pump removed from the car, so I fitted it temporarily and plugged in the pressure control valve at the end; tested it again and off the pump went for a full 5 seconds pumping diesel.
I disconnected the injectors as well, just to see, but this didn't stop the pump working.
So, it looks like my original problem isn't fuel delivery to the HP pump. That would just be too handy, wouldn't it!

Click to expand...

so have you used software to see what rail pressure the ECU is seeing..??

varesecrazy said:

so have you used software to see what rail pressure the ECU is seeing..??

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I tried to use MultiECUscan to watch the rail pressure while cranking but as soon as I cranked it disconnected so saw nothing. While towing, the ECU brought up a low pressure error, which lead me to believe the HP pump was at fault. It's all a bit of a mess, I think I'll put it back together and start from scratch again.