TD4 priming pump issue

Hello chaps,

yesterday morning i gave the hippo a service and replaced all the usual consumables but unlike all the other times the under bonnet fuel pump is not playing ball....

I have changed the fuel filter several times with no problems but this time it does seam right and just wanted to check if i am going mad..... ;-P

So replaced the filter under the bonnet and as always made sure that i fill it to the brim before fitting back, this cannot be put the wrong way round as its an under bonnet screw type so only fits one way..

Did the usual on and off procedure with the key so that the system primes and self bleeds but the pump is constantly on for about a minute at a time. before it only used to do it the fist few times but this time it seams to never end.

So far i have checked the following:
1. all connection appear to be fine and not leaking.
2. pipes are as before as i have labeled them.
3. car starts fine and runs fine.
4. was thinking maybe an airlock so i took cover off the rear seats and exposed the in tank pump, and pulled loads of fuel through the return line using a siphon pump, initially some bubbles but all clear now.

Put key in the car turn to pos 2 and under bonnet pump going round like a mad man...

If i remember correctly i could hear the pump before for a few seconds at best and then i would start the car, but now it appears to be always running but i cannot seam to get to the bottom of it.

Car has done about 130K is it maybe time for a new under bonnet pump? or am i forgetting something?

Any feedback would be appreciated.

Hi Vince.
You most likely still have the original under bonnet fuel pump, Pierburg which are the best pumps but do not last for ever, you say your FL is 130000 now so that is good for a pump, if it seems like it is louder or stays or stays on longer than before it maybe getting a bit weak, therefore having to work harder, try taking the connector of the top giving it a squirt of electrical switch cleaner, then plug and unplug it a few times, also check the wires for any cracking etc

Thanks Arctic!!

I have taken the filter housing off again tonight and checked for leaks but it all appeared fine.
i have checked and cleaned the connector but when fitter all back no joy. It still going mad.

Before giving up and calling it a night i took the pipe off the filter inlet (which would be the pump outlet) and run it for a few minutes. I was quiet thrown to see that very little diesel was actually coming out. i was under the impression that it was full off air so i siphoned pumped the line until it was running clear with no air but once i started the pump up again it started spitting out little to no diesel with lots of air!!!!

I think the pump might be on its way out so i might order a new one in the morning unless anyone has any other ideas?

Any suggestions welcome!!!

What appear to be strange is that the car starts first time with no struggle!!! maybe the fumes coming off pump are enough to start?

Hi Vince
Are you saying if you put the end of the fuel pipe coming from the pump into a container it is not a good steady flow, if so and it is spluttering then the pump is most definitely on it's last legs, always best to replace with a original pieburg one.

Yes i did similar to video but pump was still connected to car tank and the outlet into container.

The bad pump on that video has a flow at least 5 times mine.. my pump must be really bad .

Just for the record should the pump still be running when the engine is on? Surely once engine starts the main in tank pump takes over?

Vince Masi said:

Yes i did similar to video but pump was still connected to car tank and the outlet into container.

The bad pump on that video has a flow at least 5 times mine.. my pump must be really bad .

Just for the record should the pump still be running when the engine is on? Surely once engine starts the main in tank pump takes over?

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Are you sure that there's no air leak between the tank pick up and pump? If there is, air will be drawn in, reducing pump output.

Nodge68 said:

Are you sure that there's no air leak between the tank pick up and pump? If there is, air will be drawn in, reducing pump output.

Click to expand...

I haven't touched any connections going back to the tank so I wouldn't of thought that was the issue...

I will remove pump at the weekend and bench test it.... if output is still poor i will replace, if not then i will check piping going to and from tank.

It didnt do this last week before i changed filter so not sure if theres a real bad air lock, or the dry priming it may have done after the filter change was the last straw that broke it....

Vince Masi said:

I haven't touched any connections going back to the tank so I wouldn't of thought that was the issue...

I will remove pump at the weekend and bench test it.... if output is still poor i will replace, if not then i will check piping going to and from tank.

It didnt do this last week before i changed filter so not sure if theres a real bad air lock, or the dry priming it may have done after the filter change was the last straw that broke it....

Click to expand...

Are you sure the filter is sealed correctly at its joints? Also what make of filter have you used? There have been some reports of filters being blocked or restricted from the box..

Nodge68 said:

Are you sure the filter is sealed correctly at its joints? Also what make of filter have you used? There have been some reports of filters being blocked or restricted from the box..

Click to expand...

Filter is located after the under bonnet pump so why would it effect the pump when not connected to the filter?
But yes i have checked filter for leaks and it was fine.

Will bench test pump later and will report outcome

If you have under bonnet pump and filter there is also another low pressure pump in the tank - this can fail and put pressure (excuse the pun!) on the underbonnet low pressure fuel pump

Low pressure pumps should run all the time when engine is running