pipbro

**pipbro** · 17-01-2011,08:35 PM

Evening all
Can someone help me please, I have a mk 4 TDI with an ATD engine, I have previously posted my problem, HOWEVER I have some contradictary information regarding the fuel supply system. I approached my local dealer and asked if the fuel lifting pumb beneith rear seat should run continously, they said NO, just to prime the system 1 or 2 seconds at turn of key. Now I have also been told by a reputable mechanic that it should run all the time. Which is correct? the engine also has a tandem pump at the end of the camshaft but I am unsure which answer is correct. Please advise so I can either eliminate or focus on this area.

**herby0001** · 17-01-2011,09:06 PM

I think the fuel pump runs all of the time. When my fuel pump was packing up, I would hear it grinding away when primping and also I'd hear it when idling. Whilst driving, there was too much road noise to hear, but my assumption is that it runs all the time.

**jimma04** · 17-01-2011,09:15 PM

when the ignition is first turned on the pump will prime then stop when pressure is reached then when u crank the engine the pump will restart and run untill you switch off the engine

**pipbro** · 17-01-2011,09:55 PM

Thanks for that, it seems my car primes then shuts off! Any ideas?

**jimma04** · 17-01-2011,10:03 PM

does it not run at all with the engine ?? Is the car down on power or performance ?

**pipbro** · 17-01-2011,10:10 PM

no it doesnt seem to run at all after priming the fuel is being drawn by the tandem pump only. Performance wise it is ok to start for 5 or 6 miles then really bad, missfire etc. stop car sw ign off then back on again and runs ok then by which time the engine is warmer and perhaps able to cope with lesser fuel. I will check the fuel flow again in the morning but seem to think i am correct in saying priming only.

**pipbro** · 17-01-2011,10:15 PM

Oh forgot to say checked electrical feed to pump today and it primed only although i didnt check voltage at pump when running only when sw on ign. I am sure I have checked fuel flow at filter when running engine and suction only, but like I say will need to check again in morning