Hard Starting Issue when fuel tank is below Half a tank

OmegaRenegade

Vendor
Joined
Dec 15, 2005
Location
Brampton
TDI
2004 Jetta
Car: 2004 Jetta TDI ASZ (PD130) motor

I’m having a weird issue with my car the last few weeks that has started to get progressively worse. I’m hoping that perhaps someone on here can shed some light on what the issue might be.

Lately when I have a little less than half a tank of fuel in my car, and it’s been sitting for a while approx 5-10 hours, the car will really struggle to start up. It turns over after the normal crank and a half but stalls out instantly. It’s not the immobilizer. To get the car started it’ll take a good few seconds of cranking to get it to turn over. It’s the same kind of cranking you get if you’re trying to clear air out of the fuel lines. The car does turn over and runs without issue once started, its just that initial start that’s giving me problem. If I shut it down right after I get it running, it’ll fire up no problem, Its only after the car has been sitting for a while does the hard start issue arise.

The lower the fuel tank gets the less time it takes for the car jump into this hard starting ‘mode’. With a full tank or anything up till half a tank, there is no issue at all. Only once the tank falls below half.

Nothing has been replaced yet, more looking for insight on what to check first. Was thinking to start at the Thermostatic T, and then move to lift pump and tandem pump. Does that make sense?

Cheers!
 

BuzzKen

Vendor , w/Business number
Joined
May 16, 2011
Location
Markham, Ontario
TDI
'10 Touareg TDI, '09 335D, '10 X5D
I'm gonna have to say that if it is fuel level related, that kind of narrows it down to the lift pump. Backflow valve or something?
 

BuzzKen

Vendor , w/Business number
Joined
May 16, 2011
Location
Markham, Ontario
TDI
'10 Touareg TDI, '09 335D, '10 X5D
But at least the motor would sound like a proper diesel, not a diesel with a vagina.
 

OmegaRenegade

Vendor
Joined
Dec 15, 2005
Location
Brampton
TDI
2004 Jetta
But at least the motor would sound like a proper diesel, not a diesel with a vagina.
hey now!
Lol - when i drain off some more of this tank i'll swap out the lift pump and report back.

Something tells me it's gonna be Tandem pump
 

BuzzKen

Vendor , w/Business number
Joined
May 16, 2011
Location
Markham, Ontario
TDI
'10 Touareg TDI, '09 335D, '10 X5D
Run the alh beside the pd, you will see what I mean. It's like a feminine diesel.:D:D
 

mrseadog

Active member
Joined
Mar 8, 2015
Location
St. Louis, MO
TDI
2002 Jetta
This is an old thread but I figure I would post my 2 cents on the subject with regards to MKIV's 1999-2003. If the tank is low ~ 1/4 tank and hard starts are encountered due to air in the fuel lines the problem may be the o-ring sealing the sliding pickup tube in the fuel sender. If the o-ring is really bad the car can stall while driving due to the amount of air getting pulled into the fuel lines.

An easy way to diagnose the problem is to disconnect the fuel line at the filter, connect a small fuel pump and run the discharge side to a small bucket. If you seeing bubbles in the fuel, air is getting pulled in. If it only occurs when the tank is low it is most likely within the sending unit. If in doubt disconnect the fuel line at the tank sender and do the same thing. If you still see air bubbles the problem is definitely within the fuel sender unit (cracked tube or leaking o-ring). If not the problem is in the line from the tank to the filter.

The pump I use is a small $10, 12v unit easily found on eBay. I also use it to prime the filter and injection pump when work has been done. A lot easier than using a vacuum pump.
 
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