quick diagnosing help needed

[8v-of-fury]

So I am trying to help my brother out over the phone on his recent TD swap as to why its running so rough. We got it all done last night and took it for a drive. Drove nice and had lots of power. Tonight however it runs fine until you let the throttle off, where it stumbles and sometimes stalls out.. Even after its warmed up. What's going on here? Had a small fuel leak at one injector hardline, and a small drip from the return to the tank line.. But neither should cause the car to not maintain idle..

Any help needed! I am going to look at it when I get off work. But the less time outside the better, its already -15c here.. Lol

Thanks guys

[8v-of-fury]

nothing eh? Meeting of the minds? lol

[vanagonturbo]

When diagnosing problems, I like to start with the obvious. Fix the leaking fuel lines and report back although its probably not the problem, wierd shît happens...

[8v-of-fury]

yeah your probably right, amongst my thoughts.. The leak in the return line could be letting air in the pump and allowing the pump to drain back through the filter..

has anyone had luck installing a one way check valve or two? Maybe one by the tank, and one right before the filter? or at least just one right by the filter.. I think the problem is air leaking back in to the pump from the return line.. I definitely think that is the problem. I checked all the gp's when i installed the engine last night, 3-4 are bosch duraterms, 1 of them was dead so i replaced it with a used beru plug. They all work and get red hot in 4-5 seconds. While cranking it doesnt sound like its even trying to start. So i am nearly fully confident that with no fuel in the pump this would be what is happening.. Perfect.. its still -13c! uggh i hate winter for working on cars lol

[vanagonturbo]

Leaky fuel lines can easily be a culprit in a no start situation. I have had numerous TDIs towed into the shop for a no start situation because the IP was leaking. Fix the leak. Dont compound the problem by adding check valves and such. Start with factory configuration that is known and proven to work properly, then muck with it after it functions as it should

[maxfax]

Leaky fuel lines can easily be a culprit in a no start situation. I have had numerous TDIs towed into the shop for a no start situation because the IP was leaking. Fix the leak. Dont compound the problem by adding check valves and such. Start with factory configuration that is known and proven to work properly, then muck with it after it functions as it should

X2..  And check valves are the perfect location for leaks and restrictions..   My guess would be fuel leak or weak lift pump..  Both are exasperated by low temps..

[Mark(The Miser)UK]

So I am trying to help my brother out over the phone on his recent TD swap as to why its running so rough. We got it all done last night and took it for a drive. Drove nice and had lots of power. Tonight however it runs fine until you let the throttle off, where it stumbles and sometimes stalls out.. Even after its warmed up. What's going on here? Had a small fuel leak at one injector hardline, and a small drip from the return to the tank line.. But neither should cause the car to not maintain idle..

Any help needed! I am going to look at it when I get off work. But the less time outside the better, its already -15c here.. Lol

Thanks guys

What exactly did you swap?
At what idle RPM does it stumble?
Have you tried raising idling slightly?

[8v-of-fury]

Found out its also sucking a lot of air through the supply line..

I used clear lines from body hardlines, to filter, to pump, and back to hardlines.. Way good for diagnosing air leaks!

Bro is new to diesels as of this week, lol and what he told me was the return is the feed.. And there is a lot of air.. Fix that and I'm pretty sure we have fixed our rough idle and cold start issue

Thanks a bunch guys.

[8v-of-fury]

Got it all fixed up, seems the leaky return was masking a leaky injector at the pump head.. So there was two leaky injectors.. Could expplain something! LoL.

Thanks for all your help.