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Stop Me Before I Make It Worse: BHW Long Crank Hard Start When Warm

1603 Views 4 Replies 3 Participants Last post by  TvD
My 05 Passat TDI, 250K, suddenly developed the long crank when warm problem. No problem on cold start, but once it's up to temperature, it takes ten seconds or more to fire. It never didn't fire. It runs fine once it starts. Even after the long crank, it doesn't skip or smoke.

Replaced lift pump, fuel filter, thermo-t. No joy.
Replaced fuel lines with clear lines. Air is visible on the return side,, but only after warm up.
Replaced Tandem pump. Air is still visible, still long crank. Still no joy. No codes. All readings within normal limits.
Conclusion: air is getting in at the injectors because of heat-related expansion. Injector seals?
Am I missing something?
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Would that put air into the return lines?
OK ,so I re-did the injector seals. One of the rubber o-rings on one injector was visibly bad, so I was hopeful. But the long crank problem remains. I bypassed the fuel filter and fuel temp sensor, no difference. Hooked them back up,, Using clear vinyl tubing, I can see lots of air in the fuel, a solid stream of it, only on the return side. I put a stopcock in line on the return side, just before the filter. If I close that valve when I shut down the engine, 'the problem goes away; car turns over once and fires. Open the valve and I'm on my way. If I leave it open after shutdown, it takes about 20 seconds of cranking to get it to fire.

So it looks like I'm still picking up air on the return side of the injectors, and that while that does not affect the operation of the motor--The car runs fine once it starts--it is somehow related to a fuel-starved condition at the injectors--like the fuel is draining back into the tank. Or maybe being sucked back?

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