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-   -   ALH cold start issue (http://forums.tdiclub.com/showthread.php?t=503080)

turbotuff October 31st, 2019 14:50

ALH cold start issue
 
Hi there! I have a rough start issue first thing in the morning with my newly acquired 03 Jetta with 192k miles. The car takes only a couple seconds of cranking to start but runs rough for about 10 seconds and then smooths out. This doesn't seem to make a difference whether it's 40F outside or 60F. I've eliminated the thermostatic tee, drilled out the check valves in the fuel sending unit, ran new fuel lines under the hood, new fuel filter, new updated MAF, ohm'd all glow plugs to be 1.9 ohms, tested glow plug harness, verified coolant temp reads the same as intake air temp and fuel temp. Timing is dead on, IQ is ~3.5 at hot idle. No engine codes in the VCDS. Not sure where else to look. Any help would be appreciated!

mr.loops October 31st, 2019 15:11

ALH cold start issue
 
My freshly built ALH had a bad cold start stumble first thing in the morning ( lasted around 8 seconds). Starting it warm, I had no issues what so ever

Turns out my static timing was out a tad. Your belt might be stretched causing this rough start.

How do you confirm yours? Did you use the proper tools (cam plate and IP pin) or did you just do a visual check?



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turbotuff October 31st, 2019 15:17

Quote:

Originally Posted by mr.loops (Post 5547656)
My freshly built ALH had a bad cold start stumble first thing in the morning ( lasted around 8 seconds). Starting it warm, I had no issues what so ever

Turns out my was my static timing was out a tad. Your belt might be stretched causing this rough start.

How do you confirm yours? Did you use the proper tools (cam plate and IP pin) or did you just do a visual check?



Sent from my iPhone using Tapatalk

I checked it via VCDS

Fahrvegnugen October 31st, 2019 16:28

A couple of cranking seconds on cold start makes me wonder about or starter or battery. Of course it could be something else but that would be checked later

BobnOH October 31st, 2019 16:39

The fact that it runs rough for 10 seconds makes me think maybe there is a small leak in the fuel system. Once running the air dissipates.

jmodge October 31st, 2019 18:48

Have you gone to advanced measuring blocks checked your speciified against actual timing during this period.

jmodge October 31st, 2019 18:53

As mentioned above, it does start on static timing before the ecu takes over. Maybe bump it around and see what happens

WildChild80 October 31st, 2019 19:38

Diesel purge, closed loop system and see if that helps

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turbotuff October 31st, 2019 22:37

Quote:

Originally Posted by Fahrvegnugen (Post 5547673)
A couple of cranking seconds on cold start makes me wonder about or starter or battery. Of course it could be something else but that would be checked later

Maybe I wasn't clear. It fires off right away and just runs rough once it's started. It doesn't have a starting issue, more a running issuem
Quote:

Originally Posted by jmodge (Post 5547704)
Have you gone to advanced measuring blocks checked your speciified against actual timing during this period.

No, I've yet to explore the advanced measuring blocks but I'll have to do that.
Quote:

Originally Posted by WildChild80 (Post 5547716)
Diesel purge, closed loop system and see if that helps

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Already done that with no improvement

Nero Morg November 1st, 2019 00:20

Sounds like your fuel return system is bleeding down. Mine did the same thing, same symptoms and all. The thermo t wasn't sealing correctly, poorly manufactured filter. Replaced the filter and it fixed it right up. Mind you, when the fuel return system leaks, typically it'll let air in when cold, rather than leak fuel. Starts from #1 injector, goes to IP, then fuel filter thermo t. Check all the lines, and replace as necessary. Good luck.

turbotuff November 1st, 2019 00:23

Quote:

Originally Posted by Nero Morg (Post 5547748)
Sounds like your fuel return system is bleeding down. Mine did the same thing, same symptoms and all. The thermo t wasn't sealing correctly, poorly manufactured filter. Replaced the filter and it fixed it right up. Mind you, when the fuel return system leaks, typically it'll let air in when cold, rather than leak fuel. Starts from #1 injector, goes to IP, then fuel filter thermo t. Check all the lines, and replace as necessary. Good luck.

I've already bypassed the thermostatic tee and have a filter mount for a standard spin-on filter. All the lines under the hood are new with the exception of the injector return hoses, which are next to be replaced.

Tdijarhead November 1st, 2019 03:36

Try moving the IQ to 4-4.5 and see what happens.

The only other thing I notice is your glow plugs are a little high on the ohm scale. They should be in the 0.5-0.7 area, however if they are all about the same and you have no glow plug codes I would leave them alone for now. They shouldn’t affect your idle.

turbotuff November 1st, 2019 06:31

Quote:

Originally Posted by Tdijarhead (Post 5547752)
Try moving the IQ to 4-4.5 and see what happens.

The only other thing I notice is your glow plugs are a little high on the ohm scale. They should be in the 0.5-0.7 area, however if they are all about the same and you have no glow plug codes I would leave them alone for now. They shouldn’t affect your idle.

Hammer mod or via VCDS?

WildChild80 November 1st, 2019 06:38

Hammer mod but if you wanna try it with vcds to see if it makes a difference, I don't think that would hurt

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turbotuff November 1st, 2019 06:41

Quote:

Originally Posted by WildChild80 (Post 5547766)
Hammer mod

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Hot idle correct?


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