ALH - Stumbling Start

[zslnk]

Hello,
2003 ALH Jetta 5 speed - 280k-km

Background:
I bought this car from an older lady that didn't do much other than drive it around town, original owner. The intake was clogged and head ports were clogged. I did a through cleaning and walnut blasted the head on the car, it's spotless now. Car is stock, EGR working. Turbo has no play, new actuator is set correctly and has lots of power, uses no oil and runs perfectly.

Problem:
On a cold start, the car fires one/more cylinder instantly (even at -25c) but it feels like they cylinders don't all start at once. You have to keep the starter engaged a little longer than I'm used to make sure they all catch or else it will die. Once running, the RPM's are around 1100 and it runs a bit rough and smokes (smelly diesel cloud, excess fuel) for a few seconds then settles down to 900RPM and the smoke clears up.

Starter is new, battery is known good (load tested) from my BEW.
Injection pump timing is right on the target line
IQ starts around 15mg/str then trends down smoothly to around 3mg/str
Fuel, air and water temps are within 1deg.c at startup
Fuel filter is new and the car has been diesel purged x2
Injector balance starts within spec and then settles to almost even numbers (COLD -0.66,0.02,0.14,0.49) (WARM -0.16,-0.02,-0.24,0.42)
No air is present in the clear fuel line
Glow plugs are good, draw uniform current (individually checked with amp-probe)
This AM I started the car, logged some data then shut down. 30min later (coolant temp still <0c), I restarted and it still had an easy, but uneven initial idle for about 5sec.


The car had oil in the intercooler but nothing in the intake to indicate a runaway, just dry carbon buildup.
The car runs smooth with lots of power and gets great mileage (4.7l/100k on snow tires and winter fuel)

Compression or leaking down injectors? My primary TDI is a BEW and it starts uniformly and generally seems more 'refined' during a cold start. When warm the car starts instantly and smoothly.

 

[BobnOH]

Hate to ask, but what brand starter?
Check the little fuel return lines. If they need refreshed get Viton tube.

 

[zslnk]

The starter is the OEM one that a trusted shop refreshed for me. My cranking speed was in the 100's prior, it's now in the 300's(RPM's) when cold was shown on VCDS.


The injector soft lines are original and not leaking.

 

[BobnOH]

More concerned they could be plugged. Unlikely

 

[P2B]

Glow plugs are good, draw uniform current (individually checked with amp-probe)

Do they all measure the same resistance?

I had a similar issue with my ALH a couple of years back. No glow plug codes but I checked them anyway and found one reading 40 ohms while the rest were under one ohm as they should be. The suspect one lit up just fine when removed and connected to a battery, but cold starts improved markedly after I replaced that glow plug.

Simon

 

[zslnk]

All glow plugs have the same resistance and current draw. They look new(er) and the harness is new looking as well because there is a good looking splice that was not original. 13A each when first powered then the current drops as they heat up.

I’d like to test the injectors for leaking down but I’ll have to get new hose and washers first. I think this or a compression test is the next move. I’d have to procure a diesel compression tester.

 

[IndigoBlueWagon]

Despite what you've learned, I bet the glow plugs aren't heating evenly or adequately, and they may not be cycling once the car is running. Another possibility is poor injector spray, especially at higher fueling levels when cold. If you're getting some gray/white smoke that may indicated unburned fuel.

An ALH with good glow plugs and fueling should fire instantly, in less than one starter rotation, and run pretty smoothly right away, even at near 0F. I suppose it's possible you have low compression, but unless you have some evidence of that (history of a runaway, oil consumption), that's not the first place I'd look.

 

[BobnOH]

That's a good point, current to the plugs was tested, check the resistance of each plug and compare.

 

[454k30]

Wait... How cold? -25C! Sounds to me like these are just symptoms of a cold diesel starting in sub zero temperatures. You mentioned that it smooths out and the smoke clears up in just a few moments. I'd wager that there is nothing wrong with the car at all.

 

[JDSwan87]

Wait... How cold? -25C! Sounds to me like these are just symptoms of a cold diesel starting in sub zero temperatures. You mentioned that it smooths out and the smoke clears up in just a few moments. I'd wager that there is nothing wrong with the car at all.

This!

 

[zslnk]

Perhaps I wasn’t clear.

This behaviour is present at any temperature during a ‘first start of the day’ at any temp. My point was that even if it’s really cold out, I get one or more cylinders firing immediately to indicate that cranking speed, compression, timing and glow plugs are adequate (for one at least) but that other cylinders lag and it’s uneven.

A better description would be a slight miss and surging for the first few seconds. You can see the tach surging until it settles down.

 

[DoubleReflex]

I had one that acted like that. It turned out that compression was a little low in one cylinder. Have you checked compression in all cylinders?

http://forums.tdiclub.com/showthread.php?t=325980

 

[zslnk]

I have access to a leak-down test rig and I'll try and do this test next. I also have a collection of spare injectors that might be useful for troubleshooting. I do not have a diesel compression tester at this time.

 

[zslnk]

I compression tested the car at -20c after sitting overnight.
410,420,395,440

I tested one cylinder last night when engine was warmer and got 480 on #2 so I believe my numbers are healthy given the temperature outside this am.

I replaced the glow plugs, the ones in the car were NGK Y732J (12V). Bosch 025202022 were installed (11V) plug. I tested some of these out of the car and the bosch 11V plugs get hotter in half the time. The first start at -20 after the test was rough because I had air in the hardlines (had to disconnect to get the tooling into the glow plug holes) but once it started the hunting was mostly gone.

It looks like the Bosch glow plugs have resolved the issue.

 

[Cardo]

Useful thread. Just bought my first TDI a few months ago (2003 jetta sdn 175k miles) and figured it just needed motor mounts, but that uneven tumbly start happens every time my car sits for more than 8-10 hours, also it's winter here in Canada and it's always a little cold. I have new Bosche 0250202022 glow plugs (3-4 months old) in them and it still happens from time to time. I'll be doing the motor mounts soon and check back to see if that solved the issue.

 

[st0rm-]

this is 100% normal on a cold start lmao... it's a 20-year-old diesel my guy

 

[KyleMillione]

My primary TDI is a BEW and it starts uniformly and generally seems more 'refined' during a cold start.

In my experience, BEW motors always start “cleaner” than ALH motors. My 02 Jetta has always been a little rough on startup in the winter, but has never failed to start.

 

[Judson]

On my ALH, ever since I installed the in-tank lift pump, this issue has mostly gone away. It has to be very very cold indeed (0 F or less) to encounter issues.

Maybe that’s the difference between the two??!

 

[zslnk]

UPDATE:
I replaced this engine with a different one due to a stripped roller stud hole. The engine had glazed cylinder walls. The block that I got had unknown mileage but the bores were crosshatched and had a 'rougher' surface finish to them. This engine compression tested at 495psi x4 and it starts like it's 2003 in -20c.

Don't accept bad cold starting as just 'old diesel car', if it doesn't start like you believe it should, something is wrong. In my case, compression.