ALH hard cold start

Hi all,
I am still recovering after a recent head, cam, and glow plugs. All this was from FrankTDI and was an excellent resource and great parts.

I had the head redone by him after a failed lifter that slightly tore up the cam journal. New head gasket, cam, lifters, T belt and hardware. The mechanical timing was near dead on, and with a little wiggling I could get all the alignment tools back in, and the crank mark was within 1/8” of the TDC mark. The timing on the vag com was adjusted so it was right in the middle of the graph. It all went back together good but had some long starts when the weather was warmer.

Now that the weather is colder, this got worse. I replaced the injectors, IQ set to 6. Slightly better fuel economy (45mpg with 2 people and some gear / tools) the hard cold start is still present, and may be even a little worse. This is when the car is cold as in single digits, and when the car is kept warm in a shop it still cranks long. It takes 2+ glow plug cycles, and trying to crank 2-3 times for it to start. When it does start and warms up it runs excellent. Lots of power, no smoke, sounds very good. I verified that on the long cold starts no air bubbles are present in the clear fuel hose. Fuel filter has about 10K on it. My glow plugs and harness were replaced 15K ago. It seems to start with plenty of RPM as it always has in the past 7 years.

What I may do from here:
Check glow plug amperage
Recheck mechanical timing, and timing with vagcom??

What else am I missing here? Any other suggestions? Thanks!!!!

Forgot to mention I have an EGR delete with no ASV. A race pipe is in its place.

Yep - recheck mechanical timing.

On a start there is ZERO ECU control; there's no case pressure and thus no ability for the ECU to change anything.

For best starting performance, ESPECIALLY when it's cold, you need:

1. Proper cranking speed. Check the starter and especially that braided cable, primary cables and grounds. If you can't make cranking RPM it will NOT fire. As it gets colder amp draw required goes up dramatically and the battery's ability to deliver current goes down.

2. Timing needs to be bang-on because the ECU does not get control until the engine starts. Being off even a bit will impair starting, and the colder it is the more-impaired starting is.

3. You must make sure there are NO air leaks in the fuel system. If there are then until that air clears clear you will get poor or ZERO fuel into the cylinders as the air will compress -- and no fuel will get injected. It is very common to have minor air leaks, especially around the thermal "T", which do nothing when the engine is running but when the car sits for a few hours that gets into the suction side and then there's little or no fuel actually flowing into the cylinders on a cold start.

Genesis said:

Yep - recheck mechanical timing.

On a start there is ZERO ECU control; there's no case pressure and thus no ability for the ECU to change anything.

For best starting performance, ESPECIALLY when it's cold, you need:

1. Proper cranking speed. Check the starter and especially that braided cable, primary cables and grounds. If you can't make cranking RPM it will NOT fire. As it gets colder amp draw required goes up dramatically and the battery's ability to deliver current goes down.

2. Timing needs to be bang-on because the ECU does not get control until the engine starts. Being off even a bit will impair starting, and the colder it is the more-impaired starting is.

3. You must make sure there are NO air leaks in the fuel system. If there are then until that air clears clear you will get poor or ZERO fuel into the cylinders as the air will compress -- and no fuel will get injected. It is very common to have minor air leaks, especially around the thermal "T", which do nothing when the engine is running but when the car sits for a few hours that gets into the suction side and then there's little or no fuel actually flowing into the cylinders on a cold start.

Click to expand...

Came here to say point 2+3. If your filter is 10k old It might be worth changing it and checking the relevant lines for pinholes, leaks or wear.

BTW my kid's Jetta (used to be mine) currently has one bad glow plug (just lazy so far on changing it, living in FL) and two nights ago it was 19F here. Fired right up on the second revolution just as it always does irrespective of temperature.

I've (rarely) driven it up north where temps have been below 0F overnight and parked it in an open garage (e.g. one of the public ones.) No problem, but I made damn sure that I ran the (possibly not treated enough) fuel from further south nearly all the way out and filled in the nice cold areas where (presumably) it WAS treated. If you get gelled there's nothing you can do other than get towed to where it's warm and you can let the car sit and the fuel warm up, which will take a long time. But short of that provided you can make cranking RPM, timing is bang-on and there are NO AIR LEAKS in the fuel system it will fire.

Now you want to talk about fun engines, the old 6v92TAs in my former boat were a whole different kettle of fish. Straight 40wt oil is like molasses in cold weather and despite having two 8D batteries in parallel even THAT isn't enough to make minimum RPM if it gets cold enough, plus there are no glow plugs in a 2-stroke Detroit. You either make the required turns or it doesn't start and that's the beginning and end of it. I put Wolverine pan heaters on the oil pans because the real issue when you run into trouble in severely cold weather is usually the oil viscosity and its impact on cranking speed. TDIs use 5w40 which is MUCH thinner than 15w40 or (god forbid) straight-weight oil when it gets cold. But you can't get around physics and the impact on amps deliverable from the battery, so the best is to make darn sure your starter and electrical going to and from it is in A-1 condition.

Thanks Genesis & JWRB!

I will pursue checking the mechanical timing by the end of this week and report back. I just need to find a few hours to devote to it. I may also replace the batt. I truly believe this is good because it sounds like it has plenty of good RPM, but the batt I got is 2 years old from Autozone, and supposedly the same CCA, but a slightly smaller size that the VW batt it replaced. I already found one at the local dealer.

The timing does raise 1 question: If the mechanical timing was off, could the timing on the vagcom be within the range on the graph it should be?

@atmarine - Maybe as the valve timing can be slightly off and the injection timing right on by adjustment.

The first couple of times I did timing belts on these engines I more-or-less took the "if you do this right you'll be in the injection window to start" statement as "and you will need to make adjustments".

Well as it turns out that's sort of true. As I gained some experience with the procedure I came to realize that if you actually get everything EXACTLY correct you'll be almost-EXACTLY right up the middle on the VCDS graph. Does it matter if you're "close enough" or "bang-on"? For cold-start performance it does....

The 99 (probably 99.5?) has a well known problem with long cranks to start. Typically fixed by a tweak in the ecu.

Yes it does, but only manifests as long hot starts. Bad fuel map, tune fixes it right up. But my interweb guess it's the proverbial "one tooth off", the cam and crank.

Try replacing all of the rubber fuel lines. The tank to hard line, hard line to fuel filter, and fuel filter to injection pump, both sides, too and from the tank. After 20 years the rubber is cracking and you are loosing prime.
This fixed my cold start issues.

Cold start update

Thanks all for your help so far.

I’ve rechecked the mechanical timing, and with IP, and cam lock tools in the flywheel Mark was off by about 1/4-3/16”. I re timed it and now it I’d dead on, and reset the timing with the VAG Com to fall just above the middle line.

I added a jump start batt in cold weather to isolate the battery, it didn’t crank any faster indicating the batt is fine.

I checked the glow plug system, both wires going to the harness draw 26A, and the plugs all ohm out at 1.1-1.2. I did not remove them from the head to visually see them glow when voltage hits them, but I believe they are just fine.

Upon cranking when cold I never see any bubble in the fuel line, only a small 1/4” bubble when the engine is shut down.

When it is cold (5-10F) 2 cycles of glow plugs it takes about 2 tries of cranking about 10 sec each to get it to fire. With the same temps and the frost heater plugged in it starts immediately. Everything else is spot on with it, plenty of power, 45MPG, no smoke.

Other than replacing the fuel lines from tank to engine, any other suggestions on this one? I’m stumped!!

Compression test, engine cold, would be my suggestion.

Compression values

Thanks Vince.
What would acceptable psi, and leak down be for this?

I will borrow and compression tester and test this later this week. Thanks again