MK4 Jetta Hard Start When Cold

I'll start this off by saying that I've done my DD trying to research solutions to my issue, but it looks like most other posts are similar but not the same. Let me know if I'm missing something or you need more info please! I'm new to this site as well as VW ownership, but from what I've seen so far it looks like the community is ridiculously helpful relative to other brand enthusiast forums.

I just purchased a 2002 Jetta TDI (5spd manual) with about 438,000km on it (that's about 275,000 miles in freedom units). I know nothing about the previous owner's history, but it looks like they've taken pretty good care of it. It has a frost heater and cab heater.

The car starts and runs beautifully in warm weather, but when the temperature hits 0C (32F) it starts having cold start issues that are compounded the colder that it gets. When it hits -18C (0F), there's nearly no chance of it starting up first thing in the morning, however once the engine has warmed up it will start and run flawlessly until it sits in the cold for long periods of time.

It's currently around 20F here and after the glow plug cycle the car will crank for probably 10-15 seconds before it sputters to life. The cranking time increases exponentially and the turning-over becomes less convincing the colder that it gets. Sounds like a glow plug issue, right? I get 12.5V to each GP connector, good resistance on the GPs, actual GP timing vs dash light, and all GPs light up while plugged into the harness outside of the block. The length of the GP light on the dash is relative to the coolant temp. I unplugged the coolant temp sensor for a couple of days to test it, but no change. There is no CEL and I'm not sure what else I could test on the GP circuit. The only thing to mention is that my #4 cylinder GP is very tight going in and coming out for most rotations...

Here's the deal: It was -21C (-5F) a couple weeks back and I had the frost heater plugged in for about 2 hours before I left. The car fired up like a dream and ran beautifully. It cranked for <1/2 second and fired like a boss. I live in Saskatchewan, Canada (midwest, above North Dakota) and temperatures here in the winter fluctuate between 32F and -40F, and it's not always possible to have the vehicle plugged in...and I definitely don't want to be stranded when I can't start it warm.

Here is a quick list of maintenance items I did as soon as I purchased the vehicle because I like to have some service history:
Oil & filter change (Mann filter, John Deere 0W40 CJ-4 engine oil)
Air intake filter (Mann)
Cab filter (Mann)
Fuel filter (Mann, primed with Diesel Purge)
Transmission oil (Pennzoil Platinum 75W90 GL-4)
Thermostat & coolant (VW OEM on both items)
Glow plugs (NGK - I would have changed with Bosch if I had known they were OEM)
Battery (East Penn 694RMF)
Timing belt was done at 376,000 km (235,000 mi) by the 'stealership'

I purchased VCDS because I figured that if it could save me one trip to the shop it would be worth its weight. I also figured that if anyone on here would be able to help me troubleshoot, it would be a great tool to have on hand.
I checked the pump timing with VCDS and it's slightly above the 'average' line - a hair towards 'advanced'. I can save and post a graph if need be. I also downloaded GreenGiant's graph software and recorded the starter RPM on a cool day (28F).

I work at a Deere Construction & Forestry dealership and was able to test compression on each cylinder. I tested each cylinder going down the line twice: 575/600, 575/600, 550/550, 550/575
I feel like it's not a glow plug issue (I'm also not a seasoned veteran), but would be open to any suggestions or questions! Help please.

Cheers,
Chris

1. The key can be cycled 2 times off/on before moving it to the start position. That helps with warming them up.

2. Make sure the battery is fully charged and not worn out (load test needed).

3. check cranking speed of the starter. As they wear/age, they developed a lot of crud inside and crank slower. I went through all your checks, including replacing my GPs, but I found that a new starter (when it began to grind) cured my hard starts. The increased cranking speed made a radical difference in ease of starting.

Toxic, thanks for the reply!

I was actually just about to edit my post and ask if it could potentially be a starter issue.
I logged the starter RPM when it was about -3C/27F outside (right about when I start having the issue), and it cranked for about 8 seconds between 160 and 260 RPM before it decided to fire. I feel like that might be low. I'm going to try logging it tomorrow morning when it's -9C/16F to see if I can get a more accurate RPM over a longer cranking period. You wouldn't happen to have any idea what the speed of a healthy starter would be, or where I can find those specs?
I can't attach a picture of the graph, but I'll see if I can upload it elsewhere and link the picture.

The battery is brand new and fully charged & tested, and I've both cycled the glow plugs multiple times, as well as extended their glow time slightly through VCDS.

sorry, I don't. I didn't realize my starter was cranking too slow. I only changed it because it was grinding/not letting go, etc. When I replaced it, I immediately noticed the speed difference and significant improvement to start. it's been covered here in a few other threads. In older construction equipment/tractors etc a hack trick to help with starting is using a 24 volt battery instead of 12 to make it crank faster

Starter crank speed should be around 300 rpm. As Doc pointed out starters just slow down with age, I had the same experience my starter was hanging up and when I changed it out it was so much faster and starts were easier.

It doesn’t sound like you have a glow plug issue. The system is pretty good at monitoring itself and no codes usually mean no problems.

Where is in IQ set at? Injection quantity. Usually it is somewhere between 0-5. Setting it at 4-5 helps the car start easier as does setting the timing further toward the top line.

Hi

Maybe a cheap fix and it actually happened to me ....

I thought I had starter issues once but it actually turned out to be corroded connections not allowing enough juice to get to the starter itself ...

I cleaned all the electrical connections and instant starts ( personally I never thought of the collections because they looked okay and the connections were not covered with corrosion but I can't argue with the results when I clean the connections with a wire brush. .... this worked in my case hopefully it can help you also because it was a cheap and easy repair).

Hope this helps you.
Andrew

I'll start with checking and adjusting the IQ if need be, as well as removing and cleaning the connections on the starter. There's no better fix than FREE in my books!

If I'm still S.O.L. after that, I'll price out a new (reman) starter.

Thanks all, for the awesome insight!

I'd also be checking the timing. Late timing makes for more difficult starting.

Edit: Nevermind. I missed where you already checked it.

Draderade said:

I'll start with checking and adjusting the IQ if need be, as well as removing and cleaning the connections on the starter. There's no better fix than FREE in my books!

If I'm still S.O.L. after that, I'll price out a new (reman) starter.

Thanks all, for the awesome insight!

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I would do a wire integrity check on the starter wire before condemning the starter.

You might just have high resistance on that circuit causing a drop in voltage



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Well with those temps you need everything working good. Sounds like it's not timing or glow plugs. Be nice to get the start RPSs up a bit. Did you get the correct battery, only saying cause I did not when I was new and the parts people are generaly not good.
Good news is it does start. You might try running a can of diesel purge (or equal) straight. Try the double GP cycle, even leave the key on for a bit after it goes out, they continue to glow.

Great suggestions people - I love it!

Will definitely check the integrity of the wire while I'm cleaning up the terminals.

I made sure to go with the best (and highest CCA) battery I could get my hands on. Very important in the frigid winters that we face up here.

I know that diesels are a lot more finicky than gas engines when it comes to starting in the cold, so I'm fully expecting to be plugged in anywhere below -18C/0F. I'm just feeling frustrated having such a difficult time starting when it's below 0C/32F.

I AM, however, very excited to try some new troubleshooting that you guys have provided!

Over the last couple of years, I experienced long cranks with the ALH in my Vanagon (unlike those back in 2012 & 13). I removed the OE TDI starter, disassembled and cleaned and lubed. This did not help. I did the same with a spare TDI starter which resulted in a slight improvement.... Then, I said what the heck, and purchased one of those "cheap" aftermarket starters off eBay..... Bam, bam, bam, has started super great ever since.

So, considering the OPs thorough research and attention to detail and eliminating the obvious possible culprits, I tend to agree with others, an increase in RPMs while starting in sub-freezing temps, is likely the key to solving the problem. Keep in mind, a compressing the "cold air" inside the cylinders fast vs slow will make a big difference in how well the engine fires up!

Greetings from frosty Alberta where it gets just as cold as Sakabush. The only time Ive had trouble starting was at minus 26 Centigrade , not plugged in. Investigation revealed only two functioning glow plugs. Moral of the story is you should be able to eliminate your problem fairly easily.

Id concur that changing out your starter and checking the connections...... especially the braided wire going to the solenoid should be your focus right now. Dont go ebay or napa or Canadian Tire.

As as a new tdi owner you might not be aware of Roseland in Nova Scotia. He'll sell you a quality unit for less than $300 , and somehow his delivery times to the rest of Canada are very good.

Thanks for the info Andy and mining. Also, hello fellow westerner!

A litle bit of an update:

- I checked the positive connection on the starter and it was pretty corroded, so I cleaned it, the nuts, and the post up a bit. The braided ground strap from the starter solenoid to the starter itself is pretty green as well.

- I tested voltage drop on the positive cable going to the starter and I'm about .43V drop, unfortunately. Is there any easy way to test the battery ground strap?

I feel like it might be a combination of low voltage in the cold when the starter wants MORE voltage, as well as a potentially tired starter. I have a local place here that my company deals with that has a reman Bosch starter for $200 CAD my price (that's what, like 10 bucks USD? , so I may just cough that up and try it out. Maybe invest in a new positive strap if the starter doesn't fit things 95%.

Draderade said:

- I tested voltage drop on the positive cable going to the starter and I'm about .43V drop, unfortunately. Is there any easy way to test the battery ground strap?

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Same as the positive side.
Measure from the negative post of the battery to the case of the trans or engine.

You could also check from the post to a ground to one of the body grounds to check for a bad connection under the battery tray.
Have the lights, fan on full, and AC on for the ground test.
If that one is bad everything that grounds to the body is bad.

Replaced the glow plugs

I agree with the suggestions folks have made about cycling the glow plugs 3 times (or more) when it gets bitter cold. It helps quite a bit.

However, you mentioned that you changed the glow plugs out to NGK. By chance did you save the old plugs? If so, just double check that you got the same voltage as the old ones. It could be an easy mistake to get the wrong voltage. If you continue to have trouble, and you DID keep the old plugs, you could try swapping them back in just to test.

My .02 cents but you got it for free...

I'm going to follow this thread. Thanks!

Update: It was -22C (-8F) this morning when I fired her up after 2 hours of frost heater coolant heat. It fired up like a dream, but I got an engine fault code immediately. VCDS tells me "Cylinder 4 glow plug circuit (Q13) P0674 35-10 electrical fault intermittent."

I feel like it's maybe it's an intermittent harness issue, as well as a weak starter? Maybe put a sprinkle of voltage loss through battery cables.
Both the old (NGK), and the new spark plugs are functioning outside of the block, so I'm not worried about those. Like I said earlier though - when I crank below 0C/32 the starter cranks at 180-220 RPM until it hits 300 and then fires.

Starter

I may spend a little bit more on preventive maintenance than others. But, when my cars hit 150K miles I like to change the starter. They've done a bit of work by then. Your starter has nearly twice that many miles on it. It is an easy job on a MKIV Jetta. I would rather spend a few bucks more and do this type of maintenance on my terms (nicer weather) rather than when the car says it is time (usually colder weather, yes?). I pick up the starters at Napa for the most part. I've gotten them at Advance Auto Parts as well. They are usually a reman Bosch and I've never had one go bad on me. Catch them on sale and you can get them for about $100 US. If your starter is original it has to be getting tired. As AndyBees suggested you can also disassemble the existing starter and clean it up.

Good luck with this. Hope it helps.

Just wanted to add that I determined that my MAF was causing harder and harder starting as it got colder and colder. (though I live in So Cal and cold for me was like 50 deg F) .

The original MAF did not throw any engine codes so I had no way of knowing it was the culprit until I replaced it and I replaced it because one morning after driving 20 minutes and turning the car off and then driving somewhere else 10 minutes later the car started bucking under acceleration with almost no power both under load and not under load (in neutral) without any CEL coming on the car was almost un-driveable at any rpm (though just over idle was bearably OK) .

I made it to work nearly coasting the whole way as it is mainly downhill and then I disconnected the MAF on a whim and the car worked fine so I replaced it and no more bucking AND better cold starting as well! (less cycles on the starting motor)

A little annoyed and surprised It didn't throw a CEL sooner. I was error free for a long time and yet this time it would have been NICE to actually get one.

Have to chuckle a little.... "colder and colder" in So Cali hitting 50 degrees. That's not even enough to get the glow plugs going. For us midwesterners 50 degrees in Winter would be incredible.

Glad the MAF was an easy fix. I usually hit that with cleaner every second oil change. But, again, I usually spend more on maintenance than perhaps other may.

Draderade said:

Update: It was -22C (-8F) this morning when I fired her up after 2 hours of frost heater coolant heat. It fired up like a dream, but I got an engine fault code immediately. VCDS tells me "Cylinder 4 glow plug circuit (Q13) P0674 35-10 electrical fault intermittent."

Click to expand...

That means what it says; I've had to replace that harness before. The plug is in the plenum under the battery and airbox; it's easier to cut off the old plug and leave the wire rather than un-loom it all; just get some loom and wire-tie it alongside the old one.

With that said ONE not-working plug won't prevent starting or make it materially harder to start, but it will smoke like a banshee when cold. I'll bet on the starter and/or cabling (e.g. grounds, etc) that are responsible for the actual problem, but I'd change out the harness anyway.

It probably is a starter issue.
I’ve had a broken GP in #4 cylinder for about 12 years and my car fired up even when it was -10F.......wasn’t pretty for the first 10-15 seconds but it smooth out, finally replaced the head with TB, hard coolant pipe change and leaking head gasket at 394,xxx miles.

I know you said you checked timing with VCDS, but that’s dynamic timing.
Did you check the static timing first with the lockdown tools?
Because you can hide a slight miss time by adjusting the fuel pump to compensate.

Out of curiosity, where do the injection pump bolts sit in the slot on the hub.

Thanks for the great insight, all! I feel like the starter may be my next course of action. Today it was -28C/-19F and even with the coolant heater plugged in for 3 hours it took 3-4 seconds cranking before it fired (don't get me wrong - I know that's not bad). Does anybody have any stats on the RPM of a good starter in the cold? I can assume the RPM slows down a fair bit when it's significantly below freezing?

I also get a chuckle when people start talking about getting cold, only to come across an above freezing temperature. Obviously that's subjective, but it's still pretty funny.

Thanks for the heads up on the MAF sensor.

I haven't checked the static timing because I haven't got the tools to do it myself, so I assume I'd have to take it into a shop?
Also, I am not entirely sure about the bolts...I'd probably have to remove the timing belt cover to get a picture of those?

It's not timing. As you say 3-4 seconds ain't bad. Starter and battery are critical, all things being equal. Often hard to distinguish, perhaps put the battery on an overnight trickle charge, see if it clears up.

Did some quick searching with VW TDI Search Engine couldn't find a definitive answer. 200 is low, guessing it needs at least 250.

Just a heads up on tools to check static timing. You don't need much. The right size of drill bit will do for the injection pump and the crank is through a window in the bell housing. The only other is the cam and you can see if it's out by removing the vacuum pump. If it's really out you can see it and if all the above parameters are close the engine should start and run.

The IP index pin is 6mm or 15/64". Don't worry about the cam - it won't affect starting.
If the flywheel indicates TDC and the pin goes in then the pump timing is good.

Diesels, when it comes to cold start, is ALL about RPMs.

That's the following:

1. Starter itself.
2. ALL wiring to starter, both positive and ground.
3. BATTERY. Cranking amps, period.

When it REALLY gets cold, that's all there is. You either can make minimum RPMs and the engine fires or you can't.

Oh by the way, the colder it is the thicker the oil in the engine is (HARDER to turn those RPMs) and the fewer amps your battery can deliver. Yep.

^^^ This!


Gotta get 'em spinning!


I recently replaced two starters (in my two cars) because they were making noises and cranking a bit slow (very slow in my car). I buy rebuild kits and do my own rebuilding, always trying to keep a rebuilt spare on hand.


There's a big, braided wire on the starter that also breaks down. Sub-par connections result in voltage drops and increased amperage draws (higher drains on batteries).


With regards to the GP issue, you might try popping off that harness connection and stuffing some aluminum foil on top of the GP and then reseating the harness. I've done this before and it's held up for many years: up until I had to break down and replace the harness because it was totally crumbling! The connector ends on the harnesses tend to weaken and loosen up.


I've found that high IQs tend to cause slower starting, though only slightly. Really one of the last things to consider though: you don't want to drop the IQ if you've set it up to correct stumbling and or to control smoke.

I had a 2005 mk4 that wouldn’t start At -20C in the first winter I had it. Shop had a quick look, replaced the starter wire, and it started like a charm. Turned out that the previous owner had replaced the starter cable with.... wait for it.... speaker wire... but that’s obviously not your issue. Hope a “new” starter does it for you.