Hard starting when cold, for the 10,000th time!

Drivbiwire

Zehntes Jahr der Veteran
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Oct 13, 1998
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Boise, Idaho
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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Welcome, obviously you have an issue with "hard starting your car when cold" if you are reading this thread, don't worry becuase its an easy fix.

Basic background: "Pre-Glow" occurs when the temperatures drop below 40F. This means the glow-plugs activate to speed up starting due to lower temperatures and slower cranking speeds of a cold engine. Injection timing plays a VERY significant role here becuase injection must occur at the precise time of maximum compression to use the heat of the compressed air mass in the cylinder. If injection occurs after this point then you will have an engine that is very hard to start.

Injection timing tends to slowly retard as your timing belt gets some miles on it. Generally once a year before winter (August) get the injection timing checked and have it set around 70/110 in basic settings mode. What this means is that the mechanical timing will inject the fuel at the point in time where compression pressure and temperature are the highest. If your timing is below 50/110 the timing is retarded to the point that you are missing peak pressure and temperature and the car will become harder to start requiring longer cranking periods.

Back to "Pre-glow" if your timing is retarded the car will become harder and harder to start as the temperatures drop off closer to 40F then all of a sudden the car starts normally as you get below 40F due to the glow-plugs being activated by the ECU to assist in starting. Glow-plugs create a very hot point within the cylinder that helps to set off the chain reaction that causes the hundreds of thousands of fuel droplets to ignite. If the temperature during compression is so much as 1 degree below the auto-ignition temperature of the fuel... a no start of the engine will occur. Adding the Glow-Plug provides a hot spot that will set off the chain of ignition causing the fuel droplets to burn. Despite the rest of the cylinder being below the auto-ignition temperature to ignite the fuel the glow-plug compensates for this and helps to get the motor running soley using compression.

As a rule once the first cylinder fires this increases the speed of compression resulting in less time for the rapidly compressed air to lose it's heat and the engine begins to run relying on compression rather than relying on the glow-plug.

Advancing the injection timing allows your motor to start easier in all seasons but mostly you will see the greatest improvement as the temperatures drop below 60F.

Even when the temperatures are at 41F you should have a very fast start requiring only 1 or 2 cylinders to run through their compression stroke before the engine starts and runs. If it takes more than 1 second you have an issue with any one of the following in order of importance:

#1 Check injection timing, below 70/110 ADJUST it and advance the timing.

#2 Timing is at 70/110 yet the motor is still hard to start when the engine is cold:

-Check your glow-plugs for proper resistance, they should all read around .8 - 1.4 ohms. If you get no resistance or a short you have a bad plug... it happens! Change out the one bad plug and press on.

-Check the battery, VW batteries are often not "Maintenance Free" meaning you need to check the water levels! Check that all the cells are properly filled with water and consider putting the battery on a charger for 24-48 hours on a 10amp charge.


Diesels are simple,

* heat/compression + fuel injected at the right time = a running engine

* heat/compression + fuel injected too late = No running engine or at least one that does not want to start

Before getting worried GET YOUR TIMING CHECKED every year before winter sets in.

DB
 

HammerDown

Well-known member
Joined
Mar 20, 2005
Location
Glenolden Pa.
TDI
none-yet
Diesels are simple,

* heat/compression + fuel injected at the right time = a running engine

DB
Great info, but all due respects, Diesels (were) simple before the addition of all those sensors, egr's, efi's etc.
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
EGR does not function before starting.

A clogged intake also will not prevent or cause a slow start.

A Bad MAF sensor has nothing to do with the start and only limits fueling during high load situations.

The ojne item that can cause an issue with starting is the Anti-Shudder valve. If this is contaminated with excessive soot it can stick in the closed position during shutdown. Simply moving the arm to the open position will cure the problem followed by removal and cleaning of the anti-shudder valve assembly.

DB
 

nosootdzl

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Feb 15, 2004
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Northern MD
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98 Beetle, Red
DBw,
Is not the MAF in play at all times, excluding starter engage/crank? Otherwise, injection is controlled open-loop, or at least a weak closed-loop with (maybe?) a feed-forward path programmed into the ECU.
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
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Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
The MAF sensor for the most part only limits the fueling under load.

The engine will start just fine with a nearly failed MAF sensor. When you start the car fueling is controlled by the idle control which increases the input to the control collar until the engine is up and running at 903 rpm. The ECU can care less what the MAF sensor is doing at that point since it's objective is to accelerate the motor from off to stable idle. The Idle control will maintain full control of the engine until you step on the peddle, this causes the ECU to start watching the EGR map and all the other sensors to determine how much fuel to inject for the detected conditions.

Bottom line is the TDI when starting is just like the old IDI VWs in terms of whats going on. Even on the PD motors the ECU's Idle control is adjusting not one pump but four so the concept is relatively the same.

With starting issues the key is not to overcomplicate what is going on, these motors are for the most part fairly simple in the scheme of things meaning problems are related to only a few possibilities.

DB
 

wpeets

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Location
Chateaugay NY 12920
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2014 TDI Wagen Hers
I enjoy reading your posts and it all sounds real good but it takes skill, tools and equipment. Where I live there are no members that I know of with the equipment and or skill. I have to rely on a dealer in Canada who I believe to be quite good . They have been unable to make my 99.5 Jetta TDI start properly. I had them install a switch to activate the glow plugs and it starts just fine using this method. Not correct but it works for me. I am not trying to criticize its just not always that easy. I kind of envy people with exceptional skills.
 

dieseldave2006

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Aug 29, 2005
TDI
A5 Jetta DSG, 06, sliver
I have had 2 other diesels in my family while growing up, both using glow plugs ('79 Mercedes 240D, '81 Isuzu I-mark sedan). Both cars greatly improved their cold weather starts from simply letting the glow plugs heat... 2, maybe 3 or 4 times concurrently before cranking the engine over. Do you recommend this behavior for cold weather starts on a modern PD TDI engine?
 

Drivbiwire

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Joined
Oct 13, 1998
Location
Boise, Idaho
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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
No, The reason is simple the glow plugs heat up many times faster and with the 2,000F+ temperature of the tip this is all that is needed to initate ignition.

The PD motors use a different design glow plug that reaches peak temperature within a few 1/10ths of a second.

Cycling the glow-plugs only wears down the battery and does little for helping out combustion. If anything do not delay starting the engine so that you initiate the start while the glow plug is the hottest.

After the car starts the glow-plugs turn back on to smooth out combustion and reduce emissions (After-glow).

DB
 

dieseldave2006

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Thanks for the immediate reply!! I had a sneaky suspicion that glow plugs have gotten better in years!! Thanks again.
 

Drivbiwire

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Location
Boise, Idaho
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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Thanks for the immediate reply!! I had a sneaky suspicion that glow plugs have gotten better in years!! Thanks again.


The new glow plugs are rated at 4.4 volts continious and are heated with a maximum of 12volts of power during starting... peak temperature is quite high and drops off as the voltage to the plugs is stepped down to 4.4 volts to maintain peak temperature of the plug.

Repeated cycling of the plugs with 12 volts could cause failure of the heating elements.

FYI, I never cycle my plugs and allow the computer to control them, at 210,000 miles I have all four of my original plugs...

DB
 

diesel_smoke

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Mar 3, 2005
Location
Indiana
TDI
Jetta, 2001, Deep Blue
Re: Hard starting when cold, for the 10,000th time

My glow plug light stays on for just a second or even that before cranking. Is this normal?

I am use to my 6.5l TD glow light staying on for 5-10 seconds before cranking.
 

JettaJake

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Nov 26, 2002
Location
CT TDI Corral
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'03 GLS 5spd
Re: Hard starting when cold, for the 10,000th time

Normal....longest I have witnessed is about 5 seconds and that was after 10 hrs parked at about 10 below. Typical is maybe 1.36 seconds or so
 

Dave_D

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2015 Passat Titanium Beige six speed manual & Jetta, 1999.5, Tornado Red
Re: Hard starting when cold, for the 10,000th time

My glow plug light stays on for just a second or even that before cranking. Is this normal?

I am use to my 6.5l TD glow light staying on for 5-10 seconds before cranking.
What is the outside temperature when you are seeing the momentary glow plug light? If it is over 40F that is expected, if below that you might have a bad coolant temperature sensor causing the ECU to think the engine is warm. If you have a VAG-COM you can check this by reading the temperature sensors before starting the car with the key on and verifying that all three readings are about the same. If the coolant temperature is out of range replace the sensor. Without a VAG-COM you can test this by disconnecting the coolant temperature sensor, which the ECU detects and then treats as if you are under arctic conditions and glowing for the maximum time. If that solves the problem replace the sensor.
 

TonganDiesel

Well-known member
Joined
Jan 28, 2004
Location
MI
TDI
2000 Black 5 speed manual 234k miles, 2002 Black auto Jetta 309K miles
Can you tell me where the anti shudder valve is located, and what it looks like? I have major problems cold starting my tdi.
 

tadc

Top Post Dawg
Joined
Apr 13, 2001
Location
Stumptown
TDI
Golf GLS TDI, '01, Black
Antishudder is bolted to the intake(or rather bolted to the EGR, which is bolted to the intake manifold). It's the first piece of metal you run into if you follow the plastic/rubber hoses into the engine. The lever and vacuum pot that actuates it is on the back.
 

frechele

New member
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Nov 10, 2005
Location
Quebec
TDI
2000 Jetta silver
I have a 2000 jetta tdi 325,000k no check engine light. The glow plug lights for a fraction of a second at 0 deg C & it takes about 3 tries before it starts. I changed the glow plugs just in case, mine were original but no difference.
My Haynes manual says the coolant temp sensor is near the rad outlet but it isn't, I can't find it to disconnect. It is not on left side of engine(facing front)as far as I can see.Anybody know where it is exactly?
 

dieseldave2006

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Aug 29, 2005
TDI
A5 Jetta DSG, 06, sliver
I am curious about the graph. The red line is glow plug temp. in deg C with time in seconds, and the blue line is?
 

tadc

Top Post Dawg
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Apr 13, 2001
Location
Stumptown
TDI
Golf GLS TDI, '01, Black
I have a 2000 jetta tdi 325,000k no check engine light. The glow plug lights for a fraction of a second at 0 deg C & it takes about 3 tries before it starts. I changed the glow plugs just in case, mine were original but no difference.
My Haynes manual says the coolant temp sensor is near the rad outlet but it isn't, I can't find it to disconnect. It is not on left side of engine(facing front)as far as I can see.Anybody know where it is exactly?
It's on the drivers side of the head, in the "coolant flange". You'll see the coolant flange with various hoses attached, and if you have a 5-speed you'll also see 3 electrical connections bunched together (the coolant heater glow plugs). On the *back* side of the coolant flange, pointing directly at the firewall, is the connection for the coolant temp sensor. It's almost invisible on casual inspection, but it's there. I'm not sure exactly how an auto differs, but it's in the same basic location.

The electrical connection on mine was a real ***** to get off, but it's the standard VW squeeze-and-pull connector.
 

joshgb

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Jun 18, 2005
Location
Cachagua, California
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04 Jetta wagon black
Re: Hard starting when cold, for the 10,000th time

Thanks for the informative post, DB. Three small follow up questions: Can injection timing for the PD be set in roughly the same way as pre-PD engines? Are there any different considerations, as far as the peak timing point, for the PD engine? Lastly, does a high altitude location affect the setting or does the ECU just deal with the lower oxygen content?
I have heard scuttlebutt about the PD engine not having easily adjustable injection timing, but as I have not had to tackle the job yet, I haven't paid much attention.
 

whitedog

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Jul 12, 2004
Location
Bend, Oregon
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2004 Jetta that I fill by myself
Re: Hard starting when cold, for the 10,000th time

Not sure that we are at high altitude but the confuser will take care of any differences. Some folks have noticed that the glow plugs stay on longer or come on at higher temps at higher altitudes. But that info was from Colorado, so that may have been for some much higher altitudes.

No, the timing can't be changed from what I have read here
 

Drivbiwire

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Joined
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Location
Boise, Idaho
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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Altitude is a major consideration for the ECU when controlling the duration of the pre-glow cycle. Higher altitudes even in warmer temperatures will cause longer glow cycles.

If the temps are cold and you are getting very short glow plug cycles check or replace the $7.00 temp sensor. More than likely its telling the ECU that the engine is warmer than actual and causing poor starting.

DB in Kuwait...

PS, Met with a fella from Audi tonight. Got some pretty cool stuff and had a great discussion on Audi diesels and coming technology including Piezo Diesels as well as FSI. He is one of their international training reps that meets with national heads and discusses the technical as well as marketing aspects of the Audi brand. Once I get home I'll see if anything is worth posting and I will put on here. Time for bed, leaving for Bahrain in 8 hours :eek:
 

tuckster

Member
Joined
Jun 16, 2004
Our Jetta occasionally has slow starting problems and a couple times has not started at all (my wife was alone both times so I didn't witness it). After waiting a while the car finally started. From what you have described we probably have a timing or glow plug issue, but there are some other symptoms we're experiencing I haven't heard mentioned in this thread.

Sometimes when the key is turned the motor turns over very slowly while all of the gauges on the cluster dance back and forth. At night the dash lights flicker. It's almost like the battery is dead. In fact, that's what I thought the problem was when the car wouldn't start, but a few minutes later the engine turned over effortlessly without any charge or jump start. Maybe it is the battery, but it's unlike any other dead battery I have experienced.
 

Drivbiwire

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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
tuckster said:
Our Jetta occasionally has slow starting problems and a couple times has not started at all (my wife was alone both times so I didn't witness it). After waiting a while the car finally started. From what you have described we probably have a timing or glow plug issue, but there are some other symptoms we're experiencing I haven't heard mentioned in this thread.

Sometimes when the key is turned the motor turns over very slowly while all of the gauges on the cluster dance back and forth. At night the dash lights flicker. It's almost like the battery is dead. In fact, that's what I thought the problem was when the car wouldn't start, but a few minutes later the engine turned over effortlessly without any charge or jump start. Maybe it is the battery, but it's unlike any other dead battery I have experienced.
Check the grounds on the motor. I would guess you live in an area that uses salt on the roads, in that case a bad ground on the engine block where the transmission and engine meet could be the cause.

Anytime you get severe voltage drops followed by normal starting, begin looking at all the grounds to the car especially in the engine bay.

DB
 

Koreth

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Nov 7, 2005
Location
Denver, CO
TDI
2003 Golf GLS 5spd conversion, Silver
New user to the forums, first time TDI owner.

My 2k1 Golf TDI has been very good about starting in the past couple months I've owned her. I recently had an issue with the Check Engine light staying on, and when Autozone hooked up the scanner, it said my glowplugs were bad. I found the glowplug FAQ on here (very helpful!) and ended up cleaning the glowplug harness with some electrical contact cleaner.

Anyway, I don't think I still have a glowplug problem, as after turning the Check Engine light off with a scanner bought from Checker (rather expensive thing, it had better prove useful), the Check Engine light has not come back on. However, this morning in Denver it was very cold - It'd snowed the night before and everything was covered in ice. So it was certainly below 32F, I'm thinking probably about 15F. Normally after the glowplugs cycle it takes but half a second of cranking and she'll fire right up with little to no smoke. Well this morning it took longer, like 5-7 seconds of cranking before she fired up, and there was a lot of smoke. It wasn't super black or anything like those big-rig diesels, but it was very thick.

I was wondering, should this be expected of the rather low temps this morning, or should I look to see if there might be something up before it becomes a larger problem and she doesn't start at all? Would one of those coolant line heaters or oil heaters be a wise investment, considering how cold winter temps can get here in Denver?
 

ericy

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Aug 24, 2004
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Rehoboth Beach, DE
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2015 Golf TDI (wife's car)
Drivbiwire said:
Before getting worried GET YOUR TIMING CHECKED every year before winter sets in.
One other thought. As temperatures have started getting colder, I have had more and more trouble getting started. Then I got a CEL:

1 Fault Found:
16502 - Engine Coolant Temp. Sensor (G62): Signal too High
P0118 - 35-10 - - - Intermittent

According to what people around here say, this indicates a dodgy sensor. I *believe* that this is the sensor that the ECU uses to decide how long to run the glow plugs. Thus the thought comes to mind that a bad sensor might tell the engine that the engine is warm when it really isn't, and it won't run the glow plugs for very long. Leading to a difficulty getting started.

On my car, the sensor is borderline. Sometimes the CEL is on, other times it isn't. Other folks with hard starting problems might have a sensor that is weak, but not bad enough for the CEL to ever come on. I don't know if there is any kind of diagnostic one can do to test this without changing a sensor - the glowplug light on my car doesn't come on for very long, which I suppose is a further indication that there might be a problem in this area.

I still haven't gotten around to replacing the thing (first step is to find it :D). Replacement part is quite cheap. I really need to take care of this before it gets really cold...
 

tuckster

Member
Joined
Jun 16, 2004
Turns out it was the battery going dead. I replaced it and so far everything is normal (no more jumping gauges). I did check the ground while I had the battery out and everything looked fine.

Drivbiwire, not a lot of salt on the roads here in Boise.
 

pepper10

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:)2002 A4 TDI , 2006 A5:)
tuckster said:
Turns out it was the battery going dead. I replaced it and so far everything is normal (no more jumping gauges). I did check the ground while I had the battery out and everything looked fine.

Drivbiwire, not a lot of salt on the roads here in Boise.
Tuckster, also check the alternator. It could be faulty, not re-charging your battery properly. Put a multimeter set to 20v to both battery leads while the engine is running. You should get a reading over 13.5v. If not, it could be the alternator or voltage regulator.

Here's another reason for hard starting that wasn't mentionned here: glow plug relay!
 
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