www.tdiclub.com

Economy - Longevity - Performance
The #1 Source of TDI Information on the Web!
Forums Articles Links Meets
Orders TDI Club Cards TDIFest 2014 Gone, but not forgotten VAG-Com List Unit Conversions TDIClub Chat Thank You



Go Back   TDIClub Forums > VW TDI Discussion Areas > TDI 101

TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

Reply
 
Thread Tools
Old November 3rd, 2005, 10:11   #1
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Hard starting when cold, for the 10,000th time!

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
Drivbiwire is offline   Reply With Quote
Old November 3rd, 2005, 17:34   #2
edfcmc
Veteran Member
 
Join Date: Mar 2004
Location: carson city, NV
TDI(s): 2000, 5 spd
Default Re: Hard starting when cold, for the 10,000th time

bump
edfcmc is offline   Reply With Quote
Old November 4th, 2005, 06:40   #3
HammerDown
Member
 
Join Date: Mar 2005
Location: Glenolden Pa.
TDI(s): none-yet
Default Hard starting when cold, for the 10,000th time!

Quote:


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.
HammerDown is offline   Reply With Quote
Old November 4th, 2005, 06:57   #4
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Re: Hard starting when cold, for the 10,000th time!

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
Drivbiwire is offline   Reply With Quote
Old November 4th, 2005, 07:36   #5
nosootdzl
Veteran Member
 
Join Date: Feb 2004
Location: Northern MD
Fuel Economy: 51.7 mpg
Default Re: Hard starting when cold, for the 10,000th time!

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.
nosootdzl is offline   Reply With Quote
Old November 4th, 2005, 12:18   #6
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Re: Hard starting when cold, for the 10,000th time!

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
Drivbiwire is offline   Reply With Quote
Old November 5th, 2005, 05:05   #7
BathTDI
Veteran Member
 
Join Date: Jan 2003
Location: Bath, Maine
Default Hard starting when cold, for the 10,000th time!

One more- blown glowplug fuse.
BathTDI is offline   Reply With Quote
Old November 5th, 2005, 06:06   #8
wpeets
Veteran Member
 
Join Date: Dec 2001
Location: Chateaugay NY 12920
Fuel Economy: 38/39
Default Hard starting when cold, for the 10,000th time!

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.
wpeets is offline   Reply With Quote
Old November 7th, 2005, 19:20   #9
dieseldave2006
Veteran Member
 
Join Date: Aug 2005
Default Re: Hard starting when cold, for the 10,000th time!

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?
dieseldave2006 is offline   Reply With Quote
Old November 7th, 2005, 19:44   #10
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Re: Hard starting when cold, for the 10,000th time!

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
Drivbiwire is offline   Reply With Quote
Old November 7th, 2005, 19:54   #11
dieseldave2006
Veteran Member
 
Join Date: Aug 2005
Default Re: Hard starting when cold, for the 10,000th time!

Thanks for the immediate reply!! I had a sneaky suspicion that glow plugs have gotten better in years!! Thanks again.
dieseldave2006 is offline   Reply With Quote
Old November 8th, 2005, 07:31   #12
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Re: Hard starting when cold, for the 10,000th time!

Quote:
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
Drivbiwire is offline   Reply With Quote
Old November 9th, 2005, 06:59   #13
diesel_smoke
Veteran Member
 
Join Date: Mar 2005
Location: Indiana
Fuel Economy: 42mpg, auto
Default 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.
diesel_smoke is offline   Reply With Quote
Old November 9th, 2005, 07:43   #14
JettaJake
Veteran Member
 
JettaJake's Avatar
 
Join Date: Nov 2002
Location: CT TDI Corral
TDI(s): '03 GLS 5spd
Fuel Economy: ~47 lifetime mpg @ 185K miles
Default 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
JettaJake is offline   Reply With Quote
Old November 9th, 2005, 07:52   #15
Dave_D
Veteran Member
 
Join Date: Jun 2003
Location: Gaithersburg, MD, USA
Default Re: Hard starting when cold, for the 10,000th time

Quote:
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.
Dave_D is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 02:27.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2014
Contact Us | Privacy Statement | Forum Rules | Disclaimer
TDIClub Online Ltd (TDIClub.com) is not affiliated with the VWoA or VWAG and is supported by contributions from viewers like you.
1996 - 2013, All Rights Reserved
Page generated in 0.14843 seconds with 9 queries
[Output: 123.71 Kb. compressed to 103.81 Kb. by saving 19.90 Kb. (16.09%)]